| 摘要 |
PROBLEM TO BE SOLVED: To provide a power supply unit for a copying machine or the like capable of being protected, by cutting off AC input voltage automatically at the time of overload. SOLUTION: A section around the zero cross of AC input voltage is detected by a zero cross generating circuit 43 to obtain pulses. When AC input voltage is increased, the duration of the above pulse becomes narrow. Therefore, it is detected by a microcomputer 56 and a capacitor 55 is conducted, so that a power switch 54 is cut off to protect this device. |
