| 摘要 |
A magnetic tachometer sensor for a motor control circuit having a motor driven interrupter wheel in proximity thereto supplies a motor speed signal to a frequency to voltage converter. The frequency to voltage converter produces a DC signal proportional to the speed of the interrupter wheel. The DC signal is compared to a user selected reference voltage in an error amplifier, thereby producing an error signal. The error signal is supplied to an output comparator which also receives a sawtooth timing reference signal in synchronism with power supply alternating current. The output comparator switches to trigger a triac into conduction when the sawtooth signal voltage exceeds the error voltage, thereby providing highly accurate timing of the switching point of the triac. The triac is arranged to provide a phase angle speed control for an electric motor used in a household appliance. |
