Stall sensing circuit for shaded pole motors

Abstract

A motor control circuit for disconnecting the motor's power supply when the motor is stalled but maintaining it connected when it is running comprising a power loop and control loop, the former including a signal sensing means which provides an output sensing signal whose magnitude is a function of the motor's state in series with an ON, OFF switching means' input-output terminals which is responsive to the magnitude of a control signal applied to its control terminal to control its state. The control loop comprises a counter which provides a control output signal in response to a predetermined count and whose input is fed by the output of a voltage controlled oscillator whose frequency is a function of the magnitude of the output sensing signal of the signal sensing means to which it is connected. A resetting means is coupled to the reset terminal of the counter for periodically resetting the counter. The output control signal from the counter is fed to the control terminal of the switching means. The resetting signal occurs prior to the counter's predetermined count when the motor is running thereby turning the switching means ON to provide motor power; however, when the motor stalls, the reset signal occurs before the counter reaches the predetermined count, thereby producing a control signal which turns the switching means OFF, thereby disconnecting the motor's power supply.