Shunt motor control circuit for speed regulation and current limiting

Claim 1

IN A CIRCUIT FOR SUPPLYING DIRECT CURRENT TO THE ARMATURE OF A SHUNT MOTOR FROM AN ALTERNATING CURRENT SOURCE: (A) A BRIDGE RECTIFIER WITH MEANS FOR SUPPLYING ALTERNATING CURRENT FROM THE SOURCE TO FIRST AND SECOND OPPOSITE TERMINALS OF THE BRIDGE AND MEANS FOR CONNECTING THE MOTOR ARMATURE TO THIRD AND FOURTH OPPOSITE TERMINALS OF THE BRIDGE, (B) A PAIR OF SEMICONDUCTOR CONTROLLED RECTIFIERS EACH HAVING ANODE, CATHODE AND GATE ELECTRODES, THE ANODECATHODE PATH OF EACH OF THE CONTROLLED RECTIFIERS BEING CONNECTED IN A DIFFERENT ONE OF THE ARMS OF THE BRIDGE ADJACENT SAID THIRD TERMINAL, WITH THE ANODE ELECTRODES OF THE CONTROLLED RECTIFIERS BEING CONNECTED TOGETHER, (C) A PAIR OF CAPACITORS EACH HAVING ONE TERMINAL CONNECTING TO A DIFFERENT ONE OF THE FIRST AND SECOND TERMINALS OF THE BRIDGE, (D) VARIABLE RESISTANCE MEANS CONNECTING THE THIRD TERMINAL OF THE BRIDGE TO THE REMAINING TERMINALS OF THE PAIR OF CAPACITORS SO THAT THE CAPACITORS ARE CHARGED DURING ALTERNATED HALF CYCLES OF THE SOURCE TO VALUES RELATED TO ARMATURE VOLTAGE, (E) A PAIR OF THRESHOLD TRIGGER DIODES EACH CONNECTING SAID REMAINING TERMINAL OF A DIFFERENT ONE OF THE CAPACITORS TO THE GATE ELECTRODE OF A DIFFERENT ONE OF THE CONTROLLED RECTIFIERS, EACH DIODE HAVING A BREAKDOWN VOLTAGE MUCH LESS THAN THE PEAK VOLTAGE OF THE SOURCE AND EXHIBITING HIGH IMPEDANCE UNTIL THIS BREAKDOWN IS EXCEEDED BUT THEREAFTER EXHIBITING A LOW IMPEDANCE AND A DOWN VOLTAGE SOMEWHAT LESS THAN SUCH BREAKDOWN VOLTAGE, (F) A PAIR OF TRANSISTORS EACH HAVING ITS COLLECTOR-EMITTER PATH SHUNTING A DIFFERENT ONE OF THE CAPACITORS SO THAT WHEN THE TRANSISTOR IS CONDUCTIVE THE CAPACITOR WILL DISCHARGE TO A VALUE MUCH LESS THAN SAID DOWN VOLTAGE DURING ALTERNATE HALF CYCLES OF THE SOURCE, (G) AND BIASING MEANS RESPONSIVE TO ARMATURE CURRENT CONNECTED SEPARATELY TO THE BASES OF THE TRANSISTORS EFFECTIVE TO RENDER THE TRANSISTORS CONDUCTIVE ONLY WHEN THE ARMATURE CURRENT EXCEEDS A PRESELECTED MAXIMUM.