| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply capable of correctly detecting an input voltage at the secondary side even if an output voltage changes. ! SOLUTION: The switching power supply device for supplying an output voltage Vo from a smoothing capacitor C2 to a load includes: a series circuit composed of a switch element Q1, a primary winding Np of a transformer T and a capacitor C1 which are connected in parallel to a DC power supply E; and a rectifying and smoothing circuit composed of a rectifier diode D2 and the smoothing capacitor C2 which are connected to a secondary winding Ns of the transformer T; and a control circuit 10 for controlling to switch on/off the switch element Q1 according to the inter-voltage VC1 of the capacitor C1. The switching control device further includes an input voltage detector circuit 20 for detecting the input voltage VE of the DC power supply E, using a voltage obtained by adding a voltage, which is generated at the secondary winding Ns when the switch e |
