| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply which self-determines a standby mode to stop oscillation of an active filter, for improved efficiency during standby and reduced number of components. SOLUTION: An active filter control circuit is connected among an active filter circuit, a flyback converter circuit, and an output controlling photocoupler which is connected to an output voltage detecting circuit. In the control circuit, an NPN transistor Q1 is connected to a voltage division point of voltage dividing resistors R1 and R2 shown in figure. The voltage dividing resistor R1 is connected to the feedback terminal of a first control IC in the flyback converter circuit, while the collector of the NPN transistor Q1 is connected to the base of an NPN transistor Q2 in the active filter circuit, with voltage dividing resistors R1 and R2 connected parallel to the transistor of the output controlling photocoupler. The control circuit monitors a feedback terminal voltage of the control IC for self-judging a standby mode, and stops oscillation of the active filter. Compared to a conventional system in which a standby current is detected on a secondary side, and the signal is transmitted to a primary side, the consumption of power while the signal is transmitted is eliminated, while the number of components is reduced and the efficiency at standby is improved. COPYRIGHT: (C)2005,JPO&NCIPI
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