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Motor protection device

  • US 3,950,675 A
  • Filed: 07/12/1974
  • Issued: 04/13/1976
  • Est. Priority Date: 07/12/1974
  • Status: Expired due to Term
First Claim
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1. Apparatus for use in combination with an electrical load and an electrical power supply having a pair of output terminals, comprising:

  • normally open switch means connecting said load to said power source to the closed position, and disconnecting said load from said source in the open position;

    first and second input terminals connectable to said pair of output terminals;

    a first impedance element connected between said first input terminal and a circuit node;

    a second impedance element connected between said second input terminal and said node;

    a relay coil for closing said switch means when energized, being connected between said first and second input terminals and in series with a gated semi-conductor switching device having a gate terminal;

    a voltage sensitive break-down device connected between said node and said gate terminal for applying a gate control signal to said gate terminal when the voltage level at said node exceeds a predetermined value;

    said semi-conductor switching device being responsive to said gate control signal to energize said relay coil only in the presence of said signal;

    an inhibit circuit connected to said gate terminal for preventing said semi-conductor switching device from responding to said signal for a predetermined period of time after said switch means is changed from the open to the closed position;

    a third impedance element connected between said node and said second input terminal; and

    switch means connected in series with said third impedance element and responsive to energization of said coil to open the current path through said third impedance element.

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