What a great wealth of information. Thanks for taking the time to compile it and share it with us who are light challenged. 
Carl
Excellent resource. 
Thank you lagman for your great explanation!! I’m new to this forum and have been searching for a completed guide about flashlight driver but I haven’t found yet.
Could you draw simple circuit diagrams of some popular drivers and explain its components/ how it’s work…?
I have some knowledge in electrical physics but not in electronic components, the driver boards are too complicated to me :person_facepalming:
So will a linear regulator have better efficiency when using a IFR (LiFePO4) cell than ICR,IMR or INR since it is about 3.2V nominal?
A boost converter (step-up converter) is a DC-to-DC power converter that steps up voltage (while stepping down current) from its input (supply) to its output (load). Step-up switching converters, also called boost switching regulators, provide a higher voltage output than the input voltage. The output voltage is regulated, as long as the power draw is within the output power specification of the circuit. Many of our step-up switching regulators are designed for driving strings of LEDs.
If your step-up/boost application is not power intensive (IOUT < 0.5A), you may prefer a different power conversion technology for boost applications.
I would like to build a quad for solarforce with an extension tube. What driver can I use? Is it possible? Planning on buying my parts from mtn. Thank you.
What size driver would you need? Is it a 3volt LED quad your building? Is it for a P60 drop-in type (17mm driver)?
You can get a 2S 3volt 17mm driver @ 5.5amps as long as you have 6+mm of clearance for the Coil Craft Inductor from RMM.
@joker145, use a buck driver.
This will allow for fully regulated brightness with 2S over the course of the entire runtime.
Yes 3 volt led, and a P60 drop in that I bought from Kiriba-ru
Would like to use nichia led.
Thank you, also I can use one cell if needed?
The driver I linked is the one you want. You have to go with the Coil Craft Inductor to get 5.5amps 3amps is Max for the standard inductor.
does a boost driver at 9Amps Turbo, go into direct drive?.
am I wrong ?.
A boost driver cannot go into direct drive.
Few words about linguistic, psychology and marketing
In pure electronics, word “buck” and “boost” converters have no emotional content, simple engineering: must lower voltage, must increase voltage.
In flashlight area, “boost” has totally wrong build associations, to be “uber-flashlight” , be better by mere existence.
Every word catched in hands of marketers is lost for precise communication.
BTW increasing voltage isn’t for free. Perpetuum mobile does not exist.
This is exchange bigger current , small voltage to opposite (and loses in device)
“Constant current for much of the discharge of the battery”
So when is the current constant and when it’s not?
Moon Meteor Storm with parallel cells seems to have linear driver but the current with fully charged cells is 1.3A when paired with SST-20 (originally XML2) and then steadily drops.
Just found this posting. Informative and well-explained. Thanks.
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Literally never seen that. If anything, buck drivers are generally regarded as more efficient, and FET drivers more powerful, on average, even though for each of those it depends more on design than anything else. Zebralights use boost drivers and are the most efficient lights around, but in general boost is IMO not implicitly better. Are you thinking of “turbo”? (i.e. a high, thermally unsustainable brightness, often outside the usual levels)
linear drivers are usually constant-current - LEDs receive the same current all the time (which depends on the LEDs, could be between 1 and 12+A), and brightness is controlled through changing the voltage.
I’m more used to opamp-based linears, but as I understand it, the 7135 chip will allow constant-current until the battery is very low, as eventually, as the battery voltage drops, current will increase to compensate, leading to more current to the LED. Too much voltage or current will destroy an LED, so this could theoretically be bad with a fragile LED and too many stacked 7135s.
Not sure what Moon Meteor Storm is, but I’d like to hear more.
Current will not increase to compensate.
Linear drivers such as 7135 always have the same current at the input and the output, unlike boost or buck converters.
As you said, the current is regulated to be constant regardless of battery voltage.
If the led needs 3v at the set current, the excess voltage will be dissipated in the linear driver. That way, the led always receives 3v and constant current.
Moon Meteor Storm is just a flashlight suposedly optimized for bicycles. Now using it with a narrow layered cut-off beam throwy headlight which uses unusually shaped aspheric lens to strech out the beam in a horozontal plane while making upper part to appear as a bright straight line and lower part curved and slightly less bright (originally came with BBSHD motor).
As much as I don’t like marketing lies, It’s not exactly wrong though, most of the time.
With a buck driver in a single cell flashlight (most common) the ouput is limited due to how close the battery voltage is to the LED forward voltage, at some point like with a linear driver the output can’t be regulated anymore and it will decrease as the battery voltage decreases. There are other practical limitations that limit a buck driver output, like the circuit resistance and the maximum current of available buck converter ICs capable of 100% duty cycle, which is 6A as far as I know, higher current buck ICs have max duty cycle limitations, which means higher dropout voltage, for example Convoy’s 8A buck driver only does 8A for a short time when the cell is full.
A boost driver doesn’t have such limitations and higher output can be achieved vs a buck driver, but also vs linear and direct drive when the battery voltage is lower. the most common boost converter IC used in high power single cell flashlight is the MP3431, 21A peak input limit, in practice can be used up to 40W output.
The LED is also something to consider, in a single cell light a boost driver means either multiple LEDs or one/multiple mutli chip LED, which can be driven at higher power and are more efficient.
Well, sure, but the efficiency with equivalent components is virtually the same as with a buck converter, in practice better because of the ICs available. And ofcourse better than linear or direct drive.
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