# Feeler thread - 0-25A adjustable linear driver



## DIWdiver (Nov 26, 2014)

Edited 1/11/15

Yes, that's right, 25 amp adjustable driver, two modes. I'm looking to see if there's enough interest in one to make it worth building. Please let me know what you think.


$35 USD would get you all this:


It would be based on my existing IS1011 automotive driver discussed extensively here: http://www.candlepowerforums.com/vb...Automotive-linear-13-5A-LED-driver-adjustable. It would be the same size and configuration. Someone asked me if I could mod one to 21A. I figured with a new board, I could go as high as 25A.

Edit: it would be 33mm round to fit MAG-D tube.

This would probably be offered in several versions: 


One cell, input voltage 3.0-5.0V
Two-cell, input voltage 5.0-9.0V
Multi-cell, input voltage 8-35V (not sure this one makes sense, as there are other options in this range).

Edit: two versions: 3.0-5.5V, 3.5-36V.

Each version would be offered in several current ratings up to 25A. There is an onboard potentiometer that can be used to adjust the outut from zero to whatever the rating is for that particular driver.


The driver would have two modes, high (100%) and low (25%). Any adjustment to the potentiometer adjusts both high and low proportinally, so that low is always 25% of high. The 4:1 ratio can be customized upon request. The switch required to run the modes is a double throw type, so a 'clicky' type switch will not work. Something like this is needed: http://www.digikey.com/product-detail/en/100SP3T1B1M1REH/EG2376-ND/378845. With a 'clicky' type switch you could control only one of the modes, i.e. high and off or low and off. For best results I recommend switches with gold plated contacts, like the one in the link.


The driver would draw about 10 mA even when switched off. This could be a problem in a flashlight that sits idle for long periods. An alternate wiring scheme can reduce this to a few microamps using a double-pole switch like this: http://www.digikey.com/product-detail/en/M2023SS1G01/M2023SS1G01-ND/1027302 instead of the single pole switch mentioned above.

Edit: 2-3 mA normal, less than 1 mA in undervoltage cutout mode.

Like the IS1011, it would have an on-board temperature sensor to protect the driver from overheating. In order for this to work properly, the driver must be properly mounted to an aluminum or copper heatsink. There would also be a point to connect an external thermistor for protecting the LED(s) if they are on a different heatsink.


Instead of the over-voltage cutout of the IS1011, this would have an undervoltage cutout, probably at 2.7V for the single-cell version, 5.4V for the two-cell version, and disabled for the multi-cell. This could be disabled for those who would rather sacrifice the battery to keep the light running.


If it's of interest, I might set it up so the external thermistor input could also be used for a PWM input instead. PWM frequencies could be up to 20 kHz (higher on request). However, the PWM signal would be filtered in the driver to provide an analog dimming function to the LED. This is better for some digital cameras, though it can cause some tint shift in the LED. If it were desired to apply PWM to the LED, this could be accomodated. I'd have to investigate how high a frequency is practical. I'm guessing 10 kHz-ish.


Sound too good to be true?


***HERE'S THE CATCH***
The driver would be a linear driver. This means that the output voltage cannot be higher than the input voltage, and to have decent efficiency, the input voltage needs to be close to the output voltage. This limits what battery/led combinations would work well. For the single-cell driver you'd use a single cell (or several in parallel), and a single LED (or several in parallel). For the two-cell driver you'd use, obviously, two cells in series and two LEDs in series (or parallel combinations thereof).


With these combinations, the efficiency can actually be quite good. With a 3.5V LED and a 4.0V battery (LiIon batteries won't stay above 4.0V under load except perhaps very briefly), you'd get 87% efficiency. As the battery voltage falls to 3.65V, the efficiency would rise to 96%. As the voltage continues to drop, the regulator would begin to "drop out", meaning the output voltage would begin to fall. All LEDs have a voltage vs. current curve, and as the voltage falls the current drops according to the LED's curve. The efficiency would remain near 94-96% as the input voltage drops to 3.0V. After this the dropout voltage begins to increase and the efficiency begins to fall. Operation in this region (below 3.0V input) would not be guaranteed.


If your LED voltage were 2.95V, the driver would remain in regulation until the battery voltage reached 3.1V, and the efficiency would start at 74% and climb gradually to 95%.


The 'dropout voltage' of a driver is the minimum input-output voltage differential required to maintain regulated current. This is a characteristic of all linear and buck type regulators. The 0.15V dropout voltage of this driver at 25A would be considered quite low. At lower currents, the dropout voltage is even lower.

Cheers.

D


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## DIWdiver (Nov 26, 2014)

Updated specs: (Jan 15, 2015)

Wire hole sizes have been reduced, will now accept 16 AWG stranded. This is a bit small for 25A, but in a flashlight with inches of wire length, should be okay.

Input voltage options will be either 3.0-4.5V, or 3.5-36V. The higher voltage range is not automotive rated, but it should survive all but the very worst things that can ever happen in a car. 

Current is adjustable from 0 to max with an onboard potentiometer. An external pot can also be used.

boards will be offered with max currents of 10, 16.7, and 25A. Other values could be made on request.

Price is $35 USD.

Board size is 33mm diameter.


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## Illum (Nov 26, 2014)

what sort of driver IC sources 25A? I have never heard of anything in the dimension mentioned. :green:


EDIT: Maybe the BTS555 PROFET


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## DIWdiver (Nov 26, 2014)

It's not an IC. It's built from discrete components, and the main power element is a large FET, which is designed to handle that kind of power.


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## lucca brassi (Nov 27, 2014)

this would be active electronic load in base ?


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## DIWdiver (Nov 27, 2014)

lucca brassi said:


> this would be active electronic load in base ?



Sorry, I don't understand the question. The FET is the pass element in an active circuit that regulates current.


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## Epsilon (Dec 9, 2014)

I was looking for your 10.5A or 13.5A thread to combine two in parallel. So this thread is great! 
To answer the question: Yes, I would really like to have one (or two ).

But:
- It has to fit a MagD tube (33mm across)

If possible:
- Reduce the leak current to a minimum (<0.1mA), maybe with a two stage activation.

This will probably be impossible:
- Pick a FET which has an electrically insulated cooling face (so it does not matter to which surface it is mounted).


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## Hoop (Dec 9, 2014)

If you make this, it would be the most convenient option on the market for the Luminus CBT-140 or 90. I would buy 1 to support the effort. I think I would be willing to gut my Olight SR90, convert the battery pack to parallel, and replace the led with a CBT-140 if I had this driver!


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## DIWdiver (Dec 9, 2014)

Epsilon said:


> I was looking for your 10.5A or 13.5A thread to combine two in parallel. So this thread is great!
> To answer the question: Yes, I would really like to have one (or two ).
> 
> But:
> - It has to fit a MagD tube (33mm across)



Hmmm... No promises, but maybe. It would be a very tight fit. Might have to give something up. I'd definitely look at it though.



Epsilon said:


> If possible:
> - Reduce the leak current to a minimum (<0.1mA), maybe with a two stage activation.



This can be done with a double pole switch. Or if you need only one mode, even with a single pole switch. Not going to happen with single pole and multiple modes.



Epsilon said:


> This will problably be impossible:
> - Pick a FET which has an electrically insulated cooling face (so it does not matter to which surface it is mounted).



I'd ship it with an insulating thermal pad, so in most cases you wouldn't have to worry about that. The fully insulated packages have much worse thermal conductivity, thus much lower power ratings.


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## DIWdiver (Dec 9, 2014)

Hoop said:


> If you make this, it would be the most convenient option on the market for the Luminus CBT-140 or 90. I would buy 1 to support the effort. I think I would be willing to gut my Olight SR90, convert the battery pack to parallel, and replace the led with a CBT-140 if I had this driver!



Unfortunately, it looks like there would be very few sales. Until today the silence has been deafening!


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## Laser Project (Dec 26, 2014)

I'd buy four of the 25 amp drivers if I can adjust the voltage down to 2.0 VDC for a total amount of current close to 15 amps.


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## DIWdiver (Dec 26, 2014)

You don't have to adjust the voltage; the driver takes care of that. You adjust the current. The LED determines how much voltage is required for that much current (will vary from one LED to another, and over temperature), and the driver supplies the correct voltage and current.

What you do have to provide is a power source that has a voltage somewhat higher than the LED, but not so high that the driver overheats. The single-cell version of the driver would work perfectly with a source of 3.0-3.5V. Adjust to 15A and provide enough heatsinking for 15-25W, and you're done!


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## DIWdiver (Dec 28, 2014)

Okay, I've done the schematic and board layout. Looks like it will fit on a 33mm diameter board, without giving up anything!

Also looks like $35 is sufficient that I can break even after selling 20 boards or so. I'm starting to think this is a go!


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## Epsilon (Dec 29, 2014)

Arf! Wasn't counting on it and have spent hours filing aluminium to make use of two 10A versions . But nice you are going ahead with this build! Still interested in one! Have to do some mods to the current switch assembly I made but it will probably work just fine .


Thanks for the efforts!


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## DIWdiver (Dec 29, 2014)

Okay, I've decided this is definitely going to happen.

I did some more work on it today. Looks like previous plans were not sufficient to provide reasonable input voltage ranges.

New plan looks like it will be a 3.0-4.5V version, and a 3.5-36V version, the difference being one component. I'll probably offer it in 10A, 16.7A, and 25A ratings. Maybe a 5A or others if there's demand. All would have a pot to adjust from zero to max rated current.

Wow this board is this tight! Almost have to deviate from my 'normal' PCB layout rules into 'special' territory. Not quite though, at least so far.

In case anyone is getting anxious, you should keep your pants on. It will be at least a month, maybe several before this is ready for sale.


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## Dark Laser (Jan 1, 2015)

Will the pot be onboard or have you planned to provide pins for an external pot (so that you can operate the light with just the pot)?
Anyway, sounds promising :thumbsup:


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## DIWdiver (Jan 1, 2015)

There will be an onboard pot, but you can also use an external one. You'd set the max with the onboard one, than adjust within the range with the external one.


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## DIWdiver (Jan 13, 2015)

Working on ordering boards for the first build. Not sure why my password is a problem all of a sudden.

Note edits to post #1.

Would anyone be interested in a much simplified driver? This would eliminate low voltage cutout, overtemp protection, and current adjusting ability (HI and LOW would be fixed instead of adjustable). This would eliminate over half the parts on the board, thus improving the reliability. I'd probably offer it at $28-30, since the parts cost is a bit less (yes, half the parts are removed, but only about 19% of the parts cost).

If I was a cave diver or really dependent on my light for some other reason, this is what I would do.


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## DIWdiver (Jan 14, 2015)

Boards are on order!


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## bigchelis (Jan 15, 2015)

So, for an MTG2 Maglite D size


Two-cell, input voltage 5.0-9.0V......You can make it accept 8.4V input and lock in the current at 6A or 8A?

With 8.4V input and 6A that would be amazing 50watt MTG2 build.

bigC


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## DIWdiver (Jan 15, 2015)

Exactly the kind of application it's built for.


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## Epsilon (Jan 16, 2015)

My 2 cents (if it isn't it already to late ).
- Since this is a linear driver at magtube size, a low voltage cut-off in my opinion is less of a requirement since it will likely be used for handheld lights so the output is monitored constantly.
- High temp protection (80ºC?) cut-off could be a good idea, since this will only be used in high power lights which could heat up quicker than you notice at your hands. But this is not mandatory ofcourse .
- Adjustable high/low would be nice, but locked is fine, ppl should chose wisely . The IS1006 levels can be changed by adding a potmeter, this is still possible with this driver?

Thanks for the effort


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## DIWdiver (Jan 16, 2015)

Well, it probably is too late, as I just ordered a 50 boards. But I still have some options as to how I build them. Mostly that's about setting voltage and current levels, and leaving off features.

The IS1006, IS1011, and IS1013 all have similar 'mode' capability, except that the IS1011 and IS1013 have added a ground terminal that makes it easier to use an external pot to give full-off to full-on control.

Low-voltage, onboard overtemp, and offboard overtemp protections are all on the IS1013 circuitry. Any of them can be modified or disabled when I build the board (the offboard temp protection is automatically disabled if you don't connect a sensor). The on-board pot can also be left off, giving you fixed high/low like the IS1006 (still externally variable). I've considered a version that leaves them all off, making it very like the IS1006. That would save me a little in parts and some labor, so the price would be reduced some.

The overtemp controls gradually reduce the output as the temp goes from 70C to 80C at the sensor. Keep in mind that the junction temperatures will be quite a bit higher than this, especially for the onboard sensor.


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## DIWdiver (Jan 23, 2015)

Boards arrived today. Yikes! I haven't even ordered parts yet. I haven't even received notice that the boards were built.

My wife got notice yesterday from UPS that they shipped from China (thanks for telling me!). Amazing what $30 can get you.

The boards look good and fit in a MAG D tube with room to spare.

Now I have to order parts and figure out how to test them. My EZ-clips won't stand up to 25A. I know IDI makes pogo pins that can handle that. Guess what I'll be doing while snowed in tomorrow?

Oh, I guess I have to start a sales thread too. I'll post a link when it's open. If everything goes smoothly it will be a week or so. If I botched something and have to re-make the board, it will obviously be longer.


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## Epsilon (Jan 24, 2015)

Keeping an eye on this thread and the sales thread .


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## DIWdiver (Jan 31, 2015)

The first board is ready to test! Check the pictures in post #2.


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## Epsilon (Jan 31, 2015)

Nice work 

That FET is huge ^_^, positive thing is that I do not have to use insulator bushes now to screw it down.


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## DIWdiver (Feb 2, 2015)

Tested a 16.7A driver at 3V input, 2.85V output. Looks to be working great!

I see no issues with the 16.7A driver, which means the 10A will be fine too. I'm a bit worried that when I get my test fixture to the point it can test at 25A, I'll find that the dropout voltage is higher than the 150 mV that I expected at 3.0V input.

Got some other things going on, so it might be a while before I can test at 25A, but it looks like the board is fine, just a question of whether the FET can live up to my expectations at 25A. It's definitely a go at 16.7A.


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## Epsilon (Feb 19, 2015)

Epsilon said:


> If possible:
> - Reduce the leak current to a minimum (<0.1mA), maybe with a two stage activation.





DIWdiver said:


> This can be done with a double pole switch. Or if you need only one mode, even with a single pole switch. Not going to happen with single pole and multiple modes.



I'm exploring the option to use a double pole switch. To be clear, this switch needs to be in between the battery + and the board (to supply the board of power)? So it doesn't switch the current?

The FET when off will not leak any current?

Just want to clear this up . Thanks!


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## DIWdiver (Feb 19, 2015)

When powered, the board draws several milliamps, I'm going to say around 3 typical, but I haven't done anything careful about calculating or measuring actual or maximum values.

You can switch the board off using a low-current switch IF you don't wire the high side (anode) of the LED to the L+ terminal. Instead you have to connect it to the battery side of the switch, so the LED current goes brom the battery to the LED, then to L- terminal, through the FET and the sense resistor to B-, thence back to the battery. Then only the board's supply current goes through the switch. If you do this, then there WILL be some leakage through the FET when the board is switched off, but it will be microamps, trivial in a vehicle. If you want to use the same switch to control the Hi-Lo, then you need a double-pole double throw switch with a center off position.

If you want to connect the LED between L+ and L-, then the LED current will have to go through the switch. I wouldn't recommend using a single switch for power and mode control, because a high current switch won't control the modes as cleanly (it will work, just won't be as accurate and repeatable), and a low-current switch won't handle the LED current.


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## Epsilon (Feb 20, 2015)

Thanks for the reply, that is clear. The FET leaking a few microamps is fine indeed (even in a hand-held device).

Now I have to find a switch that is suitable, I would like to use a two stage clicky switch. I'm not sure if they are available in double pole configuration, but will try to locate one.


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## DIWdiver (Feb 22, 2015)

So the test fixture is finally finished, and the 25A board tested. FYI, 18 AWG wire gets pretty warm at 25A!

As I suspected, the 150 mV dropout voltage is not maintained all the way to 3.0V input. At 3V input, the dropout is almost 300 mV. At 3.2V input, dropout is 140 mV. The FET just isn't as good at 3V as the datasheet says it is. I guess by now that shouldn't surprise me.

Anyway, there's nothing to be done about it except acknowledge it, and hope a better FET can be found in the future.

The good news it that the multi-cell version works awesome! Actually works great from 3.3V on up to 35V.

So I should have the sales thread up in a day or two, and should be ready to ship the first units a few days after that. If anyone wants to put your name on the waiting list, post here and I'll copy it to the sales thread when it's open.


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## Epsilon (Feb 23, 2015)

Put me on the list for one .

And I can imagine that 18AWG (0.82mm2) gets pretty hot . I will be using at least 1.5mm2 (between 16 and 15 AWG), but more if I can fit it. Distances will be very short.

Good work!


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## DIWdiver (Feb 25, 2015)

Sales threat is up! Ready to take orders!

http://www.candlepowerforums.com/vb...es!-thermally-protected&p=4612068#post4612068


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## Epsilon (Mar 4, 2015)

PM


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## DIWdiver (Jan 9, 2016)

:bump:


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## DIWdiver (Aug 1, 2016)

Shameless :bump:

I have a bunch of these if anyone wants one.


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