| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply having an on/off control circuit of a secondary side DC voltage by using a semiconductor switch for controlling a loss of the semiconductor switch and heat even if the secondary side DC voltage decreases by an over-current. SOLUTION: In the switching power supply, a rectifying and smoothing circuit made up of a rectifying circuit DB and a smoothing capacitor C1, and an inverter Q1 are connected in series on the primary side of the output transformer T. An output terminal connected to the secondary side of the output transformer T through semiconductor switch Q2, and a control terminal connected to the semiconductor switch Q2 through an on/off control element Q3, are provided. In addition, a constant voltage circuit is provided. In the constant voltage circuit, an over-current detection circuit A is provided on the primary side or the secondary side, and a rectifying diode D2 and a resistor R2 are connected in series between the end of a secondary winding N2 and an emitter of the on/off control element Q3. A constant voltage ZD1 is connected to the resistor R2 on the side of the on/off control element and a capacitor C3 is connected on the side of the rectifying diode side thereof, while the capacitor C3 and constant voltage diode ZD1 are connected to the other end of the secondary winding N2.
|
