Cheap DIY "magic resistor" type circuit?

Ok I need to build four (4) circuits that will fit in a C mag body space, and each needs to regulate 1amp of current to an led, with an input voltage of no less than 3.6v-4v (3xC NiMH).

They can be in-efficient, no problem. Burn up the extra tenths of volts in themselves and what not. But having a voltage drop of .7 would not work, so I don't think a LM317T would work.

Something that doesn't require tons of SMT resistors/caps is nice. Like something you add resistors to and it does it's thing like the LM317T is what I'm looking for.


Runtime won't be affected much, and I don't think much heat/energy will be wasted since the batteries are really close to the VF of the leds. (Vf should be somewhere around 3.4 or so)

HELP?! Thanks

get ahold of burnt retinas... he's always ready to help

Thanks for the tip!

The LM334 circuit is cheap and easy - you can easily build each one for less than $5.

http://candlepowerforums.com/vb/showthread.php?t=75204

Here's a parts list I made once:

https://www.candlepowerforums.com/posts/956081&postcount=20

This uses the ST Micro LM334 part, but the National Semiconductor LM334 part is better (more stable).

http://www.national.com/pf/LM/LM317.html

What about those? the LM117? Do those have .7v drop?

LM317s typically have 2-3V drop in the regulator, and 1.2V in the set resistor when set up for constant current mode.

bummer

These LDO's have the same problem? My knowledge of circiuts has long since faded...

http://www.national.com/pf/LM/LM1086.html
http://www.national.com/pf/LP/LP8340.html

The '1086 has a dropout of 1.3V, and uses 1.25V of feedback, for 2.5V of dropout.
The '8340 has a dropout of about 1.0V at higher currents, and still uses 1.25V for feedback, so still 2.25V of dropout, if it can even be configured as a current regulator.

What you're wanting to do isn't very easy. How about a pair of protected 18650s in series (7.4V nominal), and a shark boost regulator from the sandwich shoppe? That ought to work nicely...though would be rather expensive.

The other option would be to forgo a regulator and just use resistors. You should get relatively flat output because of the NiMH cells, but it's definitely not as nice as a regulated light.