XHP35 output and death test + PWM efficiency test by Texas_Ace

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Texas_Ace's picture
Last seen: 19 hours 9 min ago
Joined: 03/24/2016 - 07:44
Posts: 9354
Location: Everything is brighter in Texas

The resistor was very small on the FET (4.7ohm IIRC) , it would have negligible effect for the purposes of this test. It is there to prevent ringing and improve consistency at very low modes.

You are correct that adding a larger resistor is a way of transferring the heat from the LED to the FET. Although overall efficiency does not seem to be effected much in my testing except that the driver gets hotter now but the same voltage is burned off either way.

Yes, just the plain fact it is lower current also effects the final output along with the lower temperatures (they are related naturally).

I wish I had a good function generator so I could do a more scientific test but I stand by my results based on my anecdotal experience as well. Not to mention that most professional lighting uses PWM, that would not make sense if they would be loosing ~50%-70% efficiency that some say. It makes perfect sense based on my results though where they would only be loosing 10%-20% efficiency to maintain the same tint.

Overall while FET PWM is not perfect by any means, particularly on LED’s that tint shift I will have no issues at all using PWM to adjust the output vs a constant current. The minor difference in efficiency will not effect most people / use cases.

At a given current draw the battery will last exactly the same FET vs constant current. The only change will be the lumen output and in most cases the human eye will not even be able to see the difference without having them side by side.

Agro's picture
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With commercial lightning it’s different – they don’t overdrive their LEDs like we do but run them within very efficient region all the time.

Someone (L4P?) has tested the effect of temperature on efficiency. I can’t find it now. Sad
I wonder if it would be consistent with your result…

Hank33's picture
Last seen: 5 hours 1 min ago
Joined: 11/22/2019 - 16:00
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Location: Vancouver, B.C.

Can someone recommend a driver to use for my BLF A6 mod? Is it this one?

I know I need a 3v one? I'm doing the mod with this led.