John Larkin wrote:

On Wed, 11 Jul 2007 18:59:17 GMT, Joerg
wrote:


John Larkin wrote:

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.


50 cents is a lot of money in electronics ;-)


Not in my electronics!


Yeah, I know. Wish it was so in mine. But at least I got to design one
"deluxe class" board earlier this year.


How about the old CD40106? The BCX70K seems overkill as well but only by
a cent or so. I think you need to throw in another transistor or two
because you may need a current limit, unless a short isn't going to have
nasty consequences.


After due consideration, not to mention being yelled at by junior
staff members, it looks like we'll be going to a flyback with custom
magnetics. It was an interesting diversion, anyhow.


Aw, that almost sounds like taking the chicken exit ;-)

But I guess a few bucks for custom magnetics won't matter in your case.
It is hard to find off-the-shelf transformers with air gaps that are
under 50c. That is why I usually don't do flybacks.


BTW, I'd probably be a bit squeamish about letting Vbe climb above -3V
on the BCX. But it's under abs max.


I tested some recently, and got around 5.1 typ Vbe breakdown. Beta
degradation wouldn't matter much in a common-base circuit like this!


Still I wouldn't like to hit it. Somehow that feels like driving with a
check engine light that flickers from time to time.


I'm going to have to play with the blocking-oscillator converter one
of these days, just for fun.


Absolutely. Once you have a well-tested design you can add it to your
building block collection. Blocking oscillators are a pretty good path
to make sure you won't be hit with part obsolescence issues.

--
Regards, Joerg

http://www.analogconsultants.com