EP0406116B1 - Procédé et dispositif de gradation de lumière pour lampe fluorescente d'éclairage arrière d'écran à cristaux liquides - Google Patents

Procédé et dispositif de gradation de lumière pour lampe fluorescente d'éclairage arrière d'écran à cristaux liquides Download PDF

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Publication number
EP0406116B1
EP0406116B1 EP90401866A EP90401866A EP0406116B1 EP 0406116 B1 EP0406116 B1 EP 0406116B1 EP 90401866 A EP90401866 A EP 90401866A EP 90401866 A EP90401866 A EP 90401866A EP 0406116 B1 EP0406116 B1 EP 0406116B1
Authority
EP
European Patent Office
Prior art keywords
liquid crystal
voltage
crystal screen
lamp
fluorescent lamp
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP90401866A
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0406116A1 (fr
Inventor
Georges Lavaud
Jean-Pierre Bouron
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Thales SA
Original Assignee
Thomson CSF SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Thomson CSF SA filed Critical Thomson CSF SA
Publication of EP0406116A1 publication Critical patent/EP0406116A1/fr
Application granted granted Critical
Publication of EP0406116B1 publication Critical patent/EP0406116B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
    • H05B41/14—Circuit arrangements
    • H05B41/36—Controlling
    • H05B41/38—Controlling the intensity of light
    • H05B41/39—Controlling the intensity of light continuously
    • H05B41/392—Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor
    • H05B41/3921—Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor with possibility of light intensity variations
    • H05B41/3927—Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor with possibility of light intensity variations by pulse width modulation
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/3406—Control of illumination source
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/06—Adjustment of display parameters
    • G09G2320/0626—Adjustment of display parameters for control of overall brightness
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/06—Adjustment of display parameters
    • G09G2320/0626—Adjustment of display parameters for control of overall brightness
    • G09G2320/064—Adjustment of display parameters for control of overall brightness by time modulation of the brightness of the illumination source
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S315/00—Electric lamp and discharge devices: systems
    • Y10S315/04—Dimming circuit for fluorescent lamps

Definitions

  • the present invention relates to a method and a device for dimming light for fluorescent lamps used in a rear lighting installation of a liquid crystal display device.
  • Document FR-A-2 584 845 discloses a liquid crystal screen illuminated from the bottom by a fluorescent lamp.
  • the power supply to the lamp is interrupted during writing periods and each beginning of an interruption is synchronized with a minimum of the light emitted by the lamp, in order to avoid flickering of the display face.
  • Liquid crystal displays in particular those used in color display systems for aircraft and helicopter dashboards, are backlit to provide high luminance so that they can be seen with sufficient comfort in high light bright atmosphere.
  • This luminance must be able to be made variable according to the different conditions of light environment, and it is generally necessary to control this luminance according to the day-night variations of this environment.
  • These variations impose for the light source a dynamic greater than 1000/1, that is, for fluorescent lamps, a brightness of the order of a few Cd / m2 for the minimum luminance and of approximately 15,000 Cd / m2 for the maximum luminance.
  • the light source uses fluorescent lamps because of their excellent energy efficiency and their colorimetry which is well suited to liquid crystal screens.
  • the supply voltage applied between their two electrodes is an alternating high-voltage, the amplitude of which is generally of the order of 300 to 500 volts, and the frequency of which is of the order of a few tens of kilohertz.
  • the invention aims to remedy these drawbacks. This is obtained by cutting the alternating supply voltage of a fluorescent lamp for rear lighting of a liquid crystal screen by a signal in slots of adjustable duration as a function of the desired light intensity, the start of the slots of which is synchronized on "picture synchronization" signal from the liquid crystal display.
  • a method of dimming light for a fluorescent lamp for back lighting of a liquid crystal screen consisting in applying to the lamp an alternating supply voltage cut by cutting signals formed by time slots.
  • adjustable as a function of the desired light intensity characterized in that it consists in synchronizing the switching signals on a signal corresponding to the image synchronization signal of the liquid crystal screen, divided in frequency by an integer n greater at 0.
  • the non-inverting input 10 of the comparator is connected, via a resistor 11, to the output 12 of a sawtooth signal generator 13, the signals of which are synchronized with the pulse image synchronization signal of a liquid crystal display; this impulse signal is applied at 14, to the generator 13.
  • This generator 13 includes an operational amplifier 15 which is mounted as an integrator using a capacitor 17 which connects its input and its output and a resistor 16 which connects its input to a terminal 18 to which a voltage of reference V2.
  • FIG. 2 which is a diagram of Amplitude (A) / time (t) curves
  • the image synchronization (negative) pulses 21 are represented on the upper curve A, while the saw teeth at the output 12 of the generator 13 are shown in B.
  • the adjustable continuous level applied at 8 is drawn in dashed lines at 22.
  • the elements referenced 1 to 20 constitute a generator of periodic slots, of fixed frequency but of adjustable width, these slots being synchronized by the image synchronization pulses 21 of the liquid crystal screen whose rear lighting is to be produced.
  • the output 24 of the comparator 9 (slots 23) and the output 25 of the monostable flip-flop 20 (pulses 21) are respectively applied to the two diodes 27, 22 of an OR circuit 26; the output of circuit 26 is coupled, by a resistor 29 followed by a fitness amplifier 30, to the control input 31 of another analog switch 32.
  • This switch 32 is open when a negative slot 23 or a negative pulse 21 is applied at 31, and it is closed otherwise. It constitutes a blocking switch for an oscillator 33 for supplying alternating high-voltage to the fluorescent lamp 34.
  • This oscillator 33 comprises: a transformer with a main primary winding 35 at midpoint 36, a reaction winding 40 at midpoint 41 and a secondary winding 44, two NPN transistors 37, 38, a capacitor 39, three resistors 42, 43, 60 and a shock coil, 48.
  • the transistors 37, 38 have their emitters connected to ground, their collectors respectively connected to the two ends of the winding 35 and their bases connected respectively to the resistors 42, 43; these resistors are respectively connected to the two ends of the reaction winding 40.
  • the capacitor 39 is disposed between the ends of the winding 35.
  • the secondary high-voltage winding 44 of the transformer has a terminal connected directly to ground and another terminal connected, through a ballast capacitor 45, to an electrode 46 of the fluorescent lamp 34; the other electrode, 47, of the lamp is connected to ground.
  • the voltage applied to the control input 31 of the switch 32 is then a continuous level, so that the switch 32 remains permanently open and, that the oscillator 33 operates without interruption, supplying the fluorescent lamp 34 at its maximum luminance.
  • circuit of FIG. 3 allows the lamp 34 to be started at low luminosity or at very low ambient temperature.
  • the circuit of FIG. 3 makes it possible to pair the lamps with low light.
  • each lamp has its own circuit according to FIG. 3. This pairing is carried out by adjusting the resistors 54 of each circuit so that all the lamps start for the same operating conditions. For this purpose, it is also possible to adjust the foot resistors 49, but this solution is not as good as it may increase losses.
  • the minimum luminance was obtained by cutting, or modulating, the alternating voltage of the oscillator 33 by slots whose duration corresponds to the width of the image-synchronization pulses 21.
  • these pulses 21 have a width of the order of microseconds.
  • the width L of the pulses 23 ranging from 50 microseconds to 1000 times more, that is to say 50 milliseconds.
  • a cut at 50 milliseconds corresponds to a frequency of 20 hertz, which would introduce a visible flicker ("flicker” in Anglo-Saxon literature) of the image provided by the liquid crystal screen so that in fact, in purely and simply according to this theory, the device according to the invention could not operate under the required conditions (brightness ratio of 1000/1).
  • the luminosity control potentiometer, 1 can be replaced by a photodetector providing a voltage proportional to the desired luminance.
  • the start of each slot 23 for cutting the sinusoidal voltage of the oscillator 33 is synchronized with the image synchronization signal of the liquid crystal screen.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Liquid Crystal Display Device Control (AREA)
  • Liquid Crystal (AREA)
  • Inverter Devices (AREA)
  • Discharge-Lamp Control Circuits And Pulse- Feed Circuits (AREA)
EP90401866A 1989-06-30 1990-06-28 Procédé et dispositif de gradation de lumière pour lampe fluorescente d'éclairage arrière d'écran à cristaux liquides Expired - Lifetime EP0406116B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8908807A FR2649277B1 (fr) 1989-06-30 1989-06-30 Procede et dispositif de gradation de lumiere pour lampe fluorescente d'eclairage arriere d'ecran a cristaux liquides
FR8908807 1989-06-30

Publications (2)

Publication Number Publication Date
EP0406116A1 EP0406116A1 (fr) 1991-01-02
EP0406116B1 true EP0406116B1 (fr) 1994-01-26

Family

ID=9383336

Family Applications (1)

Application Number Title Priority Date Filing Date
EP90401866A Expired - Lifetime EP0406116B1 (fr) 1989-06-30 1990-06-28 Procédé et dispositif de gradation de lumière pour lampe fluorescente d'éclairage arrière d'écran à cristaux liquides

Country Status (7)

Country Link
US (1) US5105127A (xx)
EP (1) EP0406116B1 (xx)
JP (1) JPH0364895A (xx)
CA (1) CA2019628A1 (xx)
DE (1) DE69006272T2 (xx)
FR (1) FR2649277B1 (xx)
HK (1) HK83596A (xx)

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Also Published As

Publication number Publication date
EP0406116A1 (fr) 1991-01-02
FR2649277B1 (fr) 1996-05-31
CA2019628A1 (en) 1990-12-31
HK83596A (en) 1996-05-17
FR2649277A1 (fr) 1991-01-04
JPH0364895A (ja) 1991-03-20
DE69006272D1 (de) 1994-03-10
US5105127A (en) 1992-04-14
DE69006272T2 (de) 1994-05-05

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