On Mon, 09 Jul 2007 14:30:47 GMT, "colin"
wrote:


"John Larkin" wrote in message
.. .
I need to make -12 from +12, at maybe 500 mA, and all the obvious
inverting switching regulators suck for one reason or another.

The LM5112 is a 50-cent fet gate driver.

another thought,
how about a self oscillating one with a nch mosfet,
if its a steady 12vin and 12v out it should be doable with ~50% duty cycle
so just an extra winding on the inductor.
ofc with a bjt you need less turns for the base drive.
and some bias to start it up.
not sure if you could add current limit easily,
maybe when the inductor saturates it would lose base drive
(havnt given this much thought)

Interesting idea. That would be a classic blocking oscillator, with
the output taken on the flyback. The cool thing about a blocking
oscillator is that it's simple and drives the transformer to
saturation every shot, which automatically makes optimum use of the
core. It would regulate in variable-frequency mode.

I'll see if that leads to anything useful. I don't think I've seen
that topology done anywhere.

John