Proportional AC power control with zero-fire capability

The interface circuit presented facilitates closed-loop feedback control of AC load currents under strict zero-fire switching and is primarily intended for heating applications. The circuit converts an input analog signal to a time-proportioned series of full-cycle energy pulses, interspersed with missing integral numbers of half cycles. The circuit thus provides a power average in time delivered to the load proportional to analog control voltage, continuously minimizing the number of off-power half cycles, or wink time. Lamp load transient current data show the improved zero-crossing control capability of the interface circuits driving a commercial solid-state relay. The linearity and monotonicity of the interface circuit are verified under steady-state conditions. The temperature response in time of a lamp-heated sample under PID closed-loop temperature control shows the success of the interface circuit for its intended application