Circuit for controlling application of electricity to a coil of and electric current switching apparatus
First Claim
1. A control circuit for an electrical switching device having a set of contacts which are operated by a electromagnetic coil, said control circuit comprising:
- first and second input terminals to receive a control signal for operating the electrical switching device;
a first transistor having a conduction path connected in series with the electromagnetic coil between the first and second control terminals, the first transistor having a control terminal;
a controller which generates a series of pulses that are applied to the control terminal of the first transistor, wherein the series of pulses biases the first transistor to apply a first level of current to the electromagnetic coil during a defined period of time and thereafter the first transistor is biased to apply a second level of current to the electrocmagnetic coil, where the first level is greater than the second level; and
a flyback/decay circuit having a first diode and a second transistor connected in series and to the electromagnetic coil wherein the second transistor is biased by the control signal to provide a first voltage drop for current produced by the electromagnetic coil during intervals between each pulse of the series of pulses, upon removal of the control signal the second transistor is biased to provide a second voltage drop for current produced in the electromagnetic coil, in which the second voltage drop is greater than the first voltage drop.
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Accused Products
Abstract
A control circuit drives the coil of a contactor in response to a control voltage being applied. The control circuit includes a power supply that produces a regulated output voltage from the control voltage. The onset of the regulated output voltage starts a timer which controls the width of pulses produced by a PWM controller. The pulses control a transistor that applies the control voltage to the coil. Initially the pulses cause a high current to flow through the coil to close the contactor and after an interval of time the timer signals the PWM controller to shorten the pulses which applies lesser current to the coil to keep the contacts closed. A flyback circuit provides a relatively low reverse voltage drop path in parallel with the coil to maintain the electromagnetic field during the periods between the pulses. When the control voltage is removed to open the contactor, the flyback circuit provides a high reverse voltage drop path to promptly dampen the coil current.
27 Citations
15 Claims
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1. A control circuit for an electrical switching device having a set of contacts which are operated by a electromagnetic coil, said control circuit comprising:
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first and second input terminals to receive a control signal for operating the electrical switching device; a first transistor having a conduction path connected in series with the electromagnetic coil between the first and second control terminals, the first transistor having a control terminal; a controller which generates a series of pulses that are applied to the control terminal of the first transistor, wherein the series of pulses biases the first transistor to apply a first level of current to the electromagnetic coil during a defined period of time and thereafter the first transistor is biased to apply a second level of current to the electrocmagnetic coil, where the first level is greater than the second level; and a flyback/decay circuit having a first diode and a second transistor connected in series and to the electromagnetic coil wherein the second transistor is biased by the control signal to provide a first voltage drop for current produced by the electromagnetic coil during intervals between each pulse of the series of pulses, upon removal of the control signal the second transistor is biased to provide a second voltage drop for current produced in the electromagnetic coil, in which the second voltage drop is greater than the first voltage drop. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A control circuit for an electrical switching device having a set of contacts which are operated in by a electromagnetic coil, said control circuit comprising:
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first and second input terminals to receive a control signal for operating the electrical switching device; a power supply connected to the first and second input terminals and producing a regulated output voltage; a first transistor having a conduction path connected in series with the electromagnetic coil between the first and second control terminals, the first transistor having a control terminal; a timer which has a first state for a defined period of time commencing upon application of the control signal to the first and second input terminals and has a second state after the defined period of time; a pulse width modulator connected to the timer and comprising a source of a first reference voltage derived from the regulated output voltage wherein the first reference voltage is greater during the first state than during the second state of the timer, the pulse width modulator having a current sensor which produces a sensor voltage in response to a magnitude of current flowing through the electromagnetic coil, and a comparator which produces a bias pulse that is applied to the control terminal to render the first transistor conductive whenever the first reference voltage exceeds the sensor voltage; and a flyback/decay circuit having a conduction path connected in parallel with the electromagnetic coil, the conduction path formed by a first diode and a second transistor connected in series, wherein the second transistor is biased by the regulated output voltage to provide a first voltage drop for current produced in the electromagnetic coil, and upon removal of the control signal from the first and second input terminals the second transistor is biased, to provide a second voltage drop wherein the second voltage drop is greater than the first voltage drop. - View Dependent Claims (14, 15)
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Specification