JPH095705A - Back light driving method and inverter circuit in liquid crystal display device - Google Patents

Abstract

PURPOSE: To provide a back light driving method and a inverter circuit of a liquid crystal display device capable of performing the display of high quality at low cost. CONSTITUTION: In a liquid crystal display device provided with a transmission type liquid crystal display panel 24, a back light 25 lighting the panel from the back part of the panel 24, an inverter circuit 26 AC driving the back light, liquid crystal driving circuits 22, 23 driving liquid crystal by generating liquid crystal driving pulses corresponding to graduation data and a display control circuit 19 supplying the graduation data and synchronizing signals to liquid crystal the driving circuits 22, 23, the liquid crystal driving circuits 22, 23 and the inverter circuit 26 are made to be driven by signals synchronized with each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dimming device in a liquid crystal display device, a backlight driving method and an inverter circuit, and in particular, a switching regulator controller is used to reduce image quality due to interference between an image and a backlight. The present invention relates to an inverter circuit capable of preventing the above.

[0002]

2. Description of the Related Art Conventionally, as a backlight in a transmissive liquid crystal display device, an inverter circuit is used to convert a direct current voltage such as 12 V into an alternating current voltage of 600 V and 42 to 43 kHz to light a cathode tube (fluorescent tube). There are things I tried to let you do.

As a backlight driving inverter circuit of a conventional liquid crystal display device, there is a circuit as shown in FIG. 5, for example. The inverter circuit of FIG. 5 has a transistor Tr1 whose emitter is commonly connected to the primary coil side of the transformer T.
A current switch circuit composed of Tr2 is provided, and a direct current voltage Vin is input via the choke coil L, and the current switch circuit is oscillated to output a high-voltage AC waveform to the secondary coil side of the transformer T. ing. In the inverter circuit of FIG. 5, the oscillation frequency is determined by the capacitance ratio between the primary side capacitor C1 and the secondary side capacitor C2 of the transformer T, and the magnetic flux of the transformer repeats fluctuations from one saturation value to the other saturation value. Thus, the transistors Tr1 and Tr2 are alternately turned on and off to generate an AC voltage on the secondary coil side and the fluorescent tube BL is turned on.

[0004]

In the inverter circuit of FIG. 5, the frequency is determined by the capacitance ratio between the primary side capacitor C1 and the secondary side capacitor C2, so that the frequency varies due to the variation of the parts (capacitors). There was a problem. In addition, since the frequency of the conventional inverter circuit is set independently of the video signal of the liquid crystal display device, there is a problem that screen flicker or noise occurs due to interference between the video and the light of the backlight.

In the above case, ITO (Indiun Tin Oxide)
It is possible to use a sheet to reduce flickering and noise on the screen, but using an ITO sheet will reduce the amount of light transmitted through the liquid crystal, and will also attach the sheet and wire connection work to drop the potential of this sheet to ground. It became clear that there is a problem in that the number of working steps will increase and the cost of the product will increase.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a backlight driving technique for a liquid crystal display device capable of high-quality display at low cost. is there.

[0007]

In order to achieve the above object, the present invention provides a transmissive liquid crystal display panel, a backlight means for illuminating from the back of the liquid crystal display panel, and an inverter for AC driving the backlight means. A liquid crystal including a circuit, a liquid crystal drive circuit that drives a liquid crystal by creating a liquid crystal drive pulse according to grayscale data, and a display control circuit that supplies grayscale data and a synchronization signal to the liquid crystal drive circuit. In the display device, the liquid crystal drive circuit and the inverter circuit are driven by signals synchronized with each other (claim 1).

Further, according to the present invention, a transmissive liquid crystal display panel, a backlight means for illuminating from the back of the liquid crystal display panel, an inverter circuit for AC driving the backlight means, and a liquid crystal drive according to grayscale data. In a liquid crystal display device comprising a liquid crystal drive circuit for generating a pulse to drive a liquid crystal and a display control circuit for supplying gradation data and a synchronizing signal to the liquid crystal drive circuit means, the inverter circuit is a transformer. And a pair of switching transistors connected between the terminals of the primary coil of the transformer,
A switching circuit with a built-in oscillator circuit and an output terminal connected to the base of the switching transistor.
A pulse signal having a frequency that is an integral multiple of the synchronization signal is input from the display control circuit to the oscillation signal output terminal of the switching regulator controller, and the liquid crystal drive circuit and the inverter circuit are provided. It is configured to be driven by signals synchronized with each other (claim 2).

Further, the switching regulator controller has a terminal for connecting a resistor and a capacitor for determining the oscillation frequency of the internal oscillation circuit, and the terminal selectively connects the resistor and the capacitor by a switching circuit. A capacitor may be connectable (claim 3).

[0010]

According to the invention of claim 1, since the backlight is driven in synchronization with the liquid crystal display panel, interference between the image and the light of the backlight is prevented, and the occurrence of flickering and noise on the screen can be suppressed. it can.

According to the second aspect of the invention, a general-purpose switching regulator controller is used, and a pulse synchronized with the synchronizing signal of the liquid crystal display control circuit is simply input to the oscillation output terminal of the switching regulator controller. It is possible to realize an inverter circuit that drives the backlight in synchronization with the liquid crystal display panel.

According to the third aspect of the invention, it is possible to select a switching operation according to an external synchronization signal and a switching operation according to an oscillation signal from an oscillation circuit built in the switching regulator controller. , The flexibility of the system can be improved.

[0013]

EXAMPLES The present invention will be specifically described below based on examples. FIG. 1 shows a configuration of a liquid crystal television 11 as an example of a system to which the liquid crystal display device of the present invention is applied.

The liquid crystal television 11 shown in FIG. 1 includes an antenna 12, a tuner 13, a receiving circuit 14, a synchronizing circuit 15, and an A.
/ D converter 16, gradation control circuit 17, controller 1
9, a display control system including an interface circuit 20, a liquid crystal module 21 including a signal side drive circuit 22, a scanning side drive circuit 23, a liquid crystal display panel 24, a backlight 25 such as a fluorescent tube, and an AC drive for the same. And a dimming system including an inverter circuit 26.

The antenna 12 receives the radio wave received by the tuner 13.
The tuner 13 selects a designated channel in accordance with the tuning control signal TC input from the controller 19, converts the reception radio wave supplied from the antenna 12 into an intermediate frequency signal, and outputs the intermediate frequency signal to the reception circuit 14.

The receiving circuit 14 is composed of an intermediate frequency amplifying circuit, a video detecting circuit, a video amplifying circuit, a chroma circuit and the like. The intermediate frequency signal inputted from the tuner 13 is subjected to video detection by the video detecting circuit to perform color detection. The video signal is taken out, the audio signal is taken out from this color video signal and output to an audio circuit (not shown), and the video amplifier circuit amplifies the color video signal and passes it to the chroma circuit. At the chroma circuit, the received color video signal is received. To R,
The G, B (red, green, blue) color image signals are separated and output to the A / D converter 16.

The synchronizing circuit 15 receives the horizontal synchronizing signal Ssync and the vertical synchronizing signal Vsync from the received color video signals.
Is output to the controller 19. The A / D converter 16 includes a sampling circuit, a comparator circuit, an encoder circuit, and the like, which are not shown. Functionally, analog signals of R, G and B are sampled and compared with a reference voltage by a comparator to perform A / D conversion (R
After equally dividing in the range of HH to RLL), the encoder circuit converts the data into, for example, 5-bit digital display data.

The gradation control circuit 17 creates a gradation control clock CKCB having a desired timing pattern, and outputs the R, G, and B 5-bit display data input from the A / D converter 16 to the floor. The tone data is converted and supplied to the signal side drive circuit 22 of the liquid crystal module 21 to drive the liquid crystal cell.

The controller 19 is a CPU (Central Pr
, which controls the operation of the liquid crystal television 11 as a whole. For example, a horizontal synchronizing signal (H
sync) and the vertical sync signal (Vsync) to display an image on the liquid crystal display panel 24, or the sync signal CSY in the system based on the horizontal sync signal (Hsync).
A by forming NC or generating a sampling clock.
The signal is supplied to the / D converter 16 or a control signal (pulse) for data conversion from a clock or display data to gradation data is supplied to the gradation control circuit 17.

The interface circuit 20 supplies the horizontal synchronizing signal and the vertical synchronizing signal input from the controller 19 to the signal side driving circuit 22 and the scanning side driving circuit 23 of the liquid crystal module 21, respectively, to scan the liquid crystal panel 24. The signal lines are driven while sequentially scanning the lines to display an image on the liquid crystal display panel 24.

In this embodiment, a PLL (Phase / Phase) provided for forming a pulse in the controller 19 in synchronization with the synchronization signal CSYNC.
A pulse signal formed by a (locked loop) circuit is supplied to the inverter circuit 26 as a synchronization pulse INV to generate an AC voltage in synchronization with the horizontal synchronization signal to light the backlight 25. There is.

The liquid crystal module 21 includes the liquid crystal display panel 2
4, a signal side drive circuit 22 as a liquid crystal driver for driving the liquid crystal sealed therein, and a scanning side drive circuit 23.

The liquid crystal display panel 24 is not particularly limited, but here, for example, a TN liquid crystal is sealed between two transparent substrates made of glass plates, and signal electrodes and scanning electrodes made of ITO are provided on the opposing surfaces of each substrate. A simple matrix type liquid crystal display panel in which and are arranged in orthogonal directions is used.

The signal side drive circuit 22 includes a gradation control circuit 17
Data and gradation control clock CK output from
By having the number of pulses corresponding to the gradation level corresponding to the gradation data based on CB, the pulse width control (PW
M) generated liquid crystal drive pulse is formed, and the liquid crystal drive pulse is applied to each signal electrode of the liquid crystal display panel 24 at a predetermined timing to display a gray scale.

The scanning side drive circuit 23 generates a scanning signal and sequentially supplies it to a plurality of scanning electrodes of the liquid crystal display panel 24 to bring it into a selected state, and a predetermined voltage is applied to the liquid crystal at each pixel position intersecting the signal electrode. Is applied to drive the liquid crystal.

FIG. 2 is a circuit diagram showing a specific example of the inverter circuit 26 for driving the backlight 25.

The inverter circuit 26 of this embodiment is a switching regulator controller IC (broken line 3).
0) is used, and the output terminals (11) and (14) of this switching regulator controller 30 are used.
An emitter follower type switching transistor Tr whose collector is connected to each terminal of the primary coil L1 of the transformer and whose emitter is connected to a ground point via a resistor R4.
11, the bases of Tr12 are connected, and switching by the switching regulator controller 30
The transistors Tr11 and Tr12 are alternately turned on and off to flow an alternating current through the primary coil L1 of the transformer. The switching transistor T
Common emitter terminal of r11 and Tr12 and primary coil L1
A smoothing capacitor C3 is connected between the intermediate tap and the intermediate tap.

A choke coil L is connected between the center tap of the primary coil L1 and the DC voltage input terminal Vin of the inverter circuit, and the DC voltage input terminal Vin is connected.
Between the ripple resistance capacitor C0 and the ground point,
A resistor R0 and a Zener diode ZD are connected in series between the transformer side terminal of the choke coil L and the ground point. Then, the Zener voltage generated in the Zener diode ZD is applied to the voltage input terminal (15) of the switching regulator controller 30.

Further, between the cathode side connection node of the Zener diode ZD and the terminals (12) and (13) of the switching regulator controller 30, the base currents of the switching transistors Tr11 and Tr12 are limited. The resistors R5 and R6 are connected. Although not particularly limited in this embodiment, the switching transistors Tr11 and Tr1 are not particularly limited.
Resistors R7 and R8 are also connected between the two bases and emitters, respectively. The resistors R7 and R8 may be omitted, but by inserting them, the switching transistors Tr11 and Tr12 can be reliably turned off.

The switching regulator controller 30 is not particularly limited, but it includes an oscillation circuit 31, a flip-flop 32, and a NOR logic gate 3.
3a, 33b and push-pull type output transistor 3
4a and 34b, a primary side output abnormality detection amplifier 35,
Amplifier 36 for detecting secondary side output abnormality and these amplifiers 3
A PWM comparator 37 for inspecting the output pulse widths of 5 and 36, a reference voltage generating circuit 38 for generating a reference voltage such as 5V, and a potential of the non-inverting input terminal of the comparator 37 to the ground by a control signal from the outside. It is composed of an output control transistor 39 and the like for cutting off the output by dropping it.

In this embodiment, the terminal for outputting the oscillation signal of the oscillation circuit 31 to the outside has a frequency which is an integral multiple of the synchronization signal CSYNC supplied from the controller 19 (FIG. 1) of the liquid crystal display control device. By inputting the synchronizing pulse signal INV (see FIG. 3) having the switching transistors Tr11, Tr12, the signal C
Backlight 2 driven on and off in synchronization with SYNC
5 is configured to be turned on synchronously.

The switching regulator controller 30 normally sets the oscillation frequency of the internal oscillation circuit 31 by connecting a resistor to its terminal and a capacitor to the terminal (see FIG. 4) and flips the oscillation signal. And output transistor 34
Although the switching control of a and 34b is performed, in this embodiment, the above-mentioned terminal is connected to the ground point. As a result, the internal oscillator circuit 31 stops the oscillation operation, and its output terminal is in a high impedance state.

Further, in this embodiment, the synchronizing pulse signal INV (see FIG. 3) is inputted to the oscillation output terminal. As a result, the internal oscillation circuit 31
Instead of the oscillating signal, the synchronizing pulse signal INV input to the above terminal is supplied to the flip-flop 32 at the next stage. As a result, from the terminals (11) and (14) of the switching regulator controller 30, as shown in FIGS.
A signal which has a cycle twice that of NV and whose rising and falling timings are shifted by the pulse width of INV and whose high level periods do not overlap each other is output.

Therefore, the switching transistor Tr
11 and Tr12 are never turned on at the same time. The switching transistor Tr1 is output according to the output signal.
By driving 1 and Tr12, the synchronization signal CSYNC of the liquid crystal display control device is applied to the secondary coil of the transformer.
An alternating voltage as shown in FIG. 3 (E) that is synchronized with the above is generated and applied to the backlight 25.

In the embodiment of FIG. 2, the voltage of the secondary coil of the transformer is generally input to the terminals of the switching regulator controller 30, so that the amplifier 36 can detect an abnormality in the output of the secondary side. In this embodiment, the resistance R
1, R2 and R3 are connected as shown in the figure, and the reference voltage Vref (5V) generated by the reference voltage generation circuit 38 is divided and applied to the terminal so that the amplifier 36 is placed in the common mode range. There is. As a result, the amplifier 36
The output voltage is controlled so that the input voltage of the terminal becomes equal to the input voltage of the terminal.

In the above embodiment, the sync signal CSYNC (FIG. 3) is used as the sync pulse signal INV input from the controller 19 (FIG. 1) of the liquid crystal display controller to the terminal of the switching regulator controller 30.
Sync pulse signal having twice the frequency of A) (Fig. 3B)
However, the frequency of the synchronizing pulse signal INV is not limited to this, and as shown in FIGS. 3 (F) and 3 (G) having a frequency three times or four times that of the synchronizing signal CSYNC. The pulses INV ′ and INV ″ may be input.

Further, in the above embodiment, the terminal of the switching regulator controller 30 is connected to the ground point to stop the oscillating operation of the internal oscillation circuit 31, and instead, the terminal is connected to the controller of the liquid crystal display controller. Although the configuration in which the synchronizing pulse signal INV from 19 is input has been described, a switching circuit for selectively connecting the resistor RT as shown in FIG. 4 to the terminal and the capacitor CT to the terminal is provided. The operation of the switching regulator using the oscillation signal of the internal oscillating circuit 31 and the operation of the switching regulator by the synchronizing pulse INV from the outside may be selectively performed.

Then, in that case, when the switching regulator using the oscillation signal of the internal oscillator circuit 31 is operated, as shown in FIG. 4, by selectively connecting the capacitor CA to the terminal, as shown in FIG. Similar to the output waveform shown in (D), it is possible to prevent the output transistors 34a and 34b from being turned on at the same time by causing a time difference between the rising edge and the falling edge.

In the above embodiment, a switching regulator controller having a built-in primary-side output abnormality detection amplifier 35, secondary-side output abnormality detection amplifier 36, PWM comparator 37, etc. is used in addition to the oscillation circuit 31. Although the switching regulator controller to be used is not limited to the ones described above, the terminals for connecting resistors and capacitors for setting the oscillation frequency are built-in. Any type of switching regulator controller can be used as long as it has an output terminal and an oscillation output terminal.

Further, in the above-mentioned embodiment, although the one using the cathode tube as the backlight has been described, it can be applied to any illuminating device driven by an alternating current at a high voltage. Furthermore, in the above-mentioned embodiment, the case where the present invention is applied to the liquid crystal television has been described, but the present invention is not limited to this and can be applied to other liquid crystal display devices.

[0041]

According to the backlight driving method of the liquid crystal display device of the present invention, a transmissive liquid crystal display panel,
Backlight means for illuminating from the back of the liquid crystal display panel, an inverter circuit for AC driving the backlight means, a liquid crystal drive circuit for driving a liquid crystal by generating a liquid crystal drive pulse according to gradation data, and the liquid crystal In a liquid crystal display device including a display control circuit that supplies grayscale data and a synchronization signal to a drive circuit, the liquid crystal drive circuit and the inverter circuit are driven by signals synchronized with each other. Since the light is driven in synchronization with the liquid crystal display panel, there is an effect that interference between the image and the light of the backlight is prevented, and the occurrence of flickering and noise on the screen can be suppressed.

Further, according to the present invention, for example, as described in claim 2, a transmissive liquid crystal display panel, a backlight means for illuminating from the back of the liquid crystal display panel, and the backlight means are AC driven. An inverter circuit, a liquid crystal drive circuit that drives a liquid crystal by creating a liquid crystal drive pulse according to grayscale data, and a display control circuit that supplies grayscale data and a synchronization signal to the liquid crystal drive circuit means. In the provided liquid crystal display device, the inverter circuit includes a transformer, a pair of switching transistors connected between terminals of a primary coil of the transformer, an oscillation circuit, and an output terminal at a base of the switching transistor. Switching regulator connected to
A pulse signal having a frequency that is an integral multiple of the synchronization signal is input from the display control circuit to the oscillation signal output terminal of the switching regulator controller, and the liquid crystal drive circuit and the inverter circuit are synchronized with each other. Since it is configured to be driven by the generated signal, a general-purpose switching regulator controller is used, and the pulse synchronized with the synchronizing signal of the liquid crystal display control circuit is simply switched.
There is an effect that an inverter circuit that drives the backlight in synchronization with the liquid crystal display panel can be realized by simply inputting it to the oscillation output terminal of the controller.

Further, according to the present invention, for example, as described in claim 3, the switching regulator controller connects the resistor and the capacitor for determining the oscillation frequency of the internal oscillation circuit. Since the resistor and the capacitor can be selectively connected to the terminal by a switching circuit, the switching operation according to the external synchronizing signal and the oscillation circuit built in the switching regulator controller can be performed. Since it is possible to select the switching operation according to the oscillation signal of, there is an effect that the flexibility of the system can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of a suitable liquid crystal television to which the present invention is applied.

FIG. 2 is a block diagram of an inverter circuit according to the first embodiment of the present invention.

FIG. 3 is a waveform diagram showing an example of input / output signals of the inverter circuit of the first embodiment.

FIG. 4 is a block diagram for explaining an inverter circuit according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing an example of a conventional inverter circuit.

[Explanation of symbols]

 11 liquid crystal television 12 antenna 13 tuner 14 receiving circuit 15 synchronizing circuit 16 A / D converter 17 gradation control circuit 19 controller 20 interface circuit 21 liquid crystal module 22 signal side drive circuit 23 scanning side drive circuit 24 liquid crystal display panel 25 backlight device 26 inverter circuit 31 oscillator circuit 32 flip-flop 34a, 34b output transistor L1 transformer primary side coil Tr11, Tr12 switching transistor

Claims (3)

[Claims] 1. A transmissive liquid crystal display panel, a backlight means for illuminating from the back of the liquid crystal display panel, an inverter circuit for AC-driving the backlight means, and a liquid crystal drive pulse according to gradation data. In a liquid crystal display device including a liquid crystal drive circuit that drives liquid crystal by means of a liquid crystal display device, and a display control circuit that supplies grayscale data and synchronization signals to the liquid crystal drive circuit, A backlight driving method in a liquid crystal display device, characterized in that driving is performed by synchronized signals. 2. A transmissive liquid crystal display panel, a backlight means for illuminating from the back of the liquid crystal display panel, an inverter circuit for AC driving the backlight means, and a liquid crystal drive pulse according to gradation data. In a liquid crystal display device comprising a liquid crystal drive circuit for driving liquid crystal by means of a liquid crystal display device, and a display control circuit for supplying gradation data and synchronizing signals to the liquid crystal drive circuit means, the inverter circuit comprises a transformer and the transformer. A pair of switching transistors connected between the terminals of the primary side coil, and a switching regulator controller having a built-in oscillation circuit and an output terminal connected to the base of the switching transistor,
A pulse signal having a frequency that is an integral multiple of the synchronization signal is input from the display control circuit to the oscillation signal output terminal of the switching regulator controller, and the liquid crystal drive circuit and the inverter circuit are driven by signals synchronized with each other. A liquid crystal display device characterized in that it is configured as follows. 3. The switching regulator controller comprises terminals for connecting a resistor and a capacitor for determining an oscillation frequency of an internal oscillation circuit,
The liquid crystal display device according to claim 2, wherein the resistor and the capacitor are selectively connectable to the terminal by a switching circuit.