"John Larkin" wrote in message
...
On Sun, 08 Jul 2007 19:26:32 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.

John

have you considered a MC34063A ?

might just do it wothout an external switch.
input range 40v, for voltage inverter just connect ic ground to neg op.

Colin =^.^=


Yeah, I looked at that. It would probably work, but it's an old, slow
bipolar part with a darlington switch, so it would be pretty
inefficient and would run at maybe 100 khz, so it would need a big
inductor. But it is cheap, 35 cents or something.

Yep it is realy cheap, and as you say old too.
but ive used it many times now.

it works realy well for lowish power if you have a fairly constant load,
other wise it teneds to cycle skip wich can make some audible noise.

ive used it from all sorts of combinations, from +30v to 3.3v to 3.3v to
250v lol
The size of the inductor would probably not be any bigger than say the extra
space for an external switch.

I realy wish there was a more up to date replacement that had the wide input
voltage.
many nice new ones with integral FET seem to be for low voltage.

there is also the lm259x series wich are much the same,
they run quieter but are quite expensive.

Colin =^.^=