DC controlled safety relay supplying AC load - has input synchronised two transistor photocoupled amplifier supplying current to railway signals

摘要

The relay circuit is used to control an ac supply to a load, such as railway line signals where the control to the circuit is dc level. The design is intended to prevent the generation of harmonics and their consequent interference effects and to provide an alternative arrangement to magnetic amplifier. The relay circuit is based on two transistors, pref. optically coupled, whose bases are supplied alternately by the control dc level. The input ac is fed in via a transformer and rectifier circuit and supplies the two NPN transistor amplifier. Both transistors work in synchronism with the input supply frequency. The collectors feed an output transformer in push-pull, the transformer centre tap being fed from the input rectifiers.