Method and apparatus for controlling minimum brightness of a fluorescent lamp
First Claim
1. A power conversion circuit for driving a fluorescent lamp, the circuit comprising a controller configured to generate signals with active states and inactive states, wherein durations of the respective active states are equal to or greater than an updated duration determined by a first pulse generator circuit which monitors the number of cycles of current flowing through the fluorescent lamp with respective amplitudes above a preset threshold.
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Abstract
An efficient power conversion circuit for driving a fluorescent lamp uses a minimum pulse generator circuit to control the minimum on-time of a time modulated signal to increase the dimming range of the fluorescent lamp operating over a wide range of temperature and supply voltage. A minimum number of lamp current cycles with respective amplitudes above a preset threshold is typically required to avoid flickering or shimmering during minimum brightness. The minimum pulse generator circuit counts the lamp current cycles and adjusts the on-time accordingly to guarantee the minimum number of cycles with respective amplitudes above a preset threshold under all operating conditions.
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Citations
13 Claims
- 1. A power conversion circuit for driving a fluorescent lamp, the circuit comprising a controller configured to generate signals with active states and inactive states, wherein durations of the respective active states are equal to or greater than an updated duration determined by a first pulse generator circuit which monitors the number of cycles of current flowing through the fluorescent lamp with respective amplitudes above a preset threshold.
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11. A method of controlling a reduced brightness of a fluorescent lamp comprising the acts of:
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supplying an AC voltage to the fluorescent lamp in periodic bursts; keeping track of the number of desired cycles in an AC current flowing through the fluorescent lamp in response to the AC voltage, wherein amplitudes of the desired cycles exceed a preset threshold; and adjusting durations of the bursts to achieve a predefined number of desired cycles in each burst.
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12. A power conversion circuit for driving a fluorescent lamp at a reduced brightness level comprising:
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means for providing an AC voltage to the fluorescent lamp during an on-time; means for keeping track of the number of desired cycles in an AC current flowing through the fluorescent lamp in response to the AC voltage, wherein amplitudes of the respective desired cycles exceed a preset threshold; and means for adjusting the on-time to achieve a selected number of the desired cycles.
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13. A power conversion circuit for driving a fluorescent lamp, the circuit comprising a controller configured to generate signals with active states and inactive states based in part on an input from a first pulse generator circuit which monitors the number of cycles of current flowing through the fluorescent lamp with respective amplitudes above a preset threshold.
Specification