Another DC/DC converter question

Hey guys,

This is work related again (always feel I need to state that to differentiate from my normal posts).

Anyway, "The Physicists That Be" have demanded a very efficient buck regulator with a 3V input voltage and a fixed 0.2V (yes 200mv) output voltage at a max current of 70mA. I don't know if this is even feasible (they're asking 90% eff if we can get there, but honestly if we can only get 30% they'll have to deal with that I think).

Anyway, that's pretty much the problem. I haven't been able to find any chips that will go below 0.4V out. So a custom solution may be necessary if possible.

Thanks for any help! I've got a free rail of 10 LM338K Steel 5amp TO-3's to anyone that can get me a solution

You might find **broken link removed** interesting.
The feedback network of an adjustable DC-DC converter IC is returned to a reference voltage - not to ground - and the output voltage can be less than 1.25 V.
You might evaluate this tecnique, as a starting-point for your design.

That sir, will probably win you the rail of 338k's if you want em. Or any other spare parts I can find in the lab. If I can make it work, lemme know what all you might want and I'll mail ya some spares if we got em.

This worked beautifully fwiw. We used stock parts we had on hand instead of the ones in the data sheet, and we were able to get down to 180mv at 50% efficiency into a 1 ohm load with low ripple. I doubt we're going to get much higher than 60-70% with tweaking it, but very very pleased with the 'thrown together' little board we made today. Thanks!