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Wide Dimming Range Backlight Inverter

IP.com Disclosure Number: IPCOM000115626D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Mori, M: AUTHOR [+3]

Abstract

Disclosed is an inverter circuit for a (LCD) Liquid Crystal Display backlight in which a synchronized switching circuit is used in a lamp current feedback circuit to improve both stability and dimming range.

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This is the abbreviated version, containing approximately 82% of the total text.

Wide Dimming Range Backlight Inverter

      Disclosed is an inverter circuit for a (LCD) Liquid Crystal
Display backlight in which a synchronized switching circuit is used
in a lamp current feedback circuit to improve both stability and
dimming range.

      Typical inverter circuit for a LCD backlight adopts lamp
current feedback to improve lamp current stability.  On the other
hand, to improve dimming range, low frequency ON/OFF circuit (duty
dimming circuit) is widely used.  In order to achieve lamp current
stability and wide dimming range, both lamp current feedback and low
frequency ON/OFF circuit are necessary.

      The circuit enclosed by a dotted line in a figure is an example
of this circuit.  Lamp current level, detected by a resistor R1,
rectified by a diode D1 and charged by a capacitor C1, is fed back to
a control circuit.  Control circuit operates to keep lamp current
constant.  A resistor R2 is a breeder resistor of a capacitor C1.  A
switching circuit is connected between a resistor R2 and GND, and is
controlled by a synchronized switching signal from ON/OFF circuit.
When ON/OFF circuit is on, a switching circuit is connected and when
ON/OFF circuit is off, it is disconnected.

      By this switching circuit, discharge current of a capacitor C1
flew through a breeder resistor R2 is cut off when a ON/OFF circuit
stops and lamp current is suspended.  Since feedback voltage of a
capacitor C1 does not drop during lamp current off period...