AMC7135: How much voltage can they burn off?

Flashlight Modding and DIY Parts
1

I want my weapon-light aspheric to be able to be used in a SHTF situation, meaning I need it to be able to run on lithium primaries. One primary won't cut it, but I'm afraid that two (6v) would simply be too much extra voltage for the 7135's to handle (have to burn off ~2.3v).

I know the datasheet says they can handle 6v, but the page relating to thermal considerations is greek to me. Has anyone run a 7135 driver where the input voltage is that much higher than the forward voltage of the LED? The driver will be heatsinked, but I want this to be as reliable as possible.

- Jon

2

I haven't tried, but if I was building a weapon light, I would torture test one - ie hook it up w/ no heatsinking, wrapped in saran wrap, and run it on high until the cells or the driver die. Not trying to be a smart alec. That's what I'd do...

3

I have just 1 7135 driver and wont burn it, btw tested it at 5,5v and became really hot so also less efficient, i read that the best tension is 4,5v.

If is not driving an xml you could use some thermal silicone or thermal pads to connect the 7135 to the copper pill

4

Yeah, I know it will certainly be inefficient at 6v, but I just want to make sure I can get full output from it at all times. I would be using Arctic Silver epoxy to mount the 7135's to the back side of the aluminum heatsink.

5

AMC7135 are linear so they perform the best when the input voltage is closer to the forward voltage of the LED, that way they don't have to burn anything off, The higher the voltage the higher the heat. It's not a certain voltage it's hoe close is the input voltage to what the LED requires.

Two CR123A are 6.4-6.6V fresh. Depending on the current you want to go into the LED the forward voltage of the LED changes, at higher current it's a higher voltage.

EDIT: That example was actually not good, so it's deleted.

6

Well it's a single mode driver (just 7135's, no micro controller), so it will be running between 1,050 and 1,400 amps (haven't decided if it can handle 1,400 yet on my heatsink), so forward voltage will be a constant 3.7v+. Maybe I'll just use my RCR123 and hope an SHTF situation never comes up :)