Method and apparatus for controlling minimum brightness of a fluorescent lamp
AssigneeLinfinity Microelectronics
InventorHwangsoo Choi
Life of this patent
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Abstract
All 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.
Claims7
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 a minimum duration determined by a minimum pulse generator circuit which counts cycles of current flowing through the fluorescent lamp with respective amplitudes above a preset threshold, said controller comprises:
- a pulse width modulation circuit;
- an oscillator circuit;
- and
- a dimming control circuit, wherein the dimming control circuit comprises:
- a pulse generator circuit configured to determine an initial duration for the active states;
- a minimum pulse generator circuit configured to determine a minimum duration for the active states;
- and
- a logic gate configured to output a signal to the pulse width modulation circuit with a duty cycle corresponding to a greater of the initial duration duty cycle and the minimum duration duty cycle.
Dependencies are inferred from the claim text.