PROPORTIONAL AC POWER-CONTROL WITH ZERO-FIRE CAPABILITY

An interface circuit is presented, which facilitates closed-loop feedb ack control of ac load currents under strict zero-fire switching, prim arily intended for heating applications. The circuit converts an input analog signal to a time-proportioned series of full-cycle energy puls es, interspersed with missing integral number of half cycles. The circ uit thus provides a power average in time delivered to the load propor tional to analog control voltage, continuously minimizing the number o f off-power half cycles, or ''wink'' time. tamp load transient current data, shows the improved zero-crossing control capability of the inte rface circuit driving a commercial solid state relay. The linearity an d monotonicity of the interface circuit are verified under steady stat e conditions. The temperature response in time of a lamp-heated sample under PID closed-loop temperature control shows the success of the in terface circuit for its intended application.