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Motor starting circuit

  • US 4,468,604 A
  • Filed: 03/04/1982
  • Issued: 08/28/1984
  • Est. Priority Date: 03/04/1982
  • Status: Expired due to Fees
First Claim
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1. A motor starting circuit for momentarily energizing the starting winding circuit of a single-phase, alternating current motor, comprising:

  • a triac connected, via the main terminals thereof, in series with said starting winding circuit; and

    a switching circuit having first and second input terminals and a gate terminal, wherein the switching circuit is connected, via the input terminals thereof, in parallel with the serially connected triac and starting winding circuit, the second input terminal of the switching circuit being connected to a main terminal of the triac with the opposite main terminal thereof connected to the starting winding circuit, wherein the gate terminal of the switching circuit is connected to the gate of the triac, and wherein the switching circuit comprises;

    a biasing resistor connected between the gate terminal and the second input terminal of the switching circuit, andtiming means, connected between the first input terminal of the switching circuit and the gate terminal thereof for establishing a relatively low effective resistance between the first input terminal and the triac gate for a preselected time period following connection of the motor to an electrical source and thereafter establishing a relatively high effective resistance between the first input terminal and the triac gate, said timing means including;

    a load resistor having one end thereof connected to the first input terminal of the switching circuit;

    a full-wave recifier bridge having the input terminals thereof connected between the other end of the load resistor and the gate terminal of the switching circuit;

    a first SCR connected in parallel across the output terminals of the rectifier bridge so as to substantially provide a short circuit between the load resistor and the gate terminal of the switching circuit at such time that the first SCR is in a conducting state;

    a first SCR gating branch, comprising;

    a first gating branch resistor connected between the cathode and gate of said first SCR;

    a second gating branch resistor having one end thereof connected to the junction of the first gating branch resistor and a gate of said first SCR; and

    a third gating branch resistor connected between the other end of the second gating branch resistor and the anode of said first SCR, wherein the third gating branch resistor has a resistance which is large in relation to the resistance of the load resistor;

    a timing branch, comprising;

    a timing resistor having one end thereof connected to the anode of said first SCR; and

    a timing capacitor connected between the other end of the timing resistor and the cathode of said SCR for charging through the timing resistor; and

    turn-off means, connected between the junction of the timing resistor and timing capacitor, the junction of the second and third gating branch resistors, and the junction of the first gating branch resistor and the first SCR cathode, for substantially providing a short circuit across the first and second gating branch resistors in response to charging of the timing capacitor to a preselected level.

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