Load control circuit and method for achieving reduced acoustic noise
First Claim
1. A load control circuit having first and second terminals for connection in series with a controlled load, the load control circuit comprising a bidirectional semiconductor switch for switching at least a portion of both positive and negative half cycles of an alternating current source waveform to the load, the bidirectional semiconductor switch having a control electrode, further comprising:
- a phase angle setting circuit including a timing circuit which sets the phase angle during each half cycle of the AC source waveform when the bidirectional semiconductor switch conducts;
the phase angle setting circuit including a voltage threshold trigger device connected in series with the control electrode of the switch, further comprising a rectifier bridge connected in series between an output of the timing circuit and the control electrode of the semiconductor switch, and wherein the rectifier bridge has a first pair of terminals and a second pair of terminals, the first pair of terminals connected in series between the output of the timing circuit and the control electrode of the semiconductor switch, and the second pair of terminals connected to the voltage threshold trigger device;
whereby acoustic noise generated in the load connected in series with the load control circuit is reduced.
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Accused Products
Abstract
A load control circuit having first and second terminals for connection in series with a controlled load comprises a bidirectional semiconductor switch for switching at least a portion of both positive and negative half cycles of an alternating current source waveform to the load. The bidirectional semiconductor switch has a control electrode. The load control circuit includes a phase angle setting circuit, including a timing circuit, which sets the phase angle during each half cycle of the AC source waveform when the bidirectional semiconductor switch conducts. The phase angle setting circuit includes a voltage threshold trigger device connected in series with the control electrode of the switch. The phase angle setting circuit further comprises a rectifier bridge connected in series between an output of the timing circuit and the control electrode of the semiconductor switch, wherein the rectifier bridge has a first pair of terminals and a second pair of terminals, the first pair of terminals connected in series between an output of the timing circuit and the control electrode of the semiconductor switch, and the second pair of terminals connected to the voltage threshold trigger device. The load control circuit further includes an impedance in series electrical connection with the semiconductor switch control electrode. Acoustic noise generated in the load connected in series with the load control circuit is reduced, particularly when the load is a toroidal transformer driving a magnetic low voltage lamp and the load control circuit is a two-wire dimmer.
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Citations
52 Claims
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1. A load control circuit having first and second terminals for connection in series with a controlled load, the load control circuit comprising a bidirectional semiconductor switch for switching at least a portion of both positive and negative half cycles of an alternating current source waveform to the load, the bidirectional semiconductor switch having a control electrode, further comprising:
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a phase angle setting circuit including a timing circuit which sets the phase angle during each half cycle of the AC source waveform when the bidirectional semiconductor switch conducts;
the phase angle setting circuit including a voltage threshold trigger device connected in series with the control electrode of the switch, further comprising a rectifier bridge connected in series between an output of the timing circuit and the control electrode of the semiconductor switch, and wherein the rectifier bridge has a first pair of terminals and a second pair of terminals, the first pair of terminals connected in series between the output of the timing circuit and the control electrode of the semiconductor switch, and the second pair of terminals connected to the voltage threshold trigger device;
whereby acoustic noise generated in the load connected in series with the load control circuit is reduced. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A method for reducing acoustic noise generated in an electrical load driven by a phase-cut load control circuit from an AC source waveform, the method comprising:
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setting a phase angle during each half cycle of the AC source waveform when a bidirectional semiconductor switch conducts;
providing a voltage threshold trigger device connected in series with a control electrode of the switch, whereby control electrode current is provided to the switch when a threshold voltage is exceeded;
further comprising providing the control electrode current to the switch such that the control electrode current flows in only one direction through the voltage threshold trigger device, thereby to reduce asymmetry in the control electrode current and contribute to reduced acoustic noise in the load. - View Dependent Claims (18, 19)
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20. A load control circuit having first and second terminals for connection in series with a controlled load, the load control circuit comprising a bidirectional semiconductor switch for switching at least a portion of both positive and negative half cycles of an alternating current source waveform to a load, the bidirectional semiconductor switch having a control electrode, further comprising:
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a phase angle setting circuit including a timing circuit which sets the phase angle during each half cycle of the AC source waveform when the bidirectional semiconductor switch conducts;
the phase angle setting circuit including a voltage threshold trigger device connected in series with the control electrode of the switch, further comprising a first circuit connected between the timing circuit and the control electrode of the semiconductor switch for insuring that current flowing through the voltage threshold trigger device flows in only one direction, and wherein the first circuit has a first pair of terminals and a second pair of terminals, the first pair of terminals connected in series between an output of the timing circuit and the control electrode of the semiconductor switch, and the second pair of terminals connected to the voltage threshold trigger device;
whereby acoustic noise generated in the load connected in series with the load control circuit is reduced. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35)
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36. A two-wire dimmer for delivering power from an alternating current, line voltage source to a load, comprising:
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a bidirectional semiconductor switch, adapted to be coupled between said source and said load;
said semiconductor switch having a control input and operable to provide an output voltage to said load;
a timing circuit adapted to be coupled between said source and said load and having an output;
said timing circuit operable to generate a signal representative of a desired conduction time of said bidirectional semiconductor switch;
a trigger device having a first terminal in series electrical connection with said output of said timing circuit and a second terminal in series electrical connection with said control input of said bidirectional semiconductor switch;
said trigger device having a first voltage-current characteristic when current is flowing from said first terminal to said second terminal, and a second voltage-current characteristic when current is flowing from said second terminal to said first terminal;
wherein said first voltage-current characteristic is substantially identical to said second voltage-current characteristic; and
an impedance in series electrical connection between said output of said timing circuit and said control input of said semiconductor switch such that said impedance ensures that the magnitude of the current that flows into said control input is substantially equal to the magnitude of the current that flows out of said control input. - View Dependent Claims (37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52)
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Specification