A SAFETY CIRCUIT FOR PREVENTING OR REDUCING PHASE CONTROL SYSTEM MALFUNCTION

摘要

A safety circuit for preventing a malfunction from occurring in a phase control system of the type in which the firing angle of thyristors in a thyristor bridge is controlled to regulate the rotational speed of a DC motor constituting the load of the thyristor bridge. Thyristor firing pulses are produced each time a rising analog speed command signal (FS) intersects N-number of sawtooth signals. The arrangement is such that, immediately after the generation of each firing pulse, the thyristors are not supplied with extraneous firing pulses at least for a time interval (t) equivalent to the thyristor commutation overlap time.