| 摘要 |
PURPOSE:To prevent the destruction of a semiconductor element by connecting a protective circuit to the common input side of a plurality of drive circuits which individually control the switching of power semiconductor elements. CONSTITUTION:A transistor Q is connected between the common input terminal of drive circuits FU-FZ and the positive pole of a DC power source B. In addition, by providing transistors Q5 and Q6 which turn on an overcurrent detection circuit 6 by using the output of a comparator CP2 which becomes a low level when an overcurrent occurs and photocouplers FC2 and FC3 which output overcurrent detecting signals by turning on the transistor Q6, the transistor Q is turned off by turning on the photocoupler FC2 and the overcurrent detecting signal is outputted to a control circuit CT by turning on the photocoupler FC3. As a result, the power supply to the input side of the circuits FU-FZ is discontinued and the power supply to a motor M is stopped by discontinuing a collector current by turning off the base currents of power transistors TU-TZ. Therefore even when a malfunction occurs all power transistor elements can be surely protected from destruction irrespective of the kind of the malfunction. |
