GB2481658A

GB2481658A - Display device including a backlight assembly

Info

Publication number: GB2481658A
Application number: GB201012300A
Authority: GB
Inventors: Peter Leak; Leonardo Impett
Original assignee: MANGO ELECTRONICS Ltd
Current assignee: MANGO ELECTRONICS Ltd
Priority date: 2010-07-22
Filing date: 2010-07-22
Publication date: 2012-01-04
Anticipated expiration: 2030-07-22
Also published as: GB2481658B; GB201012300D0; WO2012010906A1

Abstract

A display device includes a display panel and backlight assembly (2), wherein the backlight assembly (2) includes a length of electroluminescent wire (4) and a light diffusing arrangement (20). The device is arranged such that light emitted from the wire is transmitted towards the rear of the display panel via the light diffusing arrangement (20). In this way, the energy efficiency of an electroluminescent wire (4) is employed to form a backlight having a low power consumption. In addition, a reflective surface (6) is provided to reflect light emanating laterally and rearwardly from the wire so that it is directed towards the display panel. This surface may comprise planar, curved and/or parabolic portions. The wire extends back and forth over a plane substantially parallel to the plane of the display panel.

Description

Title: Display Device including a backlight assembly

Field of the invention

The present invention relates to display devices including a display panel and backlight assembly. More particularly, it is concerned with display assemblies having a low power consumption making them particularly suitable for use in portable devices.

Background to the invention

io Display panels, such as liquid crystal display (LCD) devices, which do not themselves emit light are commonly used in combination with a backlight to enhance contrast and increase visibility of the displayed information in a dark environment. Various types of light source are currently used in backlights, such as light emitting diode (LED) devices, electroluminescent (EL) sheets and fluorescent tubes.

Battery life is an important consideration for portable devices and generally it is desirable to reduce the power consumption of electronic products. Coupled with the increasing use of high resolution screens in portable devices, there is strong commercial demand for sufficiently bright backlights with reduced power consumption.

Summary of the invention

The present invention provides a display device including a display panel and a backlight assembly, wherein the backlight assembly includes a length of electroluminescent wire and a light diffusing arrangement, and the device is arranged such that light emitted from the wire is transmitted towards the rear of the display panel via the light diffusing arrangement.

The inventors have realised that EL wire may be employed to form a backlight having a low power consumption. Whilst in comparison to an EL sheet, and EL wire is a relatively localised source of light, the inventors have realised that it is possible to take advantage of the greater energy efficiency of an EL wire in backlight applications by distributing the light output from the wire across the area of the display panel.

Preferably, the wire is configured so that it extends over a plane parallel to the plane of the display panel. In preferred embodiments, the wire extends back and forth over this plane to illuminate the display panel area.

Preferably, a reflective surface is provided to reflect light emitted from the wire towards the display panel. Provision of such a surface adjacent to the wire on the side opposite the display panel increases the amount of light emitted from the wire which is incident on the display panel.

Preferably, the reflective surface is profiled so as to reflect at least some of the light emitted sideways from the wire towards the display panel. This further increases the proportion of the emitted light which reaches the display panel.

is The display surface may include planar portions angled with respect to the plane of the display panel to reflect light emitted sideways from the wire towards the display panel. More particularly, these planar portions may form an angle of around 45° with the plane of the display panel.

Instead of, or in addition to the planar portions, the reflective surface may include curved portions for reflecting light emitted from the wire towards the display panel.

In an alternative embodiment, the wire extends adjacent to one edge of the display panel, and the device includes a light guide to transmit light emitted from the wire towards the read of the display panel. In this way, a thinner backlight assembly may be provided whilst providing illumination across the area of the display panel.

Preferably, the backlight assembly includes an inverter circuit coupled to the wire for connection to a DC supply. This allows the backlight assembly to be powered by a DC supply such as one or more batteries in portable applications, for example.

The present invention further provides an electronic product including a display device as described herein. For example, the product may be selected from: a mobile phone, a portable music player, a portable computer, a computer monitor, and a television. A display device embodying the present invention may be incorporated in any product where a backlit display is required, and it is particularly suitable for portable products of this nature.

Preferably, the product is arranged to receive standardised batteries to provide a DC supply for the backlight assembly. This allows the use of widely available battery types instead of a dedicated rechargeable battery.

io Dedicated rechargeable batteries require the user to carry a corresponding battery charger in case the battery runs flat. This may be particularly inconvenient when travelling overseas where adaptors for the charger may also be required. Furthermore, continuity of power supply may be particularly important for portable devices such as mobile phones and a suitable power outlet may not be readily available. However, is standard format batteries are widely available, making their replacement relatively straightforward. Dedicated rechargeable batteries degrade over time and can be expensive to replace, whereas standardised batteries are manufactured in much higher volumes and so tend to be considerably less costly.

Brief description of the drawings

Embodiments of the invention will now be described by a way of example and with reference to the accompanying schematic drawings, wherein: Figure 1 is a block diagram of a backlight assembly according to an embodiment of the present invention; Figure 2 is a cross-sectional side view of part of the backlight assembly shown in Figure 1; and Figure 3 is a circuit diagram of an inverter suitable for use in the backlight assembly of Figure 1.

Detailed description

Figure 1 is a block diagram representing a backlight assembly 2 according to the present invention. An EL wire 4 is supported on a substrate 6. Power is fed to the wire from a DC power supply 8 and an inverter 10 along supply wires 12.

The wire extends back and forth over the plane of the substrate in a meandering configuration. Adjacent lengths of the wire extending across the substrate are substantially equally spaced apart to provide more even illumination.

EL wires are widely available in a variety of colours. They are usually formed with a small diameter making the wire particularly flexible. Accordingly, the wire may be arranged in the backlight in various configurations. Generally, for even illumination, it is desirable to keep adjacent lengths of wire substantially evenly spaced apart.

However, if more intense illumination is required in one or more regions, this spacing can be reduced in those areas.

In further embodiments, the EL wire may have two or more portions arranged to emit light of different colours, for example to illuminate respective areas of a display panel is in different ways. Alternatively, the backlight assembly may include two or more separate lengths of EL wire of the same or different colours.

The DC power supply 8 may comprise one or more "off-the-shelf" standardised batteries of a non-rechargeable or rechargeable type. They may be in a button cell format or AA or AAA cell format for example. Thus replacement batteries will be widely available and relatively inexpensive.

Figure 2 shows a cross-sectional side view through a part of the backlight shown in Figure 1 along the line A-A. A planar diffuser 20 is provided over the EL wire 4 and substrate 6. The diffuser may rest on the EL wire 4, or on the substrate 6 if it projects higher than the wire. Alternatively, it may be supported at a small spacing above the EL wire and substrate (as shown in the Figure).

The diffuser itself may be formed of two layers, namely a diffuser screen and a birefractive crystalline sheet (or of a plurality of such sheets). The diffuser serves to even out the distribution of light emanating from the EL wire before it is incident on the display panel (not shown).

EL wire emits light in all circumferential directions. Accordingly, the surface of substrate 6 facing the EL wire is reflective to direct light propagating away from the display panel back towards it. The reflective surface may be formed of aluminium

foil for example.

In the embodiment shown in Figure 2, a plurality of ridges 22 are formed on the upper surface of the substrate which extend parallel to the adjacent lengths of EL wire.

These ridges have a triangular cross-sectional profile, with the inclined sides forming an angle "a" of around 45° relative to the plane of the substrate 6. Thus, light emitted io laterally from each EL wire is reflected upwards towards the diffuser and display panel. Preferably, the height of each ridge is greater than the diameter of the EL wire.

Other profiles may be adopted for the reflective surface. For example, the surface may include curved portions instead of or in combination with planar portions.

Figure 3 depicts a circuit diagram of an inverter 10 suitable for use in a backlight assembly of the present invention. This circuit generates 120V AC from a 12V DC supply.

Examples of suitable component values for use in the circuit are as follows: Cl, C2: 40 uF R1,R2: 10 ohms R3, R4: 20 ohms Ti: 24Y transformer It will be appreciated that various other inverter circuits may fulfil the same function as the circuit shown in Figure 3, which is included by way of example.

For a given supply voltage, the power consumption of EL wire is proportional to frequency. The light output is also approximately proportional to frequency. A suitable frequency for backlight applications may be around 1,800Hz.

By way of illustration, the inventors have estimated the battery lifetime which may be expected using a backlight assembly embodying the present invention in a media player powered by standard batteries. For these purposes, EL wire was selected which was rated at 158V RMS and found to draw 32mA at a drive frequency of s 1800Hz with a power consumption of around 5W. 25cm of EL wire was employed in a backlight for a screen measuring 4.5 x 5cm. Accordingly the power consumption of the backlight was 1.25W. Estimating the power consumption of the processor and headphone amplifier of a portable media player at 0.1W gives 1.35W for the media player running with its screen and backlight on. i0

Three lithium watch batteries (4000mWh each) were selected as roughly equal in capacity to a lithium battery of the type used in many media players. It is estimated that a media player employing a backlight assembly of the present invention in this configuration would provide around 9 hours of continuous video playback, compared is to around S hours or less provided by well known existing media players.

Also, estimates of music playback time were calculated on the basis of 7 seconds of backlight time per 3 minute song. Averaging the power consumption of an MP3 player incorporating a backlight assembly embodying the present invention gives a power consumption of 0.1SW over the course of the 3 minute song. Using the three lithium watch batteries referred to above, this provides around 80 hours of actual playback time, compared to around 24 hours or less from well known, existing MP3 players.

Claims

Claims 1. A display device including a display panel and a backlight assembly, wherein the backlight assembly includes a length of electroluminescent wire and a light diffusing s arrangement, and the device is arranged such that light emitted from the wire is transmitted towards the rear of the display panel via the light diffusing arrangement.
2. A device of claim 1, wherein the wire extends over a plane substantially parallel to the plane of the display panel.
3. A device of claim 2, wherein the wire extends back and forth over a plane substantially parallel to the plane of the display panel.
4. A device of any preceding claim, wherein a reflective surface is provided to reflect light emanating from the wire towards the display panel.
5. A device of claim 4, wherein the reflective surface is profiled so as to reflect light emitted laterally from the wire towards the display panel.
6. A device of claim 5, wherein the reflective surface includes planar portions angled with respect to the plane of the display panel to reflect light emitted laterally from the wire towards the display panel.
7. A device of claim 5 or claim 6, wherein the reflective surface comprises curved portions for reflecting light emitted laterally from the wire towards the display panel.
8. A device of any preceding claim, wherein the light diffusing arrangement comprises a diffuser sheet and a birefractive crystalline sheet.
9. A device of claim 1, wherein the wire extends adjacent to one edge of the display panel, and the light diffusing arrangement comprises a light guide to transmit light emitted from the wire towards the rear of the display panel.
10. A device of any preceding claim, wherein the backlight assembly includes an inverter circuit coupled to the wire for connection to a DC power supply.
11. An electronic product including a display device of any preceding claim.
12. An electronic product of claim 11, wherein the product is selected from: a mobile phone, a portable music player, a portable computer, a computer monitor, and a television.
13. A product of claim 11 or claim 12, when dependent on claim 10, arranged to receive io batteries of a standardised format to provide a DC power supply for the backlight assembly.
14. A display device substantially as described herein with reference to the accompanying drawings.is
15. An electronic product substantially as described herein with reference to the accompanying drawings.Amendments to the claims have been filed as follows Claims 1. A display device including a display panel and a backlight assembly, wherein: the backlight assembly includes a length of electroluminescent wire and a light diffusing arrangement; the device is arranged such that light emitted from the wire is transmitted towards the rear of the display panel via the light diffusing arrangement; a reflective surface is provided to reflect light emanating from the wire so that it is directed towards the display panel, and the reflective surface is located adjacent to io the wire on the side opposite the display panel; and the wire extends back and forth over a plane substantially parallel to the plane of the display panel.2. A device of claim 1, wherein the reflective surface is profiled so as to reflect is light emitted laterally from the wire so that it is directed towards the display panel. L()3. A device of claim 2, wherein the reflective surface includes planar portions C) angled with respect to the plane of the display panel to reflect light emitted laterally from the wire towards the display panel.4. A device of claim 2 or claim 3, wherein the reflective surface comprises curved portions for reflecting light emitted laterally from the wire towards the display panel.5. A device of any preceding claim, wherein the light diffusing arrangement comprises a diffuser sheet and a birefractive crystalline sheet.6. A device of any preceding claim, wherein the backlight assembly includes an inverter circuit coupled to the wire for connection to a DC power supply.7. An electronic product including a display device of any preceding claim.8. An electronic product of claim 7, wherein the product is selected from: a mobile phone, a portable music player, a portable computer, a computer monitor, and a television. 9. A product of claim 7 or claim 8, when dependent on claim 6, arranged to receive batteries of a standardised format to provide a DC power supply for the backlight assembly.10. A display device substantially as described herein with reference to the accompanying drawings.11. An electronic product substantially as described herein with reference to the accompanying drawings. L() C)t::r: INTELLECTUAL . ...* PROPERTY OFFICE Application No: GB1012300.8 Examiner: Helen Edwards Claims searched: All Date of search: 5 November 2010 Patents Act 1977: Search Report under Section 17 Documents considered to be relevant: Category Relevant Identity of document and passage or figure of particular relevance to claims X,Y X-1, 2, 4-US2005/0 122308 Al 13, Y-3 (BELL ET AL) See paragraphs 0091, 0122 and figures 7a and 7b.Y 3 DE20308173U1 (ALTMANN) See English abstract and figures Categories: X Document indicating lack of novelty or inventive A Document indicating technological background and/or state step of the art.Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of before the filing date of this invention.same category.& Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:Search of GB, EP, WO & US patent documents classified in the following areas of the UKCX Worldwide search of patent documents classified in the following areas of the IPC 002F; HOIL; HO5B The following online and other databases have been ised in the preparation of this search report WPI, EPODOC, TXTEN, NPL, TDB, XPI3E, INTERNET International Classification: Subclass Subgroup Valid From GO2F 0001/13357 01/01/2006 HO5B 0033/00 01/01/2006 Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk