| 摘要 |
PROBLEM TO BE SOLVED: To realize high efficiency and low noise over a wide output voltage variable range while maintaining a soft switching operation even in the case where an input voltage of an astable converter is reduced.SOLUTION: Output of a stable converter 12 is inputted to an astable converter 14, reduction of an output voltage is instructed by an output voltage control circuit 18 and the output voltage is reduced by duty control of the stable converter 12, thereby reducing an output voltage of the astable converter 14 being controlled by a fixed duty. In accordance with a magnitude of an input voltage detected by an input voltage detection circuit 70, a switching frequency control circuit 72 provided in a switching control circuit 22 for astable converter changes a switching frequency for turning on and turning off a set of switching elements 32 and 38 in the astable converter 14 and a set of switching elements 34 and 36 in a complementary manner while providing a dead time.SELECTED DRAWING: Figure 1 |
