24 Nov
2004
24 Nov
'04
3:31 a.m.
From: ard(a)p850ug1.demon.co.uk
Hi
I just thought I'd note that you don't need feedback if the
transformer is just used to drive a square wave and not
used as a flyback type. It just comes down to turns ratios
for the voltage. If there is a post regulator, having a
regulated switcher is not needed.
Most PC supplies use a flyback type and regulate the 5V line
by the switcher to maximize efficiency but I doubt HP was
concerned about that.
Dwight
Interestingly, there's no feedback between the low-voltage side of the
switching transformer and the circuitry surrounding that SOC603B 6-pin
IC, so maybe it isn't an opto-isolator at all. All the circuitry
That does not suprise me. Since there's a pulse transformer in the
chopper base circuit, the controller IC is on the isolated side of the
PSU (the isolation is performed by the pulse transformer), so there's no
need for any optoisolator in the voltage feedback loop.
One question. Have you found how the controller IC gets its power? Is
there a separate (maybe linear) PSU for this?