Switching Circuit Having Delay For Inrush Current Protection
First Claim
1. A two-wire switching circuit for controlling the power delivered from an AC power source to an electrical load, the switching circuit comprising:
- a mechanical air-gap switch adapted to be coupled in series electrical connection between the AC power source and the electrical load;
a first turn-on delay circuit adapted to be coupled in series electrical connection with the mechanical air-gap switch when the mechanical switch is in a first position, the first turn-on delay circuit operable to conduct a control current through the mechanical air-gap switch when the mechanical switch is in the first position; and
a first controllably conductive device having a control input and coupled in parallel electrical connection with the first turn-on delay circuit, the first controllably conductive device adapted to be coupled in series electrical connection between the AC power source and the electrical load when the mechanical switch is in the first position, the first controllably conductive device operable to change from a non-conductive state to a conductive state in response to the first turn-on delay circuit after a first predetermined time from when the mechanical air-gap switch changes to the first position; and
a second controllably conductive device having a control input and coupled in parallel electrical connection with the first controllably conductive device, the second controllably conductive device adapted to be coupled in series electrical connection between the AC power source and the electrical load when the mechanical switch is in the first position, the second controllably conductive device operable to change from a non-conductive state to a conductive state in response to the first turn-on delay circuit after a second predetermined time from when the first controllably conductive device changes from the non-conductive state to the conductive state, the second controllably conductive device operable to stay latched in the conductive state;
wherein the mechanical air-gap switch and the second controllably conductive device are operable to conduct the load current when the mechanical air-gap switch is in the first position.
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Accused Products
Abstract
A two-wire switching circuit can handle a large inrush current, but does not require a neutral connection or a heavy-duty mechanical switch or relay. The switching circuit comprises a mechanical air-gap switch, a first controllably conductive device (e.g., a bidirectional semiconductor switch), and a second controllably conductive device (e.g., a latching relay), which are all adapted to be coupled between an AC power source and an electrical load when the air-gap switch is in a first position. First and second delay circuits control the semiconductor switch and the latching relay to be conductive at different times after the air-gap switch is changed to the first position. Specifically, the semiconductor switch is rendered conductive before the latching relay is rendered conductive, such that the semiconductor switch conducts the large inrush current. The latching relay conducts current from the AC power source to the electrical load after the inrush current has subsided.
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Citations
24 Claims
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1. A two-wire switching circuit for controlling the power delivered from an AC power source to an electrical load, the switching circuit comprising:
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a mechanical air-gap switch adapted to be coupled in series electrical connection between the AC power source and the electrical load; a first turn-on delay circuit adapted to be coupled in series electrical connection with the mechanical air-gap switch when the mechanical switch is in a first position, the first turn-on delay circuit operable to conduct a control current through the mechanical air-gap switch when the mechanical switch is in the first position; and a first controllably conductive device having a control input and coupled in parallel electrical connection with the first turn-on delay circuit, the first controllably conductive device adapted to be coupled in series electrical connection between the AC power source and the electrical load when the mechanical switch is in the first position, the first controllably conductive device operable to change from a non-conductive state to a conductive state in response to the first turn-on delay circuit after a first predetermined time from when the mechanical air-gap switch changes to the first position; and a second controllably conductive device having a control input and coupled in parallel electrical connection with the first controllably conductive device, the second controllably conductive device adapted to be coupled in series electrical connection between the AC power source and the electrical load when the mechanical switch is in the first position, the second controllably conductive device operable to change from a non-conductive state to a conductive state in response to the first turn-on delay circuit after a second predetermined time from when the first controllably conductive device changes from the non-conductive state to the conductive state, the second controllably conductive device operable to stay latched in the conductive state; wherein the mechanical air-gap switch and the second controllably conductive device are operable to conduct the load current when the mechanical air-gap switch is in the first position. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A two-wire switching circuit for controlling the power delivered from an AC power source to an electrical load, the switching circuit comprising:
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a mechanical air-gap switch adapted to be coupled in series electrical connection between the AC power source and the electrical load; a latching relay having a control input and operable to conduct a load current from the AC power source to the electrical load when the mechanical air-gap switch is in a first position; a bidirectional semiconductor switch having a control input and operable to conduct the load current from the AC power source to the electrical load when the mechanical air-gap switch is in the first position; a first turn-on delay circuit coupled in parallel electrical connection with the bidirectional semiconductor switch and in series electrical connection with the mechanical air-gap switch, the first turn-on delay circuit coupled to the control input of the bidirectional semiconductor switch and operable to render the bidirectional semiconductor switch conductive after a first predetermined time from when the mechanical air-gap switch changes to the first position; and a second turn-on delay circuit coupled to the control input of the latching relay and responsive to the first turn-on delay circuit, the second turn-on delay circuit operable to cause the latching relay to conduct current from the AC power source to the electrical load after a second predetermined time from when the bidirectional semiconductor switch is rendered conductive.
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14. A load control device for controlling the power delivered from an AC power source to an electrical load, the load control device comprising:
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a mechanical air-gap switch adapted to be coupled in series electrical connection between the AC power source and the electrical load; an actuator mechanically coupled to the mechanical air-gap switch for actuating the mechanical air-gap switch; a first turn-on delay circuit adapted to be coupled in series electrical connection with the mechanical air-gap switch when the mechanical switch is in a first position, the first turn-on delay circuit operable to conduct a control current through the mechanical air-gap switch when the mechanical switch is in the first position; and a first controllably conductive device having a control input and coupled in parallel electrical connection with the first turn-on delay circuit, the first controllably conductive device adapted to be coupled in series electrical connection between the AC power source and the electrical load when the mechanical switch is in the first position, the first controllably conductive device operable to change from a non-conductive state to a conductive state in response to the first turn-on delay circuit after a first predetermined time from when the mechanical air-gap switch changes to the first position; a second controllably conductive device having a control input and coupled in parallel electrical connection with the first controllably conductive device, the second controllably conductive device adapted to be coupled in series electrical connection between the AC power source and the electrical load when the mechanical switch is in the first position, the second controllably conductive device operable to change from a non-conductive state to a conductive state in response to the first turn-on delay circuit after a second predetermined time from when the first controllably conductive device changes from the non-conductive state to the conductive state, the second controllably conductive device operable to stay latched in the conductive state; wherein the mechanical air-gap switch and the second controllably conductive device is operable to conduct the load current when in the first position. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21)
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22. A method for controlling the power delivered to an electrical load from an AC power source, the method comprising the steps of:
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switching a mechanical switch to a first position; beginning to conduct a control current through the mechanical switch in response to the step of switching the mechanical switch; coupling a first controllably conductive device in series electrical connection between the AC power source and the electrical load when the mechanical switch is in the first position; controlling the first controllably conductive device to a conductive state after a first predetermined time from the step of beginning to conduct a control current through the mechanical switch; coupling a second controllably conductive device in parallel electrical connection with the first controllably conductive device, such that the second controllably conductive device is in series electrical connection between the AC power source and the electrical load when the mechanical switch is in the first position; and controlling the second controllably conductive device to a conductive state after a second predetermined time from the step of controlling the first controllably conductive device to a conductive state, such that the second controllably conductive device becomes conductive after the first controllably conductive device; conducting a load current through the mechanical switch; and latching the second controllably conductive device in the conductive state such that the second controllably conductive device is subsequently maintained conductive each half-cycle of the AC power source. - View Dependent Claims (23, 24)
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Specification