Power drive circuit for servomotors and the like

Claim 1

A POWER DRIVE CIRCUIT FOR DRIVING THE CONTROL WINDING OF AN ALTERNATING CURRENT SERVOMOTOR COMPRISING (A) A HIGH IMPEDANCE FIRST SOURCE OF CONTROL SIGNALS; (B) A SECOND SOURCE OF POWER REFERENCED TO A GROUND POTENTIAL; (C) A FIRST DRIVER STAGE INCLUDING A SMALL SIGNAL TRANSISTOR HAVING A BASE DIRECTLY CONNECTED TO THE HIGH IMPEDANCE SOURCE FOR RECEIVING THE CONTROL SIGNAL THEREFROM, A COLLECTOR, AND AN EMITTER; MEANS FOR BIASING THE SMALL SIGNAL TRANSISTOR FOR CLASS AB SERVICE; A COLLECTOR RESISTOR CONNECTING THE COLLECTOR OF THE SMALL SIGNAL TRANSISTOR TO THE SECOND SOURCE FOR MAINTAINING A SMALL VOLTAGE ON THE COLLECTOR; AND AN EMITTER RESISTOR CONNECTING THE EMITTER TO GROUND POTENTIAL; AND (D) A SECOND POWER STAGE INCLUDING A SINGLE POWER TRANSISTOR OPERATED AT CLASS B AMPLIFIER SERVICE HAVING A BASE DIRECTLY CONNECTED TO THE EMITTER OF THE SMALL SIGNAL TRANSISTOR, SAID POWER TRANSISTOR INCLUDING AN EMITTER RESISTIVELY CONNECTED TO GROUND, AND A COLLECTOR CONNECTED THROUGH THE SERVOMOTOR CONTROL WINDING TO THE SOURCE OF POWER; THE POWER DRIVER CIRCUIT PROVIDING POWER TO THE SERVOMOTOR.