Sensing and control for dimmable electronic ballast
First Claim
1. A method for controlling a triac dimmable gas discharge lamp ballast, comprising:
- sensing a duty cycle of a triac dimmer output waveform;
producing a set point signal having a value corresponding to the sensed duty cycle; and
controlling lamp current in response to the set point signal.
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Accused Products
Abstract
A sensing circuit for a triac dimmable gas discharge lamp ballast uses the duty cycle of the output waveform of a conventional triac dimmer as the parameter representing a set point for controlling the degree of clamping applied to the ballast circuit, and thus the amount of light produced by a fluorescent lamp. The sensing circuit may include a comparator that receives a rectified output waveform of a triac dimmer and produces output pulses corresponding in width to the duty cycle of the waveform, and a capacitor averaging the values of the pulses produced by the comparator to produce a set point signal representing a dimming level of the lamp. A triac dimmable ballast circuit using this sensing circuit has reduced sensitivity to line voltage and a wide mechanical range over which the light level of the fluorescent lamp is controlled by the user. The sensing circuit also enables a preheat timing circuit that eliminates the timing capacitor of prior art preheating circuits. A gas discharge lamp ballast and a method for its operation are also disclosed.
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Citations
20 Claims
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1. A method for controlling a triac dimmable gas discharge lamp ballast, comprising:
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sensing a duty cycle of a triac dimmer output waveform;
producing a set point signal having a value corresponding to the sensed duty cycle; and
controlling lamp current in response to the set point signal. - View Dependent Claims (2, 3, 4)
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5. A sensing circuit for a triac dimmable gas discharge lamp ballast, comprising:
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a comparator receiving a rectified output waveform of a triac dimmer and producing output pulses corresponding in width to the duty cycle of the waveform; and
a low pass filter averaging the values of the pulses produced by the comparator to produce a set point signal representing a target dimming level of the lamp. - View Dependent Claims (6, 7, 8, 9)
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10. A preheat timing circuit for a triac dimmable gas discharge lamp ballast, comprising:
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a comparator receiving a rectified input voltage waveform and producing output pulses; and
a timer receiving the output of the comparator and being operative of a preheat switch of the gas discharge lamp ballast after receiving a predetermined number of output pulses. - View Dependent Claims (11, 12, 14, 15, 16, 17, 18, 19, 20)
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13. A dimmable gas discharge lamp ballast, comprising:
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an a.c. to d.c. converter receiving an output waveform of a triac dimmer;
a lamp drive section powered by the a.c. to d.c. converter and driving a gas discharge lamp with an a.c. signal;
a sensing circuit producing a set point signal in accordance with a duty cycle of the output waveform of the triac dimmer; and
a clamping circuit controlling lamp current in response to the set point signal.
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Specification