| 摘要 |
PROBLEM TO BE SOLVED: To improve the efficiency of a switching power unit in a standby mode. SOLUTION: The switching power unit is constituted in such a way that the serial circuit of the primary winding 3 of a transformer 2, a main switch 4, and a current detecting resistor 5 is connected between both ends 1a and 1b of a DC power source 1. A load 11 is connected to the secondary winding 6 of the transformer 2 through an output rectifying and smoothing circuit. In addition, a switch control signal forming circuit 16 and first and second power source circuits 22 and 26 for control are provided. In the standby mode, the supply of electric power for control is interrupted by generating an interrupted ringing and turning off a transistor 33 for voltage control by means of a transistor 43.
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