A
crowbar circuit is an
electrical circuit used to prevent an overvoltage condition of a
power supply unit from damaging the circuits attached to the power supply. It operates by putting a
short circuit or low resistance path across the
voltage output (V
o), much as if one dropped a
tool of the same name across the output terminals of the power supply. Crowbar circuits are frequently implemented using a
thyristor,
TRIAC,
trisil or
thyratron as the shorting device. Once triggered, they depend on the
current-limiting circuitry of the power supply or, if that fails, the blowing of the line
fuse or tripping the
circuit breaker.