Transistorised switching stage short circuit protection - has measuring resistor between output stage emitter and supply whose voltage drop excites evaluation circuit initiating disconnection

摘要

The protective circuit is intended for several transistor stages which in addition to central protection, are given also a current limiting. A measuring resistor (R2) is provided between the output stage (T2) emitter and supply voltage (-Uv). A reference Zener diode (G3) is in parallel with the output stage base and with the supply voltage. A further measuring resistor (RS) is in series with the Zener diode (G3) whose voltage drop, exceeding a certain threshold (G2) excites an evaluation circuit (OP) which initiates a delayed short circuit disconnection. A diode (G1) decouples further circuits.