really nice little switcher

Pin 2, SW, looks hot in the IR image, but it has a long trace, which confuses things.

The eval board layout looks fine at 2 amps, which is probably all I need. It runs, pretty hot, at 3.5 amps out and thermal cycles at 4.

There are little cheap potted switching 78XX drop-in equivalents, and they invert, so I could use one of them.

I'm trying to keep this box clean and simple, which is why this sort of thing is appealing, as compared to making a Cuk or something with a lot of parts.

or this:

I've done that too; the negative output is the p-p input voltage minus two diode drops minus other losses. That 5.6r resistor adds loss but most switchers need it to prevent current-spike shutdown.

Uggggh! Throw up!

Use a coupled inductor. Provide a Schottky diode on the plus side to match one on the minus side. Symmetry is your friend. Get better than 1% matching.

Yup. This.

Also works for non-synchronous converters, but you need a minimum load on the straight-through (buck) output.

Tim

John, read my other comment and Tim's followup.

I just tested a CUI potted-blob 7805 style switcher, as a +24 to -5 converter.

This works great. It's hardly worth designing something when this is under $5.

Here's measurements if anyone is interested:

This, plus the cute little TI synchronous switchers, pretty much solves my zillions-of-rails power supply problems.

Would be nice if someone took one apart and reverse engineered it.

Seems like a high price for a small switcher, maybe one should setup a company doing small switchers like that

Cheers

Klaus

I sometimes use some of these:

These are even cheaper:

-Lasse

I'd make more money selling hot dogs on the street. The distributor price must be something like $2.00.

I wouldn't use Chinese ebay parts in a production instrument. The CUI stuff seems very good, reliable and conservatively rated.

MPS has switchers that only need input and output caps, too. Interesting stuff, though I haven't actually used one in a design yet but might throw one as a Vcore supply for a DSP on a board I'm working on.