A Linear SCR Control Amplifier

A linear general-purpose SCR control amplifier is presented in this paper. This control amplifier is composed of a fire-control circuit and a "bridge" power output circuit. The input signal is used to control the firing angle of the two inverse parallel pairs of SCRs in the full-wave power bridge. The relation between the input signal and the firing angle is designed to be the inverse of the non-linearity introduced by the power circuit. Therefore, the amplifier has an overall linear gain characteristic, it is bidirectional, has a high bandwidth, and exhibits no deadband. The power bridge balancing action is used to absorb the major portion of the negative power pulse caused by an inductive load and therefore improves the efficiency of the amplifier. The linear SCR control amplifier has been built and successfully tested with resistive-inductive loads as well as in a closed-loop positioning servo system. The testing results and the simplicity of instrumentation qualify this control amplifier for industrial applications.