Backlight apparatus for liquid crystal display

• US 20050140312A1
• Filed: 12/23/2004
• Published: 06/30/2005
• Est. Priority Date: 12/25/2003
• Status: Active Grant

• Current Assignee: Funai Electric Co., Ltd. (Funai Electric Holdings Company Limited)
• Original Assignee: Funai Electric Co., Ltd. (Funai Electric Holdings Company Limited)
• Inventors: Miyamoto, Hitoshi, Nishinosono, Kazuo
• Granted Patent: US 7,161,310 B2
• Time in Patent Office: Days
• US Class Current: 315/224
• CPC Class Codes: G02F 1/133604 with lamps
• 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: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

Abstract

A secondary winding W2 of a step-up transformer of a self-excited inverter 2 is grounded at the midpoint thereof. High-frequency voltages differing in polarity from each other are outputted from both terminals OT1 and OT2 of the secondary winding W2. Two U-shaped cold-cathode tubes L1 and L2 series-connected to each other are provided directly below a liquid crystal panel. One of terminals of the secondary winding W2 is connected to the terminal OT1 through the ballast capacitor C1. The other terminal thereof is connected to the terminal OT2 of the ballast capacitor C2. The connecting point P between the two U-shaped cold-cathode tubes L1 and L2 is ungrounded. Thus, electric currents flowing through the cold-cathode tubes are equal in value to each other.

Claims

1. A backlight apparatus for a liquid crystal display having a liquid crystal panel, the backlight apparatus comprising:

a diffusing plate that is to be provided on entirety of the liquid display panel;

a first and a second U-shaped cold-cathode tubes provided on a back surface of the diffusing plate and series-connected to each other; and

a driver circuit for driving the first and the second U-shaped cold-cathode tubes, the driver circuit including a self-excited inverter for generating high-frequency voltages differing in polarity from each other at both terminals of a secondary winding of a step-up transformer whose midpoint is grounded,

wherein the first and the second U-shaped cold-cathode tubes are connected between both terminals of the secondary winding without being interposed by ballast capacitors, and

wherein a connecting point between the first and the second U-shaped cold-cathode tubes is ungrounded.

2. A backlight apparatus for a liquid crystal display having a liquid crystal panel, the backlight apparatus comprising:

a diffusing plate that is to be provided on entirety of the liquid display panel;

a first and a second U-shaped cold-cathode tubes provided on a back surface of the diffusing plate and series-connected to each other; and

a driver circuit for driving the first and the second U-shaped cold-cathode tubes, the driver circuit including a self-excited inverter for generating high-frequency voltages differing in polarity from each other at both terminals of a secondary winding of a step-up transformer whose midpoint is grounded,

wherein the first and the second U-shaped cold-cathode tubes are connected between both terminals of the secondary winding through ballast capacitors respectively, and

wherein a connecting point between the first and the second U-shaped cold-cathode tubes is ungrounded.