pwm or current controlled ???which will give longer runtime and led life??

jjp888

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Jan 31, 2015
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161
Pardon me if Iam asking a silly qn.(Just for the sake of my curiosity).
I have seen many flashlight manufactures previously used pwm but now are shifting to current controlled.Apart from it's effect on eyes ,is there any other advandage in shifting to current controlled circuits.

Considering the longer uses ,which has better runtime?,better life?, and which produces lesser heat generation??.
 

mattheww50

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Jun 24, 2003
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SW Pennsylvania
I doubt there is much difference in run time. 1 joule=1 joule of energy, no matter how you supply it. Current control is likely to result in both less heat, and possibly better life. PWM drives the LED at full power, but the duty cycled is adjusted to change the apparent brightness. LED's in general a more efficient at lower drive levels, so for a given energy input, current control will result in higher efficiency and that translates to lower heat dissipation. I doubt it makes much difference in terms of life however, At best a slight advantage to current control. Current control is probably slightly more expensive to implement, however it has reached the point that the driver electronics represent a pretty small part of the total manufacturing cost so it probably makes little difference in cost. The tint on most LED's changes slightly with increasing drive levels, so PWM will produce the same tint no matter what the duty cycle is, since when the LED is on, it is on at full power. Current control will result in slight difference in tint as you go from moonlight to full power.
 

Wiggle

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Sep 19, 2008
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Halifax, NS
Constant current is more efficient. This is because while PWM can achieve the same effective outputs using switching of various duty cycles, the CC driver operates in a better range of the LED efficacy curve. Say for example that an arbitray LED has an efficacy of 75 lumens/watt when driven at 100% and 110 lumens/watt at 20%. The PWM uses the full 100% output it just turns it on and off for the appropriate amount of time to achieve the 20% average brightness.

I'm not sure that there is any noticeable effect on LED life, heat build up may be slightly higher but since PWM is used on lower modes only the lifetime is already extremely long. Time the LED is being driven to max levels with alot of heat build up should have much more effect and this will be comparable regardless if the light is CC or PWM.

As a1mu1e said, PWM tends to behave better in the tint department. Though I've seen some lights that maintain good tint at low drive levels on constant current (such as my Armytek A1 Pro 4000K XM-L2). PWM also needs to be a high enough frequency to make flicker invisible, some people are more sensitve to others and any modern light of good quality should not have this issue.
 
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