Browse Prior Art Database

Over-Power Suppression Method of Liquid Crystal Display Backlight

IP.com Disclosure Number: IPCOM000118993D
Original Publication Date: 1997-Oct-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 4 page(s) / 94K

Publishing Venue

IBM

Related People

Hanzawa, F: AUTHOR [+3]

Abstract

Disclosed is a method for suppressing the over-power consumption of Liquid Crystal Display (LCD) backlight during several minutes after powered on. Two implementations of this method are described.

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Over-Power Suppression Method of Liquid Crystal Display Backlight

      Disclosed is a method for suppressing the over-power
consumption of Liquid Crystal Display (LCD) backlight during several
minutes after powered on.  Two implementations of this method are
described.

      The Cold Cathode Fluorescent Lamp (CCFL) is very popularly used
in LCD backlight as its light source.  To drive the CCFL, some Direct
Current/Alternate Current (DC/AC) inverter unit(s) which generate
high voltage with high frequency is required.  Almost all the
inverters have  some kind of feedback control to light on the CCFL at
a certain brightness level.  However, the CCFL has a very sensitive
characteristic or environmental temperature, including self-warming
by the self loss.  For example, just after it is powered on, when the
CCFL is not warmed up yet, CCFL voltage is very high, and after being
warmed up by  CCFL self loss energy, the voltage goes down gradually,
as shown in Fig. 1.  Because of this characteristic, "CCFL current
regulation", which is a very major feedback method, has a
disadvantage that requires  a much bigger input power potential than
that required after saturation  (Fig. 2).

"CCFL current regulation" is a major method because it has the
following advantages:
  o  Because it controls the CCFL current, it can minimize the
      fluctuation of the brightness which is caused by the
      fluctuations of the transformer, the CCFL and the stray
      capacitance.
  o  Because it controls the CCFL current, it is easy to check
      the malfunctions of the transformer and the CCFL to prevent
      an arcing/smoke/fire problem.

      There is another feedback control called "Primary voltage
regulation" which has different characteristics of the inverter input
power.  This method controls the output voltage from the inverter
unit.  Just after it is powered on, the CCFL when the impedance of
the CCFL is high, the input power of the inverte...