Abstract: A commercial application for a four-step switching PWM single phase AC controller for a load such as an induction motor or the like has a digital microcontroller for PWM signal generation and enhanced MOSFET switching control, and provides a multiplicity of discrete speed settings to make any single phase AC driven device easily and cheaply converted to efficient variable speed operation. Only two MOSFET gate drive optocouplers are provided on the high side of line voltage for reduced cost. Series transistors are programed to be left full on at maximum motor speed for increased efficiency. Current limit and under voltage sensing for fault protection are provided.