The firing circuit, originally designed circa 1980 generates periodic pulses to the SCR gate coupled via a pulse transformer. The circuit is an analog design that relies on the B-H curve of the transformer for timing and a bunch of other analog tricks. SCR gate drive problem - Circuit design - Eng-Tips Was this helpful? Thyristor Circuit Design | SCR Silicon Controlled Thyristor Circuit Design: SCR circuits Thyristor or SCR circuits are used for many power control uses from lighting control to AC power motors, and other switching applications. SCR Circuits | How Thyristor Circuit Works | Electronics Notes Many AC thyristor, SCR circuits use a variable phase difference of a signal created at the gate to control the portion of the waveform over which the thyristor conducts. This type of circuit is relatively easy to design and construct.