loss of efficiency due to pwm

alpg88

Flashlight Enthusiast
Joined
Apr 19, 2005
Messages
5,326
how much of efficiency do i lose due to pwm with linear amc 7135 based driver, basically my question is how much shorter would run time be, if i use lower mode, as opposed to running on max, but with fewer amc chips.
 

WalkIntoTheLight

Flashlight Enthusiast
Joined
Jun 18, 2014
Messages
3,967
Location
Canada
If you're just using one 7135 chip, you're not going to lose much efficiency due to PWM if you're using a mode below 350mA. The LED is already very efficient at 350mA. However, you're already losing efficiency just because the 7135 chip "throws away" voltage above the forward-voltage of the emitter. That might be up to 25%. Still, it's better than a FET driver, though not as good as a boost-buck.

Anyway, if you plan to use your light on low a lot, stick with a single 7135 chip if that's what you're planning to use. You can probably use up to 4 chips if you want a higher max, without losing much efficiency.

All that said, on low modes you're going to get a s-load of runtime from an 18650 cell, regardless of what driver you use.
 
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