POWER SUPPLY CIRCUIT AND POWER SUPPLY SYSTEM

摘要

To provide a power supply circuit which can be applied worldwide without using a high withstand voltage switching element and can supply a load device with stable power. A charging section (14) is arranged between a turn-off capacitor (C4) and a load coil (L2). The charging section (14) has the anode connected to the positive terminal of a feedback coil (L3) and the cathode connected to the cathode of a zener diode (Z1). Thus, when a voltage of a commercial power supply (E) is high, the charging section (14) operates, the turn-off capacitor (C4) is quickly charged, an on-period of a transistor (Q1) is shortened, and an excessive voltage is prevented from being applied between the drain and the source of the transistor (Q1). At the same time, an output characteristic indicating relationship between the voltage of the commercial power supply (E) and a current flowing in the load device is permitted to be flat.