| 摘要 |
PURPOSE:To reduce the heat loss of a power transitor by turning ON or OFF both ends of a series resistor connected in series with the winding of a motor depending on the amplitude of the current of the winding. CONSTITUTION:An AC frequency voltage which is proportional to the rotating speed generated by a frequency generator 3 is converted by a F/V converter 5 to a DC voltage proportional to a the frequency, an error amplifier 6 compares the DC voltage with a reference voltage Vref and supplied a control voltage VC to a voltage controlled variable current power source 7. When the current of the winding of a motor is less than the prescribed value, i.e., when the output VA of a current detector 7a is smaller than the VS, a switch 9 is opened by the output of a comparator 7d to insert a power consumption resistor 8 in series with a power transistor 7c, thereby reducing the power consumption of the transistor 7c.
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