D. c. motor speed control using pulse width modulation

Claim 1

A VARIABLE-SPEED DIRECT-CURRENT MOTOR CONTROL SYSTEM, COMPRISING, IN COMBINATION: A DIRECT POWER SOURCE HAVING FIRST AND SECOND TERMINALS; AN ARMATURE CURRENT CONTROLLED MOTOR HAVING AN ARMATURE AND A SERIES FIELD CONNECTED IN SERIES BETWEEN SAID FIRST TERMINAL OF SAID POWER SOURCE AND A THIRD TERMINAL; A POWER TRANSISTOR SWITCHING CIRCUIT HAVING A PLURALITY OF SWITCHING TRANSISTORS CONNECTED IN PARALLEL, THE COLLECTOR-EMITTER CIRCUIT OF EACH OF SAID SWITCHING TRANSISTORS BEING CONNECTED BETWEEN SAID THIRD TERMINAL AND SAID SECOND TERMINAL OF SAID POWER SOURCE; A DRIVER AMPLIFIER TRANSISTOR HAVING ITS COLLECTOR-EMITTER CIRCUIT CONNECTED DIRECTLY TO SAID THIRD TERMINAL AND THROUGH A RESISTANCE TO SAID SECOND TERMINAL OF SAID POWER SOURCE, THE OUTPUT SIGNAL FROM SAID AMPLIFIER TRANSISTOR BEING CONNECTED TO CONTROL SAID PLURALITY OF SWITCHING TRANSISTORS; ANDA CONTROLLABLE PULSE WIDTH GENERATOR OPERABLE TO APPLY PULSES OF VARYING TIME DURATION TO SAID DRIVE AMPLIFEIR TRANSISTOR, SAID CONTROLLABLE PULSE WIDTH GENERATOR COMPRISING MEANS FOR GENERATING A RECURRENT SAWTOOTH VOLTAGE AT A SELECTED REPETITION RATE, MEANS FOR PROVIDING A CONTROLLABLE REFERENCE VOLTAGE, VOLTAGE COMPARATOR MEANS FOR COMPARING SAID SAWTOOTH VOLTAGE AND SAID REFERENCE VOLTAGE AND FOR PROVIDING AN OUTPUT VOLTAGE DURING EACH CYCLE OF SAID SAWTOOTH VOLTAGE WHEN SAID SAWTOOTH VOLTAGE EXCEEDS A PREDETERMINED PERCENTAGE OF SAID REFERENCE VOLTAGE, AND DIFFERENTIATING AND AMPLIFYING MEANS FOR AMPLIFYING AND DIFFERENTIATING SAID OUTPUT VOLTAGE WITH RESPECT TO TIME TO PROVIDE SAID PULSES OF VARYING TIME DURATION TO SAID DRIVER AMPLIFIER TRANSISTOR.