Circuit for controlling the firing angle of a semiconductor a.c. current-controllingdevice

Claim 1

A FIRING ANGLE CONTROL CIRCUIT FOR A SEMICONDUCTOR CURRENT-REGULATING DEVICE, COMPRISING A SEMICONDUCTOR HAVING AN ANODE AND A CATHODE AND AN ELECTRODE FOR ESTABLISHING THE FIRING POTENTIAL OF SAID SEMICONDUCTOR DEVICE, MEANS TO APPLY AN ALTERNATING CURRENT TO BE REGULATED TO SAID ANODE, A PULSE GENERATOR, MEANS TO APPLY SAID PULSE TO SAID ELECTRODE, SAID PULSES HAVING A PEAK POTENTIAL AT LEAST AS HIGH AS THE SAID FIRING POTENTIAL, AND MEANS TO INITIATE SAID PULSES AT A SELETED PHASE ANGLE OF SAID REGULATED AC, SAID PULSE GENERATOR BEING A RELAXATION OSCILLATOR INCLUDING AN RC CIRCUIT AND A UNIJUNCTION TRANSISTOR, SAID UNIJUNCTION TRANSISTOR INCLUDING AN EMITTER, SAID RC CIRCUIT COUPLED TO SAID EMITTER, MEANS FOR APPLYING A DC BIAS TO THE SAID EMITTER, MEANS TO APPLY AN AC POTENTIAL TO THE SAID EMITTER TO MODULATE THE SAID DC BIAS, SAID MODULATING AC HAVING A SELECTED PHASE RELATIONSHIP TO SAID REGULATED AC, SAID DC BIAS BEING, IN THE ABSENCE OF SAID AC POTENTIAL, INSUFFICIENT TO BIAS THE UNIJUNCTION TRANSISTOR IN A FORWARD DIRECTION, THE PEAK VALUE OF SAID AC POTENTIAL BEING, IN THE ABSENCE OF SAID DC BIAS, INSUFFICIENT TO BIAS THE UNIJUNCTION TRANSISTOR IN A FORWARD DIRECTION, SAID MODULATED DC BEING SUFFICIENT AT A SELECTED PHASE ANGLE OF SAID MODULATING AC AND OF SAID REGULATED AC TO FORWARD BIAS SAID UNIJUNCTION TRANSISTOR, TO INITIATE SAID PULSES AT SAID SELECTED PHASE ANGLE OF SAID REGULATED AC, SAID MODULATED AC BEING A SAWTOOTH WAVE VOLTAGE SYNCHRONOUS WITH SAID CONTROLLED AC, A HEATER RESISTOR IN SERIES WITH THE CATHODE OF SAID REGULATOR, A HEATED SPACE HEATED BY SAID HEATER, A WHEATSTONE BRIDGE, ONE OF WHOSE LEGS IS A TEMPERATURE-SENSITIVE RESISTOR IN SAID HEATED SPACE, THE OUTPUT OF SAID BRIDGE COUPLED TO THE BASE OF SAID JUNCTION TRANSISTOR.