| 摘要 |
PURPOSE:To prevent false operation due to noises from the outside and simplify constitution by a method wherein back electromotive voltage during an OFF period of a motor is detected, smoothed and compared with reference saw-tooth wave signals, and a transistor as a switch is controlled by the comparison output. CONSTITUTION:Output from an AC power source 1 is rectified by means of diodes D1-D4, and applied to a motor 2 through a transistor Tr1 as a switching element. A potential dividing circuit consisting of resistors R1 and R2 is connected to the motor 2, a diode D6 is connected at the potential dividing point, and the back electromotive voltage of the motor 2 in case of the OFF of the Tr1 is detected. The detecting signals are smoothed by means of a capacitor C, and inputted to a comparison circuit 5. On the other hand, the output voltage of a Zener diode ZD is applied to a saw-tooth wave generating circuit 4, and saw-tooth waves synchronized with the frequency of the power source are obtained by means of a synchronizing circuit 3 and inputted to the comparison circuit 5. The comparison circuit 5 emits output when the saw-tooth waves exceed the back electromotive voltage, and conducts the Tr1. |
