Solid state motor start circuit
First Claim
1. Start circuit for a single-phase AC induction motor of the type having at least one run winding connected to a pair of AC inputs and a start winding connected with or without as start capacitor to said AC inputs during a start-up operation but which is cut out from said AC inputs when said motor has achieved running speed, the motor also having a thermal cutout switch in series with the run winding that includes a heater resistor in series with said run winding developing a voltage thereacross that varies with the current through the run winding;
- the start circuit comprisinga light emitting diode connected to said heater resistor providing light output whose intensity depends on said voltage;
AC current switch means having a gate electrode and having current electrodes in series with said start winding;
photosensitive circuit means including a photosensitive element and producing an output signal that depends on the intensity of light incident on the photosensitive element having an output supplying said output signal to the gate electrode of said AC current switch means; and
light conduit means carrying said light output from said light emitting diode to said photosensitive element.
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Accused Products
Abstract
A start circuit for a single phase AC induction motor employs an impedance in series with the run winding to develop a voltage drop proportional to the current through the run winding, and a pair of LEDs or another light emitting device across this impedance to produce a light output whose intensity varies with the field current, and hence in a generally inverse relation with motor speed. A solid-state AC current switch, which can be a triac or a pair of back-to-back SCRs, is gated by a photosensitive circuit that includes a photosensitive element. A light conduit, which can be a light pipe or light dome, for example, carries the light output from the light emitting element to the photosensitive element. The device of this circuit is highly reliable, has no mechanical contacts, and is relatively insensitive to temperature and voltage fluctuation.
85 Citations
10 Claims
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1. Start circuit for a single-phase AC induction motor of the type having at least one run winding connected to a pair of AC inputs and a start winding connected with or without as start capacitor to said AC inputs during a start-up operation but which is cut out from said AC inputs when said motor has achieved running speed, the motor also having a thermal cutout switch in series with the run winding that includes a heater resistor in series with said run winding developing a voltage thereacross that varies with the current through the run winding;
- the start circuit comprising
a light emitting diode connected to said heater resistor providing light output whose intensity depends on said voltage; AC current switch means having a gate electrode and having current electrodes in series with said start winding; photosensitive circuit means including a photosensitive element and producing an output signal that depends on the intensity of light incident on the photosensitive element having an output supplying said output signal to the gate electrode of said AC current switch means; and
light conduit means carrying said light output from said light emitting diode to said photosensitive element. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 10)
- the start circuit comprising
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9. Start circuit for actuating an AC induction motor of the type having at least one run winding coupled to an AC input and a thermal cutout switch having a heater resistor in series with said run winding, the start circuit comprising:
AC current switch means having current electrodes in series with said AC powered device and a gate electrode; and
gating means having an input coupled to said heater resistor and an output coupled to the gate electrode of said AC current switch for supplying an output signal to said gate electrode that depends on the voltage across said heater resistor in which said gating means includes a light emitting diode coupled to said heater resistor to light when the current therethrough is above a predetermined value;
photosensitive circuit means including a photosensitive element and producing an output signal that is switched on or off in accordance with the intensity of light incident thereon and having an output supplying said output signal to the gate electrode of said AC current switch means; and
light conduit means carrying a light output from said light emitting diode to said photosensitive element.
Specification