Simplest PWM buck conv

[Oznog]

I have a high power Luxeon LED emitter that needs high current and low voltage. I'd power it off of a poorly regulated 12v source.

It needs to be a current regulated output, and a PWM freq of around maybe 40kHz. Now previously, I implemented it with a PIC reading the output voltage from a low ohm resistor. It's got to be low because that LED sucks like an amp and it makes a lot of heat and the driver is supposed to be small (and in a plastic box). I bootstrapped the MOSFET (it's a logic level device).

The regulation had a lot of problems. I never did have a clear diagnosis, but I think it comes down to the fact that a buck reg vs a constant voltage diode is really touchy, small duty cycle changes can make large current changes. The PIC only has so many increments it can drive the PWM in too.

I'm starting to think I should do a PWM with an analog adjustment to get tighter control. But the feedback voltage is quite low, and it'll need trimming to accurately set the output at the specified level. Now what might be a good way to do this with as few components as possible?

 

[bryan1]

Eh Oznog,
In the morning I'll scan my siliconchip mags an deres a circuit in there for driving luxeon LED's I know theres a kit availble and I'm thinking of buying one but if your interested I'll do the scan and provide the full details for you.

Cheers Bryan1

 

[Oznog]

That would really help me out bryan. I'll be on the lookout for your scan.

Thanks!