# Drivers, how leds are adapted for different battery voltages



## HKJ (Nov 4, 2009)

[size=+3]Drivers, how leds are adapted for different battery voltages[/size]
With incandescent flashlight the battery voltages has to match the bulb voltage, but with a led flashlight this is not the case, instead a electronic circuit is placed between the battery and the led to adjust the battery voltage to the led. In this article I will describe different types of drivers and what voltages/battery configurations they work with.
When adding a electronic circuit to the light, many manufacturers also includes electronic to select different brightness levels in the driver circuit. The brightness can, depending on some factors, be regulated with either PWM (*p*uls *w*idth *m*odulation) or CC (*c*urrent *c*ontrol).











These drives has to be placed in the flashlight, the usual location is in the head of the light, just behind the led. I have used a light where it is possible to remove the led/driver assembly (Called a pill), as an example.









Looking from the led side, it is possible to see the red and black wires from the driver and from the bottom the driver circuit board can be seen.



[size=+2]Voltages[/size]
In the old days with incandescent, the bulb voltage and the battery voltage had to match (Usual bulb voltage a bit less than battery voltage). But with led's it is another game, a led white will turn on at about 2.5 volt, and reach maximum brightness at about 3.7 volt, but this voltage varies between different samples of the same led, the voltage is called Vf. Depending on battery voltage and what kind of regulation is required, different types of drivers has to be used.

The battery voltage will depend on the chemistry of the battery (and number of batteries used):

Alkaline: 0.8 to 1.5 volt
NiMH: 1 to 1.4 volt
Lithium FeS2: 0.8 to 1.7 volt
Lithium: 2 to 3 volt
LiIon: 3.3 to 4.2 volt

These voltages are from a fresh battery measured without load to a nearly drained battery measured with load.

Trying to match a number of batteries to the led voltage, it is possible to select between the following drives:

With voltage below the led voltage a boost driver must be used.
When the battery voltage is just above the led voltage, it is possible to use direct drive or a current driver. 
With voltage significantly above the led voltage a buck drive is used.
With the battery voltage both below and above the led voltage a buck/boost driver is used.


Note: The Vf for green or red leds are very different from white leds.



[size=+2]PWM contra CC[/size]
There are two ways to regulate the brightness on a light, either turning the led on/off at a fast rate (PWM) or reducing the current to the led (CC), both has advantages and disadvantages.
Both types of driver can generate audible noise, this noise is generated by the inductor. The audible noise is not from the buck/boost conversion, that works at frequencies far above the audible range, but from the regulation to keep a constant output.


[size=+3]PWM (*P*ulse *W*idth *M*odulation)[/size]
This method of regulation will turn the light on/off at a fast pace, and use the ratio between on and off to regulate the brightness. The following traces are recorded with a light sensor in front of the flashlight.






The first trace is from a low level, here the light is on 13% of the time and it is flashing 1200 times each second.






Same light as above, at the medium level, here the light is on 32% of the time and the frequency is the same: 1200 flashes each second.






Same light again, this time at full power. Here the flashing is disabled and the light is running at full power all the time.






Another light, running at medium power, the light is on 33% of the time, but the frequency is much lower, the light is only flashing 100 times each second. The slow flashing rate has some disadvantages.

In PWM the light is usual driven at full power, but not 100% of the time. This makes it possible to design the driver only for the led Vf at full current, there is no need to handle the lower Vf at lower currents. The constant drive current will also secure that the led tint is stable (It changes slightly with drive current).

But PWM has some serious disadvantages:
A driver working at high current will have lower efficiency, than a driver working at a low current.
A led working at max. current will have lower efficiency than a led with lower current.
The flashing is usual invisible in static situation, but when something is moving, it can play tricks with the vision. One example is something rotating with 6000 RPM that will look like it is standing still or rotating very slowly if the light is supplied from a light with 100 flashes / second. A fan with 3 wings only need to rotate 2000 RPM, because it only need to turn 1/3 turn to look the same. 






Here I have sweept the light over a white wall while taking the picture, as expected it shows a line.






But increasing the sweep speed has an unexpected result, only a few spots are bright. This is due to PWM.


[size=+3]CC (*C*urrent *C*ontrol)[/size]
With CC a constant current is always going into the led, to change brightness the current is regulated up or down. Sometimes this regulation might leave a little noise in the current, but this has no visual impact. This noise will make the traces of the light look jagged, the one shown below is very regular, but on some lights it is much more irregular.
The following traces are recorded with a light sensor in front of the flashlight.






Low brightness, the current is low and stable.






Medium brightness, the regulation is measureable in the light, but not visible to the eye.






High brightness.

As can be seen, the current is table at all settings. This will give a better efficiency than PWM, because the lower brightness settings is using a lower current and both drive and led has better efficiency at low current (At very low current the efficiency will be worse again).

But CC also has a few disadvantages:
There will be a minor tint shift when changing brightness.
The driver must be able to supply lower voltages to the led, to make low currents possible.



[size=+2]Direct drive[/size]
This is the same way incandescent lights works, the battery is directly connected to the led (There may be small resistor in between). For this to work the battery voltage must be the same or a little bit higher than the led voltage. Looking at the above battery voltages a single LiIon fits the bill, preferable with a small resistor. 
Another solution is 3*Alkaline, this is to high a voltage, but alkaline sags under load. Using Lithium FeS2 in this kind of light, will overdrive the led and reduce the lifetime of led, because they do not sag as much as alkaline.

This kind of drive has a very long runtime, because the brightness and current consumption is declining while the power is used. I.e. with a fresh battery the light can have 200 lumen, but after a few hours in can be down to 10 lumen with corresponding much lower power consumption. This is useful for lights that must not just turn off when the battery is low (It does not work with protected LiIon).

Note: The 3xAlkaline solution is used in many cheaper lights.


[size=+3]Examples of direct drive drivers[/size]









Not all direct drive lights are without electronic, this driver here is a direct drive PWM driver, i.e. it will turn the power on/off, but not change any voltage or limit current.









Another direct drive PWM circuit with two modes and strobe.


[size=+3]Example curves of the current and brightness[/size]






A typical direct drive light. This light is designed to work with 3xAlkaline and depends on the voltage sag in the batteries, to keep the current down. The specification says it is a 3 watt light and it reaches 3 watt at 3.5 volt, but at 3.8 volt it is 7.6 watt and the light output is dropping due to heat.


[size=+3]Battery possibilities when using direct drive[/size]
It is best to stay with exactly the specified battery type, and not change chemistry or battery size.
For other battery size/chemistry, check that the light keeps the same brightnes and does not get hotter than usual.



[size=+2]Current drive[/size]
To make direct drive safer and maybe add some levels to it a constant current generator can be added in series with the battery. This is usual a chip called 7135 that can deliver 350 mA with a very low voltage drop (0.2 volt), using 3 of these will give a 1050 mA drive current (usual rounded to 1000mA).
Due to the 0.2 volt drop in the chip, the battery voltage must be 0.2 volt higher than the led voltage, but the led will not be overdriven, if the voltage is higher. The only problem for higher voltage will be heat in the driver.
This driver works well for a single LiIon and can also be used for 3*alkaline/3*Lithium FeS2.

Drivers with this chip usual include a microprocessor that can be used to turn the chip on/off very fast (PWM) to regulate the brightness of the light.


[size=+3]Examples of a current driver[/size]









The picture shows a driver with 3 x 7135 chips and one microprocessor to control the brightness.


[size=+3]Example curves of the current and brightness[/size]






This light has current drive and uses a led that start at a low voltage. The difference between current drive and direct drive is very obvious here, the current stops rising at about 4 volt and stays just above 1A, i.e. 3x7135 chips. The slightly falling output is due to heat.


[size=+3]Battery possibilities when using a current driver[/size]
Use batteries with a voltage slight above the Vf of the led, i.e. 3xAlkaline/NiMH/Lithium FeS2 or 1xLiIon will all work and be safe.



[size=+2]Boost driver[/size]
This type of drive will increase voltage and is used for battery configuration with below led voltage. If the battery voltage is above the led voltage, the current will usual pass through the driver (with a small voltage loss) and directly drive the light at higher than maximum brightness.
This makes boost driver useful for many different battery configurations:

1xAlkaline/NiMH/Lithium FeS2
2xAlkaline/NiMH/Lithium FeS2
1xLithium
And sometimes: 1xLiIon

Note: Some drives are only designed to work with voltages in the 1 to 1.5 volt range.

Because the drive can only increase voltage, it might have some problems with low brightness settings, when using batteries with more than 3 volt, but that depends on how the brightness is regulated: PWM: No problem, CC: low brightness is not low anymore.

These drivers will require a high (Usual about 1 volt) voltage to start and when started they can sustain a considerable lower battery voltage.

[size=+3]Examples of boost driver[/size]









A 0.5 A boost driver with 0.7 to 3.0 volt input range, it has only a single brightness level.









A more powerful boost driver, this driver can deliver 1 A with 0.7 to 4.2 volt input, it has only a single brightness level.












A boost driver with 5 modes, to get space for a microprocessor a second level has been added. This is sometimes done by using a boost controller to feed a direct drive controller (Note the L+ and L- legend on the lower circuit, this is probably LED+ and LED-).












All drivers has an inductor (the coil with copper wire), this shows that it is a buck or boost driver.


[size=+3]Example curves of the current and brightness[/size]






First a boost driver running at maximum output, at low voltage it is limited by a maximal current draw of about 1.4A, when the voltage reaches 1.7 volt the light will try to keep a stable output, but is not perfect at it. The driver must have a high voltage drop or the led a high Vf, because it keeps a steady dropping current up to 4.3 volt.
This light is "safe" with LiIon, the power is staying at about 3 watt.






Same light, this time on low. Here the light reaches a stable output below 1 volt, but when the battery voltages reaches 3.5 volt the current and brightness will increase, this is because leds has a lower Vf at lower output and when the battery is above the Vf + driver loss for the low setting, the circuit goes into direct drive with no control of brightness or current. But it looks safe enough, because it does not go above the maximum output from the previous graph.






Another light with better regulation, up to about 1.8 volt the light is current limited, and then it keeps good regulation, until it goes into direct drive at 3.8 volt. This light may be damaged by LiIon batteries, because the led power is considerable increased (doubled) above the designed level. At the specified voltages it uses about 3 watt, but with a fresh LiIon it will use 6-7 watt.






A very classical boost driver, it is easy to see the different phases of the regulation:
1) Below 1.4 volt the driver can not draw maximum current.
2) From 1.4 to 2.3 volt the driver is limited by current, this limit is placed at about 2.2 A for this driver.
3) From 2.3 volt to 3.7 volt the driver has good regulation.
4) Above 3.7 volt the driver goes into direct drive and the current will increase fast.






Another type of boost driver, this driver keeps a constant current load on the battery and will increase the power to the led with increasing battery voltage. The drive looks safe up to about 3 volt, above that the led does not increase much in brightness, even with increasing power consumption, this is probably because the efficiency of the led is dropping due to temperature. At 3.6 volt the driver goes into direct drive and the led output goes dramatically down, this is a very bad sign.


[size=+3]Battery possibilities when using a boost driver[/size]
Do not use a battery with more volts than the light is specified for, LiIon can be very hard on this kind of light (or work fine).
A light rated for 3 volt (Lithium or 2xAlkaline/NiMH/Lithium FeS2) might also work at 1.5 volt (i.e. 1xAlkaline/NiMH/Lithium FeS2).
Many people do use LiIon in these lights and often it will work, but the lifetime of both the led and the battery will be greatly reduced, if the drive power goes significantly up.



[size=+2]Buck driver[/size]
This type of drive will decrease voltage and is used for battery configuration with above led voltage. If the battery voltage is below the led voltage, the current will usual pass through the driver (with a small voltage loss) and directly drive the light at lower brightness.
This makes this driver useful for many different battery configurations:

4+xAlkaline/NiMH/Lithium FeS2
2+xLithium
Sometimes 1xLiIon
2+xLiIon

Note: Drivers has a maximum voltage they can stand, this is seldom specified but will usual be above 9 volt (i.e. 2xLiIon).

Because this driver can only decrease voltage, it has a problem with 1xLiIon, the minimum LiIon voltage is below what is required for maximum brightness in a led (3.7 volt). A led with a low Vf and a driver with a low voltage drop can just about keep a stable output on LiIon.
Using CC for brightness will always work and allow the full range of brightness settings.


[size=+3]Examples of buck driver[/size]









The above picture shows a single level buck driver.









This picture shows a multilevel buck driver. Because there is electronic for both buck and brightness control, the circuit contains many parts and requires both sides of the circuit board (In some lights 2 or 3 circuit boards are stacked). 









Both drivers has an inductor (the coil with copper wire), this shows that it is a buck or boost driver.


[size=+3]Example curves of the current and brightness[/size]






Here is a typical buck driver, the brightness and current will increase until the voltage reaches 4.2 volt (That is Vf and driver loss), then the brightness stabilizes and the current will drop with increasing voltage.






Another typical buck driver, here the changeover is at about 3.8 volt






This driver was a bit of a surprise, the current increases until 4 volt, then the brightness stabilizes and the current starts dropping, but at around 5 volt the current does not drop anymore, but stays constant. 


[size=+3]Battery possibilities when using a buck driver[/size]
Many lights designed for 2xCR123 will work with a single LiIon battery, either 17670 (for a battery tube with low inner diameter) or 18650, but the light output is not fully stabilized.
For 3xCR123 lights it is safe to use 2x17500 or 2x18500 LiIon batteries, it is just about the same voltage, but it might not be safe to use 3x16340 LiIon batteries.
On 2xCR123 light the batteries can often be replaced with 2x16340 LiIon batteries, many buck drivers can take the extra voltage, but this will cut the runtime in half. Check the current draw with CR123 and 16340 batteries, the 16340 must draw less current than CR123 (With fresh batteries 20-30% less current is expected).



[size=+2]Buck/boost driver[/size]
This type of drive will either increase or decrease voltage, depending on what is required. This makes it the best driver for multiple battery configurations and for light that can do both full brightness and a really low low with a supply in the 3 to 4 volt range without using PWM. 
This driver is often used on single cell LiIon lights, that both have a high and very low brightness. The driver can boost the voltage from a nearly empty LiIon to the full Vf of the led at max. brightness, but it can also buck the voltage from a full LiIon to the low Vf of a low brightness CC driven led.


[size=+3]Example curves of the current and brightness[/size]






This driver works from 0.9 to 4.2 volts, it looks like any boost driver at low voltages, but due to the buck function, it does not increase current or brightness in the 3.7 to 4.3 volt range.






Same light, this time on low level, as can be seen the driver has no problem keeping a low level independent of the battery voltage.


[size=+3]Battery possibilities when using a buck/boost driver[/size]
The reason to use buck/boost driver is to support batteries with voltage both below and above the Vf of the led, i.e. these light will support 2xAlkaline/NiMH/Lithium FeS2, 1xCR123 and 1x16340 batteries with full brightness control for both types.
They might also support lower voltages and it is safe to try batteries with lower voltages.
Do not use higher voltages, except if it is specified.



[size=+2]Notes[/size]
All voltages in here are rough values, different led voltages (Vf) and different driver architecture will have slightly different voltages.

All lumen values are scaled from lux measurement and lumen specification of flashlight.

Discharging a LiIon battery too much, can make it unsafe, be careful with unprotected LiIon batteries!

It is never completely safe to go outside the specification for a battery or flashlight, sometimes a light or a battery might get damaged or blow up, following the guidelines here will keep this risk at a minimum, but not eliminate it completely.

I usual writes 16340 to specify 3.7 volt LiIon batteries in CR123 size, because RCR123 can also mean 3.2 volt LiIon batteries.


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## csshih (Nov 4, 2009)

wow! that is in impressive writeup!
I'm going to have to go through all that again when I get home :thumbsup:


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## Linger (Nov 5, 2009)

HKJ, this is fantastic work. Excellent demonstrations, well composed pictures.

*edit - feedback for author was reviewed and I removed them

Well done,
Linger


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## HKJ (Nov 5, 2009)

Linger said:


> HKJ, this is fantastic work. Excellent demonstrations, well composed pictures.
> 
> Some questions I have for you. (I will edit my post and remove my comments later)
> 1>
> ...



Thanks for the comments, I have changed the text a bit and removed the note (It was already covered in the first part).


I have also added some pictures to show where the driver is located in most flashlights.


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## MorePower (Nov 5, 2009)

Is there any chance you could add some info as to where the various drivers came from (ie. if it was removed from a particular light, the SKU at DX or KD, or links to other websites where they were purchased).

The graphs you've generated are great, but if I knew where to get the drivers you used, that'd be even better.

Thanks.


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## HKJ (Nov 5, 2009)

MorePower said:


> Is there any chance you could add some info as to where the various drivers came from (ie. if it was removed from a particular light, the SKU at DX or KD, or links to other websites where they were purchased).
> 
> The graphs you've generated are great, but if I knew where to get the drivers you used, that'd be even better.



The drivers in the pictures are not the ones that are used for the graphs, I do not hope I have implied that anywhere in the text.

This article is not about specific lights, that is the reason I do not list the lights.
Some of the graphs are takes from my reviews other where made for this article. If you really want to know the lights they are from, check the url for them (In windows: right click and select properties)


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## Linger (Nov 6, 2009)

Sorry for missing this one,
[SIZE=+1]PWM (*P*uls
>Pulse

** *Pulse* is the english word, please give us the '*e*'
 [/SIZE]


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## Justin Case (Nov 19, 2009)

I think it is instructive to graph Power In vs Voltage In. In theory, if driver efficiency is a constant, then when the driver is running in regulation the Power In should be a constant. Thus, for example, you should see a nice, flat plateau above Vreg for a buck driver, where Vreg = Vf + driver voltage overhead.

As an example, take your very last graph in the buck driver section. Current In is essentially flat from 3.8V to 7.8V. One might be fooled in believing that the driver is working well, because the graph looks smooth and well-behaved. In fact, that is absolutely terrible performance for a buck driver. Current In should scale inversely with Voltage In. Let's assume that this driver is designed to deliver 750mA drive current to the LED in regulation. That would mean about 3.8V*0.75A = 2.85W sent to the LED. From the graph, at about 4.7V input, the driver looks like it needs about 0.8A, or about 3.8W. This gives an estimated driver efficiency of about 75%. But at 7.8V/0.8A input, the driver needs about 6.2W of power, or an efficiency of only about 45%.


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## HKJ (Nov 19, 2009)

Justin Case said:


> I think it is instructive to graph Power In vs Voltage In.
> 
> 
> 
> In theory, if driver efficiency is a constant, then when the driver is running in regulation the Power In should be a constant. Thus, for example, you should see a nice, flat plateau above Vreg for a buck driver, where Vreg = Vf + driver voltage overhead.



I agree, when doing these plot I usual have a power column to check what is going on and when I absolutely need to stop.
But I can not get Excel to do it in the same graph, I can only do two scales.

Note: The curve is not flat, the efficiency varies with input voltage.




Justin Case said:


> As an example, take your very last graph in the buck driver section. Current In is essentially flat from 3.8V to 7.8V. One might be fooled in believing that the driver is working well, because the graph looks smooth and well-behaved. In fact, that is absolutely terrible performance for a buck driver.



Yes, that one has a problem with higher voltage.


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## Justin Case (Nov 19, 2009)

HKJ said:


> I agree, when doing these plot I usual have a power column to check what is going on and when I absolutely need to stop.
> But I can not get Excel to do it in the same graph, I can only do two scales.
> 
> Note: The curve is not flat, the efficiency varies with input voltage.



Many quality drivers show quite flat Power In vs Voltage In curves. All of my SOB drivers from The Sandwich Shoppe behave this way. The driver from the old DX6090 P60 drop-in is another. The driver in the Legion II runs ruler-flat.

I can think of an easy trick to put all of your curves on a single graph. Scale your numbers so that they are all the same order of magnitude. For example, scale the lumens numbers by dividing by 100. Now the scaled lumens are the same order of magnitude as your amps values. Power In will also be the same order of magnitude. Now, just highlight the Excel columns (or however you've arranged your data) for Voltage In, Lumens, and Power In and make your scatter plot.

For your y-axis label, that's where you would note whatever units (V, A, Lm) and scaling factors might be used for the relevant ordinates.



HKJ said:


> Yes, that one has a problem with higher voltage.



Well, graphs that don't visually highlight such behavior are not as useful as they could be.


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## HKJ (Nov 19, 2009)

Justin Case said:


> Many quality drivers show quite flat Power In vs Voltage In curves.



Buck converters might show a rather flat curve, but boost converters usual has lower efficiency at low voltage.



Justin Case said:


> For your y-axis label, that's where you would note whatever units (V, A, Lm) and scaling factors might be used for the relevant ordinates.



I want to show correct labels, not scaled values, here I have added power to the above graph and this makes it difficult to see current.








Justin Case said:


> Well, graphs that don't visually highlight such behavior are not as useful as they could be.



I completely agree, but you also need to make the graph easy readable, and I have chosen the later over the former for these graphs. But I will also note "strange" behavior in my comments, for some people this will probably be more useful than showing the curve.


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## Justin Case (Nov 19, 2009)

HKJ said:


> Buck converters might show a rather flat curve, but boost converters usual has lower efficiency at low voltage.



Right. Back to the communication problem again. I never claimed that all drivers will be flat. However, you stated categorically that "The curve is not flat, the efficiency varies with input voltage." Technically true, but practically speaking not universally true, as I pointed out via counterexample. Yes, I agree that boost drivers usually have lower efficiency at lower voltage. I've seen this in The Shoppe's boost and boost/buck drivers. That's why I cited specific buck driver examples.


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## TorchBoy (Nov 19, 2009)

Justin Case said:


> As an example, take your very last graph in the buck driver section. Current In is essentially flat from 3.8V to 7.8V. One might be fooled in believing that the driver is working well, because the graph looks smooth and well-behaved. In fact, that is absolutely terrible performance for a buck driver.


Looks like a linear regulator to me. :shrug:


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## Justin Case (Nov 19, 2009)

It does have a linear regulator type behavior. Not an AMC7135, however, since the input voltage of 7.8V would cook that IC. There are many other linear regulators, though. For example, TaskLED uses one in its hipFlex and I seem to recall the max voltage is something like 24V.


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## HKJ (Nov 20, 2009)

The current consumption does, but the brightness does not. The slightly increase in brightness while voltage increases, means that the current in the led is increasing.


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## Billy Berue (Nov 22, 2009)

Thanks, HKJ. :twothumbs

I'll have to read through this carefully a few more times before it all sinks in, but really appreciate your thorough explanation. I've been looking for something like this for quite a while now.

TOI, anyone??


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## Lightcrazycanuck (Nov 23, 2009)

Excellent job HKJ.:thumbsup::thumbsup::thumbsup:

Me thinks I'm smarter after reading this.:laughing::laughing::laughing:


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## Midnight Oil (Apr 25, 2010)

Does the operating voltage range of a P60 drop-in indicate which kind of driver it has? For example, I see a drop-in designed for 1 AA, 2AAs, and 1 18650 that is rated for 0.8V-4.2V. 

Does this mean this drop-in has a boost circuit so that the output will be the same for all 3 battery configurations. 

Does it also mean output is regulated for all 3 battery configurations until the voltage falls below 0.8V and the light goes into direct drive?

Another related question...Do some P60 drop-ins have a low-voltage protection mechanism that turns off the light to prevent the Li-Ion battery or batteries from over-discharging, while others that don't simply fall out of regulation, go into direct drive, and allow the battery or batteries to continue powering the light with dimming output?

Thanks.


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## HKJ (Apr 25, 2010)

Midnight Oil said:


> Does the operating voltage range of a P60 drop-in indicate which kind of driver it has? For example, I see a drop-in designed for 1 AA, 2AAs, and 1 18650 that is rated for 0.8V-4.2V.


 
To some extend it does say what kind of circuit it has.



Midnight Oil said:


> Does this mean this drop-in has a boost circuit so that the output will be the same for all 3 battery configurations.
> 
> Does it also mean output is regulated for all 3 battery configurations until the voltage falls below 0.8V and the light goes into direct drive?



Yes, it is a boost circuit, but the output might not be regulated. 
And even if it is regulated, it will need some minimum voltage before it goes into regulation. Check my curves on boost regulation and you can see that drives usual need more than 1.5 volt for regulation.
There are also boost drivers completely without regulation, many AAA lights uses this kind of driver.


A boost driver goes into direct drive when voltage is above the desired output voltage, not at very low voltages. This direct drive can damage both driver and led, because the current can rise to unsafe levels.




Midnight Oil said:


> Another related question...Do some P60 drop-ins have a low-voltage protection mechanism that turns off the light to prevent the Li-Ion battery or batteries from over-discharging, while others that don't simply fall out of regulation, go into direct drive, and allow the battery or batteries to continue powering the light with dimming output?



Some P60 drivers has low voltage protection and others are designed to reduce output, but if the drives has to work down to 0.8 volt, it is difficult to have any protection for LiIon.


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## taschenlampe (Apr 27, 2010)

HKJ said:


> ...
> 
> 
> 
> ...


 
I am looking for information about this driver eagerly with no luck so far!

Is it 17mm in diameter?
700-800 mA on high (1*LiIon) as advertised on KD?
How low is the low mode?
Do you know the PWM frequency at low mode?
No mode memory - correct?
Is the mode sequence low–high–strobe as advertised on KD?

thanks in advance 
tl


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## VidPro (Apr 27, 2010)

Justin Case said:


> Right. Back to the communication problem again. I never claimed that all drivers will be flat. .


 
i really think for explainations sake, STARTING with examples of "Good" conversions, or even explaining "perfect" conversions , would be an assett to understanding what is being attempted. THEN showing cruddy inefficient examples AFTER that.

so people can understand the power conversion aspect of it First, in it's most simple terms. Then realise how poorly the power is converted in some junk later. Using the worse case scenarios as an example sorta makes the whole process of doing it at all look rather fruitless :sigh: But more than that it messes with understanding that watts is watts.

i am sort of agreeing with Justin, if you can go with amps and voltage in, and amps and volts out, to get the basic IDEAS of boosting and bucking into the brain first. Lumens gets in the way of understanding the simple concepts of the power conversions trying to be explained.

------------------------------------------------------------

_Ramifications can be an Assett_, everyone always wants the curcuit to Destroy batteries , I dont. automagic slowdowns might be bad for extreeme output to the end, but they are often great for the batteries. :sweat:
*At 3.6 volt the driver goes into direct drive and the led output goes dramatically down, this is a very bad sign.*
No it is not nessiarily BAD for a driver to cool out on a Li-ion battery when the voltage has dropped to 3.6V. YES it shows that it doesnt regulate down till the battery is turned into Mush  

the Perfect driver doesnt ALWAYS have to hit the batteries so hard at the end of thier discharge when they are least likly to be able to cope with the current Increases. 
IMO Drivers that ram a li-ion into the ground, or Reverse charge batteries in Series are thoughtless feinds :sick2:  unfit for use in any of my lights.

if people INSIST on drivers that take the batteries down Hard at the end of the discharge for them, they are likly to ruin ni-mhy batteries from reverse charge , discharge li-ion cells too low (especially unprotected) , and even End up with Dead reverse charged Alkalines Leaking in thier devices. :tsk:

Having Default cut-offs or slowdowns in a driver used with the right stuff, doesn't really hurt the user , so the light goes down a bit as the battery is depleated,:candle: it still working. Depending on the batteries your using , the light that dims is the light and battery that lives. :rock:
The driver that doesnt know when to slowdown or stop is the dumb one. (oops were we talking about automobiles?) :thinking:

It does have a lot to do with what your looking to get out of a light, but ramifications abound in many of the driver styles and types, what looks good to some, isnt very long term. 

Take the example of the Over-voltaged Boost, Nice fat lumens pouring out, as the LED is being tortured and eventually will output less than it did at normal currents. Ohh look its so bright, sure when ramming 2.5A into a 1amp led everything looks golden, for a while. 

or the boost curcuit designed for an 2 alklines pulling 3.4Amps at .8v, hey sheer genious the precision of the regulation, sheer ignorance of any battery specs.


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## GarageBoy (Apr 28, 2010)

Is current drive a "Low Drop Out" regulator??


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## HKJ (Apr 28, 2010)

GarageBoy said:


> Is current drive a "Low Drop Out" regulator??



It is a linear constant current regulator, preferable a low drop out type.

7135 is a low drop out constant current regulator.

Note: This is *not* the same as a low drop out voltage regulator.


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## Midnight Oil (Apr 29, 2010)

HKJ, thanks for the detailed response.


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## Midnight Oil (Apr 29, 2010)

VidPro, you've brought up a good point regarding the relationship between voltage at a given discharged capacity and the discharge rate.

I infer then, given a choice of the same drop-in offered in two operating voltage ranges (one @ say 1-4.2V and the other at 3.6-6V) in order to maximize runtime on (1) 18650 before reaching the drop-in cut-off voltage, I should select the 1-4.2V one if I'll be using the light at its highest setting all the time (high draw), but I should select the 3.6-6V one if I'll be using the light at the mid to low settings (low draw) most of the time?

I've been searching for my first drop-in based on my interpretations above; please feel free to correct me if I'm mistaken. I thought the Nailbender XPG 1-4.2V drop-in would be perfect for (1) 18650 because it had a boost circuit as well as a buck circuit, according to Nailbender, which I infer means the boost circuit would continue to power the light on high even if the battery voltage dropped to say 3.2V, which would still be above the over-discharge voltage limit for high draw. Dave, however, recommends the 3.6-(6/8V) version instead for (1) 18650, and I don't know why.

Thanks.


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## VidPro (Apr 29, 2010)

Midnight Oil said:


> Dave, however, recommends the 3.6-(6/8V) version instead for (1) 18650, and I don't know why.
> 
> Thanks.


 
because dave wants his stuff to last when people start using it.

ok now i am not talking about dave or any of his work, the rest is just general.

many of the low voltage input BOOST stuff listed for <4.2v is still boost only or boost with the curcuit resistance and it can "survive" 4.2v , they might even add a bit of resistance (of some sort) in to help that, at the cost of efficency. But boost is boost, and expects the battery voltage to be below the led voltage, and wants your usual single cr123 or a pair of 1.5v type cells or single 1.5v as the input.
they usually survive, but they often overdrive, depending on the li-ion battery keeping up high voltage at that current. 
they can discharge a li-ion below spec, if the li-ion is at least protected , that isnt a big problem.

the higher voltage stuff is usually a voltage reducing type of thing instead, which has the opposite problem, the regulation is only in play when the voltage of the battery is above the voltage of the led.

Li-Ion and LED, great matchups: just no so easy for simple drivers.
Because the voltage of the led, and the voltage of the li-ion battery are so very close, and because with any rechargables you really want a cut-off or for it to become non-operational at a low voltage, perfect drivers for single li-ions are few & far between, instead more often a choice is made to wing-it with what "works" which works "ok".

there has been many well made "wizz" type of curcuits that are indeed real full buck/boost , but they were more expencive, so they are not as often chosen, and less information about them. Then buck&boost WITH adjustable cut-off , costing more than some whole drop-ins.

If you want extreeme output, then you go with the overdriven psudo <4.2v booster, and try to get a high Vf LED.
if you want the never ending run of a dwindling voltage reduction instead, get the higher voltage driver >3.6v, and try to get a lower LED Vf.
The selection of the Led item can make small voltage differances themselves, not much, but it can help

it is just like your saying, but then you include LEVELS. a overdriven LED via a raw boost, will have better cooling going on when it is run at lower PWM levels, though even after PWM it is *still* overdriven.
(over when battery voltage is high)

The underdriven LED via the high voltage driver, wont have any problems ever at any levels, the current is never way high.
(under when battery voltage is low)

if you want a high running light, then boost the li-ion and overdrive the led(the quantity of overdrive varies) . it is usefull if the led is replaceable.
if you want a long running light that wont bail out in the middle of doing something, then buck or regulate the li-ion.
if you want everything, then pay some $20+ for just the driver.


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## Justin Case (Apr 29, 2010)

HKJ said:


> With incandescent flashlight the battery voltages has to match the bulb voltage, but with a led flashlight this is not the case, instead a electronic circuit is placed between the battery and the led to adjust the battery voltage to the led.


 
Your very first sentence is misleading and should be corrected. There are multiple problems.

First, that sentence mixes apples and oranges. Your claim regarding incans is true for direct drive. But your statement regarding LEDs pertains to using a driver. But incans can also use a driver, so what you claim for LEDs also applies to incans.

Both an incan and LED need to be matched to Vbatt if you use direct drive. Both incans and LEDs can also be regulated, and thus matching with Vbatt is far less of an issue (but it is still something that has to be considered).

The SureFire A2 Aviator is a well-known example of a regulated incandescent flashlight. A ubiquitous example of a regulated incandescent (but not a flashlight) is indoor house lighting. Light bulbs run off of regulated house voltage.

A second problem is that even with a driver, some degree of matching of Vbatt to the driver is *definitely* required. First, drivers have an operating input voltage range, so you need to observe that limitation. Second, depending on things like boost regulator IC switch current limit, if you want to actually run in full regulation, then you may have to deliver a specific min voltage. Third, buck drivers typically require some amount of voltage overhead to reach regulation. Thus, you need to select Vbatt to meet this minimum if you expect to run in regulation.


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## HKJ (Apr 29, 2010)

Justin Case said:


> Your very first sentence is misleading and should be corrected. There are multiple problems.



You are correct, but only for a very small part of the market. The purpose of the article is to describe the most common cases.



Justin Case said:


> A second problem is that even with a driver, some degree of matching of Vbatt to the driver is *definitely* required. First, drivers have an operating input voltage range, so you need to observe that limitation. Second, depending on things like boost regulator IC switch current limit, if you want to actually run in full regulation, then you may have to deliver a specific min voltage. Third, buck drivers typically require some amount of voltage overhead to reach regulation. Thus, you need to select Vbatt to meet this minimum if you expect to run in regulation.



I believe that the rest of the article is about this.


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## Justin Case (Apr 29, 2010)

HKJ said:


> You are correct, but only for a very small part of the market. The purpose of the article is to describe the most common cases.


 
Regardless of the size of the regulated incan flashlight market, your opening sentence is wrong. Shouldn't another purpose be to deliver factually correct information?



HKJ said:


> I believe that the rest of the article is about this.


 
Ok, but then why make a statement at the very beginning which you then proceed to prove false later on?


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## HKJ (Apr 29, 2010)

Justin Case said:


> Regardless of the size of the regulated incan flashlight market, your opening sentence is wrong. Shouldn't another purpose be to deliver factually correct information?



My opening sentence is a generalisation and it matches nearly everything on the market.



Justin Case said:


> Ok, but then why make a statement at the very beginning which you then proceed to prove false later on?



In fact, already the second sentence mentions that drivers has some requirements from the batteries.
If would be much more useful if you read the full article and looked for some real errors, instead of focussing on the initial generalisation.

I could have written the first sentence this way:


> With *most* incandescent flashlight the battery voltages has to match the bulb voltage, but with *most* a led flashlight this is not the case, instead a electronic circuit is placed between the battery and the led to adjust the battery voltage to the led.



But I do not really see the point in doing that.


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## Justin Case (Apr 29, 2010)

You have only one chance to make a first impression. Your opening sentence is that chance. Unfortunately, it makes factually incorrect statements, which can cause confusion since you then immediately contradict that opening statement.

IMO, it is highly debatable that your so-called second "generalization" is even defensible as a valid generalization. Just take the case of the common AMC7135 LDO regulator. Clearly one *MUST* consider the battery voltage when using a driver based on this chip. See what happens if you try to run such a driver with 2xLi-ion.


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## HKJ (Apr 29, 2010)

Justin Case said:


> You have only one chance to make a first impression. Your opening sentence is that chance. Unfortunately, it makes factually incorrect statements, which can cause confusion since you then immediately contradict that opening statement.
> 
> IMO, it is highly debatable that your so-called second "generalization" is even defensible as a valid generalization. Just take the case of the common AMC7135 LDO regulator. Clearly one *MUST* consider the battery voltage when using a driver based on this chip. See what happens if you try to run such a driver with 2xLi-ion.



I do not believe that you have read what I have written and what you write above does not really make sense in the context of this article. I will not comment any more on your criticism of my introduction.


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## MorePower (Apr 29, 2010)

HKJ said:


> [SIZE=+3][/SIZE]
> [SIZE=+2]Boost driver[/SIZE]
> This type of drive will increase voltage and is used for battery configuration with below led voltage. If the battery voltage is above the led voltage, the current will usual pass through the driver (with a small voltage loss) and directly drive the light at higher than maximum brightness.
> This makes boost driver useful for many different battery configurations:
> ...



Any chance you can generate current / output curves for the above 2 drivers? It'd be nice to get some real info about them, as KD is notably lacking. Before ordering a bunch, I'd like to get some idea of what they're actually capable of and maybe how (in)efficient they are.


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## HKJ (Apr 29, 2010)

taschenlampe said:


> I am looking for information about this driver eagerly with no luck so far!





MorePower said:


> Any chance you can generate current / output curves for the above 2 drivers? It'd be nice to get some real info about them, as KD is notably lacking. Before ordering a bunch, I'd like to get some idea of what they're actually capable of and maybe how (in)efficient they are.



I agree with you that information from both DX nor KD is inadequate, but I have not done any detailed analysis of these drivers and I do not plan on doing it at the current time.


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## TorchBoy (Apr 30, 2010)

HKJ said:


> I could have written the first sentence this way:
> 
> 
> > With most incandescent flashlight the battery voltages has to match the bulb voltage, but with most a led flashlight this is not the case, instead a electronic circuit is placed between the battery and the led to adjust the battery voltage to the led.
> ...


I don't want to sound picky, but I was under the strong impression that most LED torches *are* direct drive, with many (most?) of those using something like a 3x AAA or button cell configuration driving a number of 5 mm LEDs. So even that corrected version is still incorrect. Even if you're referring to different _models_ of LED torches instead of raw quantities of LED torches it's probably still wrong, as there are huge numbers of different models that aren't regulated by anything more than voltage sag and internal resistance.

BTW, have you seen post 7?


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## SubLGT (Dec 16, 2014)

Thanks for this tutorial HKJ. I don't have the electronics technical background to understand why your post seems to have generated a bit of technical controversy, but I found it to be a useful introduction to flashlight drivers for an electronics novice like myself.


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## HKJ (Dec 17, 2014)

SubLGT said:


> Thanks for this tutorial HKJ. I don't have the electronics technical background to understand why your post seems to have generated a bit of technical controversy, but I found it to be a useful introduction to flashlight drivers for an electronics novice like myself.



Time flies, it is four years ago I wrote that article.
You can see a couple of driver curves here: http://lygte-info.dk/info/indexLedDrivers UK.html
These curves are done with automatic equipment has has higher resolution, the above curves was done manually.


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## SubLGT (Dec 17, 2014)

Is the combination of a single 26650 Li-ion battery with a MT-G2 LED, and with a boost driver, an efficient combination? I ask this because the new PD40 from Fenix, which will arrive in 2015, has this combination. I don't recall seeing any other flashlights with a MT-G2 driven by a single 26650 (or 18650).


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## HKJ (Dec 17, 2014)

SubLGT said:


> Is the combination of a single 26650 Li-ion battery with a MT-G2 LED, and with a boost driver, an efficient combination? I ask this because the new PD40 from Fenix, which will arrive in 2015, has this combination. I don't recall seeing any other flashlights with a MT-G2 driven by a single 26650 (or 18650).



It will probably be a good combination. With a boost driver it is possible to use the full voltage range of the cell and with a 6 volt MT-G2 you do not get any problem with changing between boost and buck mode.
Lets hope the driver has a over discharge protection.


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## Poppy (Dec 18, 2014)

HKJ,
Cudos to you for a great explanation! :thumbsup:

IMO this should be a sticky, or at least listed in the "Threads of interest" in this section.


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## Pseudowok (Jun 22, 2017)

Thanks for this post, it really helped clarify some of the terms I have seen thrown around. I think it will make my search for an appropriate driver for my project a bit easier.


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## eh4 (Jul 4, 2017)

Sticky!


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## CuriousOne (Jul 7, 2017)

There are also Flyback drivers, they deliver much higher output voltage than at input, say input can be 6 volt, but output - 40-50 volts. Seen this in some chinese lanterns, where a lot of 5mm leds are connected in series and driven by higher voltage.


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## HKJ (Jul 7, 2017)

CuriousOne said:


> There are also Flyback drivers, they deliver much higher output voltage than at input, say input can be 6 volt, but output - 40-50 volts. Seen this in some chinese lanterns, where a lot of 5mm leds are connected in series and driven by higher voltage.



I do just call it a boost driver, it could be based on flyback, but at the time I wrote this multichip leds was not common.


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## CuriousOne (Jul 9, 2017)

These designs use transformer to boost voltage, and with just two transistor circuit, it is possible to have CC mode, which is definite plus for cheapivitiy


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## Arizona_Mike (Jul 19, 2017)

This is a great write-up.

Mike


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