Liquid crystal display device having an improved lighting device

• US 20070052664A1
• Filed: 11/06/2006
• Published: 03/08/2007
• Est. Priority Date: 10/12/2000
• Status: Active Grant

• Current Assignee: Panasonic Liquid Crystal Display Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Hitachi, Ltd., Hitachi Device Engineering Co., Ltd. (Japan Display Incorporated)
• Inventors: Ono, Kikuo, Shingai, Akira, Hirakata, Junichi
• Granted Patent: US 7,683,899 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G02F 1/133604 with lamps
• CPC Class Codes: G02F 1/133612 Electrical details
• CPC Class Codes: G09G 2310/024 Scrolling of light from the illumination source over the display in combination with the scanning of the display screen
• 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 2320/041 Temperature compensation
• CPC Class Codes: G09G 2320/0633 by amplitude modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/066 for control of contrast
• CPC Class Codes: G09G 2330/045 Protection against panel overheating
• CPC Class Codes: G09G 3/342 using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
• CPC Class Codes: H05B 41/2821 by means of a single-switch converter or a parallel push-pull converter in the final stage H05B41/285 takes precedence
• 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

A liquid crystal display device includes a liquid crystal display panel having plural pixels, a lighting device having at least one light source and projecting light generated by the light source on the liquid crystal display panel, and a circuit supplying a first current during a first period and a second current smaller than the first current during a second period to the light source alternately. The circuit includes a current monitoring circuit which measures the first current and the second current, and a light control circuit which adjusts a ratio of the first period to the second period based upon a signal from the current monitoring circuit.

Claims

1. A liquid crystal display device comprising:

a liquid crystal display panel having a plurality of pixels;

a lighting device having a light source and projecting light generated by the light source on the liquid crystal 15 display panel; and

an AC-generating circuit which comprises an inverter circuit), a transformer, and a control circuit, and which generates and supplies an AC current to the light source,

wherein;

the AC-generating circuit is configured such that the AC-generating circuit supplies a first current during a first period and a second current smaller than the first current during a second period to the light source alternately;

the control circuit generates rectangular DC voltage pulses based on a ratio of the first period to the second period;

the inverter circuit converts the rectangular DC voltage pulses from the control circuit into an AC current to be supplied to a primary side circuit of the transformer; and

a secondary side circuit of the transformer is coupled to the light source.

2. A liquid crystal display device according to claim 1, wherein the AC-generating circuit further comprises a current monitoring circuit which measures the first current and the second current.

3. A liquid crystal display device according to claim 1, wherein the light source is a fluorescent lamp.

4. A liquid crystal display device according to claim 3, wherein the AC-generating circuit further comprises a ballast capacitor in the secondary side circuit.