Title:
BACKLIGHT CONTROLLER
Document Type and Number:
Japanese Patent JP3541644
Kind Code:
B2
Abstract:
PROBLEM TO BE SOLVED: To supply inverter voltage with stability, even when a supply voltage fluctuates large, and to inexpensively control luminance by separating a control circuit for varying the luminance from a control circuit for inverter input voltage, and using a switch circuit in common.
SOLUTION: A current to a fluorescent lamp 4 is converted into a voltage through a resistor 4, and the voltage is turned into a rectifying voltage through a diode D1 and a capacitor C3 to extract a mean voltage. The mean voltage and a dimming voltage Vcon are divided through resistors R1, R2 and input to a dimming control circuit 1. On/off control signals to a transistor Q1 are sent at a frequency, which includes a fraction to reciprocal of several tens of the oscillation frequency of an inverter circuit. When the dimming voltage Vcon is reduced, the voltage input to the dimming control circuit 1 is reduced, and operation is performed so that the on duration of the transistor Q1 is increased, and the period for which a current is passed through the fluorescent lamp 4 is increased. The brightness of backlight can be varied according to the ratio of the duration, for which the fluorescent lamp 4 is on to the duration for which the fluorescent lamp 4 is off, and the dimming range can be widened.
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Inventors:
Takahiro Kosaka
Application Number:
JP27838797A
Publication Date:
July 14, 2004
Filing Date:
October 13, 1997
Export Citation:
Assignee:
Matsushita Electric Industrial Co., Ltd
International Classes:
G02F1/133; H02M7/48; H02M7/538; H05B41/392; (IPC1-7): H02M7/48; G02F1/133; H02M7/538; H05B41/392
Domestic Patent References:
| JP6178548A | ||||
| JP8149850A | ||||
| JP4149993A |
Attorney, Agent or Firm:
Fumio Iwahashi
Tomoyasu Sakaguchi
Hiroki Naito
Tomoyasu Sakaguchi
Hiroki Naito