Turnoff-controllable thyristor and method of its operation

Claim 1

A THYRISTOR COMPRISING A SEMICONDUCTOR BODY HAVING OPPOSITE SPACED SURFACES AND ALTERNATELY OPPOSED CONDUCTIVITY TYPE LAYERS FORMED THEREIN, A FIRST END LAYER OF DETERMINED CONDUCTIVITY TYPE FORMING A P-N JUNCTION WITH A SECOND INTERMEDIATE LAYER OF OPPOSITE CONDUCTIVITY TYPE AND A THIRD INTERMEDIATE LAYER OF SAID DETERMINING CONDUCTIVITY TYPE FORMING A P-N JUNCTION WITH SAID SECOND LAYER AND ANOTHER P-N JUNCTION WITH A FOURTH END LAYER OF SAID OPPOSITE CONDUCTIVITY TYPE; A CONDUCTING MEMBER IN OHMIC CONTACT WITH ONE OF THE SURFACES OF SAID SEMICONDUCTOR BODY; A RING-SHAPED ELECTRODE POSITIONED ON AND FORMING A P-N JUNCTION WITH THE CONDUCTIVITY TYPE LAYER AT THE OTHER SURFACE OF SAID SEMICONDUCTOR BODY; A SECOND ELECTRODE POSITIONED INSIDE AND SPACED FROM SAID RINGSHAPED ELECTRODE AND FORMING AN OHMIC CONNECTION WITH A LAYER OF SAID SEMICONDUCTOR BODY; A THIRD ELECTRODE POSITIONED INSIDE AND SPACED FROM SAID RING-SHAPED ELECTRODE AND SPACED FROM SAID SECOND ELECTRODE AND FORMING AN OHMIC CONNECTION WITH A CONDUCTIVITY TYPE LAYER OF SAID SEMICONDUCTOR BODY DIFFERENT FROM THE LAYERS CONTACTED BY SAID RING-SHAPED ELECTRODE AND SAID SECOND ELECTRODE; AN ELECTRICAL CONDUCTOR CONNECTED TO EACH OF SAID RINGSHAPED, SECOND AND THIRD ELECTRODES AND TO SAID CONDUCTING MEMBER; AND CIRCUIT MEANS CONNECTED TO THE CONDUCTORS CONNECTED TO SAID ELECTRODES FOR APPLYING A FIRST CONTROL VOLTAGE OF SELECTIVELY REVERSIBLE POLARITY BETWEEN A FIRST PAIR OF SAID CONDUCTORS AND FOR APPLYING A SECOND CONTROL VOLTAGE OF SELECTIVELY REVERSIBLE POLARITY TO A SECOND PAIR OF SAID CONDUCTORS.