Patent ID: 7642735
Filing Date: 2010-01-05
Classification: H05B

Abstract:
1. A method for controlling dimmable electronic lighting ballasts using pulse density modulation, said method comprising the steps of: generating a first plurality of pulses operating at a first number of pulses per second during a filament preheating time period, wherein filaments of a fluorescent lamp are heated thereby, wherein the first number of pulses per second is above a series resonant frequency of a dimmable electronic lighting ballast and the fluorescent lamp; generating a second plurality of pulses operating at a second number of pulses per second during a lamp-on time period, wherein the second number of pulses per second is less than the first number of pulses per second and whereby gas in the fluorescent lamp is ionized when the second plurality of pulses is applied thereto; generating no pulses during a lamp-off time period; generating the first plurality of pulses for a filament heating time period after the lamp-off time period; and the lamp-on, lamp-off and filament heating time periods are within a lamp dimming frame time period that repeats during dimming of the fluorescent lamp.