Solid state relay circuit

A solid state relay circuit of the alternating impulse type comprising a pair of thyristors each having a first and a second primary terminal and a gate terminal;

• a pair of loads each being connected in series with said first primary terminal of one of said thyristors;
• means for connecting an AC source voltage in series with said second primary terminals of said thyristors;
• and a triggering circuit connected to said gate terminals for alternately triggering said thyristors into conduction to alternately provide currents to said loads, said triggering circuit comprising means for receiving an input trigger signal, a pulse shaping circuit connected to said last named means for shaping said input trigger signal into a squared pulse, a toggle flip-flop having two output states connected to the output of said pulse shaping circuit, said flip-flop being connected to said pulse shaping circuit so as to provide alternate output states for successive input pulses, an optically isolated switch connected between the output of said flip-flop and the gate terminals of said thyristors, a power supply for said optically isolated switch separate from the power supplies for the other components in said triggering circuit, and a secondary switching element connected between said optically isolated switch and one of said gate terminals to provide a gate activating current at said one gate terminal when said optically isolated switch is not conducting a gate activating current to the other of said gate terminals and to block the gate activating current to said one gate terminal when said optically isolated switch is conducting a gate activating current to said other gate terminal.