Howdy - I need to generate a supply that is just slightly negative. Like I only need -.25V or so. A bit more would be fine - but not much. Certainly no more than -1V. It will be sinking about 15ma. I have a 6-8V input on this board. I already have a Vin to 3.3V buck converter and a Vin to 10V boost converter on this board.
I'm thinking I might replace the inductor on the buck with a coupled inductor, and have one side of the secondary grounded, and have the other side have a diode in series with a grounded capacitor. Line up the dots so that the diode is on when the buck converter switch is on. That way I'd only have (Vin - 3.3V - 0.5V (diode)) or about 2.2-4.2V on the output. Still more than I want though.
Anybody got a better idea?
edit: supply needs to be fairly clean - but I can put a big fat LC filter in front of it to take care of that. The supply voltage can fluctuate - it's going to be powering an op-amp that I want to operate to the rail. My Op-amp is strange enough that I don't think I'll be able to find one with similar specs that can operate at the very rail (it can output about 15mV from the rail - but I need to get within a few uV of the rail)