Den 09-05-2013 22:12, Mike skrev:
In article ,
wrote:
I have here a CyberPowerSystems 1500VA (950W) UPS

Not the same model, but I have a PowerCOM PCM "Black Knight" 500VA that I
roughly traced the circuit of.

.3A fuse, then a full-wave rectifier (made of discrete diodes), expected fi=
lter cap, and then... a mosfet. a 60V 80A n-channel mosfet. Source and drai=
n. The gate goes back to a collection of surface-mount parts which my eyeba=
lls can't seem to follow.

Similar, but the "fuse" seems to be a 0.1R resistor, bridge, then an FET
right across the supply feeding onward to the battery charger section.

I can't see any reason for this mosfet OTHER than to blow that fuse (which =
is exactly what it did. the mosfet is failed short).

Your posting reminds me of the same puzzlement I had. On mine, a pin on the
MicroController operates an intermediate transistor that feeds the FET,
and seems to be an emergency shutdown to forcibly stop the charger dead.

Some kind of controlled crowbar. Or a "warranty expired, time to replace me"
timer

Crowbar is the correct term. Here is an explanation of the function:

http://en.wikibooks.org/wiki/Practic...rowbar_circuit



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Uffe