| 摘要 |
PURPOSE:To obtain a low-power consumption circuit by applying the output of high-efficiency power supply to a motor driving circuit at a constant load, and changing said power supply to another power supply when the load is increased. CONSTITUTION:Under the steady state wherein the load of a motor 5 is small, the voltage generated across a resistor 20 is small, a low output voltage which is converted highly efficiently in a DC-DC converter 13 is applied to an emitter follower 4 through a switch 21. Therefore, the loss in the emitter follower 4 is small. The motor 5 is driven in this way. When the load is varied at the starting of the motor 5 or by the disturbance and the like, the output of an error-signal amplifier 2 is increased so that the current flowing in a motor coil becomes large, and a large voltage is generated across the resistor 20. The switch 21 is switched to the side of a power supply 7 by said voltage, the large voltage is applied to the motor without saturating the transistor of an emitter follower 4, thereby the motor 5 is controlled so as to obtain a constant rpm. |
