Motor starting circuit

• US 4,761,601 A
• Filed: 08/15/1984
• Issued: 08/02/1988
• Est. Priority Date: 03/04/1982
• Status: Expired due to Term

• Current Assignee: Andrew Zaderej
• Original Assignee: Andrew Zaderej
• Inventors: Zaderej, Andrew
• Primary Examiner(s): Smith, Jr., David
• Application Number:
  US06/640,866
• Time in Patent Office: 1,448 Days
• Field of Search: 318/778, 318/786
• US Class Current: 318/786
• CPC Class Codes: H02P 1/44 by phase-splitting with a capacitor

Abstract

A motor starting circuit in which a triac connected in series with the starting winding of the motor is gated into conduction for only a preselected time period following motor start-up. A switching circuit, in parallel with the serially connected triac and starting winding, includes an SCR which provides a low resistance signal path to the gate of the triac at such time that the SCR is in a conducting state. The SCR is gated by a resistance network and the time period is established by an RC circuit which gates a switch at the end of the selected time period to short out the portion of the resistance net work to which the gate of the SCR is connected so as to turn off the SCR and leave a high resistance path through the switching circuit to the gate of the triac.

Claims

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, and

timing 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 full-wave rectifier bridge having the input terminals thereof connected between the first input terminal of the switching circuit and the gate terminal of the switching circuit;

a load resistor having one end thereof connected to one output terminal of the rectifier bridge;

a SCR connected between the load resistor and the other output terminal of the rectifier bridge so as to substantially provide a short circuit between the load resistor and said other output terminal of the rectifier bridge at such time that the SCR is gated into a conducting state;

a SCR gating branch comprising;

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

a zener diode having its anode connected to the junction of the first gating branch resistor and the gate of said SCR; and

a second gating branch resistor connected between the cathode of said zener diode and the end of the load resistor connected to the rectifier bridge, wherein the second 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 end of the load resistor connected to the rectifier bridge; 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 said zener diode and second gating branch resistor, and the junction of the first gating branch resistor and the SCR cathode, for substantially providing a short circuit across the first gating branch resistor and said zener diode in response to charging of the timing capacitor to a preselected level,

said turn-off means including a switch having an anode and cathode responsive to a turn-off voltage applied between its anode and cathode, said switch having the cathode thereof connected to the junction of the SCR cathode and the first gating branch resistor, said switch having the anode thereof connected to the cathodes of a pair of diodes, the anode of one of said pair of diodes connected to the junction of said zener diode and second gating branch resistor, the other of said pair diodes having its anode connected to the junction of the timing resistor and timing capacitor.

2. The motor starting circuit of claim 1 wherein said switch is a silicon unilateral switch.

3. The motor starting circuit of claim 1 wherein said switch is a silicon bilateral switch.