| 摘要 |
PURPOSE:To save components and to reduce the size of a switching power source by providing a second secondary winding in a transformer, and connecting a load to the output when a voltage drops to suppress the decrease of a power induced in the second secondary winding. CONSTITUTION:A switching power source circuit has a switching transformer 1, switching elements 5-6, a DC power source 7, an oscillation control unit 8, etc., and the unit 8 alters the duty ratio of an oscillation output waveform by the signal from an error detector 12. The output from a first secondary winding 3 drives a brushless motor 20 through rectifying and smoothing circuits 9-11 and a 3-phase inverter 22, and the output from a second secondary winding 4 is supplied through rectifying and smoothing circuits 14-15 and a constantvoltage circuit 17 to a main control microcomputer 18 and an energization switching unit 19 of the motor 20. Thus, the power of the winding 4 is simultaneously reduced and a load applying voltage is also decreased at the time of a light load, but the load is connected to the output when the voltage drops, thereby suppressing the decrease of the power induced in the winding 4.
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