Liquid crystal display device having an improved lighting device

• US 7,138,974 B2
• Filed: 08/08/2003
• Issued: 11/21/2006
• Est. Priority Date: 10/12/2000
• Status: Expired due to Fees

• Current Assignee: Panasonic Liquid Crystal Display Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Hitachi Device Engineering Co., Ltd., Hitachi, Ltd.
• Inventors: Ono, Kikuo, Shingai, Akira, Hirakata, Junichi
• Primary Examiner(s): Patel, Nitin
• Application Number:
  US10/636,612
• Publication Number:
  US 20040051692A1
• Time in Patent Office: 1,201 Days
• Field of Search: 345/52, 345/74.1, 345/205, 345/211, 345/213, 345/101, 345/102, 345/106, 345 63- 66, 345 77- 87, 345 88-100, 345/204, 345/207, 345/214, 205/777.5, 257/72, 323/282, 327/536, 327/561, 340/57
• US Class Current: 345/98
• 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 at least one light source and projecting light generated by the at least one 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 at least one light source alternately,

wherein the circuit has 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.

2. A liquid crystal display device according to claim 1, wherein a sum of the first period and the second period is kept constant without reference to the ammeter the signal from the current monitoring circuit.

3. A liquid crystal display device according to claim 1, wherein an integral of brightness produced by the at least one light source over the second period is equal to or lower than 90% of brightness of the at least one light source during the first period.

4. A liquid crystal display device according to claim 1, wherein the signal from the current monitoring circuit reflects a temperature variation of the at least one light source.

5. A liquid crystal display device according to claim 1, wherein the at least one light source is a fluorescent lamp.