Strange driver problem...

Hello, i am recycling an old post for another question BTW Some comments below are in relation to the old thread's question, so don't wonder what on earth theyre talking about.
I bought an aixiz 80-500mW linear driver. It arrived very quickly, and thats where the problems began... I was setting the current with a single 4.2V cell to 450mA, and that went nice and smooth but as soon as i added another cell, the current doubled to over 900mA. i have tried different cells and every one makes the driver have a different output!
I dont trust this driver at all, so i am purchasing a different one but i still want to know what on earth would cause that...?
Thanks for reading

Re: LM317 Driver for S06J Questions

The power dissipated is calculated by (Battery voltage - diode voltage) * output current.

So assuming 2 fully charged LiIons, at 8.4V, and a regular 445nm/405nm Vf of 4.5V, at 420mA:

(8.4 - 4.5) * 0.420 = 1.6W. You will probably be OK with that heatsink, however:

Yes, you can mount the LM317 to it, but you MUST use an insulating pad and washer/nylon screw/non conducive thermal plaster. The tab of the LM317 is connected to Vout, so must be isolated.

No, the cap isn't needed, however it's recommended as in rare occasions the LM317 may oscillate. If you're totally strict for room, maybe try a 1uF, just any decent capacitance will help, but if not, I wouldn't worry about it.

Your components seem fine, however I'd probably go for a 1W resistor just to be safe, as at 420mA it'd be dissipating 0.53W, which will heat up a regular 1/2W resistor very quickly and to quite a high temperature.

Re: LM317 Driver for S06J Questions

^ Thank you for an excellent reply After that info, I will probably go for a pre-made driver for duty cycle's sake.
But i did think of a solution for isolation- Just thermal glue the plastic side to the host and heatsink the other side of the regulator with an isolated heatsink
+REP to you for the excellent information

Re: LM317 Driver for S06J Questions

np, buck drivers are definitely an easier/more efficient way to go.

You could mount the 317 on the plastic side, but remember it's thermal condunctivity is greatly reduced. Thermal insulation sets for TO-220 packages are cheap:
http://www.jaycar.com.au/productView.asp?ID=HP1176
http://www.jaycar.com.au/productView.asp?ID=HP1142

Re: LM317 Driver for S06J Questions

Jaycar is amazing lol. I have gone there only intending to spend $5 but i end up spending $50+ :0

Re: LM317 Driver for S06J Questions

Yup, I was the same .. until I started working there Now it's even worse.

Re: LM317 Driver for S06J Questions

HAHA I hope you get staff discounts =D

Re: LM317 Driver for S06J Questions

You bet

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