| 摘要 |
PURPOSE: A circuit for protecting a power switching device is provided to make a switching device interrupted during a predetermined period of time according to a result of sensing whether over current flows through the switching device. CONSTITUTION: A circuit for protecting a power switching device an NPN transistor(Q2) and a PNP transistor(Q3) which are connected serially between an auxiliar power(Vcc) and a ground. A control signal(Sg) is applied to bases of the transistors(Q2,Q3). An NPN transistor(Q4) has a collector connected to the power via a resistor(R1), an emitter grounded and a base connected to a connection node of the transistors(Q2,Q3) via a resistor(R3). An NPN transistor(Q5) has a collector connected to the power via a resistor(R2), an emitter grounded and a base connected to the collector of the transistor(Q4). A zener diode(ZD1) has a cathode connected to a node for outputting an over current detection signal(fo) and connected to the collector of the transistor(Q5) and an anode grounded via a resistor(R4). A power switching device(Q1) has a base connected to the connection node of the transistors(Q2,Q3) via a gate resistor(Rg), and is connected between main power lines(P,N).
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