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Abstract

An amplifier circuit for controlling a direct drive motor has an input circuit for converting the digital control word to a pulse width modulated signal which is coupled to a control input of the amplifier through an isolation device. This isolation device and the other gain devices as well as many of the test circuitry devices and the feedback circuitry are referenced to a common, internally generated, stable reference level voltage. An input position control signal is coupled to an operational amplifier whose other inputs is a signal representing the current through the coil at any time. The output of the operational amplifier is a signals which will seek to equalize the two inputs signals. The output of the operational amplifier is coupled to the two controlling transistors which provide the drive current to the motor coil. Diodes are appropriately coupled to the switching transistor to incorporate regeneration effects for the minimization of power consumption. A monitor is also provided to track current flow out of the high voltage source to detect any shorts in the output system or load. Two transistor switches are provided between the initial high-voltage source and the coils. A simplified logic circuitry is provided which responds to the detection of failure mode operating conditions and terminates the operation of these switches to cut off high voltage to the coils.

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