JPH06118902A - Device using flat fluorescent tube and method of driving flat fluorescent tube - Google Patents

Abstract

(57) [Abstract] [Purpose] The circuit configuration does not require a blocking member such as a shield and is not affected by noise generated by a flat fluorescent tube used as a light source of a backlight. A timing of a first edge portion at which a pulse signal P2 for intermittently driving a flat fluorescent tube 20 of a backlight rises or falls is within a front porch during a horizontal blanking period of a demodulated video signal. Therefore, a pulse position adjusting circuit 21 for performing timing control is provided so that the timing of the second edge portion where the pulse signal P2 falls or rises is adjusted within the horizontal synchronizing pulse during the horizontal retrace line period. .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus using a flat fluorescent tube and a method for driving the flat fluorescent tube.

[0002]

2. Description of the Related Art Conventionally, a lot of liquid crystal televisions having a liquid crystal display panel having a backlight as a display portion have been commercialized, and are widely used especially for portable and in-vehicle devices because of their small size and light power consumption. It is popular. In this type of liquid crystal television device, it is generally a cylindrical fluorescent tube that is used as a light source of a backlight, and a plurality of fluorescent tubes are used to directly arrange the liquid crystal display panel on the back surface, or the rear surface of the liquid crystal display panel. It is arranged on both sides of the liquid crystal display panel, and the structure is such that the entire back surface of the liquid crystal display panel is illuminated by using a reflection plate.

However, in a liquid crystal television set that is required to be downsized, the fluorescent tube must be arranged near the back side of the liquid crystal display panel. Therefore, no matter how the cylindrical fluorescent tube is arranged, However, it was difficult to irradiate the entire surface of the liquid crystal display panel with uniform brightness.

Recently, however, a flat fluorescent tube (hereinafter abbreviated as "flat fluorescent tube") has been developed, and a liquid crystal television device using this flat fluorescent tube as a light source of a backlight has been commercialized. This flat fluorescent tube can illuminate the entire surface of the liquid crystal display panel with uniform brightness because of its surface emission, and can be made thinner than a cylindrical fluorescent tube, so that downsizing is required. Suitable for LCD TV devices.

FIG. 5 partially shows a circuit configuration of a liquid crystal television device using a flat fluorescent tube as a light source of a backlight. In the figure, the radio wave received by the antenna 11 is converted into an intermediate frequency signal by the tuner 12, is selected, and is sent to the video detection circuit 13. The video detection circuit 13 obtains a video signal from the transmitted intermediate frequency signal and outputs this video signal to the chroma signal processing circuit 14 and the sync separation circuit 16. The chroma signal processing circuit 14 reproduces the R, G, B chroma signals from the video signal to display the display section 15 composed of a liquid crystal display panel.
To display and display.

On the other hand, the sync separation circuit 16 extracts and separates the sync signal c-sync from the video signal, and outputs the obtained sync signal c-sync to the sync detection circuit 17.
The synchronous detection circuit 17 obtains an HD signal (horizontal synchronization signal) and a VD signal (vertical synchronization signal) by applying a PLL to the synchronization signal c-sync, and sends the obtained HD signal to the pulse width adjustment circuit 18. The pulse width adjusting circuit 18 is composed of, for example, a monostable multivibrator, and outputs a switching pulse P2 adjusted to an appropriate pulse width so that the flat fluorescent tube 20 emits light with a predetermined brightness based on the rising or falling of the HD signal. Generate and drive backlight (BL) drive circuit 19
Supply to. The backlight drive circuit 19 intermittently drives the flat fluorescent tube 20 in response to the switching pulse P2.

FIG. 6 shows an example of the structure of the backlight drive circuit 19, and here it is assumed that it is composed of an N-channel FET 19a and a transformer transformer 19b. That is, the switching pulse P2 from the pulse width adjusting circuit 18
Is supplied to the gate terminal of the FET 19a, the source terminal of the FET 19a is grounded, and the drain terminal is connected to one end of the primary winding of the transformer transformer 19b. And the transformer transformer 19b
For example, a voltage of 9 V is applied to the other end of the primary winding of the transformer, and both ends of the secondary winding of the transformer transformer 19b are connected to both electrodes of the flat fluorescent tube 20.

The ratio of the primary winding to the secondary winding of the transformer transformer 19b is, for example, 1:37, and while the switching pulse P2 is input to the FET 19a and is turned on, the flat fluorescent tube 20 has about 330V. Is applied, and a voltage of about 500 to 1000 V is applied at the peak-to-peak value of the actual voltage to drive the lighting. Also, F
Even when the switching pulse P2 is not input to the ET 19a and is turned off, the flat fluorescent tube 20 is turned on due to the afterglow phenomenon while gradually decreasing the brightness.

However, before the emission brightness of the flat fluorescent tube 20 is completely lowered, the switching pulse P2 is input to the FET 19a again to turn it on, and the flat fluorescent tube 20 is driven to light. By performing such intermittent driving, stable driving with low power consumption is possible.

The flat fluorescent tube 20 has a pair of rectangular parallel line opposite sides as electrodes, and discharges and emits light between them, and each electrode has a long structure. Therefore, when a low applied voltage is applied between both electrodes, discharge and light emission are performed only for a part of each electrode, and uniform light emission cannot be obtained over the entire plane. Therefore, as mentioned above, a sufficiently high pulse-like voltage is applied to the flat fluorescent tube 20 by controlling the switching pulse P2.

[0011]

In a liquid crystal television device using the flat fluorescent tube configured as described above as a backlight, the voltage applied to the flat fluorescent tube 20 is a high voltage and has a pulsed waveform. Therefore, a steep rise or fall portion of the voltage is likely to become noise, and the noise may interfere with other circuits to adversely affect the image.

It is conceivable, however, to strengthen the shield between the flat fluorescent tube and the circuit to prevent the noise from interfering with the circuit. However, such a coping method excludes reduction in size and weight of the device. Therefore, it cannot be said that the method is suitable for a liquid crystal television device that places importance on portability. Further, there has been no liquid crystal television device having a circuit configuration in which noise particularly generated in the flat fluorescent tube is taken into consideration.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a flat fluorescent tube used as a light source of a backlight without requiring a blocking member such as a shield. An object of the present invention is to provide an apparatus using a flat fluorescent tube and a method for driving the flat fluorescent tube, such as a liquid crystal television set having a circuit configuration that is not affected by generated noise.

[0014]

That is, according to the present invention, the timing of the first edge portion at which the pulse signal rises or falls for intermittently driving the flat fluorescent tube used as the light source of the backlight is changed. , The timing of the second edge part, which is in the front porch during the horizontal blanking period of the video signal and falls or rises of the pulse signal, is adjusted within the horizontal synchronizing pulse during the horizontal blanking period. A pulse position adjusting means for performing timing control is provided in the device, and the pulse signal for driving the flat fluorescent tube is adjusted to a position at which the video signal is not affected by noise. Does not have any adverse effect on the video signal, such as the shield between the flat fluorescent tube and the television circuit. The cornerstone.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a liquid crystal television device using a flat fluorescent tube as a light source of a backlight will be described with reference to the drawings. FIG. 1 partially shows the circuit configuration, and since the basic configuration is the same as that shown in FIG. 5, the same portions are denoted by the same reference numerals and the description thereof will be omitted.

The HD signal output from the synchronous detection circuit 17 is sent to the pulse position adjusting circuit 21. The pulse position adjusting circuit 21 is composed of, for example, a monostable multivibrator and adjusts the position of the pulse in the signal by delaying the HD signal sent from the synchronous detection circuit 17 at an appropriate timing. The pulse signal P1 is supplied to the pulse width adjusting circuit 18. The pulse width adjusting circuit 18 uses a backlight (BL) driving circuit 19 to output a switching pulse P2 adjusted to have an appropriate pulse width so that the flat fluorescent tube 20 emits light with a predetermined brightness based on, for example, the fall of the pulse signal P1. Supply to.

FIG. 3 exemplifies a case where the pulse position adjusting circuit 21 and the pulse width adjusting circuit 18 are each configured by using a monostable multivibrator (hereinafter abbreviated as "monomulti"). In the figure, the pulse position adjustment circuit
21 is composed of two monomulti MM1 and MM2, and the pulse width adjusting circuit 18 is composed of one monomulti MM3.

Assuming that the time constants of the monomulti MM1 and MM2 are ta and tb and the time constant of the monomulti MM3 is tON, the monomulti MM1 is first sent from the synchronous detection circuit 17 as shown in FIG. A falling edge of the HD signal is used as a trigger to generate a pulse signal which is at a high level for a time ta shown in FIG. 3B and is output to the monomulti MM2. The mono-multi MM2 generates a pulse signal P1 which becomes a high level for the time tb shown in FIG. 3 (3) by using the fall of the pulse signal as a trigger, and outputs this to the mono-multi MM3 of the pulse width adjusting circuit 18. Then, the mono-multi MM3 of the pulse width adjusting circuit 18 receives the pulse signal P1.
The pulse signal P2 which is at the high level for the time tON as shown in FIG. Next, the operation of the entire embodiment will be described with reference to FIG.

FIG. 4 (1) shows a video signal obtained by the video detection circuit 13, which has a timing t0 in the signal waveform.
From the timing t1 to the timing t, the period indicated by a from the timing t1 to the timing t1 is the front porch during the horizontal retrace line period.
The period indicated by b up to 2 is a horizontal synchronizing pulse in the horizontal retrace period, the period indicated by c from timing t2 to timing t3 is the back porch during the horizontal retrace period, from timing t3 to timing t4 (= The period indicated by d up to the timing t0) becomes the actual video signal.

The sync separation circuit 16 selects one of the video signals shown in FIG.
The sync signal c-sync as shown in (2) is extracted and separated, and output to the sync detection circuit 17. The synchronous detection circuit 17 generates an HD signal which rises in synchronization with the end timing t2 of the horizontal synchronizing pulse as shown in FIG. 4C by the transmitted synchronizing signal c-sync to adjust the pulse position. It is sent to the circuit 21.

The pulse position adjusting circuit 21 appropriately delays the HD signal to generate a pulse signal P1 as shown in FIG. 4 (4), which is the first pulse signal P1.
As a condition of, the fall timing t5 is positioned within the front porch period a during the next horizontal blanking period. The pulse width adjusting circuit 18 has a switching pulse P that rises in synchronization with the falling timing t5 of the pulse signal P1 located within the front porch period a.
Generates 2.

As a second condition of the pulse signal P1, the timing t6 when the switching pulse P2 falls after the time t5 has elapsed from the timing t5 is surely included in the horizontal synchronizing pulse period b. . That is, the time width tON is variably set by the pulse width adjusting circuit 18 with a predetermined width in advance depending on the brightness of the flat fluorescent tube 20, the stability of lighting, the transmittance of the liquid crystal display panel forming the display unit 15, and the like. . The pulse position adjusting circuit 21 ensures that the timing t6 at which the switching pulse P2 falls falls within the horizontal synchronizing pulse period b regardless of whether the minimum value or the maximum value of the time width tON is set. Then, the position of the pulse signal P1 is adjusted. Summarizing the above, at each timing t0 to t6, t0 ≤ t5 <t1 (1) t1 <t6 <t2 (2), and the pulse position adjusting circuit 21 (1)
The position of the pulse signal P1 is adjusted so that the condition (2) is simultaneously satisfied.

The FET in the backlight drive circuit 19 is turned on / off based on the switching pulse P2 whose pulse position is adjusted as described above, and the voltage signal P3 having a waveform as shown in FIG. It is applied between both electrodes of 20. In the figure, even if noise occurs at the edge portion e at the timing t5, this portion is in the front porch as described above, so that it does not affect the display and does not affect the separation of the horizontal synchronizing pulse.

Further, even if noise is generated at the edge portion f at the timing t6, this portion is set so as not to reach the front and rear edges of the horizontal synchronizing pulse as described above. It does not affect the phase disturbance of the separation. The adjustment of the pulse position does not depend on the monostable multivibrator as in the above embodiment,
For example, a counter that counts clock signals may be used.

[0025]

As described above, according to the present invention, the timing of the first edge portion, which is the rise or fall of the pulse signal for intermittently driving the flat fluorescent tube used as the light source of the backlight, is set. , The timing of the second edge part, which is in the front porch during the horizontal blanking period of the video signal and falls or rises of the pulse signal, is adjusted within the horizontal synchronizing pulse during the horizontal blanking period. Since the pulse position adjusting means for performing the timing control is provided in the device, the timing of the pulse signal for driving the flat fluorescent tube is adjusted to the position where the noise is not exerted on the video signal, so that only a simple circuit is added. Therefore, it does not require a blocking member such as a shield and has no adverse effect on the video signal even if noise is generated. , It is possible to provide a driving device and method of flat fluorescent tubes using a very flat fluorescent tube such as a liquid crystal television apparatus suitable for portability.

[Brief description of drawings]

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

FIG. 2 is a diagram illustrating a specific configuration of a partial circuit of FIG.

FIG. 3 is a diagram showing each signal waveform of FIG.

FIG. 4 is a diagram showing each signal waveform of FIG. 1.

FIG. 5 is a block diagram partially showing a conventional television circuit.

FIG. 6 is a diagram showing a configuration of a backlight drive circuit and a flat fluorescent tube of FIG.

[Explanation of symbols]

11 ... Antenna, 12 ... Tuner, 13 ... Video detection circuit, 14 ...
Chroma signal processing circuit, 15 ... Display unit, 16 ... Sync separation circuit,
17 ... Synchronous detection circuit, 18 ... Pulse width adjustment circuit, 19 ... Backlight (BL) drive circuit, 20 ... Flat fluorescent tube, 21 ... Pulse position adjustment circuit.

Claims (6)

[Claims] 1. A liquid crystal display panel for displaying an image, a flat fluorescent tube provided on the back side of the liquid crystal display panel as a light source of a backlight, and a driving means for intermittently driving the flat fluorescent tube with pulse signals. The timing of the first edge portion where each pulse signal supplied to this drive means rises or falls is within the front porch during the horizontal retrace line period of the video signal,
Pulse position adjusting means for performing timing control so that the timing of the second edge portion at which the pulse signal falls or rises is adjusted within the horizontal synchronizing pulse during the horizontal retrace line period. Characteristic liquid crystal television device. 2. A flat fluorescent tube driving method for driving a flat fluorescent tube in synchronism with a video signal, the first edge portion being a rising or falling edge of a driving signal intermittently applied to the flat fluorescent tube. Is located on the front porch during the horizontal blanking period of the video signal, and the timing of the second edge portion at which the drive signal falls or rises is located within the horizontal synchronizing pulse during the horizontal blanking period. A method of driving a flat fluorescent tube, which is characterized by the above. 3. A flat fluorescent tube and a pulse having a leading edge which is supplied with a horizontal synchronizing signal separated from a video signal and which rises or falls in synchronization with the horizontal synchronizing signal within a front porch period of the video signal. It is provided with a first pulse generating means for generating and a second pulse generating means for generating a drive pulse for the flat fluorescent tube by using the pulse generated by the first pulse generating means as a switching pulse. Back light device. 4. The first pulse generating means generates the trailing edge or rising edge of the generated pulse such that the trailing edge is located within the horizontal blanking period of the video signal. Backlight device described. 5. The backlight device according to claim 3, wherein the first pulse generating means has means for adjusting a phase of the generated pulse. 6. The backlight device according to claim 3, wherein the first pulse generating means has means for adjusting the pulse width of the generated pulse.