Dimming method and device for fluorescent lamps used for backlighting of liquid crystal screens
First Claim
Patent Images
1. A dimming device for fluorescent lamp used for the backlight of liquid crystal screen with an image synchronizing signal applied to the screen, comprising:
- a switching generator for producing switching signals, at a fixed frequency, the switching signals being rectangular periodic signals comprising pulses having adjustable widths;
synchronizing means for synchronizing the switching signals with at least some of the image synchronizing signals;
an alternating voltage supply oscillator, connected to a first supply voltage, for applying an alternating voltage to the fluorescent lamp; and
blocking means, controlled by the switching signals, to allow the alternating voltage supply oscillator to function only during the duration of the pulses of the rectangular periodic signals, the blocking means comprising switching means for applying a second supply voltage, opposite in polarity to the first supply voltage, to the alternating voltage supply oscillator, the second supply voltage temporarily blocking application of the first supply voltage to the alternating voltage supply oscillator.
1 Assignment
0 Petitions
Accused Products
Abstract
A dimming device, with a brightness dimming ratio of 1 to 1000, for a fluorescent lamp used for the backlighting of a liquid crystal screen comprises a periodic signal generator for delivering rectangular pulses with an adjustable duty cycle. The pulses are synchronized with the image synchronizing signal of the liquid crystal screen. An alternating voltage generator provides power to the lamp only during the pulses. The decrease in tube efficiency for very short pulses allows the required dimming intensity to be achieved without image flickering.
-
Citations
8 Claims
-
1. A dimming device for fluorescent lamp used for the backlight of liquid crystal screen with an image synchronizing signal applied to the screen, comprising:
-
a switching generator for producing switching signals, at a fixed frequency, the switching signals being rectangular periodic signals comprising pulses having adjustable widths; synchronizing means for synchronizing the switching signals with at least some of the image synchronizing signals; an alternating voltage supply oscillator, connected to a first supply voltage, for applying an alternating voltage to the fluorescent lamp; and blocking means, controlled by the switching signals, to allow the alternating voltage supply oscillator to function only during the duration of the pulses of the rectangular periodic signals, the blocking means comprising switching means for applying a second supply voltage, opposite in polarity to the first supply voltage, to the alternating voltage supply oscillator, the second supply voltage temporarily blocking application of the first supply voltage to the alternating voltage supply oscillator. - View Dependent Claims (2, 7, 8)
-
-
3. A method for dimming a fluorescent lamp used for the backlighting of a liquid crystal screen to which image synchronizing signals are applied, the method comprising the steps of:
-
generating switching signals at a fixed frequency, the switching signals being rectangular periodic signals comprising pulses having adjustable widths; synchronizing the switching signals with at least some of the image synchronizing signals; applying an alternating voltage, via a transformer connected to a primary supply voltage, to the fluorescent lamp; and selective connecting a blocking supply voltage, opposite in polarity to the primary supply voltage, to the transformer, which temporarily blocks application of the alternating voltage to the lamp, via the transformer, for adjustable periods of time determined by an absence of the pulses of the rectangular periodic signals. - View Dependent Claims (4, 5, 6)
-
Specification