On Sun, 08 Jul 2007 15:29:59 -0700, John Larkin
wrote:

On Sun, 08 Jul 2007 19:18:30 GMT, qrk wrote:

On Sat, 07 Jul 2007 21:15:31 -0700, John Larkin
wrote:

On Sat, 7 Jul 2007 22:13:26 -0500, "Tim Williams"
wrote:

Why does a UC3842, etc. suck, exactly? Wrong sign? (I don't remember if
the 14-pin version has + and - inputs at the pins.) Not cheap enough?

Yup, wrong feedback and gate drive signs, and the current-limit thing
would be damned awkward with a p-fet switch.


6W is a little much for a, say, cap switcher?...

Probably, and it would lose some voltage, too. It would have to be
done with a *lot* of discretes, since the IC charge pump things
couldn't handle the net 24 volts across the chip.

A Cuk converter would be nice, even with the dual inductors, but I
haven't found one that will flip +12 to -12 at this current. I think
the math gets messy.

An unregulated p-p forward converter would be OK, but the transformer
would have to be 1ct to 1.1ct or something like that, custom
magnetics, always a huge hassle.

There are a bazillion buck regulators on the market, and very few
inverters.


John

LT1372 will do the job in a Cuk configuration. LT1372 is a bit pricy
at $4.30 in unit quantities, but you do get a built in switch. You can
get dual inductors from Coilcraft and Coiltronics (Digikey). You do
get some sort of overload protection with the LT1372.

---
Mark

What's the output current in your cukfun sim? National has a similar
part, LM2611, with a 1.2 amp current limit switch. In the +12 to -12
config, it's only good for 170 mA out.

All the LTC stuff is "a bit pricey."

John

I have a 24 Ohm resistor on the output = 0.5A. The LT1372 current
limit is somewhere around 1.5A. The LM6211 in a SOT23 package has a
256 deg/W thermal resistance which is probably why the output current
is limited to such a low level. The LT part is around 125 deg/W for
their SO8 package. Guess these little controllers with internal
switches are pretty limited.

---
Mark