Liquid crystal display device

• US 20040041782A1
• Filed: 06/18/2003
• Published: 03/04/2004
• Est. Priority Date: 06/18/2002
• Status: Active Grant

• Current Assignee: Panasonic Liquid Crystal Display Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Hitachi Displays Limited (Japan Display Incorporated)
• Inventors: Tachibana, Tadayoshi
• Granted Patent: US 7,405,721 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G09G 2310/0237 Switching ON and OFF the backlight within one frame
• CPC Class Codes: G09G 2320/0261 in the context of movement of objects on the screen or movement of the observer relative to the screen
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: H05B 41/2822 using specially adapted components in the load circuit, e.g. feed-back transformers, piezoelectric transformers; using specially adapted load circuit configurations
• CPC Class Codes: H05B 41/2824 using control circuits for the switching element H05B41/2822 takes precedence
• CPC Class Codes: H05B 41/3927 by pulse width modulation H05B41/3922 takes precedence

Abstract

According to the present invention, in a liquid crystal display device which intermittently drives (burst driving) a light source device having a discharge tube which is arranged to face a main surface of a liquid crystal display panel in an opposed manner and is turned on in response to an alternating electric field, the resistance between first and second active elements which constitute a resonance circuit at a primary side of a driving circuit of the light source device and the reference potential in the driving circuit is set higher when burst driving of the discharge tube assumes the turn-OFF state than when the burst driving of the discharge tube assumes the turn-ON state. Due to such a constitution, it is possible to lower the luminance when the burst driving is in the turn-OFF state than when the burst driving is in the turn-ON state without extinguishing the discharge tube when the burst driving is off whereby it is possible to suppress blurring of motion picture s whereby blurring of the motion picture can be suppressed and luminance of the image can be increased.

Claims

1. A liquid crystal display device comprising a liquid crystal display panel, a light source device arranged to face one main surface of the liquid crystal display panel and having a discharge tube which is driven by an alternating electric field, and a light source driving circuit which generates the alternating electric field, wherein

the light source driving circuit includes a primary side circuit which generates the alternating voltage by intermittently receiving a direct voltage, a transformer circuit which boosts the alternating voltage generated by the primary side circuit and outputs the boosted alternating voltage, and a secondary side circuit which applies the alternating voltage outputted from the transformer circuit to the discharge tube,

the primary side circuit includes first and second active elements which control an electric current generated between respective end portions of the transformer circuit and the reference potential side with respect to the direct current, and a third active element and a passive element which are arranged in parallel between the first and second active elements and the reference potential, and

the passive element exhibits the resistance which is higher than the resistance of a current path when the third active element is in a turn-ON state and lower than the resistance of the current path when the third active element is in a turn-OFF state.

2. A liquid crystal display device according to claim 1, wherein the first and second active elements are made to assume the turn-ON state alternately.

3. A liquid crystal display device according to claim 1, wherein the direct voltage is intermittently generated in response to control signals and a turn-ON/turn-OFF control of the third active element is also performed in response to the control signals.

4. A liquid crystal display device according to claim 3, wherein the control signals are generated in response to image forming timing in the liquid crystal display panel.

5. A liquid crystal display device according to claim 1, wherein the third active element is made to assume the turn-ON state when the direct voltage is applied to the primary side circuit and is made to assume the turn-OFF state when the direct voltage is not applied to the primary side circuit.