| 摘要 |
PURPOSE:To prevent mis-energizing of a switching element and destruction thereof by keeping the switching element on an off only for a time from turn-on of AC power until an output voltage of DC power circuit reaches a normal operation voltage of a control circuit. CONSTITUTION:When an AC power is turned on, the drain source voltage VDS of a switching element 10c rises and then, an output voltage VCC of a DC power circuit 12 rises behind VDS. A gate source voltage VGS of the element 10 begins rising in a period of time for which VCC does not reach a voltage at which a control circuit 11 works normally. However, when VGS reaches such a voltage that a base current can be supplied to a transistor Tr 13f of a protection circuit 13 through a resistor 13d, the Tr 13f conducts so that VGS never rises up higher than that voltage. If a control voltage is set lower than the threshold voltage of the element 10c, the VGS of the element 10c does not exceed the threshold voltage, so that it is possible to prevent misenergizing of the element 10c and its destruction. |
