Brainstorming making PSU for 24+3 White LED flashlite

[lordvader88]

I was given a broken flashlite that ran off 3 series AA batteries with 1 current liming resistor, on V+.

It has a switch between 3 edge or 24 front white LEDs in parallel. I know some will pass a lot more current than others. I want to make something using old pulled transistors with 1 overall variable resistor turning the max current up to 30mA average on LEDs that pass the most current.

I can adapt the PCB to 4 rows of 6, or even 6 rows of 3. I don't want to make 9 current mirrors(although it would be fun to solder).

I also don't want to use an LM317, I want to use my basic know how of BJT regulators and current mirrors. I have lots of adjustable voltage references like TL431 and 2.5V LM336.

I also want it to run off 9V or 12V since they are the walwarts I have. I could use a switch between 2 biasing paths or IDK yet.

I'm disappointed at the brightness of 24LEDs at 325mA Thas was with 3.1V across 24. So this won't help much as the soldering station lights vs my room lights. Oh well.

Any thoughts ?

[Audioguru]

The LEDs in parallel on my cheap Chinese 24 + 3 flashlight are matched pretty well so all the LEDs draw about the same current. But the cheap switch is failing to make good contact so I must turn it on and off a few times to make it work. When the switch works it makes plenty of light.

24 LEDs totalling 325mA is 13.5mA each. Their absolute maximum current is probably only 30mA each if you cool them somehow which will appear only a little brighter.
For more light you need many more little LEDs or a few large 3W to 10W LEDs.

[lordvader88]

Yeah I don't know about guessing the trace size, etc but I don't want to try 0.96A total . With the 5.7R 1/2W resistor in there I tried ages ago, at 325mW its too hot to touch for long. I think it had a 1R or 10R in there, and at a max of 4.5V none of them are on much tho.

With V+3.88 and 3.03V arcoss the LEDs it pulls 165mA. At 2.94V+ and 2.75V LEDs its only 44mA or about 1.83mA each.