Two-wire dimmer switch for low-power loads
First Claim
1. A load control device for controlling the amount of power delivered from an AC power source to an electrical load to a desired amount of power, the load control device comprising:
- a bidirectional semiconductor switch adapted to be coupled in series electrical connection between the AC power source and the electrical load for conducting a load current from the AC power source to the electrical load, the bidirectional semiconductor switch having a control input for rendering the bidirectional semiconductor switch conductive and non-conductive; and
a control circuit receiving a signal representative of a voltage developed across the bidirectional semiconductor switch, the control circuit operable to determine a half-cycle start time near the beginning of a half-cycle of the AC power source in response to the signal representative of the voltage developed across the bidirectional semiconductor switch;
wherein the control circuit;
conducts a control current through the load so as to generate a gate drive signal that is operatively coupled to the control input of the bidirectional semiconductor switch;
drives the gate drive signal to a first magnitude to render the bidirectional semiconductor switch conductive after a first variable amount of time has elapsed since the half-cycle start time;
maintains the gate drive signal at the first magnitude after the bidirectional semiconductor switch is rendered conductive, such that the bidirectional semiconductor switch remains conductive independent of the magnitude of the load current conducted through the bidirectional semiconductor switch;
drives the gate drive signal to a second magnitude to render the bidirectional semiconductor switch non-conductive after a second fixed amount of time has elapsed since the half-cycle start time;
controls the second fixed amount of time to be approximately equal during each half-cycle of the AC power source;
varies the first variable amount of time in response to the desired amount of power to be delivered to the load to control the amount of power delivered to the load to the desired amount;
further comprising a rectifier circuit for receiving the voltage developed across the bidirectional semiconductor switch and generating a rectified voltage;
wherein the signal representative of a voltage developed across the bidirectional semiconductor switch comprises the rectified voltage generated by the rectifier circuit;
wherein the control circuit is operable to determine the half-cycle start time in response to the magnitude of the rectified voltage exceeding a threshold when the rectified voltage is increasing in magnitude with respect to time, such that the half-cycle start time occurs after the beginning of a half-cycle of the AC power source; and
wherein the control circuit comprises a microprocessor.
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Accused Products
Abstract
A two-wire load control device (such as, a dimmer switch) is operable to control the amount of power delivered from an AC power source to an electrical load (such as, a high-efficiency lighting load) and has substantially no minimum load requirement. The dimmer switch includes a bidirectional semiconductor switch, which is operable to be rendered conductive each half-cycle and to remain conductive independent of the magnitude of a load current conducted through semiconductor switch. The dimmer switch comprises a control circuit that conducts a control current through the load in order to generate a gate drive signal for rendering the bidirectional semiconductor switch conductive and non-conductive each half-cycle. The control circuit may provide a constant gate drive to the bidirectional semiconductor switch after the bidirectional semiconductor switch is rendered conductive each half-cycle. The bidirectional semiconductor switch may comprise, for example, a triac or two field-effect transistors coupled in anti-series connection.
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Citations
48 Claims
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1. A load control device for controlling the amount of power delivered from an AC power source to an electrical load to a desired amount of power, the load control device comprising:
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a bidirectional semiconductor switch adapted to be coupled in series electrical connection between the AC power source and the electrical load for conducting a load current from the AC power source to the electrical load, the bidirectional semiconductor switch having a control input for rendering the bidirectional semiconductor switch conductive and non-conductive; and a control circuit receiving a signal representative of a voltage developed across the bidirectional semiconductor switch, the control circuit operable to determine a half-cycle start time near the beginning of a half-cycle of the AC power source in response to the signal representative of the voltage developed across the bidirectional semiconductor switch; wherein the control circuit; conducts a control current through the load so as to generate a gate drive signal that is operatively coupled to the control input of the bidirectional semiconductor switch; drives the gate drive signal to a first magnitude to render the bidirectional semiconductor switch conductive after a first variable amount of time has elapsed since the half-cycle start time; maintains the gate drive signal at the first magnitude after the bidirectional semiconductor switch is rendered conductive, such that the bidirectional semiconductor switch remains conductive independent of the magnitude of the load current conducted through the bidirectional semiconductor switch; drives the gate drive signal to a second magnitude to render the bidirectional semiconductor switch non-conductive after a second fixed amount of time has elapsed since the half-cycle start time; controls the second fixed amount of time to be approximately equal during each half-cycle of the AC power source; varies the first variable amount of time in response to the desired amount of power to be delivered to the load to control the amount of power delivered to the load to the desired amount; further comprising a rectifier circuit for receiving the voltage developed across the bidirectional semiconductor switch and generating a rectified voltage; wherein the signal representative of a voltage developed across the bidirectional semiconductor switch comprises the rectified voltage generated by the rectifier circuit; wherein the control circuit is operable to determine the half-cycle start time in response to the magnitude of the rectified voltage exceeding a threshold when the rectified voltage is increasing in magnitude with respect to time, such that the half-cycle start time occurs after the beginning of a half-cycle of the AC power source; and wherein the control circuit comprises a microprocessor. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A load control device for controlling the amount of power delivered from an AC power source to an electrical load to a desired amount of power, the load control device comprising:
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a bidirectional semiconductor switch adapted to be coupled in series electrical connection between the AC power source and the electrical load for conducting a load current from the AC power source to the electrical load, the bidirectional semiconductor switch having a control input for rendering the bidirectional semiconductor switch conductive and non-conductive; and a control circuit receiving a signal representative of a voltage developed across the bidirectional semiconductor switch, the control circuit operable to determine a half-cycle start time near the beginning of a half-cycle of the AC power source in response to the signal representative of the voltage developed across the bidirectional semiconductor switch; wherein the control circuit; conducts a control current through the load so as to generate a gate drive signal that is operatively coupled to the control input of the bidirectional semiconductor switch; drives the gate drive signal to a first magnitude to render the bidirectional semiconductor switch conductive after a first variable amount of time has elapsed since the half-cycle start time; maintains the gate drive signal at the first magnitude after the bidirectional semiconductor switch is rendered conductive, such that the bidirectional semiconductor switch remains conductive independent of the magnitude of the load current conducted through the bidirectional semiconductor switch; drives the gate drive signal to a second magnitude to render the bidirectional semiconductor switch non-conductive after a second fixed amount of time has elapsed since the half-cycle start time; controls the second fixed amount of time to be approximately equal during each half-cycle of the AC power source; varies the first variable amount of time in response to the desired amount of power to be delivered to the load to control the amount of power delivered to the load to the desired amount; wherein the bidirectional semiconductor switch comprises first and second switching transistors coupled in anti-series connection. - View Dependent Claims (8, 9)
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10. A load control device for controlling the amount of power delivered from an AC power source to an electrical load to a desired amount of power, the load control device comprising:
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a bidirectional semiconductor switch adapted to be coupled in series electrical connection between the AC power source and the electrical load for conducting a load current from the AC power source to the electrical load, the bidirectional semiconductor switch having a control input for rendering the bidirectional semiconductor switch conductive and non-conductive; and a control circuit operable to conduct a control current through the load in order to render the bidirectional semiconductor switch conductive and non-conductive each half-cycle of the AC power source, the control circuit including a timing circuit for generating a timing signal that increases in magnitude with respect to time, the timing circuit starting to generate the timing signal at a start time shortly after a zero-crossing of the AC power source, the control circuit also including a drive circuit for receiving the timing signal and rendering the bidirectional semiconductor switch conductive each half-cycle in response to the magnitude of the timing signal, so as to control the amount of power delivered to the electrical load to the desired amount; wherein the timing circuit is operable to continue generating the timing signal after the bidirectional semiconductor switch is rendered conductive each half-cycle, such that the drive circuit continues to render the bidirectional semiconductor switch conductive and the bidirectional semiconductor switch remains conductive independent of the magnitude of the load current conducted through the bidirectional semiconductor switch; and wherein the bidirectional semiconductor switch comprises first and second switching transistors coupled in anti-series connection. - View Dependent Claims (11, 12)
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13. A lighting control system adapted to be coupled to an AC power source, the lighting control system comprising:
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a high-efficiency lighting load including a high-efficiency light source and a load regulation device electrically coupled to the high-efficiency light source for controlling the amount of power delivered to the high-efficiency light source, the load regulation device characterized by a capacitive impedance; and a two-wire dimmer switch adapted to be coupled between the AC power source and the high-efficiency lighting load, the dimmer switch comprising a bidirectional semiconductor switch adapted to be coupled in series electrical connection between the AC power source and the high-efficiency lighting load for conducting a load current from the AC power source to the high-efficiency lighting load, the dimmer switch further comprising a control circuit operable to conduct a control current through the high-efficiency lighting load in order to render the bidirectional semiconductor switch conductive each half-cycle of the AC power source; wherein the bidirectional semiconductor switch remains conductive independent of the magnitude of the load current conducted through the bidirectional semiconductor switch, and is operable to conduct the load current to and from the high-efficiency lighting load during a single half cycle of the AC power source; and wherein the bidirectional semiconductor switch of the dimmer switch comprises first and second FETs coupled in anti-series connection. - View Dependent Claims (14)
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15. A two-wire load control device for controlling the amount of power delivered from an AC power source to an electrical load to a desired amount of power, the load control device comprising:
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a bidirectional semiconductor switch adapted to be coupled in series electrical connection between the AC power source and the electrical load for conducting a load current from the AC power source to the electrical load, the bidirectional semiconductor switch operable to be rendered conductive and to remain conductive independent of the magnitude of the load current conducted through the semiconductor switch; an analog control circuit coupled so as to conduct a control current through the electrical load and to generate a timing voltage that increases in magnitude with respect to time; and a drive circuit for receiving the timing voltage and rendering the bidirectional semiconductor switch conductive and non-conductive each half-cycle, so as to control the amount of power delivered to the electrical load to the desired amount; and wherein the bidirectional semiconductor switch comprises first and second switching transistors coupled in anti-series connection. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48)
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Specification