WO2002103665A1 - Inverter for liquid crystal display, and power supply arrangement comprising such an inverter - Google Patents

Inverter for liquid crystal display, and power supply arrangement comprising such an inverter Download PDF

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Publication number
WO2002103665A1
WO2002103665A1 PCT/IB2002/002061 IB0202061W WO02103665A1 WO 2002103665 A1 WO2002103665 A1 WO 2002103665A1 IB 0202061 W IB0202061 W IB 0202061W WO 02103665 A1 WO02103665 A1 WO 02103665A1
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WO
WIPO (PCT)
Prior art keywords
inverter
voltage
power supply
power
power converter
Prior art date
Application number
PCT/IB2002/002061
Other languages
French (fr)
Inventor
Thomas A. J. Haus
Hendrik W. J. De Groot
Original Assignee
Koninklijke Philips Electronics N.V.
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 Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Priority to JP2003505902A priority Critical patent/JP4168145B2/en
Priority to DE60216459T priority patent/DE60216459T2/en
Priority to KR10-2003-7002038A priority patent/KR20030027024A/en
Priority to EP02733142A priority patent/EP1402511B1/en
Priority to US10/480,129 priority patent/US7119496B2/en
Publication of WO2002103665A1 publication Critical patent/WO2002103665A1/en

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • 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
    • H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
    • H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
    • H05B41/282—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices
    • H05B41/2821—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices by means of a single-switch converter or a parallel push-pull converter in the final stage
    • H05B41/2822—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices by means of a single-switch converter or a parallel push-pull converter in the final stage using specially adapted components in the load circuit, e.g. feed-back transformers, piezoelectric transformers; using specially adapted load circuit configurations

Definitions

  • Inverter for liquid crystal display and power supply arrangement comprising such an inverter
  • the present invention relates to an inverter for use in a liquid crystal display unit.
  • the invention also relates to a power supply arrangement for supplying power to a plurality of back or edge illumination devices in a liquid crystal display unit, comprising a mains connection, a power converter and at least one inverter.
  • a power supply for discharge lamps in a liquid crystal display device is known from e.g. US 4,865,425.
  • a power supply is provided with an inverter for each lamp, said inverter comprising an oscillator and a step-up transformer to generate a voltage that is high enough to ignite the lamp.
  • Conventional liquid crystal display devices have a mains-isolated power supply located in the pedestal of the monitor, where there is sufficient space, or in a separate adapter. From this power supply, a lower voltage (e.g. 12 V DC) is supplied to the screen portion, where a plurality of inverters are arranged. Each inverter converts forms the lower DC voltage to an appropriate level (e.g. 3 kV) needed for igniting the lamps.
  • a lower voltage e.g. 12 V DC
  • an appropriate level e.g. 3 kV
  • the mains voltage must be first converted down to 12 V and then converted up to the required voltage in the inverters. This is an inefficient procedure. Furthermore, several inverters are required for driving the lamps, typically four inverters for driving eight lamps.
  • a second object of the invention is to provide an improved power supply arrangement in an LCD.
  • a power supply arrangement for supplying power to a plurality of back illumination devices in a liquid crystal display, wherein the power converter is arranged to convert an AC voltage input to a DC voltage output, the inverter is connected to said DC voltage output and is arranged to convert said output to a voltage level adequate for driving said illumination devices, and the inverter is provided with mains isolation.
  • the LCD unit typically comprises also a circuit power supply, which is connected to said power converter output, and arranged to generate voltage levels required by control circuitry in the LCD.
  • This circuit power supply is preferably also provided with mains isolation, so that the entire LCD is isolated from the mains.
  • the mains isolation normally present in the adapter has been divided and moved forward to the inverter and the circuit power supply, respectively.
  • the power converter and the inverter are arranged in a screen portion of the LCD. This leads to a very practical and efficient design, where the mains is simply connected to the screen portion of the LCD. Thus, no connection wires are required in the moving joint between the pedestal and the screen.
  • the power converter output preferably has a voltage level that it higher than the voltage level of the AC input, and that ranges for example from 200-600 V. This voltage level makes it possible to generate the power required for driving several, for example eight, lamps, without excessive power losses.
  • the power converter can be a PFC circuit.
  • a second aspect of the present invention relates to an inverter for use in a LCD, provided with mains isolation means. It is noted that this concept is novel in LCD power supply, and that it enables a more cost effective and power effective power supply arrangement.
  • Fig. 1 is a schematic view of a power supply arrangement in an LCD unit according to an embodiment of the invention.
  • Fig. 2a-c show various perspective views of the inverter in fig. 1.
  • Fig. 3 is a schematic sectional view of the coil former of the inverter in fig. 2.
  • Fig. 4a-b show examples of LLC and LLCC circuits.
  • Fig. 1 shows a schematic view of a power supply arrangement in a LCD unit according to an embodiment of the invention.
  • the LCD unit 1 has a pedestal portion 2 and a screen portion 3 in which the liquid crystal display 3 a is housed together with its control electronics 4.
  • the screen portion also contains a number of background illumination devices in the form of lamps 5 with reflectors 5 a.
  • a power converter in the form of a power factor correction (PFC) circuit 6 is arranged in the lower part of the screen portion 3, and is connected to the mains 7, normally 90 - 250 V AC, in the illustrated example 230 V AC.
  • the PFC circuit 6 delivers a 400 V DC, and comprises no mains isolation.
  • PFC power factor correction
  • the DC output is supplied to an inverter 8, also arranged in the screen portion 3.
  • the inverter 8 is adapted to convert the PFC DC output to a voltage more suitable for driving the lamps 5, typically around 3 kV.
  • the DC voltage from the PFC is also supplied to a conventional low- voltage transformer 9 that is adapted to generate voltages required by the control electronics 4 of the LCD, typically 3 V, 5 V and 12V.
  • the inverter 8 and the power transformer 9 are both provided with mains isolation, thereby satisfying the safety requirements for the LCD. While this is straightforward in the case of the conventional low voltage transformer 9, it is more complicated in the case of the inverter 8.
  • the transformer section 11 of the inverter 8 is shown in figs. 2-3, and comprises a core consisting of two E-shaped parts 12a and 12b, and a coil former 13 for forming compartments 14, 15 for the primary and secondary coil windings (the winding turns are not shown).
  • the coil former 13 is formed with flanges or flares 16 dividing the secondary winding compartment into several sections. On each side of the windings, the separating flanges are double, forming so called labyrinths 17.
  • the secondary sections have varying wall thicknesses towards the core 12a, 12b, in order to avoid corona and breakdown problems between the secondary winding and the core.
  • the material thickness b in each section increases with the distance from the primary winding, the first section having a wall thickness of 0.7 mm, the second section having a wall thickness of 1.5 mm and the third section having a thickness of 2.1 mm.
  • the width a of the sections 15a-c can nevertheless be equal, so that each layer in each section contains an equal number of turns, in the preferred embodiment 19 turns.
  • the inverter in fig. 2-3 has a primary winding with 110 turns, and a secondary winding with almost 1000 turns divided among the three sections. The design described herein eliminates the need for filling the inverter with resin or the need to use insulating tape, thus saving costs.
  • the coil former 13 Before the core 12a, 12b is inserted into the corresponding opening of the coil former 13, the coil former 13 is placed in a casing 18.
  • the portion 19 of the coil former 13 intended to receive the core is arranged in a groove 20 of the casing, said groove having openings 21 on either side.
  • the core parts 12a, 12b are then inserted into the coil former 13 through these openings 21, thereby fixing the coil former 13 and the casing 18 together.
  • the outer sections 22 of the core 12a, 12b are separated from the sides of the casing 18 by a small distance d, preferably 1-2 mm. This distance further reduces corona problems.
  • Flanges 24 along the sides of the groove 20 in the casing 18 are adapted to be received by grooves 25 formed in the above-mentioned labyrinths 17 in the side of the coil former 13.
  • the inverter in accordance with the design illustrated herein generates an output voltage on the secondary side of around 2,5 kV when the input voltage on the primary side is 250 V.
  • the inverter constitutes a LLC or a LLCC circuit, such as illustrated in figs. 4a and 4b.
  • the spread between the primary and secondary windings is preferably selected so that the self-inductance can function as a substitute for a ballast coil in the LLC or LLCC circuit.
  • the distance X between the centers of the primary and the secondary windings is in approximately 2 cm in order to accomplish the desired spread.

Abstract

The present invention relates to a power supply arrangement for supplying power to a plurality of back and/or edge illumination devices (5) in a liquid crystal display unit (1), comprising a mains connection (7), a power converter (6) and at least one inverter (8). The power converter (6) is arranged to convert an AC voltage input to a DC voltage output, and the inverter (8) is connected to said DC voltage output, and arranged to convert said output to a voltage level adequate for driving said illumination devices (5). Furthermore, the inverter (8) is provided with mains isolation. By virtue of this arrangement, no conventional adapter is required, and the LCD can be connected directly to the mains. The conversion down to a low DC voltage is eliminated, without violating the current-limitation safety requirements. This leads to a more effective power supply.

Description

Inverter for liquid crystal display, and power supply arrangement comprising such an inverter
The present invention relates to an inverter for use in a liquid crystal display unit. The invention also relates to a power supply arrangement for supplying power to a plurality of back or edge illumination devices in a liquid crystal display unit, comprising a mains connection, a power converter and at least one inverter.
A power supply for discharge lamps in a liquid crystal display device is known from e.g. US 4,865,425. Such a power supply is provided with an inverter for each lamp, said inverter comprising an oscillator and a step-up transformer to generate a voltage that is high enough to ignite the lamp.
Conventional liquid crystal display devices have a mains-isolated power supply located in the pedestal of the monitor, where there is sufficient space, or in a separate adapter. From this power supply, a lower voltage (e.g. 12 V DC) is supplied to the screen portion, where a plurality of inverters are arranged. Each inverter converts forms the lower DC voltage to an appropriate level (e.g. 3 kV) needed for igniting the lamps.
In order to fulfill the safety requirements related to current limitations, conventional inverter transformers have a limited power output of approximately 10W. Therefore, each inverter only drives one or two lamps.
Even though safety regulations would allow an increase of the power supplied by the power supply to maximally 47 V DC, this would only lead to a minor power increase and most of the power would be wasted as losses in the inverters.
As will be clear from the foregoing, the mains voltage must be first converted down to 12 V and then converted up to the required voltage in the inverters. This is an inefficient procedure. Furthermore, several inverters are required for driving the lamps, typically four inverters for driving eight lamps.
It is an object of the present invention to overcome the above-mentioned problems and provide a power supply for the back or edge illumination of an LCD that only requires one inverter. A second object of the invention is to provide an improved power supply arrangement in an LCD.
According to the invention, these and other objects are achieved by a power supply arrangement for supplying power to a plurality of back illumination devices in a liquid crystal display, wherein the power converter is arranged to convert an AC voltage input to a DC voltage output, the inverter is connected to said DC voltage output and is arranged to convert said output to a voltage level adequate for driving said illumination devices, and the inverter is provided with mains isolation.
By using this arrangement a conventional adapter can be dispensed with and the LCD can be connected directly to the mains. The conversion down to a low DC voltage is eliminated without violating the current-limitation safety requirements. This leads to a more effective power supply. Another advantage is that a larger power output can be delivered by the inverter, also without violating the current-limitation safety requirements. As a consequence, only one inverter is required for driving several, at least four, back illumination devices. This reduces the complexity and the cost of each LCD.
The LCD unit typically comprises also a circuit power supply, which is connected to said power converter output, and arranged to generate voltage levels required by control circuitry in the LCD. This circuit power supply is preferably also provided with mains isolation, so that the entire LCD is isolated from the mains. In comparison with a conventional LCD power supply, the mains isolation normally present in the adapter has been divided and moved forward to the inverter and the circuit power supply, respectively. According to a preferred embodiment, the power converter and the inverter are arranged in a screen portion of the LCD. This leads to a very practical and efficient design, where the mains is simply connected to the screen portion of the LCD. Thus, no connection wires are required in the moving joint between the pedestal and the screen.
The power converter output preferably has a voltage level that it higher than the voltage level of the AC input, and that ranges for example from 200-600 V. This voltage level makes it possible to generate the power required for driving several, for example eight, lamps, without excessive power losses.
The power converter can be a PFC circuit. A second aspect of the present invention relates to an inverter for use in a LCD, provided with mains isolation means. It is noted that this concept is novel in LCD power supply, and that it enables a more cost effective and power effective power supply arrangement.
These and other aspects of the invention will be apparent from the preferred embodiments more clearly described with reference to the appended drawings.
Fig. 1 is a schematic view of a power supply arrangement in an LCD unit according to an embodiment of the invention.
Fig. 2a-c show various perspective views of the inverter in fig. 1.
Fig. 3 is a schematic sectional view of the coil former of the inverter in fig. 2.
Fig. 4a-b show examples of LLC and LLCC circuits.
Fig. 1 shows a schematic view of a power supply arrangement in a LCD unit according to an embodiment of the invention. The LCD unit 1 has a pedestal portion 2 and a screen portion 3 in which the liquid crystal display 3 a is housed together with its control electronics 4. The screen portion also contains a number of background illumination devices in the form of lamps 5 with reflectors 5 a. A power converter in the form of a power factor correction (PFC) circuit 6 is arranged in the lower part of the screen portion 3, and is connected to the mains 7, normally 90 - 250 V AC, in the illustrated example 230 V AC. The PFC circuit 6 delivers a 400 V DC, and comprises no mains isolation.
The DC output is supplied to an inverter 8, also arranged in the screen portion 3. The inverter 8 is adapted to convert the PFC DC output to a voltage more suitable for driving the lamps 5, typically around 3 kV. The DC voltage from the PFC is also supplied to a conventional low- voltage transformer 9 that is adapted to generate voltages required by the control electronics 4 of the LCD, typically 3 V, 5 V and 12V.
The inverter 8 and the power transformer 9 are both provided with mains isolation, thereby satisfying the safety requirements for the LCD. While this is straightforward in the case of the conventional low voltage transformer 9, it is more complicated in the case of the inverter 8.
The transformer section 11 of the inverter 8 is shown in figs. 2-3, and comprises a core consisting of two E-shaped parts 12a and 12b, and a coil former 13 for forming compartments 14, 15 for the primary and secondary coil windings (the winding turns are not shown).
In order to avoid problems caused by breakdown and corona, in spite of the limited space available in the transformer 11, the coil former 13 is formed with flanges or flares 16 dividing the secondary winding compartment into several sections. On each side of the windings, the separating flanges are double, forming so called labyrinths 17.
Furthermore, the secondary sections have varying wall thicknesses towards the core 12a, 12b, in order to avoid corona and breakdown problems between the secondary winding and the core. In the example illustrated in fig. 2-3, there are three secondary sections 15a-
15c. The material thickness b in each section increases with the distance from the primary winding, the first section having a wall thickness of 0.7 mm, the second section having a wall thickness of 1.5 mm and the third section having a thickness of 2.1 mm. This means that a decreasing number of layers can be housed in each section; 22 layers in the first section, 17 layers in the second and 12 in the third section. The width a of the sections 15a-c can nevertheless be equal, so that each layer in each section contains an equal number of turns, in the preferred embodiment 19 turns. The inverter in fig. 2-3 has a primary winding with 110 turns, and a secondary winding with almost 1000 turns divided among the three sections. The design described herein eliminates the need for filling the inverter with resin or the need to use insulating tape, thus saving costs.
Before the core 12a, 12b is inserted into the corresponding opening of the coil former 13, the coil former 13 is placed in a casing 18. The portion 19 of the coil former 13 intended to receive the core is arranged in a groove 20 of the casing, said groove having openings 21 on either side. The core parts 12a, 12b are then inserted into the coil former 13 through these openings 21, thereby fixing the coil former 13 and the casing 18 together. Note that the outer sections 22 of the core 12a, 12b are separated from the sides of the casing 18 by a small distance d, preferably 1-2 mm. This distance further reduces corona problems.
Flanges 24 along the sides of the groove 20 in the casing 18 are adapted to be received by grooves 25 formed in the above-mentioned labyrinths 17 in the side of the coil former 13.
The inverter in accordance with the design illustrated herein generates an output voltage on the secondary side of around 2,5 kV when the input voltage on the primary side is 250 V. Apart from the transformer functionality, the inverter constitutes a LLC or a LLCC circuit, such as illustrated in figs. 4a and 4b. The spread between the primary and secondary windings is preferably selected so that the self-inductance can function as a substitute for a ballast coil in the LLC or LLCC circuit. In the transformer illustrated in figs. 2-3, the distance X between the centers of the primary and the secondary windings is in approximately 2 cm in order to accomplish the desired spread.
A number of modifications of the described embodiments are possible within the scope of the appended claims. For example, the details regarding the inverter design, such as wall thickness, number of flares, number of primary and/or secondary winding sections etc., may be modified by persons skilled in the art.
It should be understood that by increasing the winding compartments and the core, and increasing the number of windings, a larger power can be taken from the inverter.

Claims

CLAIMS:
1. Power supply arrangement for supplying power to a plurality of back and/or edge illumination devices (5) in a liquid crystal display unit (1), comprising a mains connection (7), a power converter (6), and at least one inverter (8), characterized in that the power converter (6) is arranged to convert an AC voltage input to a DC voltage output, in that said inverter (8) is connected to said DC voltage output and is arranged to convert said output to a voltage level adequate for driving said illumination devices (5), and in that said inverter (8) is provided with mains isolation.
2. Arrangement according to claim 1, wherein said inverter (8) is arranged to supply power for driving at least four lamps (5).
3. Arrangement according to claim 1 or 2, further comprising a circuit power supply (9), connected to said power converter (6), and arranged to generate voltage levels required by circuitry (4) in the LCD, said circuit power supply (9) also being provided with mains isolation.
4. Arrangement according to any one of the claims 1-3, wherein said LCD unit (1) comprises a screen portion (3), and wherein said power converter (6) and said inverter (8) are arranged in said screen portion (3).
5. Arrangement according to any one of the claims 1-4, wherein said power converter output has a voltage level that is higher than the voltage level of the AC input.
6. Arrangement according to any one of the claims 1-5, wherein said power converter output has a voltage in the range 200V - 600 V.
7. Arrangement according to any one of the claims 1-6, wherein said power converter is a Power Factor Correction (PFC) circuit (8).
8. An inverter for use in a liquid crystal display unit (1), provided with mains isolation means.
PCT/IB2002/002061 2001-06-14 2002-06-05 Inverter for liquid crystal display, and power supply arrangement comprising such an inverter WO2002103665A1 (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
JP2003505902A JP4168145B2 (en) 2001-06-14 2002-06-05 Power supply device and liquid crystal display unit having such power supply device
DE60216459T DE60216459T2 (en) 2001-06-14 2002-06-05 INVERTER FOR A LIQUID CRYSTAL DISPLAY AND POWER SUPPLY WITH SUCH A INVERTER
KR10-2003-7002038A KR20030027024A (en) 2001-06-14 2002-06-05 Inverter for liquid crystal display, and power supply arrangement comprising such an inverter
EP02733142A EP1402511B1 (en) 2001-06-14 2002-06-05 Inverter for liquid crystal display, and power supply arrangement comprising such an inverter
US10/480,129 US7119496B2 (en) 2001-06-14 2002-06-05 Inverter for liquid crystal display, and power supply arrangement comprising such an inverter

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP01202295 2001-06-14
EP01202295.0 2001-06-14

Publications (1)

Publication Number Publication Date
WO2002103665A1 true WO2002103665A1 (en) 2002-12-27

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PCT/IB2002/002061 WO2002103665A1 (en) 2001-06-14 2002-06-05 Inverter for liquid crystal display, and power supply arrangement comprising such an inverter

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US (1) US7119496B2 (en)
EP (1) EP1402511B1 (en)
JP (1) JP4168145B2 (en)
KR (1) KR20030027024A (en)
CN (1) CN1287347C (en)
AT (1) ATE347158T1 (en)
DE (1) DE60216459T2 (en)
TW (1) TWI236653B (en)
WO (1) WO2002103665A1 (en)

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US7291987B2 (en) * 2005-06-17 2007-11-06 Hon Hai Precision Industry Co., Ltd. Power supply system for flat panel display devices
US20070279350A1 (en) * 2006-06-02 2007-12-06 Kent Displays Incorporated Method and apparatus for driving bistable liquid crystal display
US7675239B2 (en) * 2006-08-11 2010-03-09 Kent Displays Incorporated Power management method and device for low-power displays
KR101336285B1 (en) 2007-02-13 2013-12-03 삼성디스플레이 주식회사 Lamp driving circuit, inverter board and display apparatus having the inverter board
KR101042032B1 (en) * 2009-03-11 2011-06-16 주식회사 비에스이 Micro-speaker
KR102522283B1 (en) * 2015-11-19 2023-04-19 삼성디스플레이 주식회사 Backlight unit
KR102481864B1 (en) 2018-01-29 2022-12-28 삼성전자주식회사 Electronic apparatus and method for controlling thereof

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EP0413991A1 (en) * 1989-07-28 1991-02-27 Toshiba Lighting & Technology Corporation Discharge lamp lighting apparatus for driving discharge lamp according to rating thereof
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KR20030027024A (en) 2003-04-03
TWI236653B (en) 2005-07-21
JP2004531030A (en) 2004-10-07
EP1402511A1 (en) 2004-03-31
DE60216459D1 (en) 2007-01-11
CN1516864A (en) 2004-07-28
JP4168145B2 (en) 2008-10-22
EP1402511B1 (en) 2006-11-29
US7119496B2 (en) 2006-10-10
US20040160791A1 (en) 2004-08-19
DE60216459T2 (en) 2007-09-20
CN1287347C (en) 2006-11-29
ATE347158T1 (en) 2006-12-15

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