JP2002278471A - Backlight device and method for turning on the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a return cable and a return board for connecting one electrode to the other electrode of a fluorescent lamp or the like in a backlight device and a method for turning on the device to downsize the housing and avoid the complexity of the manufacturing process. SOLUTION: The electrodes on one side of a pair of cylindrical light sources 3, 3 are connected in series and the cylindrical light sources are driven in an opposite phase to each other, and the return cable up to an inverter circuit board 7 to be arranged on the other electrode side is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device for a liquid crystal display used as various display devices such as a personal computer and a method of lighting the backlight device. The present invention relates to a backlight device and a lighting method of the backlight device.

[0002]

2. Description of the Related Art LCs used as display devices for electronic devices such as microcomputers and television receivers.
Since D (liquid crystal display) is non-luminous, it requires a light source for external irradiation such as a backlight device.

[0003] As such a backlight device, a small-diameter fluorescent tube such as a cold cathode tube or a hot cathode tube is generally used as a cylindrical light source, and the fluorescent tube is arranged on the side surface of a light guide plate. With the edge light method, a reflector (hereinafter referred to as a “reflector”) and a fluorescent tube are housed inside the housing, and the light transmitted from the fluorescent tube and the fluorescent tube are transferred to a light transmitting / diffusing plate provided in the opening of the housing. There is known a direct type in which the light reflected by a reflection plate is incident and diffused by a light transmission / diffusion plate to emit uniform planar light.

The above direct type or edge light type is L
It is selected according to the required performance of the CD, but the direct type uses the direct light of the fluorescent tube, so the light use efficiency is higher than the edge light type, and high brightness for monitors, television receivers, etc. Suitable for required applications.

FIG. 5A is a plan view showing a conventional backlight device of a direct type, FIG. 5B is a sectional view taken along the line CC ′ of FIG. 5A, and FIG. Is D- in FIG.
FIG. 6 (A) is a conventional plan view schematically showing a transformer and a cylindrical light source of the backlight device, and FIG.
(B) is a conventional connection diagram of the transformer and the cylindrical light source, FIG.
FIG. 7A is a circuit diagram of a conventional in-phase inverter, and FIG.
(B) is an explanatory view of the principle when the conventional cylindrical light source is turned on.

5 (a) to 5 (c), a housing 1 serving as a lamp house of a backlight device has an opening 1a on an upper surface, and front, rear, right and left side walls are expanded upward and a cross section is formed. It is formed in a trapezoidal shape and is integrally molded with a white high-reflection grade molding resin, or is made by a metal plate or a combination of a metal plate and a molding resin.

A high-reflection paint is applied to the inside of the housing 1, or a high-reflection film material or the like is attached to the bottom of the housing 1, and its end is bent into a trapezoidal cross section, and the front, rear, left, right, and The reflection plate 2 as a reflector is formed by being fixed to the inner surface of the side wall.

The cylindrical light source 3 such as a fluorescent tube is held at a position spaced from the bottom surface of the housing 1 by about 1 to 2 mm.
The support bases 5L and 5R for cylindrical light sources are fixed to the left and right side walls of
A plurality of sockets 12L and 12R are provided on this.

A light transmitting / diffusing plate 4 made of a milky acrylic material or the like is disposed on the upper surface of the housing 1 so as to cover the opening 1a, and a light condensing sheet 4a is provided on the light transmitting / diffusing plate 4.

A printed circuit board 10 is provided inside the right frame member 15, and an inverter circuit board 7 constituting an inverter circuit provided with a plurality of transformers 8 is provided on the left bottom surface of the housing 1. I have. Reference numeral 9 denotes a return cable to be described later.

The above-mentioned backlight device 6 is mounted via a frame member 15 in a box-shaped casing, and when fixed, the light emitted radially from the cylindrical light source 3 can be directly or a reflection plate in the housing 1. The light is reflected by the light 2 and reaches the light transmission / diffusion plate 4, and is converted into surface light by the light transmission / diffusion plate 4 and the condensing sheet 4 a.

FIGS. 6A and 6 are schematic plan views and connection diagrams of the above-described inverter circuit substrate 7 and cylindrical light source.
(B) and FIG. 7 (A) which is an inverter circuit diagram,
The connection relationship between the left and right ends of a plurality of conventional cylindrical light sources 3 will be described. The winding start point of each secondary winding of the plurality of transformers 8 corresponding to the number of cylindrical light sources 3 provided in the inverter circuit board 7 is The secondary winding is connected to one of the left socket groups 12L shown in FIG. 5B, and the winding end point of the secondary winding is grounded to a common ground point of the inverter circuit board 7.

The socket group 12R on the right side of the cylindrical light source 3 is commonly connected to a rectangular plate-shaped grounded printed circuit board 10 provided on a frame member 15 as shown in FIGS. 6 (A) and 6 (B). The substrate 10 and the inverter circuit substrate 7 are connected to a common ground point of the inverter circuit via a return cable 9.

FIG. 7A shows a conventional Royer's circuit (Royer's circuit).
s Circuit), the secondary winding N ₂ of the transformer group 8 (8a, 8b, 8c),
N ₂ ′} is a plurality of cylindrical light sources 3 (3a, 3b, 3c), respectively.
‥‥) is connected as described above.

The primary windings N _1a and N 1 of the transformers 8a and 8b
_1b and N _1a ′, N _1b ′ are wound in the same number of turns, and the primary winding N
_1a and N _1b are connected in series, and similarly, the primary windings N _1a ′ and N _1b ′ are also connected in series. Primary windings N _1b and N _1b ′
Starts from the second switching transistor Q ₂
Of the primary windings N _1a and N _1a ′ are connected to the collector of a first switching transistor Q ₁ . The emitters of the first and second switching transistors Q ₁ and Q ₂ are commonly connected and dropped to the ground potential E.

The series connection points of the primary windings N _1a , N _1b and N _1a ′, N _1b ′ of each of the transformers 8 a, 8 b さ れ る are commonly connected, and the anode of the DC power source V and one end of the bias resistor R are connected. , The cathode of the DC power supply V is connected to the ground potential E, the other end of the bias resistor is connected to the base of a _first transistor Q1 for switching, and the base of the first transistor is a tertiary winding. is connected to the winding start point of the line N _3,
A second transistor Q ₂ of the base 3 of switching
It is connected to the winding end point of the primary winding N _3. Further, the collectors of the first and second transistors Q ₁ and Q ₂ are connected to each other via a capacitor C.

The operation of the above circuit configuration will be described with reference to FIGS. 7A and 7B and FIG. In FIG. 7A, the power supply current I immediately after closing a switch (not shown) of the DC voltage V is a bias resistor R and transformers 8a and 8b.
The primary winding N _1a, N _1b of the N _1a ', N _1b' branches to the current I ₂ and I ₁ flows in the direction, the inductance L _O capacity C _O and transformer 8a and 8b of the capacitor C, the oscillation frequency f = 1 / 2π√L _O C _o to start the oscillation of Hz.

The current I ₁ is supplied to the primary winding N _1a of the transformer 8a,
The primary winding N _1a of the current I ₅ and the transformer 8b branching to N _1b ', N _1b' is branched into a current I ₆ to be branched into. Current I ₅ and I ₆ are current I ₇ + I _9, the current I ₈ + I ₁₀ flows in accordance with the "on" and "off" states of the transistors Q ₁ and Q ₂ first and second for switching.

The current I ₂ branched to the bias resistor R is the first current I ₂
Current I give bias to the base of the transistor Q _1
3 and is divided into a current I ₄ is supplied to the tertiary winding N _3.

With the above-mentioned oscillation frequency f, the tertiary winding N
A voltage of the opposite phase is induced at ₃ . Now, assuming that the second transistor Q ₂ is in the “off” state, this induced voltage produces a positive feedback at the base of the second transistor Q ₂ ,
The transition to the "on" state occurs with sufficient base current.

As shown in the waveform diagram of FIG. 4, the first transistor Q
₁ is "on", the second transistor Q ₂ is "off", the first transistor Q ₁ to the ascent "off", the second
Of the transistor Q ₂ is "on". In FIG. 4, _Vce of the first and second transistors Q ₁ and Q ₂ indicates a collector-emitter voltage, I _C indicates a collector current, and V _be indicates a base-emitter voltage.

The winding end shown in FIG. 7 (A) the primary winding N _1a and N _1a of the first and second transformers 8a and 8b for driving the two cylinder lights 3a and 3b in one Royer circuit ' The points are connected in common and connected to the collector of the first transistor Q1, and connected to _one of the first and second transformers 8a and 8b.
The winding start points of the next windings N _1b and N _1b ′ are connected in common and
Because of being connected to the collector of the transistor Q _2,
As shown in FIG. 7B, an in-phase alternating current is generated in the cylindrical light sources 3a and 3b.

The above-mentioned bias current I ₂ and the branched current I
₁ is branched into a current I ₅ and I ₆ with a common connection point of the primary winding N _1a and N _1b of the transformer 8a, 1 transformer 8a if current I ₅ is first transistor Q ₁ is "ON" the current I ₇ flowing through the primary winding N _1a. On the other hand, the current I ₆ becomes a current I ₉ flowing through the primary winding N _1a ′ at the common connection point of the primary windings N _1a ′ and N _1b ′ of the transformer 8b, and the current I ₇ + I ₉ becomes the first transistor Q via the emitter is ₁ of the collector current reaches the ground potential E.

Further, current I ₅ is next current I ₈ flowing through the primary winding N _1b of the second transistor Q ₂ is turned "on" as on ordination transformer 8a, current I ₆ trans 8b
Of the primary winding N _1b 7 'of the current I ₁₀ becomes current I ₈ + I ₁₀ secondary coils N ₂ and N ₂ of the second transistor Q ₂ of the transformer 8a and 8b become a collector current' ( in time T ₁ as B) + direction at time T ₂ - AC voltage direction in the same phase flow simultaneously into a cylindrical light source 3a and 3b.

[0025]

According to the above-described backlight device and the method of lighting the backlight device, two sets of cylindrical light sources 3a and 3b can be driven by one set of lower circuit, and these two sets of cylindrical light sources can be driven. As shown in FIG. 7B, 3a and 3b are driven by AC voltages having the same phase. But
In this configuration, as shown in FIGS. 5 (B), 6 (A), and 6 (B), since a board 10 and a return cable 9 are required, a housing for the board 10 provided on the frame member 15 is provided. This has been an obstacle to downsizing the body 1 and making the frame member 15 a narrow frame. Further, it is necessary to extend the return cable 9 from the right side to the left side of the casing 1, and when the casing 1 is enlarged, the operation becomes extremely complicated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a return substrate and a return cable without substantially changing a driving circuit of a fluorescent tube comprising a cylindrical light source. It is an object of the present invention to provide a backlight device capable of operating a pair of fluorescent tubes normally and a lighting method of the backlight device.

[0027]

According to the first aspect of the present invention, a reflector and an even number of cylindrical light sources 3 are arranged in a flat casing 1 having an opening 1a on the upper surface, and light is transmitted through the opening 1a. A backlight device 6 provided with a diffusion plate 4, wherein at least two cylindrical light sources 3 are paired and one of the electrodes is connected to an inverter means 7 capable of applying an alternating-phase AC voltage, and the other is connected to the other electrode. A backlight device characterized in that they are connected to each other in common.

According to a second aspect of the present invention, there is provided a method of lighting a backlight device in which an even number of cylindrical light sources 3 are disposed in a housing 1, wherein each of at least two cylindrical light sources 3 is paired. This is a lighting method for a backlight device, characterized in that an alternating voltage of opposite phase is applied to one electrode and two cylindrical light sources 3 in a pair are connected in series with each other.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a backlight device and a method of lighting the backlight device according to the present invention will be described in detail with reference to FIGS.

FIG. 1A is a plan view showing a direct type backlight device of the present invention, and FIG. 1B is a plan view of FIG.
1 (C) is a sectional view taken along the line CC ′ of FIG.
FIG. 2A is a plan view schematically showing a transformer and a cylindrical light source of the backlight device of the present invention.
(B) is a connection diagram of the transformer of the present invention and a cylindrical light source, FIG.
(A) is a circuit diagram of the antiphase inverter of the present invention, FIG.
(B) is a principle explanatory diagram when the cylindrical light source of the present invention is turned on.

In FIGS. 1A to 1C, FIG.
Parts corresponding to (A) to FIG. 5 (C) are denoted by the same reference numerals and described. 1 (A) to 1 (C), a housing 1 serving as a lamp house of a backlight device 6 has an opening 1a on an upper surface, and front and rear, right and left side walls are expanded upward, and a cross section is formed into a trapezoidal shape. Then, it is integrally molded with a white high-reflection grade molding resin, or a metal plate or a combination of a metal plate and a molding resin is produced.

A high-reflection paint is applied to the inside of the housing 1, or a high-reflection film material or the like is attached to the bottom of the housing 1, and its end is bent into a trapezoidal cross-section. A reflector 2 as a reflector is formed by being fixed to the inner surfaces of the left and right side walls.

The cylindrical light source 3, such as a fluorescent tube, is held at a position spaced from the bottom of the housing 1 by about 1 to 2 mm.
The support bases 5L and 5R for cylindrical light sources are fixed to the left and right side walls of
A plurality of sockets 12L and 12R are provided on this, and an inverter circuit board 7 constituting an inverter circuit having a transformer 8 is provided on the bottom surface of the housing 1.

A light transmission / diffusion plate 4 made of a milky white acrylic material or the like is arranged on the upper surface of the housing 1 so as to cover the opening 1a.
A condensing sheet 4a is provided on the light transmitting / diffusing plate 4.

A plurality of transformers 8 are provided on the bottom surface on the left side of the housing 1.
And an inverter circuit board 7 which constitutes an inverter circuit provided with.

The above-mentioned backlight device 6 is mounted via a frame member 15 in a box-shaped casing, and when fixed, the light emitted radially from the cylindrical light source 3 can be directly or a reflection plate in the housing 1. The light is reflected by the light 2 and reaches the light transmission / diffusion plate 4, and is converted into surface light by the light transmission / diffusion plate 4 and the condensing sheet 4 a.

FIGS. 2A and 2 are a schematic plan view and a connection diagram of the inverter circuit substrate 7 and the cylindrical light source.
(B) and FIG. 3 (A) which is an inverter circuit diagram,
The connection relationship between the left and right ends of the plurality of cylindrical light sources 3 of the present invention will be described. In the present invention, the number of cylindrical light sources 3 is selected to be an even number,
A pair of cylindrical light sources are driven in pairs. Accordingly, an even number of transformers 8 are mounted on the inverter circuit board 7, and the inverter circuit board 7 is disposed on the left bottom surface of the housing 1 as in the conventional case, and the secondary windings of these transformers 8 are provided. The left side is a left socket group 12L of the cylindrical light source 3 shown in FIG.
And a socket group 1 for the other electrode of the cylindrical light source 3
The 2R side has a configuration in which a pair of cylindrical light sources 3 and 3 are connected in series by a connection wire 13 as shown in FIGS. 2A and 2B.

Therefore, the rectangular printed circuit board 10 arranged inside the conventional frame member 15 described with reference to FIG. 5B is omitted, and the space of the housing 1 in this portion is reduced to reduce the size. Can be achieved. Further, it is possible to omit the return cable 9 provided between the substrate 10 and the inverter circuit substrate 7, and it is possible to improve work efficiency at the time of assembly.

FIG. 3A is a circuit diagram of an inverter circuit using the lower circuit of the present invention, and FIG. 3B is a diagram explaining the driving principle of the present invention, and FIG. FIG. 4 is a circuit diagram of an inverter in a case where a pair of cylindrical light sources 3a and 3b are driven by alternating currents of opposite phases.

In FIG. 3A, cylindrical light sources 3a and 3b are connected to the secondary windings N ₂ and N ₂ ′ of a pair of transformers 8a and 8b of the transformer group 8, and a pair of transformers 8a Starting point of the secondary windings N ₂ and N ₂ ′ of the cylindrical light source 3
It is connected to one electrode (socket 12L) of a and 3b, 2 winding winding end point of N _2, N ₂ 'is dropped to the ground potential, the other electrode of the cylindrical light source 3a and 3b (sockets 12
The R) side is dropped to the ground potential.

A lower circuit is formed by using a pair of transformers 8a and 8b and a pair of switching transistors having the same characteristic, and the secondary winding N of the pair of transformers 8a and 8b is formed.
₂ , and N ₂ ′ are output with alternating-phase alternating current.

A pair of transformers 8a and 8b of the transformer group
, The primary windings N _1a and N _1b and N _1a ′ and N _1b ′ are wound in the same number of turns, and the primary windings N _1a and N _1b are connected in series.
The secondary windings N _1a ′ and N _1b ′ are also connected in series. Winding start point of the primary winding N _1b 'of the primary winding N _1a of winding end point and the second transformer 8b of the first transformer 8a is connected to the first collector of the transistor to Q ₁ for switching, winding start point of the primary winding N _1b of the first transformer 8a, and winding end point of the primary winding N _1a 'of the second transformer 8b is connected to the second collector of the transistor Q ₂ for switching ing. First and second switching transistors Q ₁
And the emitters of Q ₂ are commonly connected and dropped to ground potential E.

The series connection point of the pair of transformers 8a and 8b is
Commonly connected, anode of DC power supply V and bias resistor
R is connected to one end of the DC power supply V.
Connected and the other end of the bias resistor is for switching
Of the first transistor Q₁Connected to the base of this
One transistor Q₁Is the tertiary winding N_ThreeBeginning of winding
A second transistor Q connected to a point for switching_Two
Is the tertiary winding N _ThreeIs connected to the end point.
Further, the first and second transistors Q₁And Q_TwoCollection of
Are connected to each other through a capacitor C.

The operation of the lower circuit constituting the inverter of the present invention described above is shown in FIGS. 6 (A) and 6 (B) and FIG.
6A and 6B and FIG.
The description that overlaps with is omitted, and only different operations will be described below.

The winding end point of the primary winding N _1a of a pair of transformers 8a and 8b in the inverter circuit shown in FIG. 3 (A) and 1
The winding start point of the secondary winding N _1b ′ is connected to the collector of the first transistor Q ₁ , and the winding start point of the primary winding N _1b of the pair of transformers 8 a and 8 b is connected to the primary winding N _{1 a} ′. plus winding end point to a second pair of cylindrical light sources 3a and 3b as shown in the principle diagram shown in FIG. 3 (B) by being connected to the collector of the transistor connected in series, the time T ₁ in the cylindrical light source 3a ( an AC voltage of +), minus the cylindrical light source 3b in the forward direction (- AC voltage) is applied to the reverse direction, a minus (the time T ₂ in the cylindrical light source 3a - AC voltage) to the forward direction, the cylindrical light source A positive (+) AC voltage is applied to 3b in the backward direction.

That is, in the circuit diagram of FIG.
And the second transistor Q₁And Q _TwoAre in-phase transformers.
On and off are controlled alternately according to the same principle as that of the switch.
Now, the first transistor Q₁Is the bias current I_ThreeBy
If it is turned on and turned on, the second transistor Q_TwoIs
Is turned off and the primary winding N of the transformer 8a is turned off._1a, N_1bExchange
Current I flowing through a point_FiveIs the primary winding N_1aAnd the current I₇Becomes

Similarly, primary windings N _1a ′, N 1 of transformer 8 b
_The current I ₆ flowing at the intersection of the primary winding N _1b ′
₁₀ and becomes the collector current I ₇ + I ₁₀ a first collector of the transistor Q ₁ at the same time - via a common emitter potential E
To form a voltage supply closed circuit of the DC power supply V.

[0048] If the second transistor Q ₂ is "on" is the first of the transistor Q ₁ is in the "off" transformer 8a
The primary winding N _1a, current I ₅ which is supplied to the intersection of N _1b 1
Made a current I ₈ with winding N _1b, the primary winding N _1a of the transformer 8b ', N _1b' current I ₆ to be supplied to the intersection of the made the current I ₉ with the primary winding N _1a ', The current I ₈ + I ₉ becomes a collector current and is supplied to the collector of the second transistor Q ₂ to form a power supply closed circuit via the collector-emitter and the ground potential E, and the secondary winding N ₂ of the transformers 8a and 8b And N ₂ ′, a pair of cylindrical light sources 3a, 3a as shown in FIG.
The alternating voltages having opposite phases are applied to b and lighting is performed.

Using the inverter circuit shown in FIG. 3A, 12 cylindrical light sources having a screen size of 54 cm are arranged side by side, and when a tube current of 3.5 mA is supplied to light the lamp, the power consumption is the conventional type. In both cases, the brightness unevenness on the illuminated surface was almost unchanged at 44 W as compared with the conventional type (FIG. 6A), and it was found that there was no change due to the circuit change.

According to the present invention, the socket 12R on the right side of the housing 1 is simply connected to the pair of cylindrical light sources in series with the control wire 13, so that the substrate 10 and the return cable 9 can be omitted, and the substrate 10 The mounting space required 13 mm in the conventional case having the above-described configuration, but is 6 mm in the present invention, so that the frame portion of the frame member 15 of the case 1 can be reduced.

In the above configuration, the backlight device for liquid crystal has been described. However, the present invention is also applicable to a method of lighting a backlight device for public notice such as a subway.

[0052]

According to the backlight device and the method of lighting the backlight device of the present invention, the space of the return substrate mounting portion is reduced by connecting the ends of the cylindrical light sources and eliminating the return substrate and the return cable. This makes it possible to reduce the size of the frame of the housing.
Further, by removing the return board and the return cable, it is possible to reduce member costs and man-hours, and to achieve effects such as omitting the step of routing the return cable.

[Brief description of the drawings]

FIG. 1 is a plan view and a side sectional view showing a configuration of a backlight device of the present invention.

FIG. 2 is a schematic plan view and connection diagram of a cylindrical light source and a transformer of the backlight device of the present invention.

FIG. 3 is an inverter circuit diagram and a principle explanatory diagram of the backlight device of the present invention.

FIG. 4 is an operation waveform diagram of the inverter circuit of the present invention.

FIG. 5 is a plan view and a side sectional view showing a configuration of a conventional backlight device.

FIG. 6 is a schematic plan view and a connection diagram of a cylindrical light source and a transformer of a conventional backlight device.

FIG. 7 is a diagram illustrating an inverter circuit and a principle of a conventional backlight device.

[Explanation of symbols]

1 ‥‥ housing, 2 ‥‥ reflector, 3 ‥‥ cylindrical light source, 5L, 5
R support, 6 backlight device, 7 inverter circuit board, 8 (8a, 8b, 8c) transformer, 9 return cable, 10 board, 15
Frame members

Claims (2)

[Claims] 1. A backlight device comprising a reflector and an even number of cylindrical light sources disposed in a flat housing having an opening on an upper surface, and a light transmission / diffusion plate disposed in the opening. A backlight device characterized in that one of the paired cylindrical light sources is connected to inverter means capable of applying an alternating-phase AC voltage, and the other electrode is commonly connected. 2. A lighting method for a backlight device in which an even number of cylindrical light sources are provided in a housing, wherein at least two cylindrical light sources are paired and one of the electrodes has an opposite-phase AC voltage. , And the two cylindrical light sources of the pair are connected in series with each other.