Repeating again, I don't see any evidence of an overvoltage problem in
the multitude of switchers that cross my bench.
I like switchers.
** But you are an utter ass.
Of course. But I'm still right.
--
Jeff Liebermann
It is very common for the cheapo Chinese switchers used in items like DVD
players, to fail in this way. They are extremely susceptible to secondary
side filter cap failure - typically bulging and high ESR. This usually
results in the rail voltage dropping. Most of these supplies take their
control loop reference from just one of the output rails, and if it happens
to be the one that's got the bad cap on - often the case - then the supply
tries to crank it back up to the correct level, which results in all the
other rails going way up. This often results in destruction of LSIs
elsewhere in the item.
As a matter of interest, better quality multi-rail switchers used in some TV
sets, do have a form of 'crowbar' in that all of the rails are monitored for
output voltage, and if any become excessive, they trip a shutdown circuit on
the main supply control IC. The Vestel 17PWxx series that were used in a
number of manufacturer's TVs, are a good example of such.
Arfa