multi-current driver design

[bfromcolo]

In my circuit I have a 9.6v NiMH voltage source, 2 CREE XR-E P4 white LEDs I want to drive in series at 700ma and one CREE XR red LED I want to drive at 350ma. I am running it with resistors now but they get hot, and I could improve run time.

I see plenty of surface mount ICs that I could use in building a circuit, but I have trouble with these tiny chips, does anyone make efficient constant current regulator chips that are not in a surface mount package?

I guess I could just order some cheap flashlight drivers, but thought I might build my own.

Thanks

 

[SafetyBob]

I don't know if this will help, but I have a couple of MicroPucks that I am about ready to use on a single cree setup. I know someone in the homemade and customs flashlight forum has pictures and a short tutorial on how he did it. I would think you could parrallel two 350mA pucks for the two crees and use a seperate one for the red one. As soldering of wires and stuff into the flashlight. Mini switches as necessary for control.

One place to get them is www.theledlight.com. I have gotten alot of crap from them and never been dissappointed with anything.

Bob E.

 

[VidPro]

i cant work with the hairline connections either, or mabey i dont want to so the flashlight drivers have the teeney stuff mounted, that makes them good candidates, because the small junk is already mounted. of course that doesn't make them 4times what is needed, and therfore very robust and forgiving.

you can build a current regulator with a 317 type adjustable voltage regulator, but it has a huge voltage drop, and much waste that it burns off itself. be as bad or worse than a resister, but at least it is a brute part.

as mentioned above, you can buy drivers, and potted drivers which are very robust http://www.ledsupply.com/led-drivers.php (cheaper there by a bit)

when you have such high offset voltages , some sort of dc converting things are usefull. you cant improve runtime and heat with a Power WASTING type of driver, cause they will do the same as your resisters , just with more regulation.

 

[TorchBoy]

I have gotten alot of crap from them

You shouldn't put up with it.

You could use a standard "Kennan" buck driver to drive the two white LEDs (at 750mA) and use another tweaked one to drive the red LED. Replace the 0.27 ohm set resistor with a 0.56 ohm resistor to get the lower current wanted. Total driver cost $6.20, plus a resistor.

 

[bfromcolo]

Thanks for the replies. I ordered a 700ma and 350ma buckpuck for this.

I have a couple of the Kennan regulators on hand and have used them for other projects. I don't know that trying to replace that tiny resister is any better than messing with surface mount ICs. Guess I am getting old and blind, I have enough trouble soldering the LED connection wires to the front of the Kennan as it is. I have used these for bike lights and although I have not had any problems with this regulator I don't trust the connections on the front or back to be mechanically sound.

I have some of the 317s on hand as well, but as you note they aren't much more efficient or cooler than the resisters.

I would still like to be able to buy high efficiency regulator chips in "standard" IC packages to mess with.

 

[TorchBoy]

Advantages of the buckpucks? Let's see, potted, waterproof, dependable, mechanically sound, rugged. Should do you nicely for biking - I presume that's what it's for, with the mix of white and dimmer red. If you don't mind me asking, where have you mounted the battery?

 

[bfromcolo]

Should do you nicely for biking - I presume that's what it's for, with the mix of white and dimmer red. If you don't mind me asking, where have you mounted the battery?

Yes its for one of my bikes. I have a small bag on the drive side of my rear rack that I plan to put the battery in. The electronics and rear light will be mounted on top of the rack. This is my commuter, I use a pannier for my clothes and laptop, so there is lots of free space on top of the rack for this sort of thing. Once I get all the piece parts put together I will post it in the bicycle section.

 

[radellaf]

In case solder bridges are what are giving some of you fits with the surface mount...

Use a TON of flux. Slather the thing with it. You can solder .5mm pitch FPGAs with a 3mm chisel tip iron that way. The solder just goes where it is needed, and excess sticks to the iron. Too much? Wipe off the iron, touch it to the bridge, and solder will come right off onto the iron.

I'd recommend a good Kester water-soluble flux for this. Water in the sink gets it off, and an alcohol (isopropyl) bath is good for good measure and to avoid water spots.

Rosin is a pain to clean off, and no-clean really isn't.