KR101097611B1 - Backlight and Liquid Crystal Display device having the same - Google Patents

Abstract

Disclosed are a backlight for controlling a PWM using a digital method and a liquid crystal display including the same.

The backlight according to the present invention uses a transformer for generating a high-voltage AC voltage, a half-wave rectifier for converting the AC voltage to a constant voltage level, an analog-to-digital converter for converting the constant voltage to a digital signal, and using a specific signal. A counter for generating a timing signal in a predetermined operation sequence, a square wave generator for generating a square wave having a predetermined period using the digital signal and the timing signal, and a switch for turning on / off using the square wave.

Analog-to-Digital Converters, Counters

Description

Backlight and Liquid Crystal Display device having the same}

1 is a view showing a backlight of a conventional liquid crystal display device.

FIG. 2 is a diagram illustrating the PWM control unit of FIG. 1 in detail. FIG.

FIG. 3 is a diagram illustrating an output waveform of a comparator and a second reference voltage Vref2 waveform of FIG. 2.

4 is a view showing a backlight of the liquid crystal display according to the present invention.

5A and 5B illustrate square waves generated by the square wave generator of FIG. 4.

<Brief description of the main parts of the drawing>

101: lamp 110: power supply

111: Transformer 113: Inverter

116: half-wave rectifier 117: switch

118: analog-to-digital converter 119: counter

120: square wave generator

The present invention relates to a liquid crystal display device, and more particularly, to a backlight using a digital method and a liquid crystal display device having the same.

In general, a liquid crystal display (LCD) is used as a screen of a portable device such as a notebook, and a battery is used as a power source. Since the liquid crystal display itself does not generate light, it uses a backlight lamp to provide light required by the liquid crystal display, and a high voltage of several hundreds to thousands of V is required to drive the lamp. Therefore, the backlight driving unit as shown in FIG. 1 is used to convert the low DC power provided from the battery into a high voltage AC power and provide the same to the lamp.

1 is a view illustrating a backlight of a conventional liquid crystal display.

As shown in FIG. 1, the backlight converts the DC power supplied from the power supply unit 10 into a DC voltage of a predetermined level by a pulse width modulation (PWM) control method and outputs the DC / DC converter 12. And an inverter 13 which receives the DC voltage output from the DC / DC converter unit 12 and converts the DC voltage into a high voltage AC voltage and outputs the AC voltage of the high voltage output from the inverter 13 as a stable power source. It is composed of a stable capacitor (C) to make and provide to the lamp (1).

The DC / DC converter unit 12 level converts the DC power provided from the power supply unit 10 through pulse width modulation (PWM) control so that a constant DC voltage is always provided to the input of the inverter 13. The DC / DC converter unit 12 includes a PWM control unit 6 for controlling the magnitude of the waveform of the high voltage AC voltage generated by the inverter 13.

As shown in FIG. 2, the PWM control unit 6 includes a switch 17 for controlling a DC voltage generated by the power supply unit 10 and an inside of the inverter 13 to generate a high voltage AC voltage. The transformer 11, the capacitor C2 and the resistor R for converting the high voltage AC voltage generated from the transformer 11 into the DC voltage, and the capacitor C2 and the resistor R. An error detector 18 that receives the supplied DC voltage and amplifies and outputs a DC voltage equal to the difference between the DC voltage and the first reference voltage Vref1, and the DC voltage and the second reference output from the error detector 18. And a comparator 19 for comparing the voltage Vref2.

The high voltage AC voltage generated by the transformer 11 is supplied to the lamp (1 in FIG. 1) and is converted into a DC voltage through the capacitor C2 and the resistor R. The DC voltage converted through the capacitor C2 and the resistor R is supplied to the error detector 18.

The error detector 18 receives the DC voltage through an inverting input terminal (-) and amplifies and outputs a difference voltage between the first reference voltage Vref1 and the DC voltage applied to the non-inverting input terminal (+). . The output voltage is also supplied to the comparator 19 as a DC voltage. That is, the error detector 18 converts the high voltage AC voltage into the DC voltage through the capacitor C2 and the resistor R in order to measure whether the high voltage AC voltage generated in the transformer 11 is correct. Thereafter, the DC voltage is compared with the first reference voltage Vfer1 to compensate for the difference between the first reference voltage Vref1 and the DC voltage. In this case, the first reference voltage Vref1 refers to a voltage obtained by converting an AC voltage having a high voltage generated by the transformer 11 into a DC voltage. Therefore, when a difference between the converted DC voltage of the high-voltage AC voltage generated by the transformer 11 and the first reference voltage Vfer1 occurs, the error detector 18 amplifies the difference value to a DC voltage. The output is supplied to the comparator 19.

The comparator 19 receives the DC voltage as a non-inverting (+) input terminal and compares the DC voltage with the second reference voltage Vref2 applied to the inverting (−) input terminal. In this case, the second reference voltage Vref2 applied to the inverting (−) input terminal means a voltage having a triangular waveform.

FIG. 3 is a diagram illustrating the second reference voltage Vref2 waveform and the output waveform of the comparator of FIG. 2.

As shown in FIG. 3, the second reference voltage Vref2 waveform is a triangular wave form. The second reference voltage Vref2 waveform affects the output waveform of the comparator 19. That is, since the section in which one cycle of the triangular wave of the second reference voltage Vref2 ends is the same as the section in which one cycle of the square wave which is the output waveform of the comparator 19 ends, the waveform of the second reference voltage Vref2 is This affects the output waveform of the comparator 19.

The output of the comparator 19 at a point where the diagonal of the triangular wave of the second reference voltage Vref2 and the DC voltage supplied to the non-inverting (+) input terminal of the comparator 19 intersect (hereinafter referred to as a cross point). The period of the waveform is determined. Therefore, the period of the output waveform of the comparator 19 may vary depending on the position of the intersection point. The minimum and maximum values are determined in the period of the output waveform of the comparator 19. As a result, the minimum and maximum values of the period of the output waveform are determined according to the triangular wave of the second reference voltage Vref2.

When the DC voltage supplied to the comparator 19 intersects the diagonal of the triangular wave of the second reference voltage Vref2 at a portion corresponding to the minimum value of the second reference voltage Vref2, the output waveform of the comparator 19 As shown in FIG. 3, the cycle has a minimum value.

When the DC voltage supplied to the comparator 19 and the oblique line of the triangular wave of the second reference voltage Vref2 cross at a portion corresponding to the maximum value of the second reference voltage Vref2, the output of the comparator 19 The waveform has a period of maximum value, as shown in FIG.

As such, the second reference voltage Vref2 and the DC voltage supplied to the comparator 19 affect the period of the output waveform of the comparator 19. The square wave output from the comparator 19 is supplied to the switch 17.

The switch 17 recognizes ON / OFF according to the high and low intervals of the supplied square wave and controls the high voltage AC voltage generated by the transformer 11. That is, when the square wave supplied to the switch 17 is a high section, the switch 17 is turned on, and the power supply voltage supplied to the switch 17 is supplied to the transformer 11. The power supply voltage generated by the power supply unit 10 of FIG. 1 is supplied to the transformer 11 when the switch 17 is turned on, and when the switch 17 is turned off, the power supply voltage is transformed into the transformer 11. ) Is not supplied.

As the switch 17 is turned on / off, the power supply voltage is supplied to the transformer 11 in the form of a square wave having a high section and a low section. The transformer 11 converts the AC voltage into a high voltage using the square wave voltage. The high voltage AC voltage generated by the transformer 11 is supplied to the lamp (1 in FIG. 1) to drive the lamp 1.

The inverter 13 converts the DC voltage provided from the DC / DC converter unit 12 into a high voltage AC voltage using a transformer (not shown) and outputs it.

When the high voltage AC voltage is applied from the inverter 13, the lamp 1 emits light by flowing a current. The safety capacitor (C) is such that when the lamp (1) is driven, a high-voltage AC voltage is applied directly to the lamp (1), and after driving the lamp to apply some output voltage to the stable capacitor (C) Let (1) work stably.

On the other hand, the PWM control unit 6 is composed of an analog system composed of a plurality of circuits, the PWM control unit 6 consisting of a plurality of circuits, due to the internal resistance and malfunction of the circuit, etc., precise control of the PWM control unit 6 Difficult to do. In addition, since the PWM controller 6 composed of the plurality of circuits increases the cost according to the circuit and the circuit has a limit value, the PWM controller 6 controls the PWM more limitedly than the digital method. Therefore, it is urgent to study the digital configuration of the PWM control unit 6 made of an analog method.

SUMMARY OF THE INVENTION An object of the present invention is to provide a backlight including a digital PWM control unit and a liquid crystal display device having the same.

The backlight according to the embodiment of the present invention for achieving the above object is a transformer for generating a high voltage AC voltage, a half-wave rectifier for converting the AC voltage to a constant voltage level, and an analog to convert the constant voltage into a digital signal- A digital converter, a counter for generating timing signals using a specific signal in a predetermined operation sequence, a square wave generator for generating a square wave having a predetermined period using the digital signal and the timing signal, and an on / off using the square wave It includes a switch.

According to an exemplary embodiment of the present invention, a liquid crystal display device includes a transformer for generating a high voltage AC voltage, a half-wave rectifier for converting the AC voltage to a constant voltage level, and converting the constant voltage into a digital signal. An analog-to-digital converter, a counter for generating timing signals using a specific signal in a predetermined operation sequence, a square wave generator for generating a square wave having a predetermined period using the digital signal and the timing signal, and an on / off using the square wave And a liquid crystal panel which is provided with a backlight for switching off and a predetermined voltage to be supplied with the AC voltage of the high voltage.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention.

4 is a view illustrating a backlight of the liquid crystal display according to the present invention.

As shown in FIG. 4, the backlight includes a power supply 110 for supplying a DC voltage, a switch 117 for controlling on / off of the DC voltage supplied from the power supply 110, and the switch ( An inverter 113 for generating a high voltage AC voltage using the DC voltage controlled from the 117; a lamp 101 for generating light using the AC voltage of the high voltage generated by the inverter 113; and the inverter. The half-wave rectifier 116 converts the high-voltage alternating voltage generated in the 113 into a DC voltage having a constant voltage level, and the ADC converts the DC voltage generated by the half-wave rectifier 116 into a digital signal. 118, a counter 119 sequentially executing the clock cycle using a clock signal, and a square wave generator 120 generating a square wave using the digital signals generated from the ADC 118 and the counter 119. It includes.

The power supply unit 110 is supplied with a DC voltage having a constant voltage value to the switch 117, is supplied to the inverter 113 according to the on / off of the switch 117.

The inverter 113 converts the DC voltage of the square wave shape controlled according to the on / off of the switch 117 into a high voltage AC voltage by using the transformer 111 mounted on the inverter 113. The high voltage AC voltage generated by the inverter 113 refers to a driving voltage for driving the lamp 101.

The lamp 101 generates light by generating a tube current using an AC voltage of a high voltage supplied from the inverter 113. The light generated from the lamp 101 is supplied to a liquid crystal panel (not shown) to affect the brightness of the liquid crystal panel.

The half-wave rectifier 116 receives the high voltage AC voltage generated by the transformer 111 and serves to convert the AC voltage into a DC voltage to have a DC voltage level between 0 and 5V, for example. The high voltage AC voltage generated by the transformer 111 through the half-wave rectifier 116 is converted into a DC voltage level between 0 and 5V and supplied to the ADC 118.

The ADC 118 converts a DC voltage having a constant voltage level generated from the half-wave rectifier 116 into a digital signal. The digital signal is supplied to the square wave generator 120.

The counter 119 proceeds in a predetermined order according to an input pulse supplied from the outside. In this case, the input pulse uses a clock signal. The counter 119 generates a timing signal for controlling an operation sequence according to the period of the clock signal. The counter 119 generates a timing signal that counters, for example, from 0 to 511 having one period of 512. A timing signal of 0 to 511 having a period of 512 generated by the counter 119 is supplied to the square wave generator 120.

The square wave generator 120 generates a square wave according to the digital signal supplied from the ADC 118 and the timing signal supplied from the counter 119. That is, whenever the digital signal supplied from the ADC 118 and the timing signal supplied from the counter 119 change, the period of the square wave generated by the square wave generator 120 changes.

The pulse width adjustment of the square wave generated by the square wave generator 120 is determined according to the digital signal value supplied from the ADC 118. For example, if the digital signal supplied from the ADC 118 is a value corresponding to 0 V, the square wave generator 120 may set a high section from 0 to 383 in the timing signal supplied from the counter 119. And generate a square wave with a low section from 384 to 511. In addition, when the digital signal supplied from the ADC 118 is a value corresponding to 5 V, the square wave generator 120 sets a high period of 255 to 383 among the timing signals supplied from the counter 119. Generates a square wave with 0 to 254 and 384 to 511 as the low section.

That is, as illustrated in FIG. 5A, when the digital signal supplied from the ADC 118 is a value corresponding to 0 V, the square wave generator 120 may have a value between 0 and 383 in the period (T = 512) of the timing signal of the counter. A square wave having a high section in the range of and a low section in the range of 384 to 511 is generated. In this case, the period of the high section of the square wave refers to a maximum value among the high sections of the square wave generated by the square wave generator 120.

When 5V of the DC voltage generated from the half-wave rectifier 116 is supplied to the ADC 118, the ADC 118 converts the 5V into a digital signal and supplies it to the square wave generator 120. The counter 119 generates a timing signal having a constant period (T = 512) and continues to supply the square wave generator 120. As illustrated in FIG. 5B, when the digital signal supplied from the ADC 118 is a value corresponding to 5 V, the square wave generator 120 has a range of 255 to 383 in the period T-512 of the counter's timing signal. In FIG. 3, a square wave having a high section and a low section in a range of 384 to 511 and 0 to 254 is generated. In this case, the period of the high section of the square wave refers to a minimum value among the high sections of the square wave generated by the square wave generator 120.

The square wave generated by the square wave generator 120 is set to always have a low range of 384 to 511 of the timing signals supplied from the counter 119. The high section of the square wave generated by the square wave generator 120 is determined according to the digital signal and the timing signal supplied from the ADC 118 and the counter 119, and the low section of the square wave generator. Is fixed.

The high voltage AC voltage supplied from the transformer (111 of FIG. 4) is converted into a DC voltage having a voltage level of 0 to 5 V through the half-wave rectifier (116 of FIG. 4), and the converted DC voltage is converted into a digital signal. The square wave generated by the square wave generator 120 is determined by using the ADC 118 to convert and the counter 119 which generates a timing signal using a clock signal supplied from the outside in a predetermined operation sequence. .

As described above, the high section of the square wave generated by the square wave generator 120 is determined according to the digital signal supplied from the ADC 118 and the timing signal supplied from the counter 119.

The square wave generated from the square wave generator 120 is supplied to the switch 117 of FIG. 4, and the switch 117 is turned on / off according to a high section and a low section of the square wave. And supplies the DC voltage generated by the power supply unit 110 to the transformer 111. The switch 117 is turned on in the high section of the square wave generated by the square wave generator 120, and supplies the DC voltage supplied from the power supply unit 110 to the transformer 111. In addition, the switch 117 is turned off in the low section of the square wave generated by the square wave generator 120, so that the DC voltage supplied from the power supply 110 is not supplied to the transformer 111. .

As a result, the DC voltage supplied to the transformer 111 has a square wave shape. The switch 117 becomes longer when the high section of the square wave generated by the square wave generator 120 is the maximum value. Accordingly, when the high section of the square wave is maximum, the on time of the switch 117 becomes long, and the DC voltage supplied from the power supply unit 110 passes through the switch 111 to the transformer 111. ) Is supplied corresponding to the time when it is turned on. When the high section of the square wave is minimum, the on time of the switch 117 is shortened, and the DC voltage supplied from the power supply 110 is turned on by the transformer 111. It is supplied in correspondence with the time when it becomes.

As the on time of the switch 117 is determined by a high section of the square wave generator 120 supplied from the square wave generator 120, the DC voltages supplied to the transformer 111 take the shape of square waves having different periods. . The transformer 111 generates an AC voltage of high voltage by using the DC voltage supplied through the switch 117.

The driving sequence of the backlight according to the present invention converts the high voltage AC voltage supplied from the transformer 111 into a DC voltage having a voltage level between 0 and 5V, for example, by using the half-wave rectifier 116. The DC voltage is supplied to the ADC 118, and the ADC 118 converts the DC voltage into a digital signal. The counter 119 generates a timing signal indicating one cycle (T = 512) by using a clock signal supplied from the outside. The square wave generator 120 receives a digital signal from the ADC 118 and a timing signal from the counter 119 to generate a square wave having a predetermined period. When the digital signal supplied from the ADC 118 is a value corresponding to 0 V, the square wave generator 120 sets a high section within a range of 0 to 383 of one period of the timing signal supplied from the counter 119. And a square wave having a low section in a range of 384 to 511. In addition, if the digital signal supplied from the ADC 118 is a value corresponding to 5V, the square wave generator 120 has a high range of 255 to 383 of one period of the timing signal supplied from the counter 119. Generates a square wave having a section, and having a low section in a range of 0 to 254 and 384 to 511. The square wave is supplied to the switch 117. The switch 117 is turned on in the high section of the square wave and supplies the DC voltage supplied from the power supply unit 110 to the transformer 111. The transformer 111 converts the DC voltage into an alternating voltage of high voltage and supplies the converted voltage to the lamp 101 of FIG. 4. The lamp 101 emits light using the AC voltage of the high voltage. The backlight of the present invention is digital, so that the switch 117 can be accurately turned on and off. In the conventional liquid crystal display device, the switch is turned on / off in an analog manner. When the switch is controlled in the analog manner, the switch is caused by internal resistance of a plurality of circuits used in the analog manner and a malfunction of the circuits. It's hard to control exactly. If the switch is not controlled correctly, the DC voltage supplied through the switch is distorted. To prevent this, the backlight of the present invention is driven digitally to control the switch accurately.

The backlight of the present invention is a half-wave rectifier that receives a high-voltage alternating voltage generated by a transformer and converts it into a DC voltage having a constant voltage level, an ADC that converts the DC voltage into a digital signal, and a timing signal using an external clock signal. A square wave generator for generating a square wave having a constant high section using a digital signal supplied from the ADC and a timing signal supplied from the counter, thereby generating a square wave digitally. By controlling the switch accurately, it is possible to overcome the problems caused by controlling the switch in a conventional analog manner.

Claims (8)

A transformer for generating a high voltage AC voltage; A half-wave rectifier for converting the AC voltage to a constant voltage level; An analog-digital converter for converting the constant voltage into a digital signal; A counter for generating a timing signal in a predetermined operation sequence using the specific signal; A square wave generator for generating a square wave having a predetermined period using the digital signal and the timing signal; And a switch for turning on / off using the square wave. The method of claim 1, And the square wave generator determines a high or low section of the square wave according to a digital signal supplied from the analog-digital converter. The method of claim 1, And the counter generates a timing signal using a clock signal supplied from the outside. The method of claim 1, The switch is turned on during the high section of the square wave generated by the square wave generator, and is turned off during the low section of the square wave. A transformer for generating a high voltage AC voltage, a half-wave rectifier for converting the AC voltage to a constant voltage level, an analog-to-digital converter for converting the constant voltage to a digital signal, and a timing signal in a specific operation sequence using a specific signal A backlight for generating a square wave generator for generating a square wave having a predetermined period using the digital signal and the timing signal, and a switch for turning on / off using the square wave; And And a liquid crystal panel to which the high voltage AC voltage is supplied to display predetermined data. The method of claim 5, Wherein the square wave generator determines a high or low section of the square wave according to a digital signal supplied from the analog-digital converter. The method of claim 5, And the counter generates a timing signal using a clock signal supplied from the outside. The method of claim 5, And the switch is turned on during a high section of the square wave generated by the square wave generator and is turned off during a low section of the square wave generator.

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