| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply in which a variation in the input voltage of a controller IC can be suppressed for the voltage variation of a tertiary winding, and thereby a process of a high withstand voltage is not required and power can be saved efficiently during standby. SOLUTION: A rectifier circuit 5 applies a DC voltage to a primary winding 8a of a transformer 8. A switch element 48 turns a current flowing through the primary winding 8a on/off. A control circuit 51 performs the on/off-control of the switch element 48. A diode 31, a resistor 32 and capacitors 33, 34 output a voltage Vcc obtained by rectifying/smoothing the voltage of the tertiary winding 8c of the transformer 8 to the control circuit 51. When the voltage Vcc reaches a first voltage (11V), a voltage detection circuit 44 turns a switch 43 off, and raises the voltage Vcc by reducing the current flowing through the resistor 32. When the voltage Vcc reaches a second voltage (23V), the voltage detection circuit 44 turns the switch 43 on, and lowers the voltage Vcc by increasing the current flowing through the resistor. COPYRIGHT: (C)2007,JPO&INPIT
|
