LOW COST INSTANT REVERSING CIRCUIT

In a single phase AC induction motor having a main winding and an auxiliary winding both connectable to an AC power source , and having a start switch for automatically connecting and disconnecting the auxiliary winding to and from the AC source in starting and running modes, respectively, and having a user operated reversing switch for reversing the voltage polarity applied from the AC source to one of the windings relative to the other winding, low cost circuitry is provided for detecting the polarity reversal by sensing when one of the main and auxiliary winding voltages shifts from a leading to a lagging position relative to the other winding voltage, whereupon the circuit automatically instantly reconnects the auxiliary winding to the AC source to immediately apply reverse torque. A first voltage comparator senses a given polarity and magnitude of main winding voltage, and a second voltage comparator senses a given polarity and magnitude of auxiliary winding voltage. The output of the second comparator is differentiated , and a third voltage comparator compares output pulses from the first comparator and differentiated output pulses from the second comparator and instantaneously senses polarity reversal when one of the pulses shifts relative to the other, and in turn actuates the start switch