| 摘要 |
PROBLEM TO BE SOLVED: To easily regulate an output voltage at a secondary side in a switching power supply of a primary side control type including an inductor in a power supply circuit for rectifying and smoothing a voltage that is generated in an auxiliary coil.SOLUTION: A switch SW is provided in parallel with an inductor L of a power supply circuit for control circuit that is connected to an auxiliary coil Naux, and a load state at a secondary side of a transformer T is detected by an output voltage detection part 16 that is connected to the auxiliary coil Naux. In a control circuit 13, an error amplifier 22 and a capacitor C4 generate a voltage Vcomv (error signal) corresponding to the load state from a difference between a voltage that is obtained by sampling a signal VS detected by the output voltage detection part 16 by a sample/hold circuit 21, and a reference voltage Vref. A comparator 24 controls the switch SW into an OFF state under a heavy load and into an ON state under a light load. Thus, influences of the inductor L at a light load time can be ignored, such that it is enough to consider only a case of heavy load for regulating an output voltage Vout at the secondary side.SELECTED DRAWING: Figure 1 |
