JPH07281148A - Planar fluorescent tube driving circuit and back light device provided with it - Google Patents

Abstract

PURPOSE:To always light and drive a planar fluorescent tube with uniform surface light emission. CONSTITUTION:This device is provided with a boosting transformer 12 to one end of the primary winding of which a source voltage is applied, and supplying a voltage between both ends of the secondary winding to the planar fluorescent tube 11 to light and drive it, an FET 13 as a switching element connected to the other end of the primary winding of the boosting transformer 12 and intermittently applying the source voltage to the primary winding of the boosting transformer and a switch part 22 successively inverting the polarity of the voltage supplied from the secondary winding wiring of the boosting transformer 12 to the planar fluorescent tube 11 synchronizing with the intermittent voltage application of the FET 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat fluorescent tube driving circuit for driving and controlling a flat fluorescent tube provided as a light source of a backlight on the back side of a liquid crystal display panel and the like, and a backlight device having the flat fluorescent tube.

[0002]

2. Description of the Related Art Recently, a flat fluorescent tube has been commercialized as a light source of a backlight for illuminating a liquid crystal display panel, which is a display portion of a liquid crystal television device, from its back side. This flat fluorescent tube has a thin plate-like structure, which makes it possible to further reduce the size of the display unit. It is more suitable as a light source for a backlight than a fluorescent tube, and it is expected that the number of liquid crystal televisions and other electronic devices that employ this flat fluorescent tube as a light source for a backlight will increase.

FIG. 4 shows a general circuit configuration for driving a flat fluorescent tube used as a light source of this backlight, and 11 is a flat fluorescent tube to be driven. A pair of electrodes 11a and 11b formed on one side of the flat fluorescent tube 11 are connected to both ends of the secondary winding of the step-up transformer 12. The backlight drive voltage V is applied to one end of the step-up transformer 12 on the primary side.
cc is applied, and the drain terminal of the P-channel FET 13 is connected to the other end. The FET 13 operates as a switching element by inputting a switching pulse from the timing controller 14 which is turned on at a sufficiently short constant period to the gate terminal, with its source terminal grounded.
The timing controller 14 adjusts the phase and pulse width based on the pulsed horizontal synchronizing signal HD used for display on a liquid crystal display panel (not shown) to form a switching pulse, and supplies this to the gate terminal of the FET 13.

In the above configuration, when the timing controller 14 supplies the switching pulse created from the horizontal synchronizing signal HD to the gate terminal of the FET 13, the FET 13 is turned on while the switching pulse is at "H" level. The backlight drive voltage Vcc is applied to the primary winding of the step-up transformer 12. Therefore, 2 of the step-up transformer 12
Normally, 1300 [V] is boosted between the electrodes 11a and 11b of the flat fluorescent tube 11 connected to the secondary winding according to the winding ratio between the primary winding and the secondary winding of the step-up transformer 12. A voltage value of about a certain level is applied, and glow discharge is generated in the flat fluorescent tube 11 to cause surface emission.

Since the flat fluorescent tube 11 has an afterglow characteristic, until the switching pulse next becomes "H" level,
The luminous state is maintained while gradually decreasing the brightness. By performing the lighting drive intermittently in this way, as a result, it is possible to perform constant lighting, and it is possible to realize stable driving.

The horizontal synchronizing signal HD is used as a reference for generating the switching pulse and is synchronized therewith in order to prevent the driving noise of the flat fluorescent tube 11 from affecting the display screen. In a liquid crystal television used in a mobile phone, the horizontal synchronization signal HD may change due to missing or superimposition of noise depending on the reception state of television radio waves. Therefore, here, the horizontal synchronization signal HD is generated by the drive circuit that drives and displays the liquid crystal display panel. The horizontal synchronizing signal HD is used.

[0007]

In the above-mentioned drive circuit for a flat fluorescent tube, depending on the state of the flat fluorescent tube 11, the flat fluorescent tube is affected by factors such as ambient temperature, variations in the step-up transformer 12, and the shapes of the electrodes 11a and 11b. Part of the vicinity of the electrode on the high voltage side of 11 does not emit light, and uniform surface emission may not be obtained. This is particularly noticeable when the flat fluorescent tube 11 is used as a backlight of a liquid crystal television when the flat fluorescent tube 11 is mounted between the flat fluorescent tube shield case, the liquid crystal display panel and the liquid crystal display panel shield case. Appear in.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a flat fluorescent tube drive circuit and a flat fluorescent tube which can always be driven for lighting with uniform surface emission. It is to provide a backlight device.

[0009]

That is, according to the present invention, a power source voltage is applied to one end of a primary side winding, and a voltage between both ends of the secondary side winding is supplied to a flat fluorescent tube to drive lighting. A transformer, switching means connected to the other end of the primary winding of the step-up transformer, for intermittently supplying the power supply voltage to the primary side winding of the step-up transformer, and a secondary side winding of the step-up transformer. Inverting means for sequentially inverting the polarity of the voltage supplied to the flat fluorescent tube in synchronism with the intermittent energization of the switching means.

[0010]

According to the above-described structure, the position of the dark portion that does not emit light is moved or disappears every time the polarity of the voltage supplied to the flat fluorescent tube is reversed, and the generation of the dark portion is halved. The surface emission is made uniform in the entire fluorescent tube.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a drive circuit for lighting and driving a flat fluorescent tube as a backlight of a display section of a liquid crystal television device or the like. Since it is basically the same as that shown in FIG. Are denoted by the same reference numerals and description thereof will be omitted.

The horizontal synchronizing signal HD supplied to the timing controller 14 is also supplied to the inverted signal generator 21. The inverted signal generator 21 is composed of, for example, a D flip-flop (hereinafter abbreviated as "F / F") 21a as shown in FIG.

In this case, the horizontal synchronizing signal HD is F / F21a.
Is supplied as the operation clock of the above, and its inverted output is fed back as a delay input, so that the non-inverted output alternately inverts "H" level and "L" level in response to the pulse input of the horizontal synchronizing signal HD. It is used as an inverted signal to be output.

However, the inversion signal output from the inversion signal generator 21 is the step-up transformer 12 and the electrode 11 of the flat fluorescent tube 11.
It is provided to a switch unit 22 provided between a and 11b.
The switch unit 22 is composed of, for example, two sets of interlocked c-contacts, and alternately switches the polarity of the voltage from the secondary winding of the step-up transformer 12 in response to the inverted signal from the inverted signal generator 21. Is applied between the electrodes 11a and 11b.

In the above configuration, when the horizontal synchronizing signal HD is applied as shown in FIG. 3A, the inverted signal generating section 21 synchronizes with the rising edge of the pulse of the horizontal synchronizing signal HD. An inverted signal as shown in FIG. 3B is generated and output to the switch unit 22.

On the other hand, in the timing controller 14, the phase and pulse width of the pulse of the horizontal synchronizing signal HD are adjusted and processed so that it is slightly delayed from the horizontal synchronizing signal HD.
A signal as shown in (3) is generated and is applied to the FET 13 as a drive signal. The FET 13 is intermittently turned on by this drive signal, and the backlight drive voltage Vcc is applied to the primary winding of the step-up transformer 12, so that the boosting required for driving the flat fluorescent tube 11 from the secondary winding is performed. The boosted voltage is applied between the electrodes 11a and 11b of the flat fluorescent tube 11 via the switch section 22.

However, for example, when the inverted signal from the inverted signal generator 21 is at "H" level, the switch section 22 has one end on the high voltage side of the secondary winding of the step-up transformer 12 as the electrode 11a and the other end as the electrode. 11b, if the inverted signal is at "L" level, the same end is connected to the electrode 11b, the other end is connected to the electrode 11a, and so on. The voltage from the secondary winding is alternately inverted in polarity and applied between the electrodes 11a and 11b. Therefore, the drive voltage is alternately applied to the electrodes 11a and 11b of the flat fluorescent tube 11 for each pulse of the horizontal synchronizing signal HD as shown in FIGS.

Thus, the electrodes 11a and 11b of the flat fluorescent tube 11 are
By alternately inverting the polarity of the drive voltage applied to
Even if a dark portion that does not emit light occurs in a part of the flat fluorescent tube 11 due to variations in the temperature of the flat fluorescent tube 11, variations in the step-up transformer 12, the shapes of the electrodes 11a and 11b, etc., the dark portion is always on the high potential side electrode. Since it has a characteristic that it is generated in the vicinity, the position is alternately moved for each pulse of the horizontal synchronizing signal HD, or it occurs only when a high potential is applied to one of the electrodes 11a and 11b. The brightness of the entire fluorescent tube 11 is made uniform. This is, for example, the horizontal synchronization signal HD
If the frequency is about 15 kHz, the movement of the dark portion or the dark portion in the state where a high potential is applied to one of the two electrodes does not occur at half the frequency, and the flicker does not occur. Is.

[0019]

As described above, according to the present invention, each time the polarity of the voltage supplied to the flat fluorescent tube is reversed, the position of the dark portion that does not emit light is moved or disappeared, and the generation of the dark portion is halved. Therefore, it is possible to provide a flat fluorescent tube driving circuit capable of uniformizing the surface emission of the entire flat fluorescent tube and driving the lighting, and a backlight device including the flat fluorescent tube.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit configuration according to an embodiment of the present invention.

FIG. 2 is a diagram showing the internal configuration of the inverted signal generator of FIG.

FIG. 3 is a diagram showing each signal waveform according to the embodiment.

FIG. 4 is a diagram showing a configuration of a drive circuit for a general flat fluorescent tube.

[Explanation of symbols]

11 ... Flat fluorescent tube, 11a, 11b ... Electrode, 12 ... Step-up transformer, 13 ... FET, 14 ... Timing controller, 21 ... Inversion signal generating section, 21a ... F / F, 22 ... Switch section.

Claims (2)

[Claims] 1. A step-up transformer in which a power supply voltage is applied to one end of a primary side winding and a flat fluorescent tube is supplied with a voltage between both ends of the secondary side winding to drive lighting, and a primary side of the step-up transformer. Switching means which is connected to the other end of the winding and intermittently supplies the power supply voltage to the primary winding of the step-up transformer, and voltage supplied from the secondary winding of the step-up transformer to the flat fluorescent tube. And a reversing means for sequentially reversing the polarity of the switching means in synchronism with the intermittent energization of the switching means. 2. A flat fluorescent tube for illuminating a liquid crystal display panel, and a power supply voltage is applied to one end of a primary winding, and the flat fluorescent tube is supplied with a voltage between both ends of a secondary winding to illuminate. A step-up transformer to be driven, a switching means connected to the other end of the primary side winding of the step-up transformer, for intermittently energizing the primary side winding of the step-up transformer with the power supply voltage, and a secondary side of the step-up transformer. A backlight device having a flat fluorescent tube, comprising: a reversing means for sequentially reversing a polarity of a voltage supplied from a winding to the flat fluorescent tube in synchronism with intermittent energization of the switching means.