| 摘要 |
A motor control circuit controls the speed of a single-phase split capacitor or shaded pole electric motor, and permits operation of the motor over a wide range of speeds without stalling. A first gated bilateral switch such as a triac is connected in series with the motor, and is fired by an integrating circuit through a second bilateral switch such as a diac. The integrating circuit charges through the start winding of the motor and a potentiometer which adjusts the rate of charging of the integrating circuit for the minimum speed setting desired. The motor control circuit also includes a temperature sensing bridge which becomes unbalanced as a function of increasing temperature. A light emitting diode connected to the bridge emits light as a function of the unbalance of the bridge. A charging circuit is provided which supplies additional charging current to the integrating circuit, and includes photosensors which vary the amount of charging current supplied to the integrating circuit as a function of the light received from the light emitting diode. As the amount of charging current is varied, the rate of charging of the integrating circuit varies, and the diac and triac are triggered earlier in each half cycle of the AC input voltage. Earlier triggering of the motor in each half cycle causes the motor to run at a faster speed.
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