LSI Based Three-Phase Thyristor Firing Circuit

A three-phase thyristor firing circuit has been developed to meet the needs of the static power conversion industry. The circuit consists of a three-phase phase-locked loop with digital countdown and phase division to provide delayed equidistant thyristor firing pulses. The delay angle is unaffected by frequency or phase rotation. The major portion of the circuit is implemented in a low-cost 22-pin large-scale integrated (LSI) circuit.