| 摘要 |
PURPOSE:To remove the ripple section of back electromotive force by extracting the high frequency of the variation section of voltage drop between the emitter and collector of a transistor connected in series with an armature circuit as pulses and sampling the output of a back electromotive force detecting circuit by the pulses. CONSTITUTION:A bridge circuit is formed by the motor 2 and resistors 3-5, and a differential amplification circuit 6 detects the back electromotive force of the motor 2 from voltage between the terminals A, B of the bridge circuit. Voltage drop between the collector and emitter of the transistor 11 increases in order to hold constant currents because the impedance of an armature drops when a commutator is short-circuited by means of a brush. The voltages pulses are shaped to predetermined width by means of a by-pass filter 9 and a monostable circuit 10. An analog switch 7 is controlled by the pulses, and the output of the difference amplifier 6 is transmitted to a sample holding circuit 8. |
