# bench testing of incandecent soft start ckt



## wquiles (Dec 17, 2005)

In this post Andrew posted a circuit to give a soft start to an incandecent bulb, and I decided to try it out today.

Here is the modified schematic from Andrew that I implemented:







my very mesy bench:






my test circuit OFF:






my test circuit ON:






In these two following shots, the top trace (channel 1) is the voltage at the ON side of the switch, while the bottom trace (channel 2) is the voltage accross the capacitor C1. The vertical scale is 2V/div and the horizontal scale is 100mS/div. Trigger is set off channel 1 on the upward pulse of 1.0V.

Digital Storage Scope of a single, short pulse on the switch. You can actually see the drop in the battery pack's voltage when the FET finally turns ON - see the short dip, before the battery pack recovers, about 150mS after the trigger point:






and two, back to back short pulses:






- battery source: modamag 4xAA series adapter with freshly charged CBP1650 cells
- lamp: standard 3xcell M*g bulb
- R3 = 5K
- R4 = 200K
- C1 = 33uF (100V since it was all I had!)
- 3A, 100V rated N.O. switch
- N-channel FET: International Rectifier IRL3713PBF (super low Rds(on) at 4.5Vgs of 3.3 miliOhms !!!)

Per the scope, the soft start is more or less about 150mS, which to the human eye is VERY fast 

I eventually want to build this circuit for powering 3x17670 (protected) cells for a SF MN60 or MN61 bulb on a custom adapter for my M6, so this early sucess with the circuit is a good start. Adapter would look something like this, with the circuit in that open space - of course the rods would be flush with the bottom plate and I would create a new positive end on the top plate:





Thanks Andrew and js for your advice/help so far :bow:

Will


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## andrewwynn (Dec 18, 2005)

Ok.. very excellent so far.. however.. more work involved.. so far i can only see that you have a delaed start, not too much evidence of a 'soft' start.. if there is a sag in Vbat it means the FET turns on hard, correct? 

you need to put like a 0.05ohm sense resistor (you can use a few inches of like 24ga wire (1/2 mohm per inch.. and the amount is not that important).. in series with the lamp and get a current measurment over time.. there is obviously a current spike when the FET turns on and we want to limit how bad that spike is. 

Once you get that figured out and what values to use for the C1 and R3. 

If you are using the FET for soft start you might as well loose the switch from the current path... it will more than double the circuit resistance, just controlling the FET will shut the lamp off and you only need mili or micro amps to control the FET. 

With the big cap you have it might take a really long time to shut off i suspect is why you moved the switch? you need a smaller C1 to make this ckt sing (or you might be able to use about 15-20k for R4 so that the cap will discharge to shut off the FET. 

When i was down in the 200msec or less turn on, i still was getting current surges 2-3x running, so you need to get a sweep of the current spike that's causing the Vbat dip, and tweak the RC values to get that to be nice.

incredible to see an idea develop, i only invented that ckt like 1/2 a day ago or something and to see it runnign on a bench.. so cool.. saved me the work .

-awr


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## andrewwynn (Dec 18, 2005)

ok i just did a little reasearch and it looks like it might be harder to match the voltage you are aming for.. the MN61 i found a reference that shows it takes only 8.35v.. now that's probablky average so it can probably handle 9.. but you will def. need regulation not just a resistor to drop that much voltage.. and at 2.3A.. x 1.8V = 4W.. that's a lot of heat to lose.. (much less than what is generated in the MB20 pack so i don't think it's that big of a deal actually).. just that is' something that has to be dealt with. 

Oh.. btw.. i do have an extremely simple driver circuit design you could probably build into that holder.. search for 'ludicrously' in cpf in batteries included you should find it. 

Otherwise another ckt design just uses an opamp and vref a couple resistors .. i found an 8 pin chip that has both the opamp and voltage reference buiolt into one.. and had plans on making a simple regulator ckt out of that. 

I want to get a nice ckt out there people can build themselves for $4 rather than have to pay 10-15x that to get the 'full boat fancy' one. 

-awr


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## andrewwynn (Dec 18, 2005)

ok.. for reference.. here are the original ckts:









'mark 1' is on the lef 'mark 2' is on the right. 

Now that you have 'mark 1' operational i think you need to move up to mark2.. it's far more refined.. 

as described in the initial post.. most of the delay is just waiting for the FET to start turning on.. and that's not a 'soft' start at all... though it does put the vGate into a slower deriviative than initially.. however.. with mark2 of the circuit you should be able to 'skip' most of that initial delay and get right to the important part.. turning on the FET but slowly. 

You need to measure bulb voltage and current.. if you can get those two on your scope top/bottom would be very helpful.. and for setting purposes having vgate vs ibulb might be extremely useful.. ideally having vGate, vBulb and iBulb at once. 

as mentioned.. in the final ckt you would not want to break the power from the battery that's the FETs job also.. why introduce physical high-resistance contacts into a ckt with a 3.3mohm FET? 

The theory behind the mark 2 ckt is that with R5 set just right.. the Vgate will jump instantly when the switch is thrown to just below the threshold voltage.. than the R3/C1 time constant can be reaaaly streteched out.. make it so that it takes a good second to get the lamp to turn on all the way (a good way to find out how slow the lamp is turning on is meausre the Vfet vs Vlamp). 

if you are putting in your own switch, using a SPDT switch and having the common on the bottom and having the 'out' terminals toggle between Vbat and ground will greatly speed up the reset time.. i'm still working on a way to short out C1 quickly when the swtich is opened.. but w/o introducing a differnet type of switch, because ideally we can just use the stock mag switch w/o modification 'as is'. 

I think i came up with a really clever way to solve the quick-reset. 

Ok.. take a pch FET and put it from the gate on FET1 through a small resistance like 10 to 100k.. to ground... The gate of FET2 goes to the wiper of a high resistance pot that goes from the bottom of C1 to the wiper of R3 (also the neg of switch 1).. (also means the pot3 just goes from wiper to highV of R5).. 

Theory.. you set the pot 3 so that when the ckt is on.. the Vgate is high enough that it doesn't conduct.. but near the threshhold voltage.. 

When Sw1 is opened.. immediately the wiper of R5 goes to zero basically dropping 2V from the base ground on pot3.. that will pull the voltage-bridged wiper down across the threshold voltage which will turn on FET2 and very quickly empty C1. 

Since there are no caps in series with R5.. when you turn the switch back on.. it will instantaneously raise the gate voltage above the threshold voltage and turn off FET2 allowing the ckt to charge and work normally. 

This should work unless i missed something.. gets a little bit complicated with 3 pots and two FETs but simple to master.. and once the values are figured out a wide range of voltage solutions could be had with only 1 trim pot to decide how fast to turn on the FET. 

(some of my designs incorporate a Vreg to put a constant voltage downstream of the switch so you have more accurate control of turn on (not based on Vbat).. but i think a pre-set value for top/bot of R5 would work very well.. 

Oh.. i'm also realizing.. it could easily be re-worked by putting the top of R5 to the wiper of R3.. but that means that the base of C1 is not constant, but it might make the recycle time low enough to not need the second FET. 

-awr


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## wquiles (Dec 18, 2005)

Andrew,

Thanks to your great feedback and suggestions I will be doing further bench testing today (Sunday). Answering a couple of your questions:

1) You might be right in that at the moment it might be working more of a delayed start, rather than the soft start. I will also be expanding the scope reading on the area where the FET is turning on to get more detail.

2) Where you are placing the switch is in fact the most efficient setup, for a M*g. Since at the moment I am concentrating on the SF M6 variant, having the switch in-line with the battery is more realistic of the tailcap of the M6.

3) I only used the huge 33uF 100V since that is all I had at the time. I am about to leave for Fry's to pick up some "smaller" units 

4) I like your idea of the sense resistor with just some wire - that will help us determine what is going on. 

5) Once I get 'mark 1' running better, I will try the 'mark 2' version, but I will not try anything with two FET's anytime soon. I really want to keep this super simple to start with .

6) About the MN60/61 with 3x17670 cells and these bulbs being 9V - Kiu and others have done it for many cycles, so it works. I just want to make it better by limiting the bulb-killing current inrush. However, if you have a spare LDO circuit for me to bench test on that space on my custom holder, please PM me with details - I will gladly pay for the parts and your trouble 

Question: What program are you using to make these very simple circuit diagrams? I need something simple like that!

Will


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## andrewwynn (Dec 18, 2005)

aah that's right.. M6 solution, yup you want the switch where you have it. 

i knew you adapted the ckt to the cap on-hand.. been there done that.. my M66 right now has a couple capacitors i took off an only CD burner from the 90s. (real pain to find out the values.. can't read them in-ckt so have to desolder first, and i think they were glued on before soldering so it's really tough). 

the sense resistor thing is a must.. i don't think voltage is as big of a deal as current.. i.e. i think i would start with the two inputs being Vgate and Ifet. 

i think in the M6 variation you can take advantage of using the tailcap switch.. i'm just not sure how.. i was trying to figure out a way to use a diode for example.. putting a diode from the gate of the FET to the + of the lamp. The theory being.. that when you break the switch Vlamp goes to zip, but the FET is still on because of the charge on the cap.. drain the C1 through the diode and lamp through the FET, you can probably get away with no extra resistance though i would use a small resistance like 10k.

Logically enough when the cap drains enough the FET will shut off, right at the thresholod, but the other resistance will continue to drain the cap. 

Another nifty idea that would get it to shut off quickly.. yet another pot.. to set up a maximum voltage to the gate.. so that rather than puttting Vbat on the gate.. keep it to like 4-5V (well of cousre i think in your tester that's all you're using).. but when you have it in a 10.8V ckt it'll act a bit differently with the same gate threshold.. anyhow if they Vgate is close enough to the threshold when you open the switch it will reset the cap quickly so multi-clicking will soft-start each time. It will make the mark2 variation more of a necessity. 

The 'simple LDO' is only 'on paper' right now.. the schematic is shown on the ludicrously simple ldo thread. I think it only uses a diode for Vref and a couple NPN or PNP transistors with a couple bias resistors.. it's pretty ludicrously simple as the title suggests. 

To me simple means less active components, so i like the idea of the chip with the Vref and op-amp built in.. all you need is a pot from the Vbulb to ground and the wiper goes to the (- in) on the op-amp.. you should be able to find a dip-version of that chip at fry's actually.. it should be a ludicrously simple ckt as well.. you might need a cap in there somwehre to keep the thing from oscillation.. and you would use the output of that ckt as the input to the one you are making now.. that would give you voltage regulation and soft start as well. 

-awr


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## wquiles (Dec 18, 2005)

Andrew,

I am convinced now that 'mark 1' is a gonner. For the reasons you stated, I need to work with 'mark 2' from now on 

As it turned out, the circuit is not a delayed start nor a soft start - it is really doing both of them . I measured today a long delay, a short one, and no circuit at all - just DD to the poor bulb :naughty:. If I watch the voltage at the battery pack, I can clearly see that the 'mark 1' circuit does help and it makes the hit on the battery less intense and the short circuit current is definitely lower than with just a DD connection.

Vnoload = 5.35V

When C1=4.7uF and R3=5K (shortest delay/soft-start), the Vdip at the battery pack was = 1.14V






When C1=4.7uF and R3=42K (medium delay/soft-start), the Vdip at the battery pack was = 0.70V






When C1=33uF and R3=42K (very long delay/soft-start), the Vdip at the battery pack was = 0.46V






With just a DD, the Vdip at the battery pack was = 1.44V !!!






Since the "real" load is the same in all cases, the circuit "does" help by providing a soft start and lowering the short circuit current going through the bulb. Of course, the unacceptable delay in 'mark 1' is not good, so I will play with 'mark 2' which "pre-loads" the voltage at a higher point but still provides a soft-start function 

Thanks again for your help/guidance so far - this is fun  

Will


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## andrewwynn (Dec 18, 2005)

fun from this end too.. i kinda like just designing the concept and seeing somebody else take it from there and build the circuit.. usually i'll build one and they copy me but coming direct from theory is something a lot different. 

Not sure what is on ch2... FET v? if so, the soft start is working fine, you can see the voltage drop logarithmically.. or inverse of exponentially whichever is.. just very quickly on the short models. 

I would aim for 1/2 to 2/3 sec turn on time. i 'lucked out' in my driver ckt with a top-secret solution that make the voltage immediately turn on the gate but slowly rise at about 1/10th the RC time constant.. means i can use really small capacitors (1µF makes for like a full second turn on!).. which is awesome news for me.. SMD caps are cheap up to about 10µF than they are extremely expensive.. a 22µF cap is over $2. 

The important value is not really shown here. .the difference between final voltage and the dip represents the extra current 'spike' at turn on.. (when measuring vbat). 

It looks like your deltaV is from restingV? the important spike is the difference from the dip and the running voltage... and on the slower start you can see that the voltage spike is almost completely eliminated on the slower start.. is the time scale for the large divisions? what was the turn on delay for each? 

-awr


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## andrewwynn (Dec 18, 2005)

fun from this end too.. i kinda like just designing the concept and seeing somebody else take it from there and build the circuit.. usually i'll build one and they copy me but coming direct from theory is something a lot different. 

Not sure what is on ch2... FET v? if so, the soft start is working fine, you can see the voltage drop logarithmically.. or inverse of exponentially whichever is.. just very quickly on the short models. 

I would aim for 1/2 to 2/3 sec turn on time. i 'lucked out' in my driver ckt with a top-secret solution that make the voltage immediately turn on the gate but slowly rise at about 1/10th the RC time constant.. means i can use really small capacitors (1µF makes for like a full second turn on!).. which is awesome news for me.. SMD caps are cheap up to about 10µF than they are extremely expensive.. a 22µF cap is over $2. 

The important value is not really shown here. .the difference between final voltage and the dip represents the extra current 'spike' at turn on.. (when measuring vbat). 

It looks like your deltaV is from restingV? the important spike is the difference from the dip and the running voltage... and on the slower start you can see that the voltage spike is almost completely eliminated on the slower start.. is the time scale for the large divisions? what was the turn on delay for each? 

-awr


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## wquiles (Dec 18, 2005)

Andrew,

In the first three screenshots, the top trace is the Vbat. The 2nd trace is the Vds - so as the FET turns ON, the voltage quickly moves toward ground as it should, which of course turns the lamp ON 

Specially in the fourth shot (DD), you can see the resting Vbat, then being hit with a short circuit very fast (the deep spike down), then the battery recovers and enters steady state, and then when the switch is open, the Vbat goes back to steady state resting.

As to the scales, I was hoping they would show in the photos:

- first is 40mS/div

- second is 100mS/div

- third is 200mS/div

- fourth is 40mS/div (this is the one with no circuit - just DD).

So do you think I am ready now for circuit 'mark 2'? :naughty: 

Will


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## andrewwynn (Dec 18, 2005)

so on the final one it took 1.2s to start turning on and .2s to actually be turned on? 

so i think if mk2 does what i've planned you can short-circuit most of that 1.2s.. and stretch out the .2 turnon.. though from the voltage dip it might not even be necessary. As you can see from the trace.. the voltage sweeps pretty fast down to zip on the Vds. 

Now we need to get a current trace... iLamp v vGate might be an interesting trace. It's very interesting to see where on the curve the turn on happens. 

That looks like a nice scope.. that's pretty high on my list of tools to get.

-awr


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## wquiles (Dec 18, 2005)

Yes, that 1.2 second is a very, very long delay indeed 

I have a 0.1 Ohm 5W resistor that I can put in series with the bulb - I should be able to read the voltage across to get the current 

The scope is a Tektronix TSD3034, 4-ch, 300Mhz bandwidth,, 2.5GS/s, with all of the FFT options. I am borrowing it from work for the holidays :naughty:

Will


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## andrewwynn (Dec 19, 2005)

tell work i want in on that passaround 

I haven't used a scope since '88.. i was trying to remember if the /div was the big or small.. that had to be kinda funny when you first flip the switch and nothing happens for a full second or more than finally 'blink'. 

I'm kinda surprised i actually pre-conceived that problem before building the ckt. I was actually trying to solve the problem with an PN device.. like using a diode that would only be forward biased when the FET is off.. for example from the 'D of FET to the G of FET... which in your ckt would probably work.. you could try that.. 

theroy: when you flip the switch and it energizes the ckt, voltage is applied to the drain of the FET, forward biases the diode and hits the gate.. well of course once the FET turns on and with the diodes Vf, it will no longer be forward biased, but that diode will automatically get the fet to the threshold.. use a very small series resistor. 

I can't use that design in my ckt because i have Vbat on the FET any time there is no current through the lamp. 

i'm very interested to see the Mk2 of this ckt. 

-awr


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## wquiles (Dec 19, 2005)

Andrew,

I got some measurements of the current with the DD circuit - in other words, worst case scenario for the poor bulb :devil: 

Per the scope, and per my Fluke voltmeter, using a 0.1 Ohm series resistor with the bulb, the steady state current is right at 1.0 Amp. Now that I can plot the initial current, look at how high is the peak current.

- Top trace is the Vbat at 2V/div

- Bottom/red trace is Vrsense at 1V/div for the first two, and 200mV/div on the last one (the one that looks noisier).

In here, at 100uS/div, as the switch is closed, the peak current is at least 14-15 amps!. I say at least since it is hard to measure the absolute peak with my setup and my not-so-current scope-using skills:






As time pases by, the bulb approaches steady-state, and the battery pack slowly recovers. This is at 1mS/div:






Finally, at steady state, the pack is happy and the bulb is drawing 1Amp. This is at 40mS/div:






Of course, I need to measure now "with" the circuit in place, but based on the much smaller Vbat dip that I saw earlier, I am expecting the inrush current to be smaller than 15Amps!!!. I will report later on this 

Will


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## andrewwynn (Dec 19, 2005)

i was a little suprised myself to be getting double digit peaks.. 1msec.. but with 100msec 'surges' being usualy in the 2-3x running current still pretty amazing. I will be very interested to see the difference with mark1 and then mark2 of the soft starter. 

with mark2.. it should be possible to get the best of both worlds.. quickly getting to the threshohold voltage but slowly ramping through the gate transition voltage so the FET turns on relatviwly slowly. 

Based on the initial results, it did look like the votlage changed in a controlled manner, but somehow it'd be better if we could contol the voltage based on the current initially.. a negative feedback based on the current draw would be cute... but would require more active devices. 

I would be happy just to have the soft voltage ramp work to cause a relatively soft current ramp, even if there is a relative spike at the beginning.. having it be more like 2-3A not 15 sounds good to me. (there is a good chance that the 1msec spike will always be pretty high). 

-awr


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## wquiles (Dec 19, 2005)

Andrew,

With 'mark 1' in place I was able to get down to 4-5Amps, and if I had a very long time it got in to the 2Amp range - but with an unaceptable delay.

I started playing today with 'mark 2', and it is getting much better, but since now I have more components, it is taking a while to figure out the initial voltage and the appropriate soft-start. I ran out of time today but I hope to be able to post some screen shots tomorrow night 

Will


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## andrewwynn (Dec 20, 2005)

determine that set point of the pot 2 by making note of the vGate on mk1 when the FET turns on.. i would start about 0.1V below that value.. maybe put on the scope.. vGate (to ground) and iLamp would be good to plot.. it should jump up to like 1.8V or something than ramp up based on the RC. 

it would be interesting also to plot vGate to ground vs pot2 wiper to ground and see how that 'jump start' compares. 

oh.. i also realized .. that you might be able to utilize the pot2 gnd that will 'jump' between that 1.8V and ground as some input into shorting out the c1 when the ckt is off to reset it.. i would not worry about that initially though.. 

first.. expect that i'll take longer to turn off than on.. if it takes 2 sec. to turn off but 1/2 sec. to turn no that is fine initially. 

-awr


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## wquiles (Dec 21, 2005)

Andrew,

I have been making good progress on testing 'mark 2'. Unfortunately, I found a fatal flaw with the circuit, specially if you do more than just one "ON-OFF" cycle right after each other  

What happens is that C1 continues to charge all of the way towards Vbat, so if you turn it OFF and then ON fairly quickly (less than 1 second) then Vc1 is still high enough that the FET turns ON hard and fast, therefore sending a spike of current (again!) to the poor lamp, just as if you had no circiut in there  

Top/BLUE trace is Vbat
Bottom/YELLOW trace is Vgs

Here is a picture of the steady-state behavior. Notice how nice is the soft start and how there is no spike on the Vbat, just a nice gradual load condition as the FET turns on, then a short time for the battery to stabilize (horizontal scale is 100mS/div ; vertical is 1v/div): 






Notice now what happens if I turn it ON, quickly OFF, and then ON again. Notice the strong Vbat dip for the second ON, and then even deeper on the 3rd:
(horizontal scale is 200mS/div ; vertical is 1v/div): 






This is another closeup of a quick ON-OFF-ON cycle. On this case it is almost worst case since there is almost no soft start for the second cycle:
(horizontal scale is 200mS/div ; vertical is 1v/div): 






And it actually gets worst if you wait a little after the first ON since Vc1 is even larger and the FET turns ON hard for the second and third cycles, each time harder (negative Vbat spike is getting larger):
(horizontal scale is 1S/div ; vertical is 1v/div): 






On this last one, I do many quick, back to back cycles, and I am getting a pretty hard spike on each cycle after the first one:
(horizontal scale is 1S/div ; vertical is 1v/div): 






I even put a 1N004 diode in parallel to the lower part of R3 (to shorten the discharge cycle), and although it helps, it is just not enough - we would need a very fast path to discharge C1 within 100mS or so 

Now, if you just turn it ON, use it, and turn it OFF, it works perfect!. It is only the quick ON/OFF/ON/OFF behavior that has a problem. I think that adding a transistor (to detect Vbat=zero) might force the C1 to discharge quicker, although I am not sure how I would wire it to make it work properly. 

The other point that I have yet to investigate, is what happens as the battery looses power with use. Since the lower starting set point will become smaller (being a constant ratio) then the circuit "should" take longer and longer to turn ON since it will take longer to achieve the same Vgs to turn the FET ON. Maybe this behavior will be a built-in indicator that the battery is starting to run low? :naughty: 

Isn't interesting how this "simple" circuit is now getting more complicated 

Will


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## andrewwynn (Dec 21, 2005)

I believe i did suggest a 3rd pot that would be the 'high gate' voltage.. so you could have a voltage bridge to get the maximum gate voltage.. i did predict that would happen. The best way would be to drain the cap with some active device like a cheap FET that only is active when voltage is not applied .. that is biased in a way that when lower pot is above ground it turns off, but when it goes back to ground it turns on and drains the cap with a very small resistance, like 5k or something. 

Vds might be more useful to plot, or Vgs vs Vds .. i can't tell where the exact threshold voltage is, but i think i see it happen in one or two of the plots.. very cool to see the Vgs ramping up and then somewhere in there the Vbat starts to sag.. good stuff. 

'going fancy' you would put in a vreg that would keep the ckt constant voltage that controls the FET so there is no variation when the battery dies. 

I will try to get to the computer that has the schematic software.. did i ever mention what it is.. 'design works light' i think it might only be for mac, but if you look on versiontracker.com you might find something simlar that is freeware for windows, given the odds that's what you are using. 

Looking at the spikes, they don't look all that terrible.. yes some spike but on a warm lamp you just turned off less than a second ago.. need to see how much of a current spke is going on.. and notice that it's in the milisecond variety still, not 1/0th of a second variety. 

i think this would probably work: put a pch fet this orientation:

gate to the bottom of C1.. Drain to the gate of FET1 and Source through a relatively small resistance to ground. 

I just realized that if the gate voltage gets high enough it might bias the thing on even while the ckt is running but all it would do is keep putting current through the high resistance of R3 and it would keep the Vgate lower.. so just a matter of tweaking the pot settings and would probably achieve the desire of having that 3rd pot. 

So.. might get what you want with just that 3rd pot (voltage bridge on the whole ckt.. put the pot from SW1 to ground.. wiper to top of R3.. use a relatively low resistance like 50K (compared to 1M in the design)... i think you are using lower Rs so adjust accordingly... than you can get Vgate-max closer to the Vgate-threshold so it recycles faster.

Otherwise.. trying for an active solution.. putting a pch fet like described.. you might need a bias resistor or two.. but have the Vgate set so the threshold plays nice with the voltage base at C1 so that when the ckt is turned off it instantly will be 'full on'.. and when the ckt is first turned on (no voltage on c1).. the FET2 will be full off. 

It would be very interesting if it's set up such that as C1 charges eventually it will turn FET2 on and maintain a precise value on C1, as long as FET1 is full on,that would be a nearly ideal solution. 

-awr


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## andrewwynn (Dec 21, 2005)

oh.. speaking of 'simple getting complicated'.. 









and 'under the hood'





(hand made traces with 24ga bare wire).. and now it has like 4 more 'traces' since this picture was taken... but it also has soft-start and i fixed the startup issues. 

-awr


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## wquiles (Dec 22, 2005)

Andrew,

Thanks much for the information about DesignWorks Lite. They "do" offer it for Windows, and I have 30 days to try - only $40 to register, and it is very easy to use . Here is my redrawn 'mark 2' without the pots, as I recall the actual values used (have not been to the bench yet today, so these values are from memory and might be off a little!):






I think I will try the additional FET/transistor this coming weekend for the discharge path. Even as it is today, it works great with the charged battery pack, so I want to do some more tests while the pack discharges. Theory is great, but nothing beats actual bench testing "and" being able to see/measure using the scope 

Will


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## andrewwynn (Dec 22, 2005)

Oh.. in the case of using LiONs to power SF lamps.. i would be prepared to include like 0.075 to 0.01 ohm power resistor (high powered sense resistors) in series with the whole shabang to keep the initial voltage low enough to protect the lamp.. might not be necessary from the 10.8V solution but from the 7.2V solution it is. 

I just noticed.. that with R3 there.. you could put a zener in parallel witht he C1 and it would make for a maximum voltage on the gate and consistant operation with any battery voltage. I love how this is coming together, hope some people will clone it for their own use. 

-awr


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## wquiles (Dec 22, 2005)

You mean like this below? If I pick a Zenner with a voltage around 3 Volts (which is above the Vgs required to turn it on, which I think it was 2.8V or so), that could work well


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## andrewwynn (Dec 23, 2005)

exactly what i'm talking about.. but maybe a little higher value... thre reason being that the Rdson is lower with higher Vgs.

Z1 might make D1 obsolete

doncha love having DWL? 

-awr


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## wquiles (Dec 23, 2005)

I picked up a 3.0V Zenner today at Fry's - I hope to try it tonight if I can get my kids to sleep early 

Yes, DWL simply rocks, and it was so EASY to use and setup. The very large library, easy way to create new simbols, and easy routing makes it a bargain for $40 

Will


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## wquiles (Dec 24, 2005)

Andrew,

Well, I really have no clue what is going on :mecry: 

The zener is not working like I expected at all  , and in fact never seems to get to the 3V it should :thinking:. From what I have measured, it seems to clamp at about 1.2 volts or so :thinking: :thinking: :thinking:

Instead of using the 3V zener (NTE5065A) across C1 and R3, I decided to try it just accross C1, and guess what, even though the zener is not behaving like it should, the whole circuits works perfect now  

Here is the new circuit:






Here is the circuit with the zener disconnected (to show the "before" view of things). Note how between each switch closure the Vc3 keeps increasing since there is not enough time between presses to discharge it properly and since there is nothing preventing the cap's voltage from rising towards Vbat:






Here is the "mistery" circuit above with the zener connected across C1 (this is the "after" view of things). Note now how the circuit is just perfect, and how there is never a Vbat spike and how the Vc3 is now capped (somehow) by the misterious 3V zener who is not working according to what I expected. 






The awesome thing about this circuit is that now, I get a soft start (I can actually see the bulb getting brighter until is full ON, so it is not just delayed start) after each switch press, not just the first one like before.

I also tested not connecting D1, but it does help to speed the discharge of C1, so I kept it in there. I tried playing with various values of R2 and C1, but these values matched the strange (to me) behavior of the zener.

I tried different values of R3, but the circuit (with the zener) is very particular to these values as when I tried 20K the whole balance of the zener was ruined since the starting voltage was now higher and the C1 effectively gave the gate of Q1 a higher voltage quicker than before, so now I loose the soft-start for switch presses #2 and so on. With a lower value (10K) then (because of the zener), there is never enough voltage at the gate to fully turn Q1 ON.

So, do you have some clues/suggestions for me?

Will


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## andrewwynn (Dec 24, 2005)

What you ended up with was my design.. i looked too quick at your first mark3 design... with the zener to ground, it might work with a 5V zener. 

When making small ckts.. big caps = sucky.. that's why i originally did a design with 4.7uF for the cap.. did you work on the ckt with a smaller cap? you should be able to just use exactly proportional increase in R2 but can leave R1/R3 the same.. 

What are you kidding? we have a circuit! 

R1/R3 set up a voltage bridge that is non-capacitive.. they simply have to be a ratio that puts a voltage just below the gate threshold voltage.. the only time you'd hvae to tweak R3 is if you change the voltage of the bat... or a different FET that had a different threshold voltage. 

It would be a 'cleaner' design to have yet another zener in parallel with R3 or even in replacment of R3.. but better put at least a small (200ohm maybe) resistance in series.. because when the ckt is turned off C1 will dump a bunch of charge through very quickly. 

with the relatively small fractional value from Vbat to Vbase (bottom of C1) based on R3/(R1+R3).. it won't swing enough during typical voltage swings, but you have to make sure that with fresh batteries C1 base doesn't have enough voltage to turn on the ckt immediately. 

I am thinking your 1.2V measurement was across C1? when you had the zener across C1, R3 ? that would make sense if your base voltage is 1.8V which is right about what i'd expect... 

It helps greatly to have the zener only across C1.. what happens is when it's working.. you get 1.8V at the base and that puts 4.8V on the gate.. not a bad gate voltage.. that's usually going to get you the fast majority of your Rdson taget (i.e. some FETs will be 4mohm at 4Vgs and 3.3mohm at 10Vgs).. it's a moot point as long as you get to that first target value. Anyhow.. in this same example.. as soon as you turn off the ckt, you will have 3V on the cap, but now the base of the cap immediately drops to ground which puts the gate at 3V, which is right at the threshold of being on, but the diode will quickly discharge that 3V through only 50kohm.. that actually could be lower for a faster discharge.. but it seems that could be a moot point, looks like the turn on and turn off is working great even for 'blinking'. 

I would work on putting in a lower cap and higher R2.. the rest should work as-is with that solution.. the RC calculator says 431 msec to 23% which is my rough guess of 1V increase from the start before FET sweeps from 'just starting' to 'full on'.. if you use 4.7uF cap, the calculator says 350kohm is the proper resistance. 

with the bigger R2, it would necessitate D1 sticking around, but would make an even bigger difference in the discharge vs charge rate. 

I really like how the D2 comes into play and does exactly what i planned for it.. the best part is that it means it works with a wide range of Vbat without the ckt changing performance much.. R3 could be exchanged for a different zener that would have to match the needs of the particular FET.. come to think of it.. probably can't replace R3.. would have to have it parallel to R3.. that way if Vbat is higher, it clamps the 'base' voltage, but keeping R3 is needed to do the quick 'drop' on the Vgs. 

Wow, it was really neat to see those o-scope traces.. thanks for doin' all the legwork for me. very exciting project.

-awr


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## wquiles (Dec 24, 2005)

Andrew,

You make multiple excellent points/comments, so I will try to address them one by one 




andrewwynn said:


> R1/R3 set up a voltage bridge that is non-capacitive.. they simply have to be a ratio that puts a voltage just below the gate threshold voltage.. the only time you'd hvae to tweak R3 is if you change the voltage of the bat... or a different FET that had a different threshold voltage.
> 
> It would be a 'cleaner' design to have yet another zener in parallel with R3 or even in replacment of R3.. but better put at least a small (200ohm maybe) resistance in series.. because when the ckt is turned off C1 will dump a bunch of charge through very quickly.
> -awr


That makes sense. That is why changing R3 (once I had a nice value) makes such a big difference in circuit performance. I might try the additional zener with R3 later, once I figure out why the current 3V zener is not working as expected.





andrewwynn said:


> I am thinking your 1.2V measurement was across C1? when you had the zener across C1, R3 ? that would make sense if your base voltage is 1.8V which is right about what i'd expect...
> 
> It helps greatly to have the zener only across C1.. what happens is when it's working.. you get 1.8V at the base and that puts 4.8V on the gate.. not a bad gate voltage.. that's usually going to get you the fast majority of your Rdson taget (i.e. some FETs will be 4mohm at 4Vgs and 3.3mohm at 10Vgs).. it's a moot point as long as you get to that first target value. Anyhow.. in this same example.. as soon as you turn off the ckt, you will have 3V on the cap, but now the base of the cap immediately drops to ground which puts the gate at 3V, which is right at the threshold of being on, but the diode will quickly discharge that 3V through only 50kohm.. that actually could be lower for a faster discharge.. but it seems that could be a moot point, looks like the turn on and turn off is working great even for 'blinking'.
> 
> -awr


Actually, that is not how the circuit is working. That is why I am still confused. The measured steady-state voltage across C1 once the circuit is ON is right at 1.20V. The measured steady-state Vgs, (or across C1 and R3 - which is the same voltage) is exactly 2.90V, which is what I already had measured to be the minimum voltage necessary to have Q1 turn ON - these two measurements clearly confirm that although the 3V zener is helping and make the circuit work perfect, the 3V zener does not "trigger" at 3V as expected/proyectec by theory. When I had the 3V zener in paralell with R3, the lamp would never come ON . I know I should be happy that the circuit is working perfect "as is", but I "need" to know why the zener is not working as expected  




andrewwynn said:


> I would work on putting in a lower cap and higher R2.. the rest should work as-is with that solution.. the RC calculator says 431 msec to 23% which is my rough guess of 1V increase from the start before FET sweeps from 'just starting' to 'full on'.. if you use 4.7uF cap, the calculator says 350kohm is the proper resistance.
> 
> with the bigger R2, it would necessitate D1 sticking around, but would make an even bigger difference in the discharge vs charge rate.
> -awr


I will try to use different values for R2 and C1 today - in theory it should work just the same way 




andrewwynn said:


> I really like how the D2 comes into play and does exactly what i planned for it.. the best part is that it means it works with a wide range of Vbat without the ckt changing performance much..
> -awr


Yes, assuming we can explain why the zener works when it shouldn't 





andrewwynn said:


> Wow, it was really neat to see those o-scope traces.. thanks for doin' all the legwork for me. very exciting project.
> -awr


You are welcomed. I would also "love" to work with you on the regulated circuit and/or LDO if you can use the help.

This has been a very simple circuit, but most interesting to test on the bench. Once I understand the weird zener behavior, then I will move to the 3xprotected 17670 battery pack with the MN60/61, since ultimately that is the "goal" of my project for my SF M6 .


One more thing - For testing with the 3x17670 cells, I will NOT be doing the "initial" bench work with the MN60 nor MN61 - I want to "debug" the circuit with a much, much cheaper bulb that is close enough for the early development work. What other "similar" bulb, even if it uses/requires less power, can I use? I have even considered using three of the 3xcell M*g bulbs in series to simulate a realistic load of about 1Amp with the right voltage - what do you think?

Will


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## andrewwynn (Dec 24, 2005)

the zener is not working exactly as expected i think because your Vbat is not high enough to make the zener conduct until you turn off the switch. 

If C1 is 1.20V and Vgs is 2.9 that means that the Vbase (of C1) is 1.7V.. I think i need some voltage reference from each of the important points.. also crank up the msec/div and see if you are just reading funny voltage readings because of an oscilation or such. 

I'm not sure what the reading on the oscope is.. Vgs or Vc1.. it would be good to see both of those.. also let it run longer 'til it reaches steady state maybe just do two or three cycles. 

I use a 12V, 20W lamp for my testing or an 1185.. running the 1185 at 1/2 voltage it still draws over 2A and just glows nice... yuou can pick up a 20W 12V bulb from just about anywhere for like $3-5.. the likes of home depot.. look in the lighting dept for a 'quartz halogen' bipin bulb. 

keep it coming.. hey i do have another LDO solution in the works very similar to what you are working on.. send me an email.. flashlight at rouse.com 

-awr


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## wquiles (Dec 25, 2005)

Andrew,

I took some additional steady state measurements last night with my Fluke 87:

Vbat = 4.97V (this is under load, of course)
Vr1 = 3.30V
Vr2 = 2.07V
Vr3 = 1.66V
Vgs = 2.85V
Vds = 0.058V
Vbulb = 4.7V

The circuit just plain works awesome. I will keep draining the battery as I want to see what happens when the battery is depleted. By depleted, I mean something about 1.1Vx4 (with no load) is my guess at the moment as a good place to stop. Sound right to you?

I showed the working unit on my bench to my neightbor next door (a little bit of a flashaholic as well, but not as "committed" as I am!) and he was "oohhh, aahhh" over how cool the circuit works 

Email sent to you as well 

Will


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## wquiles (Dec 26, 2005)

Another data point from tonight. I put the 4xAA back into my 1D modamag host, driving the WA1319 (about 250B Lumens or so) long enough that I detected it "spent", and when I was done I got a Vnoload of about 4.75V. Guess what? At this "low" voltage the circuit no longer turns the M*g 3D bulb ON - barely lits at all!. What this means is that by careful picking of R3, you can have a built-in low voltage "detector" since the light will dim from the FET not being turn ON all of the way, and, this low point can be set above the point where the cells would be damaged by overdischarging - very nice 

If I changed R3 from 16K to 20K I was able to once again get the 3D bulb to lit, so somewhere around 15-17K seems to be the sweet spot. I am recharging the battery pack and will try again tomorrow with it - if I recall the no-load voltage was like 5.6 to 5.7 volts, which would of course be the worst case for the circuit in terms of inrush current :naughty: 

Of course, now what I have this working, I have to try with the actual WA1319 to fine-tune the values to the actual bulb, and then again in the future once I move to the 3x17670 pack 

Will


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## wquiles (Dec 26, 2005)

Andrew,

Today I tried using a smaller C1 and R2. For some weird reason (probably becuase we artificially set the voltage with R1 and R3) when I changed C1 to 4.7uF, the value that worked OK was much smaller than I expected - somewhere around 70K for R2 was about the same delay as before :thinking:. Since I also wanted to speed up the ON time a bit, I ended up with a value of 60K for R2, which works well as shown in these shots here - horizontal is 400mS/div:






I then also proceeded to work with the actual bulb for this battery pack, the WA1319. Since the load on the battery is greater, I needed a larger value on R3 to get enough voltage on Vgs to turn on the FET fully (around 2.9V). I got to a value of 19K which works like this - horizontal is 400mS/div:






Look at the circuit without the soft start (removing R3). Look at the almost two volts negative spike (blue trace - never mind the yellow trace since it is floating here) - horizontal is 100mS/div:






And here with the circuit fully operational - horizontal is 100mS/div:






Since for R3=19K I had to use a 50K-POT to get, I tried a "standard" value of 20K. It does not work as well, but almost good enough  - horizontal is 100mS/div. 






and here is the same circuit, also with R3=20K, but with multiple ON-OFF cycles. Note how the battery dips a little bit more than before, but probably still "acceptable" - horizontal is 400mS/div.






Next thing to try is to let the battery discharge so that I can fine-tune R3 

Will


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## wquiles (Dec 26, 2005)

Here is an image of the latest circuit (Rev 5):






Will


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## wquiles (Dec 26, 2005)

Andrew,

Some more tests today with the battery pack getting discharged. Due to the larger load of the WA1319 (compared to the 3xcell M*g bulb) I need to increase R3 to around 24K to have enough voltage left to be able to still barelly keep the bulb operational when the pack reaches a loaded voltage of about 4.1-4.2 volts (4.7v unloaded). This of course means that although the initial voltage spike is still going to be contained (mainly determined by the R2*C1 delay), additional, very quick ON-OFF cycles will suffer a little since C1 will still have some charge in it. At this point I am re-charging the pack to test with the 24K and a fully loaded setup (worst case again). I will plot some screens once the pack is ready again  

Additionally, since I will be building this prototype in my 1D setup, I went ahead and setup the switch to be in-line with R2 (as you initially had it) and direct connect the bulb to the battery "+". I did change this on my bench setup and was able to instantly gain some brightness since (as we all know), that "normal" switch consumes some power compared to my super efficient FET switch 

Will


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## NewBie (Dec 26, 2005)

Have you made any current spike measurements lately (red trace on your older circuits-yes I know you can infer them from the battery voltage)?

Another thing to consider, is that 0.1 ohm sense resistor does serve to help limit the in-rush current to the bulb, altering the reality of the final circuit.

After moving the power on switch to R2, did you go back and look at the battery sag, since you removed the power switch resistance from the main current path?

Andrew, there was a thread awhile back where I listed a whole shebang of op-amp/comparator combos, such as the LM392 (which are under a dime each). I think I was talking to Al at the time. (in case you want to go down that path in the future).

Good work fellas on your circuit.

Question, does this circuit work as is, when a person changes to different bulbs, or do you need a different circuit for each bulb (part value changes)?

Say like when a person uses a PR-6 and then swaps to a 1181, 1185, 1329, 100W H4, or a 64623?

What happens if someone uses a different set of cells, with different internal resistances?

As far as the zener, consider at 1V across it, there could be up to 50uA of current flowing. Try sticking it in series with your meter on uA scale to a power supply, and turning up the power supply voltage to the voltage you were reading across it, and checking out the leakage current.

With only 81uA flowing through R1 and R3, the leakage in both C1 and D2 can have an effect on the circuit's operating points, especially if temperature changes. D1 only has leakage currents in the nA range, and you can probably not worry about that. 

Typical DC leakage for tantalums can easily reach 2uA or more.

Some information on leakage currents and temperature, when using tantalum capacitors can be found here (a 40C change can alter the leakage current by a factor of two):
http://www.avx.com/docs/Catalogs/techsuml.pdf


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## wquiles (Dec 26, 2005)

Newbie,

Thanks so much for jumping in here - I always appretiate your feedback 

In all of the recent posts I have eliminated the 0.1 power series resistor. I only had it initially while investigating how many amps I was getting on a cold bulb (post #14 above). Once I started fine-tunning the R/C values, I removed it to make sure I had a more realistic circuit. I have since not used the 0.1 ohm recently, once I knew what to look for on the Vbat spikes, but you are right, I should do a couple more measurements with a freshly charged pack again.

As of right now, the circuit only works efficiently for the battery and bulb combination. I had to change R3 for the bulb change (3xD M*G to WA1319) and I also had to fine-tune R3 to account for the initial and depleted battery status. By no means this is perfect or trully versatile, but it sorta-works well enough for now 

After all of the teaking involved, I would predict that the following values will have to be adjusted with each new battery pack/bulb combo:
- R3: A larger value is needed if the load on the pack is greater since the ration of R1/R3 dictates the starting point for C1 to charge. Unfortunately, too large of a value on R3 will cause a bigger negative spike on the battery, and too low a value will make the circuit dim before the battery is really depleted. The key is to maintain about 2.9V on Vgs of the FET - this or a higher voltage makes the FET conduct very well, specially since this FET has a 3mOms at Vgs=4.5V (in my tests this voltage, due to the zener, goes to about 3.1V). Because these are all competing forces, the circuit will only work "well" on a narow range. Also note that with a completely new battery pack, the ratio of R1/R3 would have to be changed as to achieve a Vgs of about 2.80V with a depleted battery pack.
- R2/C1: Might need to be adjusted as with a larger battery voltage the currents will get proportionaly higher and affect the effective charge times. I have not done any tests on this particular area, so I am not 100% sure - just an educated guess at the moment.
- For large currents (I am only testing at about 2 amps), the metal tab (thermal path) on the FET should be potted to the metal body since when the FET is not fully ON, the current will heat the FET some 


Now, not that I am done with this fun project, but after all of this time/work on this purely analog soft start circuit, I think that it "might" be far more effective/efficient to have a small 8-pin PIC microcontroller (with a built-in A/D) use PWM to monitor and then control the duty cycle to achieve the "appropriate" startup voltage and regulation. The firmware can then monitor the battery voltage and/or voltage at the bulb and adjust the PWM to the FET as necessary, and also perform the low battery condition and shutdown sequence (even gaving some warning pulses, or something similar). That might be the next evolution of this work, at least for me 

Will


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## NewBie (Dec 26, 2005)

Hi Will.

Go back and read my post, I put more information in there.

Also note, ceramics typically have lower leakage currents...

With your uC A/D and PWM deal, pay particular attention to the conversion and setup time, you may find that you will want to do this in an analog fashion to get the speed you need to prevent surges from hitting the bulb, since at time zero, you will in fact be hitting the bulb with 20-100 Amps, depending on the bulb type. You will be hitting it with full current, each time you switch the FET, which will reduce over time, as the filament heats up. In this case, you are still slamming the filament, but you are spreading it out over more time, in smaller chunks, so it isn't stressed as bad. Not as easy on the filament as the linear softstart solution.

The next step is to go to a L-C switcher, where you can actually control the in-rush current. One thing that will help is a driver that can command the mosfets to 100% duty cycle- they do exist.

Yes, it gets complicated in a hurry, once you go beyond the basic standard linear softstart.

If you need to monitor the high side current off the cell, you can always use a:
http://focus.ti.com/docs/prod/folders/print/ina193.html

The advantage of this part, is you have a gain of 20, which helps alot when measuring currents, and you can use much lower values for sense resistors. Don't be tempted to the higher gains, as you will have a lower bandwidth, and you may not see the full surge (slow response). In this case, you could lower your 0.1 to 0.005 ohms. Remember to kelvin connect it to the sense resistor, so you don't introduce the error of the copper board resistance.

Otherwise, go with a low side sense resistor, it takes less parts (just hook up scope to the resistor), and isn't bandwidth limited at all (the probe and scope may be...)


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## andrewwynn (Dec 27, 2005)

nice on figuring out the low-volt hack.. i don't think it's important to 'eliminate' the spike, just reduction is fine.. and i personally don't often 'blink' my lights.. i'm more concerned about when it's been sitting over night and i turn it on.

newbie makes a good point about the sense resistor it will already be helping to limit in-rush.. i usually just measure mV drop across a wire somewhere to measure current.. for example in my bench supply i have a 40mohm resistance.. it's perfect for getting an accurate current measurement... just divide the mV drop by 40. 

I actually ordered some of those opamp/comp combos they are cool.. i had a whole ckt designed around one of them, but re-designed it around one of the micrel LDO drivers.. i found a cheaper source for them.. they are 'double' the price i'd expect to pay for the opamp/comparator so i will probably build that ckt i described since it's already designed.. i'll be a buck 20 less to build.

to ans. the question about load.. this particular ckt is fine-tuned to the voltage it outputs.. you would need to tweak the base resistor 

newbie has a very good point about the leakage through the zener.. i meant to mention that is likely a cause of biasing the voltage levels and perhaps why things don't read as you expected. 

The beauty of this ckt is it is a buildable by anybody ckt.. you can wire discrete components right to each other in a bundle and fit into a light host. (of course heat-sink the FET to the body of the light somehow).. 

I have the 'next generation' design lined up for full regulation in a simpler design than the one in my hotdriver.

For this simple soft starter.. one more mod that would maybe make it work better.. either using an active component to take place of the diode for helping discharge.. that will get you another 1/2V quicker drop.. and the other thought.. rather than clamping C1 with the zener.. clamp that whole ckt branch.... with a larger value zener.. actually i'm realizing that means you could eliminate R1, and replace with the appropriate zener.. so the 60k/4.7uF always gets the same voltage regardless of Vbat.. i guess that'd screw up the D1 discharge.. so we might have to work in that active discharge ckt. 

It'll be a moot point for me n you.. the regulation ckt is not much more difficult to wire up and the regulator is $2.50, so for about $3.00 (or 7 if you want a really nice trimpot).. you can build a full regulator. 

I'm working on re-designing the requlator to have the FET below the lamp like in this design.. it's tricky, but i think i solved the main problem (since the ground of the regulator is the drain on the FET it's regulationg!).. it needs a 'hack' to jump start.. once running it should stay running.. feels a little bit like perpetual motion.. hoping it won't oscillate. 

I still have the 'ludicrously simple' ckt to build.. maybe Will can breadboard one of those... it uses only discrete components so just about anybody could hand-wire one on one of those neat prototyping boards avail. at RS. 

here post in the thread with the final design.. can be built completely from discrete components. I think this is the ckt you want to play with next. You can scroll up on that thread to read the prequil... i can't remember what the value of the D1 is.. pay attention to the fact the ckt is 'upside down'.. Mr Al convereted it to nch fet for me and it was easier than re-drawing it. 

Oh i could probably send you the DWL file i'm curious if they are cross-platform compatible anyhow. 

Oh.. btw.. per usual i made a quick reference to this thread and that one.. 

http://softstart.rouse.com leads to this thread
http://ldo-simple.rouse.com leads to that other one.
http://hotdriver.rouse.com leads to the hotdriver 

http://cpf.rouse.com leads to my flashlight collection of links

-awr


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## wquiles (Dec 27, 2005)

OK guys, I have what I think will be my final scope screen shots for this circuit . In all of them, the blue trace is Vbat and the yellow trace is Vgs, and both are on a 1Volt/div.

These two were created with R3=24K and a fully charged battery pack (Vnoload=5.65Volts):
(this one at 100mS/div)





(this one at 400mS/div)







These two were created with R3=22K and a fully charged battery pack (Vnoload=5.65Volts):
(this one at 100mS/div)





(this one at 400mS/div)







I tried putting the 0.1Ohm resistor in series with the bulb, and although it did not seem to affect the circuit much, I was never able to get reasonable measurements of the peak current. I ended up measuring the steady-state current with my Fluke M87 with no resistor in series, of about 1.97Amps (exactly where it should be), and with the resistor in series, by measuring the voltage right accross the 0.1Ohm I got 1.95Amps, which again is perfect. Sorry I was not able to give you nice screen shots of the pulsed current during the initial ON cycle 

Will


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## wquiles (Dec 27, 2005)

NewBie said:


> After moving the power on switch to R2, did you go back and look at the battery sag, since you removed the power switch resistance from the main current path?


Yes, it was a tad larger, but not my much. All of the screen shots on post#39 have the switch only in the path of the FET circuit.






NewBie said:


> As far as the zener, consider at 1V across it, there could be up to 50uA of current flowing. Try sticking it in series with your meter on uA scale to a power supply, and turning up the power supply voltage to the voltage you were reading across it, and checking out the leakage current.
> 
> With only 81uA flowing through R1 and R3, the leakage in both C1 and D2 can have an effect on the circuit's operating points, especially if temperature changes. D1 only has leakage currents in the nA range, and you can probably not worry about that.
> 
> ...


Thanks. That actually helps in understanding why the circuit in the bench behaved a little bit different from what I expected 





NewBie said:


> With your uC A/D and PWM deal, pay particular attention to the conversion and setup time, you may find that you will want to do this in an analog fashion to get the speed you need to prevent surges from hitting the bulb, since at time zero, you will in fact be hitting the bulb with 20-100 Amps, depending on the bulb type. You will be hitting it with full current, each time you switch the FET, which will reduce over time, as the filament heats up. In this case, you are still slamming the filament, but you are spreading it out over more time, in smaller chunks, so it isn't stressed as bad. Not as easy on the filament as the linear softstart solution.


Thanks so much. I suspected it was not going to be that easy!. Maybe a future project then 




NewBie said:


> The next step is to go to a L-C switcher, where you can actually control the in-rush current. One thing that will help is a driver that can command the mosfets to 100% duty cycle- they do exist.
> 
> Yes, it gets complicated in a hurry, once you go beyond the basic standard linear softstart.


I think I will stick with the simpler circuits first, before I go to the L-C switcher, where how you route wires can and does make a difference. I don't think I am ready for that yet 




NewBie said:


> If you need to monitor the high side current off the cell, you can always use a:
> http://focus.ti.com/docs/prod/folders/print/ina193.html
> 
> The advantage of this part, is you have a gain of 20, which helps alot when measuring currents, and you can use much lower values for sense resistors. Don't be tempted to the higher gains, as you will have a lower bandwidth, and you may not see the full surge (slow response). In this case, you could lower your 0.1 to 0.005 ohms. Remember to kelvin connect it to the sense resistor, so you don't introduce the error of the copper board resistance.
> ...


I will read into this. It might come handy in a future circuit - thanks!




andrewwynn said:


> nice on figuring out the low-volt hack.. i don't think it's important to 'eliminate' the spike, just reduction is fine.. and i personally don't often 'blink' my lights.. i'm more concerned about when it's been sitting over night and i turn it on.


Then, we are done. The current circuit does that perfectly 





andrewwynn said:


> For this simple soft starter.. one more mod that would maybe make it work better.. either using an active component to take place of the diode for helping discharge.. that will get you another 1/2V quicker drop.. and the other thought.. rather than clamping C1 with the zener.. clamp that whole ckt branch.... with a larger value zener.. actually i'm realizing that means you could eliminate R1, and replace with the appropriate zener.. so the 60k/4.7uF always gets the same voltage regardless of Vbat.. i guess that'd screw up the D1 discharge.. so we might have to work in that active discharge ckt.
> 
> It'll be a moot point for me n you.. the regulation ckt is not much more difficult to wire up and the regulator is $2.50, so for about $3.00 (or 7 if you want a really nice trimpot).. you can build a full regulator.
> 
> ...


Yes, please send me the Mac version of the final DWL drawing for the simple LDO design. I will start working on it today or tomorrow, since I am still on vacation and have "some time" available


----------



## NewBie (Dec 27, 2005)

As I recall, cells don't sag linearly with load current, so from what I figure, you are what, a little over 2x for the surge current, and probably less than 3x, right?


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## wquiles (Dec 27, 2005)

Not with the WA1319, but with the 3xD M*g bulb I was able to more-or-less measure at least 15Amps peak with no circuit (this with the very low impedance CBP1650 cells). I would expect that with the WA1319 it would be even higher (since the steady state current in the WA1319 is twice as large!).

With the circuit in place, my last measurements (which I was not able to capture properly on the scope  ) gave me an indication that with a steady-state current right at 2Amps for the WA1319, the peak pulsed current was about 4-6Amps, very much aligned with your expectations. I really need to buy a few of the TI/Burr-Brown Current Shunt Monitor chips you recommended so that I can make accurate current measurements 

EDIT: I just ordered a few of these chips, along with a few precision resistors (0.01 and 0.001) to go with it 

Will


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## NewBie (Dec 28, 2005)

wquiles said:


> Not with the WA1319, but with the 3xD M*g bulb I was able to more-or-less measure at least 15Amps peak with no circuit (this with the very low impedance CBP1650 cells). I would expect that with the WA1319 it would be even higher (since the steady state current in the WA1319 is twice as large!).
> 
> With the circuit in place, my last measurements (which I was not able to capture properly on the scope  ) gave me an indication that with a steady-state current right at 2Amps for the WA1319, the peak pulsed current was about 4-6Amps, very much aligned with your expectations. I really need to buy a few of the TI/Burr-Brown Current Shunt Monitor chips you recommended so that I can make accurate current measurements
> 
> ...




Here is something that will help with that scope you are using, if you haven't done it.

To capture the peak surge, without the soft start, turn on glitch detect, and dial your time base down to 1 nanosecond per division. If you have not done that, you might be surprised.


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## andrewwynn (Dec 28, 2005)

nice (current chips n resistors).. def. a little more resolution than my power supply lead = sense resistor solution (however that is amazingly accurate and simple!)..

I get a 'base' resistance by cranking a known current (3A) through the wire and using my fluke 87III set to 4 1/2 digits to measure the milivolt drop.. I'll get a reading like 120mV.. and simple division will get me 3A/120mV = 40mOhm resistance. 

Since the power supply lead is in the equation anyhow, it works very good for me.. and i can measure current spikes otherwise impossible. 

I did notice that when i finally got the soft start working on the hotdriver.. that the power supply would no longer click into current limit every time i turned on the light. Even when i could still measure some pretty high startup peaks at 1msec.. there was not enough energy behind that tiny spike. 

I'm sure the nsec spikes have to be insane! 

-awr


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## NewBie (Dec 28, 2005)

andrewwynn said:


> I'm sure the nsec spikes have to be insane!
> 
> -awr




You can figure roughly where they get to, if you add the battery internal resistance (and in parallel they don't add, but two cells makes 1/2 the resistance), measuring the resistance of your current path, and the cold resistance of the bulb.

Then just divide the battery voltage by that total. Thats pretty close to where your initial current spike will be.

One of the H4 bulbs I have measures 0.075 ohms cold. The current path in the light has been modified to get it down to 0.050, and the cell resistance for the UPS cell is 0.012 ohms. We have a total of resistance of 0.137 ohms, and the battery voltage is 12V. 12 V / 0.137 Ohms = 87.6 Amps which agrees with a very fast 15 GHz scope, and high bandwidth probe. (It actually measured higher, as the cell was a little over 13V before the switch was closed)


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## wquiles (Dec 29, 2005)

NewBie said:


> Here is something that will help with that scope you are using, if you haven't done it.
> 
> To capture the peak surge, without the soft start, turn on glitch detect, and dial your time base down to 1 nanosecond per division. If you have not done that, you might be surprised.


I have not done that yet. Sure looks like "fun". I will try to sneak to the garage for a little while today if/when I get both of my kiddies to sleep in the afternoon 






andrewwynn said:


> I did notice that when i finally got the soft start working on the hotdriver.. that the power supply would no longer click into current limit every time i turned on the light. Even when i could still measure some pretty high startup peaks at 1msec.. there was not enough energy behind that tiny spike.
> 
> I'm sure the nsec spikes have to be insane!
> 
> -awr


Yep, even though not measuring current, just looking at the negative voltage spikes I was able to capture really gives you an indication of how hard the batteries get hit during the initial ON cycle :naughty: 



Will


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## wquiles (Dec 29, 2005)

Newbie,
Andrew,

I tried once again today to capture the elusive pulsed current during initial turn ON. I got some graphs, but the values from the scope don't make sense, as I will explain below.

I have a shunt resistor for many months now, but I have not been able to measure accurately its resistance value, supposed to be 0.001 ohms or so, back a million years ago then it was first put into service!:






Along with the scope that I am borrowing from work, I also got a presicion, calibrated bench supply:






I used a wire-wound, 3.9Ohm, 25W resistor (large white block on this picture) along with the bench supply to find out the shunts' value:






Since the bench supply measures the current at any given set voltage, I took some measurements at 1A and at 1.5A, and it seems like the value of the shunt is somewhere around 0.0218 Ohms (averaging the two values recorded). The power resistor is also shown here above my hand-written notes:






I then moved to playing with the shunt resistor in-line with the bulb to see what happened. First, to get a baseline, I first measured the steady-state current without the shunt resistor using the power supply instead of the battery pack since I wanted really steady values (values shown in the power supply's built-in displays):
Vps=5.12V ; Ibulb=1.905A
Vps=5.62V ; Ibulb=2.009A

I then put the shunt resistor in series with the bulb, and I was able to measure the operating steady-state value of current and voltage for the WA1319 bi-pin bulb, again using the power supply until I got the same 1.9 and 2.0 Amps as before (values shown in the power supply's built-in displays):
Vps=5.12V ; Ibulb=1.918A ; Vshunt=52mV (calculated Rshunt=0.0271 Ohms)
Vps=5.52V ; Ibulb=2.000A ; Vshunt=54.2mV (calculated Rshunt=0.0271 Ohms)
These higher values of Rshunt make sense since these were taken on the actual breadboard and the breadboard contains additional small wires to make interconnections, so everything seems good so far . 

Now I used the scope to measure the spike of voltage right across this Rshunt (0.0271 Ohms), but this time I used the battery pack instead of the PS, since that is the end goal after all. In all of these screen captures, the top two traces are the instantaneous voltage at each side of the resistor, and the red (lower) trace is the scope's math of substracting these two channels. The top traces are at 1V/div and the red trace is at 100mV/div.

This first one, at 20mS/div, shows the peak value to be 378mV, which would correspond to a peak current of 0.378/0.0271=13.94Amps, which we know is too high since the circuit is operational:






This next one, at 400mS/div, shows the same signals, but also the steady-state voltage at an average 242mV, which would correspond to a current value of .242/0.0271=8.9Amps, which we know its wrong since the steady state current has been measured by many methods/meters, and with a fresh battery pack it is always between 1.9 and 2.0 Amps.






So clearly I am either doing something wrong, or not setting up the scope properly, or the scope is limited in its ability to perform this in-circuit measurement. I am too tired to keep trying for ever, since I want to move on to the simple LDO regulator from AWR, so I will likely leave it as is for now. At least I now have an accurate value for my shunt resistor so that I can use it in the future 

Will


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## NewBie (Dec 29, 2005)

I'd try next time, just hooking the scope probe gnd on one side of the resistor, and the other end of the same probe, on the other side of the resistor. This should work alot better than what you were trying to do.

Comments....

Normally you have to use identical probes and do a "calibration", and once done, with no power, you'd have zero volts.

You have about 160mV offset, with no power.

Another thing I see there is alot of noise, so thats going to make measurements tough.

You'd need to subtract the offset from your measurement...
" correspond to a current value of .242/0.0271=8.9Amps,"

0.242 - 160mV offset = 82 mV 0.082/0.0271= 3.03A, which is alot closer, but not exact yet.

But you know the current is 2A, so we'd be able to guestimate a correction factor of 2/3. 2/3 * 3.03 = 2.02A, for the average current.

Looking at the surge, I see 115mV above the offset average.

0.115/0.0271 = 4.24 A * 2/3 (the scaling correction factor) 2.8 A surge.

But the scope is on a very slow 400mS per division, so it is not likely to catch the leading edge of the surge anyhow.


Anyhow, on the lighter side of things, I remembered from the 1970's, a special circuit that was used to make light bulbs last much longer than normal. It was used in areas where there was limited access, accessing them was dangerous, or where you were using a bulb as a flasher, and wanted to get a long life out of it. So I searched high and low, and finally found the circuit. It is another softstart circuit, a little more complicated:


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## wquiles (Dec 30, 2005)

NewBie said:


> I'd try next time, just hooking the scope probe gnd on one side of the resistor, and the other end of the same probe, on the other side of the resistor. This should work alot better than what you were trying to do.


Good idea - easy to try indeed. Can I also move the shunt to the "ground" side of the lamp's circuit path, from the source of Q1 to ground, or would (as I think more about it) affect the bias of Q1 enough to affect the circuit's behavior?





NewBie said:


> Comments....
> 
> Normally you have to use identical probes and do a "calibration", and once done, with no power, you'd have zero volts.
> 
> ...


Totally awesome - you are d'man :bow:. Now things start making sense. I will try to look into this aspect for sure since it does affect "all" measurements on the scope a little :thumbsup: 





NewBie said:


> Anyhow, on the lighter side of things, I remembered from the 1970's, a special circuit that was used to make light bulbs last much longer than normal. It was used in areas where there was limited access, accessing them was dangerous, or where you were using a bulb as a flasher, and wanted to get a long life out of it. So I searched high and low, and finally found the circuit. It is another softstart circuit, a little more complicated:


Interesting circuit - not all that complicated. However, not as good as using a true MOSFET, right? Maybe the transistor(s) were heat-sinked also?

Will


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## NewBie (Dec 30, 2005)

Since your light is battery powered, wherever you connect the scope ground becomes ground, if you don't have the other probes connected... Since you just need a current measurement, you could hook the ground to the sense in the high side, and the tip on the other side of the resistor.

You don't get all the other traces this way, but what you are really after is current anyhow.

The No.44 bulb draws 0.25A and the No. 47 draws 0.15A.

With a little thought, you could modify for a 2N3055, or more thought would get you to a MOSFET for the drop transistor.


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## andrewwynn (Dec 30, 2005)

I'm not sure you measured your shunt resistance correctly.. if you are calculating based on the 3.9ohm power resistor (i.e. subracting voltage).. not the best way.. just measure with 4 1/2 digits and a multimeter the voltage drop on the Rsense.. hooking up separate leads right on the shunt terminals for the meter.. it looks like you might have the leads down to the breadboard in the equation which will throw off your measurements dramtically. 

My bench supply will output a preset current regardless of voltage.. i actually set the current by shorting the leads and dialing the current.. If you don't know if yours can handle that it's best to stick the 3.9ohm in the ckt as well.. but just put your two resistors in series and with a known measurement of current (your bench supply displays the current).. now measure the mV drop on just the shunt resistor.. I'm pretty confident you'll have a much lower measurement of resistance. 

Even with the fancy driver in the hotdriver and using slow start.. there is an initial spike of current that can be double-digits. it has no energy in it just voltage akin to a static spark can be 15,000 V but won't hurt you. 

I think you need to re-calibrate your shunt.. it should be like a 100 or 200A shunt based on the apparent physical size, but the value you are saying calculates to more like a 2A shunt.. (should have 35mV at full scale).. 17.5mohm = 2A shunt. 

You will be quite amazed to see the difference when you measure the shunt directly w/o wires.. you can't have any add'l wires in the measurement.. you probably have at least 3-4mohm of wires.. and each contact on a breadboard can be at least 10-20 more mohm.. a shunt that big typically has a resistance of 3-4mohm.. a 100A shunt is only 35/100ths of a mohm! consider that an entire inch of 18ga wire is merely 1/2 a mohm of resistance.. and now look at that big block of metal.. 

If i had to guess you have a 50 or 100A possibly 200A shunt there.. it should be on the order of 1/3 mohm to 3.5mohm of resistance. 

put your 3.9ohm and the shunt in series with the power supply set to a precise current.. 2A or 3A is good.. hook up some leads separate to the shunt terminals and measure the voltage... you will find you introduced a LOT of resistance you didn't realize.. looks like you have a switch or two possibly in the loop. 

I noticed when i tried to take voltage measurements in my hotdriver on the breadboard.. that i couldn't get accurate voltage measurements on the FET until i SOLDERED the test leads.. so when i need accuracy that's exactly what i do.. tack on some 30ga wire-wrap wire to my terminals.. the only way to be sure. 

-awr


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## wquiles (Dec 30, 2005)

andrewwynn said:


> I'm not sure you measured your shunt resistance correctly.. if you are calculating based on the 3.9ohm power resistor (i.e. subracting voltage).. not the best way.. just measure with 4 1/2 digits and a multimeter the voltage drop on the Rsense.. hooking up separate leads right on the shunt terminals for the meter.. it looks like you might have the leads down to the breadboard in the equation which will throw off your measurements dramtically.
> 
> My bench supply will output a preset current regardless of voltage.. i actually set the current by shorting the leads and dialing the current.. If you don't know if yours can handle that it's best to stick the 3.9ohm in the ckt as well.. but just put your two resistors in series and with a known measurement of current (your bench supply displays the current).. now measure the mV drop on just the shunt resistor.. I'm pretty confident you'll have a much lower measurement of resistance.


For the actual measurement I setup the simple circuit as in my hand-written notes, outside of the soft-start circuit, so I have minimal stuff in the way. I actually setup the PS (which measures the output current) to output exactly 1Amp and then 1.5Amp and used my Fluke 87 in high resolution mode to read the mV drop at the shunt. I am fairly confident that the average value of 0.0218 Ohms is pretty close, although of course it "does" include the two short wires coming out of it.






andrewwynn said:


> I think you need to re-calibrate your shunt.. it should be like a 100 or 200A shunt based on the apparent physical size, but the value you are saying calculates to more like a 2A shunt.. (should have 35mV at full scale).. 17.5mohm = 2A shunt.


At least on the little sticker (barely visible) it says that the shunt (when new?) was supposed to be 0.00065 Ohms, and it is rated at 5Amps max.






andrewwynn said:


> You will be quite amazed to see the difference when you measure the shunt directly w/o wires.. you can't have any add'l wires in the measurement.. you probably have at least 3-4mohm of wires.. and each contact on a breadboard can be at least 10-20 more mohm.. a shunt that big typically has a resistance of 3-4mohm.. a 100A shunt is only 35/100ths of a mohm! consider that an entire inch of 18ga wire is merely 1/2 a mohm of resistance.. and now look at that big block of metal..


Maybe I am missing the point, but a shunt with no wires attached to it means it is a nice piece of metal in my bench. The only way I can insert a shunt this big into a circuit for measurements is to actually have some wires attached to it, just like I show in my pictures. That is why when making my measurements for the shunt I included the value of those small wires into my measurement. True, 0.0218 Ohms is not the "real" value of the shunt by itself, but I honestly don't care what is the shunt's value by itself. Am I trully missing the point you are trying to make here? Please help me understand what you meant.





andrewwynn said:


> I noticed when i tried to take voltage measurements in my hotdriver on the breadboard.. that i couldn't get accurate voltage measurements on the FET until i SOLDERED the test leads.. so when i need accuracy that's exactly what i do.. tack on some 30ga wire-wrap wire to my terminals.. the only way to be sure.
> -awr


That is a great tip indeed. I must do this next time - the little interconnect wires in the breadboard can't be condusive to accurate values, right? 

Will


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## wquiles (Dec 30, 2005)

NewBie said:


> Since your light is battery powered, wherever you connect the scope ground becomes ground, if you don't have the other probes connected... Since you just need a current measurement, you could hook the ground to the sense in the high side, and the tip on the other side of the resistor.
> 
> You don't get all the other traces this way, but what you are really after is current anyhow.


Thanks. I seem to vagely remember from my EE days (10-15 years ago!) that I had to be careful with conecting the ground of the scope right across a resistor when the actual circuit ground was somewhere else. However, you are right - since the circuit is battery powered, as long as I don't have any other instruments connected while making this ONE measurement, the whole circuit should really be "floating" regarding the "real" ground of the scope 






NewBie said:


> The No.44 bulb draws 0.25A and the No. 47 draws 0.15A.
> 
> With a little thought, you could modify for a 2N3055, or more thought would get you to a MOSFET for the drop transistor.


Ahhhh - that explains the smallish transistors and not using a MOSFET like I do. In the circuit I am using my currents at at least 1Amp, 2Amps with the WA1319, and possibly up to 3-4Amps steady-state with other WA bulbs, so the MOSFET was more of a "requirement" 

Will


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## photo2000a (Dec 30, 2005)

this was agreat post, i noticed the 3 transistors in the pix and said himm sure enough modern electronics those were great magazine i had a ton of fun building those projects even build this soft start way back then i was only a kid guess i just loved lights


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## wquiles (Dec 30, 2005)

photo2000a - Glad this post was able to revive some interesting memories 


Andrew,
You were right about Rsense being hard to use due to contact resistance. I had to re-arange the place where I was inserting Rsense since I was not getting consistent reading due to variable contact surface on the breadboard!!!. Once I was able to test with the battery and with the bench PS (at the same steady-state current), I was able to measure again and came up with Rsense = 0.0265 Ohms, which of course includes the short wires from the shunt to the breadboard.

Newbie,
Your idea worked great. I was able to measure the Voltage drop across Rsense with the scope (with nothing else attached!) and got the following shots with less noise and now at only 50mV/div (and 100mS/div). The first one shows the measurement cursor on the peak value (82mV) and the second shows the average value (54mV). Based on the accurate measurements above, these are about 10% higher than they should be, so once I account for this, the average value was about 1.851Amps (the battery has discharged some, so I am not at the 2.0Amp rate) and the peak would be about 2.9Amps or so. So even with a full pack, a max. of about 3 to 3.5Amps (with the soft-start circuit in place, of course) beats the 15Amps that I measured earlier with no circuit in place. Of course, at some point I will have to re-do the direct drive peak pulsed current now that I have a working Rsense  :










Will


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## NewBie (Dec 30, 2005)

That looks much better:






When you do the deal without the soft start in there, get some shots at 1nS per division, and 1uS, with glitch detect on...

Glad to be of help.

I think what Andrew is trying to say, in engineering terms, is called a Kelvin connection (for the sense resistor). That should ring some bells and shake out the dust upstairs...or what do they call it up north...oh, permafrost on the brain.


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## andrewwynn (Dec 30, 2005)

that little hump is exactly what i'd expect from the ckt.. absolutely wonderful. 

obviously to include the Rsense in the ckt you need to use the short wires to the BB.. if they are 24ga wire, that would be about 1/2 the resistance of your whole Rsense.. it would be better to just use a loop of wire... 4.67 inches of 24ga wire is 10 mohm.. very easy to calculate from that.. whatever the mV measurement is.. divide by 10 and get A.. the key is you have to measure right on the wire, not through the contact.. if you are taking the measurements from another lead that is across a breadboard contact you can estimate 5 to 10mohm PER CONTACT.

you should get a measurement right to the posts on the shunt.. it's ok that it uses the wires but you can't get an accurate measurement if using them.. though you basically made your own resistor including the wires etc.. if you want accurate you have to measure right no the posts of the shunt.. just add two more pigtails going nowhere that you can use with your meter leads. 

-awr


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## wquiles (Dec 30, 2005)

andrewwynn said:


> that little hump is exactly what i'd expect from the ckt.. absolutely wonderful.


Thank you . I could have not gotten here without your help :bow:





andrewwynn said:


> obviously to include the Rsense in the ckt you need to use the short wires to the BB.. if they are 24ga wire, that would be about 1/2 the resistance of your whole Rsense.. it would be better to just use a loop of wire... 4.67 inches of 24ga wire is 10 mohm.. very easy to calculate from that.. whatever the mV measurement is.. divide by 10 and get A.. the key is you have to measure right on the wire, not through the contact.. if you are taking the measurements from another lead that is across a breadboard contact you can estimate 5 to 10mohm PER CONTACT.
> 
> you should get a measurement right to the posts on the shunt.. it's ok that it uses the wires but you can't get an accurate measurement if using them.. though you basically made your own resistor including the wires etc.. if you want accurate you have to measure right no the posts of the shunt.. just add two more pigtails going nowhere that you can use with your meter leads.


OK, now I get what you were trying to tell me . I will add the extra pigtails and will measure the voltage drop right on the shunt this weekend. Thanks 

Will


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## wquiles (Dec 30, 2005)

NewBie said:


> That looks much better
> 
> When you do the deal without the soft start in there, get some shots at 1nS per division, and 1uS, with glitch detect on...
> 
> ...


Thanks very much Newbie :bow:. I have been very frustrated until now trying to get this important measurement, but you "really" helped me understand how get a good current measurement with the scope 

Yes, when I run the Direct Drive, I will use the glitch function of the scope (which I finally found, by the way ).

Will


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## NewBie (Dec 30, 2005)

Tektronixs does a great job of hiding their features under menus, don't they?


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## petrev (Feb 20, 2006)

Hi AWR
Re-Posted from wrong thread

is this the M6-Reg you are talking about 
http://candlepowerforums.com/vb/showthread.php?t=101677
?
Are you going to be providing this as a mod or as a set of plans (final parts list and diags ) by any chance as it seems just the ticket - 2x3 17500 drop in holder with soft start.
Tried following the post but not being totally technical - just an average bodger - got a bit lost and cannot tell what stage you are at. Hope I'm not asking too many questions that have already been covered somewhere !



andrewwynn said:


> . . . (i.e. if the switch is 'on'.. can you interrupt power and will soft-start and such still work).


You do seem to have spotted the big question with this board for an M6 !

Thanks 
Pete




andrewwynn said:


> you could build one into the tailcap simlar to how i'm building my M6 regulator.. if you build the battery pack with a solid threaded rod top to bottom it brings the 'pos' back to the tailcap.. you can wire from the 'pos' side of the batteries with a wire past the batteries back to get power to the tailcap.. Winny would have to answer if you can keep the 'switch' hard wired so that you can use the tailcap connection to operate the light (i.e. if the switch is 'on'.. can you interrupt power and will soft-start and such still work).
> 
> The soft start should solve the problem with protected cells.. I would work out a solution with 2x3 17500 like my M6x6 pack i made.
> 
> -awr


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## petrev (Feb 20, 2006)

Hi Again
? Will 2x3 17500 fit without tail mods and how close are you to something to fit on the side of a pack ? I take it using 2x3 R123 is needed to use a tail circuit ?
Cheers Pete




> Originally Posted by andrewwynn
> you could build one into the tailcap simlar to how i'm building my M6 regulator.. if you build the battery pack with a solid threaded rod top to bottom it brings the 'pos' back to the tailcap.. you can wire from the 'pos' side of the batteries with a wire past the batteries back to get power to the tailcap.. Winny would have to answer if you can keep the 'switch' hard wired so that you can use the tailcap connection to operate the light (i.e. if the switch is 'on'.. can you interrupt power and will soft-start and such still work).
> 
> The soft start should solve the problem with protected cells.. I would work out a solution with 2x3 17500 like my M6x6 pack i made.
> ...


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## andrewwynn (Feb 20, 2006)

2x3 17500 needs a minor modification to the tailcap, i did myself in minutes with hand-tools.. when i make my M6 pack i will make a replacement tail cap cup that will swap out so you won't have to mutilate your original. 

I wouldn't bother with R123s.. why put in 15 WH when you can put in 24WH.. the 6-pack i made will run for like 40 minutes with the MN21 lamp! 

The link to the soft-start was just that.. soft-start only.. not a regulator.. the regulator i will be making for M6 is more like this one: http://hotdriver.rouse.com

It will be a complete pack.. two-parts.. a drop-in battery pack with regulator attached and a replacement inner tail-cap cup.. to give that extra 1/4 inch needed to fit DOUBLE the battery capacity!

ps.. the M6 will run a WHOLE LOT cooler with this design.. it will not be putting out 22W of power into heating the battery packs (i've measured over 180F on a battery pack inside an M6!). 

-awr


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## wquiles (Feb 20, 2006)

andrewwynn said:


> 2x3 17500 needs a minor modification to the tailcap, i did myself in minutes with hand-tools.. when i make my M6 pack i will make a replacement tail cap cup that will swap out so you won't have to mutilate your original.
> 
> -awr


Andrew,

I got some aluminum in the right diameter, so I will be using my mini-lathe to try and create a new cup for the tail cap so that we can experiement with it 

Will


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## petrev (Feb 21, 2006)

Kit sounds great - any idea of a time scale ?


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## andrewwynn (Feb 21, 2006)

will.,. sweet... i sent you the eMachineshop file, right? 

I hope to have the kit in the works by May. (i can't work on it 'til nanos are mostly done). 

-awr


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## wquiles (Feb 21, 2006)

andrewwynn said:


> will.,. sweet... i sent you the eMachineshop file, right?
> 
> I hope to have the kit in the works by May. (i can't work on it 'til nanos are mostly done).
> 
> -awr


Yes, I have it, and I hope to start cutting the first prototype in the next couple of weeks 

I will keep you posted!

Will


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## andrewwynn (Feb 21, 2006)

nice! you can just hit the 'price' button on the file to see what they will cost to make like 100-200 of them for the full-run. it's pretty amazing actually. 

-awr


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