Electronic analog for an electromechanical relay

Claim 1

A static relay comprising: an input transformer and an output transformer each having a primary winding and a secondary winding, the input transformer further having an auxiliary secondary winding, a switching voltage source connected across the primary winding of the input transformer for supplying an AC switching voltage, a control circuit for functioning like the control winding of an electromechanical relay, the control circuit including a full-wave control bridge rectifier having a pair of AC terminals and a pair of DC terminals, the AC terminals connected in series with the secondary winding of the input transformer and the primary winding of the output transformer, the control circuit further including a control transistor having emitter and collector electrodes connected across the DC terminals of the control bridge rectifier and having a base electrode, the transistor rendered fully conductive between the emitter and collector electrodes in response to a predetermined potential difference between a control signal applied to the base electrode and a bias signal applied to the emitter electrode thereby to apply the AC switching voltage from the secondary winding of the input transformer to the primary winding of the output transformer, a control signal source connected to the base electrode of the control transistor for applying a control signal to the transistor, a bias signal source connected to the emitter electrode of the transistor for applying a bias signal to the transistor, a Zener diode effectively connected between the base and emitter electrodes of the control transistor between the control signal source and the bias signal source for protecting the control transistor from an excessive potential difference between the control signal and the bias signal, a switching network for functioning like the normally closed switching contacts of an electromechanical relay, the switching circuit including first and second full-wave switching bridge rectifiers, the first switching bridge rectifier connected across the auxiliary secondary winding of the input transformer for producing a first rectified DC output voltage having a first polarity in response to the AC switching voltage, the second switching bridge rectifier connected across the secondary winding of the output transformer for producing a second rectified DC output voltage having a second polarity in response to the AC switching voltage, the switching circuit further including a filter connected to the first and second switching bridge rectifiers for averaging the first and second rectified DC output voltages to produce a DC drive voltage having a first magnitude in response to the first rectified DC output voltage and having a second magnitude in response to both the first and second rectified DC output voltages, the switching circuit also including a power transistor having emitter and collector electrodes connected in series with a load and having a base electrode connected to the filter, the power transistor rendered fully conductive between the emitter and collector electrodes to energize the load when the drive voltage applied to the base electrode is at the first magnitude and rendered fully nonconductive between the emitter and collector electrodes to deenergize the load when the drive voltage applied to the base electrode is at the second magnitude.