"isw" schreef in bericht
]...
I have a little circuit board, salvaged from a washing machine, that is
a nice multi-output switcher. I'd like to use it in a project, but
there's one problem: all the output voltages are negative.

I measured the voltages and traced the circuit. The transformer has four
secondary pins; three have diode rectifiers, and one does not; it goes
straight to what I think is the "ground" output. All the filter caps for
all three outputs have their positive pins connected to that lead too.

The three diodes point in the direction that makes all the outputs
negative, too (cathodes to the transformer).

The outputs are -5, -12, and -22 volts; very reasonable for a small
supply, except that they are *backwards*.

So my question is, can I just reverse the diodes and capacitors, and
swap the two leads that send one of the output voltages to the reference
used to control the optically isolated feedback, and have a nice supply
with *positive* outputs?

Or is there something about the waveform from the transformer -- or
something else -- that would prevent this from working?

Isaac

Most likely not. Fastest way to make sure is looking at the waveforms with
an o'scope. But even if the waveforms look like good enough and you want to
give it a try, you'll have to reverse elco's and maybe other components as
well. It's almost sure that there is a kind of feedback from the secondary
to the primary that also has to be modified too.

petrus bitbyter