led driver

[bogdan]

anyone cand suggest a led driver chip? one that requires few external components? it should be able to drive 1-2 white leds from a suply voltage like 2-5V....any ideas?

[ante]

Why use a chip for this, just a couple of resistors will do the job.

Ante ::)

[Ldanielrosa]

For driving white LEDs from a lower voltage than Vf there are chips from Maxim, Microchip, and (probably) National. You'll have to do a parametric search for them.

http://www.maxim-ic.com/index.cfm
http://www.microchip.com/1010/index.htm
http://www.national.com/

There are also discrete component circuits for them. These have several topologies, each suited to specific needs.

http://elm-chan.org/works/led2/report.html
http://members.shaw.ca/novotill/LedSupplyRegAA/index.htm
http://www.satcure-focus.com/hobby/page2.htm
http://www.elektor-electronics.co.uk/miniproj/download/010130uk.pdf

The first three are variations on a blocking oscillator. The last one is different- it does not require a tapped inductor, but does need two transistors.

[bogdan]

well, do you know any common driver, because here components are quite hard to find, so i need something common.
maybe some other suggestions?

[ante]

Sorry. All white led:s I have seen so far are 3.6V drop so 5 Volts will to fine. Unless it was 2.5 V stated in the question instead of 2 - 5 Volts, as I believed.

Ante ::)

[bogdan]

well, i meant to say that the circuit should work for 2 to 5V, and produce enough voltage for the led to light up in the same way, no matter the input voltage.
so any suggestions?

[Ldanielrosa]

Microchip and Maxim give away free samples. Just answer their questionnaires honestly. Unfortunately the packages are all SMT.

As for the discretes, if you can get some used disposable cameras with flash units (some places will give them away since they're garbage) the charging transistor is ideal. The toroid core is not critical.

One place I neglected to mention is

http://209.67.62.186/ubbthreads/ubbthreads.php

Here you can find people whose passion for LED flashlights borders on psychosis. There are articles on many design topologies that surface frequently.

If your locale is really starved for parts connections, I may be able to help if the postage isn't too high. PM your address and I'll look into it.

[ante]

If you only have 2 volts, what

[Ldanielrosa]

Second question: Yes.

First question: Three external components help with the task of step-up voltage conversion. One inductor, one capacitor, and one schottky diode.

[ante]

Ok, I have missed it then, what is the chip id please?

Ante ::)