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Motor speed control circuit with electronic clutch

  • US 5,410,229 A
  • Filed: 02/28/1994
  • Issued: 04/25/1995
  • Est. Priority Date: 07/31/1992
  • Status: Expired due to Term
First Claim
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1. A motor control circuit for supplying energy from a power source to a motor to deliver a user-selected torque, comprising:

  • a solid-state switching device having ON and OFF states and having first and second semi-conductor terminals connected in series with said motor between said power source and ground for conducting drive current through said motor when said switching device is in said ON state, a third semi-conductor terminal for controlling the conductive state of said switching device, and a fourth semi-conductor terminal for producing a low current sense signal the magnitude of which is related to the current flowing across said first and second semi-conductor terminals and hence through said motor;

    modulator circuit means coupled to said third semi-conductor terminal and responsive to said sense signal for supplying a speed control signal to said third semiconductor terminal to control the conductive state of said switching device, said modulator circuit means varying a characteristic of said speed control signal in accordance with said sense signal;

    user-settable means for providing a torque signal indicative of a user-selected torque; and

    torque control comparator means coupled to said user-settable means and to said fourth semi-conductor terminal of said switching device for comparing said torque signal and said sense signal and for causing said modulator circuit means to place said switching device in its OFF state when said sense signal bears a predetermined relationship to said torque signal.

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