| 摘要 |
PURPOSE:To raise the reliability by constituting an overcurrent protecting circuit of a conductive modulation type MOSFET (BIFET), of a drain-source voltage detecting circuit, and a circuit for dropping a gate-source voltage of the BIFET by an output of said circuit. CONSTITUTION:When an accident is generated in a load 3, and an overcurrent flows to a conductive modulation type MOSFET 1, a voltage corresponding to an on-voltage of the FET 1 is obtained in a resistance 13 of a voltage detecting circuit. This voltage is applied to a gate of a MOSFET 14 through a diode 17, and when this gate voltage exceeds a threshold value, a gate-source voltage of the FET 1 drops to the sum of an on-voltage of the FET 14 and a forward voltage of a diode 15 and cuts off the overcurrent of the FET 1. In this case, a charge which has been accumulated in a gate input capacity of the FET 14 and a discharge time constant by a resistance 16 are made large, and a discharge time of the MOSFET 14 is made longer than a vibration period of a source-drain voltage of the FET 1. As a result, it is prevented that the FET 1 is turned on again. |
