| 摘要 |
PURPOSE:To prevent any opening of a fuse or a circuit breaker by providing an AC voltage detecting circuit equipped with a resistor, one end of which is connected to the collector of a PNP transistor and the other end connected to a dead time control terminal of a switching control circuit. CONSTITUTION:When an AC voltage V0 is applied from AC voltage input terminals 54 and 55, an output voltage V1 from a rectifying and smoothing circuit 1 begins to rise, a voltage V2 divided by a resistor R1 rises up, a base current flows through a resistor R3 and a transistor Q2 is turned to ON. Also, a power supply voltage of a switching control circuit 4 rises through a mobile resistor R1 12, the reference voltage begins to rise and then a base current flows to a transistor Q3 and it is turned to ON state. The transistor Q3 is kept being ON until the voltage V2 exceeds the Zener voltage of a Zener diode Z2, so that the switching control circuit 4 can be made inoperative for a period of time where the Zener voltage is kept below the minimum operating power supply voltage of the switching control circuit 4. |
