22 Jul
2006
22 Jul
'06
2:35 p.m.
Been trying to work out this board. It's one
daughtercard in the PSU, the=
chopper transisors are on another. Yet, there are 3 TO-3 cased bipolar
(2Nxxx parts) scattered amongst the rectifier diodes. Similar units are n=
ot present in the +5V channel. Would this have linear regulators on the n=
on-main channels?
It's possible. On most SMPSUs, the main output (here the 5V line) is used
to provide the feed back to the chopper control circuit (so that output
comes out at the right voltage), the other just 'tag along'. Some better
machines put linear regulators on the minor outputs (the HP9000/217
currently on my bench has an SMPSU that gives out 5V and +/- 14.4V, the
latter 2 rails are regulated down to 12V by linear circuits on the
backplane).
It's not unheard-off for the minor outputs to have their own _switching_
regulators running off unregulated outputs of the main supply. Obviosuly
tese regulators don't have to provide any isolation between input and
output, and are fairly simple (The HP9845B PSU is one such, with, IIRC, 2
main chopper circuits, each with its own feedback loop from its main
output, and several switching regulator circuits for the minor outputs. I
think there's a total of 5 chopper controllers in that supply...)
-tony