Patent ID: 7675727

Claim:
A protection circuit for a power semiconductor device having a collector, a gate, and an emitter, the circuit comprising: a first comparator which detects a collector voltage of said power semiconductor device to output a first detection signal when the detected collector voltage exceeds a first reference voltage; a second comparator which detects a gate voltage of said power semiconductor device to output a second detection signal, when the detected gate voltage exceeds a second reference voltage which is set, relative to the potential at the emitter of said power semiconductor device, to be lower than a line power voltage of a drive circuit for outputting a drive signal that drives said power semiconductor device and to be higher than a terraced voltage of the power semiconductor device, the terraced voltage being a gate voltage allowing a rated collector current to flow at the collector of the power semiconductor device and being higher than a threshold voltage to turn on said power semiconductor device, the rated collector current being higher than an initial current flowing at the collector when the threshold voltage is applied to the gate; logic means for outputting a protection start signal when both the first and second detection signals are being output; and gate voltage reduction means for reducing said gate voltage in accordance with the protection start signal from said logic means.