MALFUNCTION PREVENTING CIRCUIT FOR SEMICONDUCTOR ELEMENT

PURPOSE:To improve the voltage rise tolerance of a semiconductor three- terminal element and to prevent the noises mixed through a signal line, by securing the connection between control terminals via the short circuit or a specific impedance when the noise is applied. CONSTITUTION:The DC voltage 22 is connected in the solid line direction of a switch 23 and the voltage is applied to a capacitor 24 to be used as a supply source for pulse voltage. The switch 23 is opened when the application is through with said voltage. In this case, an SCR1a is controlled by a control signal 25 and the DC voltage controlled by the signal 25 is applied to a load 20. Then a switch 26 is applied for application of the pulse voltage to the load 20. While the pulse voltage having a sharp rising rate is applied to an SCR1b connected antiparallel. At the same time, the noises are transmitted via a signal line in response to the discharge of the capacitor 24. Thus the SCR1b has a malfunction. In this case, a switch 26 is short-circuited with both switches 7b and 8b opened respectively. Thus it is possible to cope with the pulse voltage having a sharp rising rate and the mixture of noises. Then the malfunction of the SCR1b can be avoided.