"Phil Allison" wrote in message
...

"Arfa Daily"
"Phil Allison"
"Arfa Daily"

I've been given a number of switchers to look at, by a company that I
do other work for. The one that concerns me here, is an open frame
type, single 12 volt output at, I would guess, 3 - 4 amps. It appears
to be a very simple design, in that the chopper drive circuit is
discrete, employing two bipolar transistors as an astable. The output
of this is fed pretty much directly to the gate of a single FET. In the
drain of the FET, is a single primary winding up to the raw rail from
the input bridge.


** What sort of SMPS is this ??

One that puts out regulated DC ???

Or is it for driving 12V halogen lights with raw high frequency energy.



No, it's regulated DC.


** With just two transistors and one mosfet ?

That is what you have told us.

And SFA else.


... Phil


You shouldn't take things quite so literally, Phil. I was talking about the
primary side only when I said that, but yes, it pretty much has a pair of
small TO92 transistors, and a TO220 mosfet. Obviously, it also has input
filtering, a bridge, made of 4 discrete diodes, a main filter cap, and
assorted R and C to make those two little transistors into an oscillator.
About 20 components altogether. The secondary side is exactly like any other
fixed voltage typical design, and there is, of course, a perfectly normal 6
pin opto for regulation feedback. Better ?

Arfa