Switching circuit utilizing two silicon controlled rectifiers with transient protection for the rectifiers

Claim 1

A STATIC SWITCHING APPARATUS COMPRISING: (A) FIRST AND SECOND SOLID STATE CONTROLLED RECTIFIERS EACH HAVING AN ANODE, A CATHODE AND A GATE CONTROL ELEMENT, (B) SAID FIRST RECTIFIER BEING ADAPTED TO BE CONNECTED IN SERIES CIRCUIT RELATIONSHIP WITH A LOAD DEVICE ACROSS A SOURCE OF ELECTRICAL ENERGY, (C) AN ON TRIGGERING CIRCUIT COUPLED TO THE GATE ELEMENT OF SAID FIRST CONTROLLED RECTIFIER FOR SWITCHING SAID FIRST RECTIFIER FROM ITS NONCONDUCTING TO ITS CONDUCTING STATE, (D) A SUBSTANTIALLY UNDAMPED QUENCHING CIRCUIT CONNECTED ACROSS SAID FIRST CONTROLLED RECTIFIER AND COMPRISING SAID SECOND CONTROLLED RECTIFIER AND A COMMUTATING CAPACITOR CONNECTED IN SERIES CIRCUIT RELATIONSHIP WITH EACH OTHER, SAID SECOND RECTIFIER AND SAID FIRST RECTIFIER BEING CONNECTED FOR CONDUCTION IN THE SAME DIRECTION WITH RESPECT TO SAID SOURCE, (E) MEANS FOR PRECHARGING SAID CAPACITOR IN A POLARITY TENDING TO PRODUCE FORWARD VOLTAGE ACROSS SAID SECOND CONTROLLED RECTIFIER AND INVERSE VOLTAGE ACROSS SAID FIRST CONTROLLED RECTIFIER, (F) AN OFF TRIGGERING CIRCUIT FOR SAID FIRST CONTROLLED RECTIFIER COMPRISING MEANS FOR SUPPLYING AN ON TRIGGERING SIGNAL TO THE GATE ELEMENT OF SAID SECOND RECTIFIER, AND (G) MEANS FOR LIMITING THE MAGNITUDE OF THE RECOVERY VOLTAGE TRANSIENT APPEARING ACROSS SAID FIRST CONTROLLED RECTIFIER WHEN SWITCHED TO ITS NON-CONDUCTING STATE COMPRISING A DAMPED BRANCH CIRCUIT SHUNTING SAID COMMUTATING CAPACITOR AND INCLUDING SUBSTANTIAL AMOUNT OF RESISTANCE AND CAPACITANCE.