With respect to conventional driving circuits for power semiconductor elements, in the case where the circuit is used with a self-turn-off power semiconductor element such as an IGBT (Insulated Gate Bipolar Transistor) made of Si (Silicon), or the like, when a voltage change dv/dt occurs between collector-emitter terminals of the power semiconductor element in OFF state, the gate voltage increases due to the parasitic capacitance associated with the gate of the power semiconductor element. Thus, there is a problem that, if the gate voltage exceeds a specified threshold voltage, the power semiconductor element in OFF state is falsely turned ON to cause an arm short-circuit in a power converter such as an inverter or the like, resulting in breakage of the power semiconductor element. In order to avoid this problem, there is a method in which a negative bias voltage is applied between the gate-emitter terminals when the power semiconductor element is in OFF state.
However, with respect to the power converters such as an inverter and the like, driving power of the power semiconductor element is supplied from a power supply for the main circuit in many cases. Thus, there is a possibility that a voltage change occurs between the gate-emitter terminals before the negative bias voltage to be applied to the power semiconductor element is established, so that the gate voltage increases to cause the false operation. Meanwhile, in the case where a MOSFET (Metal-Oxide-Semiconductor Field-Effect-Transistor) is used as the power semiconductor element, if a voltage change occurs between the drain-source terminals before the negative bias voltage to be applied to the power semiconductor element is established, there is a possibility that the gate voltage increases to cause the false operation.
In Patent Document 1, a circuit (driving circuit) for driving a semiconductor element having a low threshold voltage is described. In the driving circuit of Patent Document 1, a normally-on-type FET (Field-Effect-Transistor) 132 is connected between the gate terminal and the source terminal 144 of a switching element 130 so as to short-circuit between the gate-source terminals when the power supply of a driving-pulse generation circuit 118 becomes in OFF state.