KR100577790B1 - Error detection system of backlight unit in liquid crystal display - Google Patents

Abstract

The present invention relates to an error detection system capable of detecting an error of a backlight unit in a liquid crystal display device.

The backlight error detection system of the present invention includes a backlight unit including a fluorescent lamp for emitting light, a reflector for preventing leakage of light emitted from the fluorescent lamp, and a return wire for transmitting a signal for driving the fluorescent lamp. And an inverter for generating a driving signal in the fluorescent lamp, a converter connected between a main power supply and the inverter and detecting a tube current flowing to the inverter and converting the tube current into a voltage, and a backlight using the output voltage of the converter. And a display unit for displaying an output signal of the detector unit to detect an error state of the backlight unit.

Description

ERROR DETECTION SYSTEM OF BACKLIGHT UNIT IN LIQUID CRYSTAL DISPLAY}

1 is a perspective view of a backlight unit provided in a general liquid crystal display device;

2 is a block diagram of a backlight error detection system according to an embodiment of the present invention;

3 is a circuit diagram of a converter unit, a detector unit, and a display unit in a backlight error detection system according to an exemplary embodiment of the present invention.

(Name of the code for the main part of the drawing)

100: backlight unit 10: fluorescent lamp

130: inverter 140: converter unit

150: detection unit 160: display unit

Vcc: main power

141: first amplifier 142: second amplifier

151: first detector 152: second detector

161: first display portion 162: second display portion

A1, ..., A4: OP amplifier Q21, Q31: NPN transistor

I: tube current r: sensing resistance

R1, ..., R33: Resistor Vref1, Vref2: Reference Voltage

LED21, LED31: Light Emitting Diode

The present invention relates to a thin film transistor liquid crystal display (TFT-LCD), and more particularly, to an error detection system capable of detecting an error of a backlight unit.

Cathode Ray Tube (CRT) cathode ray tube (CRT), which is the most widely used display device, has been spotlighted as a display device including TV and computer monitor because of its easy color and fast operation speed. However, the cathode ray tube has a disadvantage in that the portability is not only thick because of the structural characteristic of securing a certain distance between the electron gun and the screen, but also because the power consumption is large and the weight is considerably heavy.

In order to overcome the disadvantages of the cathode ray tube as described above, various various display devices have been devised. Among them, the most practical device is a liquid crystal display (LCD).

Although the LCD is darker in screen and somewhat slower in operation than the cathode ray tube, each pixel may be operated according to a signal scanned on a plane without having an electron gun. It can be used as a very thin display device such as a wall-mounted TV. In addition, since the liquid crystal display device is light in weight and consumes considerably less power than the cathode ray tube, it is recognized that the liquid crystal display device is most suitable as a portable display device such as being used as a display of a battery operated notebook computer.

Since the liquid crystal display device does not include a light emitting unit unlike a cathode ray tube, a light source other than a liquid crystal screen is required, and a fluorescent lamp is used as a light source of the liquid crystal display device.

The liquid crystal display is classified into a direct backlight unit and an edge-light backlight unit according to the installation position of the fluorescent lamp.

The direct type backlight unit has a structure in which light generated from a fluorescent lamp is uniformed by a diffusion plate and then incident on a liquid crystal panel. On the other hand, the edge light type backlight unit has a structure in which the light of the fluorescent lamp is incident on the liquid crystal panel through the light guide plate.

Such an edge-lit backlight unit is shown in FIG. Referring to FIG. 1, the fluorescent lamp 1 is attached to the side of the light guide plate 3 to scatter and uniformize light, and is surrounded by a lamp housing 2. Here, the lamp housing 2 supports the fluorescent lamp 1 and at the same time prevents the emitted light of the fluorescent lamp 1 from leaking to the side. The diffusion plate 4 may include an upper surface of the light guide plate 3, a lower substrate on which a thin film transistor and a pixel electrode are arranged, an upper substrate on which a color filter is formed, and a lower substrate, although not shown in the drawing. It is arrange | positioned between the panel lower polarizing plates comprised from liquid crystal between upper boards. The reflector 5 serves to prevent light from leaking to the lower portion of the light guide plate 3.

As a light source radiating from the fluorescent lamp 1, a cold cathode fluorescent lamp (CCFL) or a halogen cathode fluorescent lamp (HCFL) is selected and used.

In addition, in order to drive the fluorescent lamp 1 as described above, a high voltage line (High Voltage Ling) and a return wire (Return Wire) is connected to the inverter (Inverter) to transfer a drive signal, generally 40 to 60 KHz Use a signal with a frequency. At this time, the voltage and the current of the driving signal applied have a root mean square (RMS) value of 400 to 600 volts and 3 to 6 mA, respectively.

However, since the return wire for applying the drive signal is connected to the fluorescent lamp by welding, a short circuit with the reflector or a case of opening occurs frequently.

As described above, when the return wire is shorted to the reflector, the tube current flowing to the inverter rises to the maximum value, and thus, a malfunction may occur in the backlight unit. ) Appears.

In spite of the serious problems as described above, conventionally, as an inspection device for detecting an error of the backlight unit, the error of the backlight unit was inevitably detected by checking only an imbalance of luminance or a decrease in luminance using time.

Moreover, when using conventional inspection equipment, only the short between the return wire and the reflector can be inspected. Therefore, when the return wire is opened, the luminance decreases in more than half of the backlight, but it is not easily detected. Many could not.

An object of the present invention is to provide a system capable of detecting an error occurring between a reflector and a return wire by sensing a current flowing through an inverter connected to a backlight unit.

In order to achieve the above object, the backlight error detection system of the present invention includes a fluorescent lamp for emitting light, a reflector for preventing the leakage of light emitted from the fluorescent lamp, a return wire for transmitting a fluorescent lamp driving signal A backlight unit including an inverter, an inverter for generating a driving signal to the fluorescent lamp, a converter unit connected between the inverter and the main power source and detecting a tube current flowing to the inverter and converting the tube current into a voltage; And a display unit for displaying an output signal of the comparator unit so as to externally recognize the backlight state using a voltage detector for checking an error of the backlight using a voltage.

The converter unit includes a sensing resistor connected between a main power supply and an inverter, a first amplifier for amplifying a voltage difference across the sensing resistor, and a second amplifier for amplifying an output voltage of the first amplifier. It features.

The first amplifier includes a first OP amplifier and a plurality of resistors, and comprises a comparison amplifier for amplifying the voltage difference between the sensing resistors.

The second amplifier part is characterized in that the amplifier comprises a second OP amplifier and a resistor.

The detector may include a first detector configured to detect whether the return wire is open by using an output voltage of the converter, and a second detector configured to detect whether the return wire and the reflector are shorted.

The first sensing unit may include an OP amplifier for comparing a first reference voltage with an output voltage of the third converter.

The second sensing unit may include an OP amplifier for comparing a second reference voltage with an output voltage of the third converter.

The display unit may display the first display unit to externally indicate whether the return wire is opened by using the output signal of the first detector, and the external signal to externally indicate whether the return wire and the reflector are shorted by using the output signal of the second detector. And a second display portion.

The first and second display units may include light emitting diodes (LEDs) and transistors.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The present invention detects the opening of the return wire and the short circuit of the return wire and the reflector using the tube current flowing to the inverter for driving the fluorescent lamp.

2 illustrates a block diagram of a backlight error detection system according to an embodiment of the present invention. Referring to FIG. 2, the backlight error detection system of the present invention includes a fluorescent lamp 10 for emitting light, a reflector (not shown) for preventing leakage of light emitted from the fluorescent lamp 10, And a backlight unit 100 including a return wire (not shown) for transmitting a driving signal to the fluorescent lamp 10.

The backlight unit 100 drives the fluorescent lamp 10 with a drive signal transmitted from the inverter 130 to inject light from the fluorescent lamp 10 into the liquid crystal panel.

The main power source Vcc for driving the inverter 130 is applied at a level of about 12 volts through the converter unit 140, and emits light from the fluorescent lamp 10 by a signal transmitted from the inverter 130. Let's do it.

In the process of driving the fluorescent lamp 10 in the inverter 130 to inject light into the liquid crystal panel to display the liquid crystal screen, when the return wire and the reflector are short-circuited, the tube current is greatly increased, on the contrary, the return wire. When is open, almost no tube current flows.

Therefore, in order to detect a short circuit between the return wire and the reflector or an error due to the opening of the return wire, a converter unit 140 for converting a tube current into a voltage between the main power supply Vcc and the inverter 130, and the converter. The detection unit 150 determines whether the return wire and the reflector are short-circuited or the return wire is opened by using the output signal of the unit 140, and displays a state externally according to the output signal of the detection unit 150. The display unit 160 is provided.

3 illustrates an internal circuit diagram of the converter 140, the detector 150, and the display 160.

Referring to FIG. 3, the converter 140 includes a sensing resistor r and a sensing resistor r to measure a tube current I flowing between the main power supply Vcc and the inverter 130. A first amplifier 141 including a first OP amplifier A1 to sense and amplify a voltage difference between both ends node1 and node2 and a second amplifier to amplify an output voltage of the first amplifier 141. It consists of a second amplifier 142 including two OP amplifier A2.

The first amplifier 141 is configured to amplify the voltage difference between both nodes 1 and 2 of the sensing resistor r generated by the tube current I, and thus, the first node node1 of the sensing resistor r. A first resistor R1 is connected between the first input amplifier A1 and the inverting input terminal (-) of the first OP amplifier A1, and feeds back the output signal of the first OP amplifier A1 to the inverting input terminal (-). The second resistor R2 is provided. In addition, a third resistor R3 is connected between the second node node2 of the sensing resistor r and the non-inverting input terminal + of the first OP amplifier A1, and the non-inverting input terminal + The fourth resistor R is connected between the ground and the power supply.

The output voltage V141 of the first amplifier 141 is represented by Equation 1 below by the voltages V1 and V2 of the first node node1 and the second node node2 of the sensing resistor r. Is displayed as:

V141 =-(R2 / R1) V1 + [(1 + R2 / R1) / (1 + R3 / R4)] V2

In this case, when the ratio of the resistors R1 and R2 connected to the inverting input terminal (-) of the first OP amplifier A1 is the same as the ratio of the resistors R3 and R4 connected to the non-inverting input terminal +, that is, In the case of R2 / R1 = R4 / R3, Equation 1 is expressed by Equation 2 below.

V141 = R2 / R1 (V2-V1) = R2 / R1 (I × r)

In the second amplifier 142, a fifth resistor R11 is connected between the output terminal of the first amplifier 141 and the inverting input terminal (−) of the second OP amplifier A2 and the second OP amplifier. A sixth resistor R12 is connected to feed the output signal of (A2) to the inverting input terminal (−). At this time, the non-inverting input terminal (+) of the second OP amplifier A2 is connected to the ground power source.

As a result, when the ratio of the first resistor R1 and the second resistor R2 is equal to the ratio of the third resistor R3 and the fourth resistor R4, the voltage V140 output from the converter 140 is equal. It is expressed as (Equation 3).

V140 = (R2 / R1) (R4 / R3) (I × r)

In addition, the sensing unit 150 may compare the output voltage V140 and the first reference voltage Vref1 of the converter unit 140 to detect whether the return wire is open, and the first sensing unit 151. The output voltage V140 of the converter 140 and the second reference voltage Vref2 are compared to each other, and the second sensing unit 152 is configured to detect whether the return wire and the reflector are short-circuited.

The first detector 151 receives the output voltage V140 of the converter 140 to the inverting input terminal (−) and receives the first reference voltage Vref1 to the non-inverting input terminal (+). 3 OP amplifier A3. When the output voltage V140 of the converter unit 140 is smaller than the first reference voltage Vref1, a positive output signal is generated, and conversely, the output voltage of the converter unit 140 ( When V140 is greater than the first reference voltage Vref1, a negative output signal is generated.

The second sensing unit 152 receives the output voltage V140 of the converter unit 140 as the non-inverting input terminal (+), and receives the second reference voltage Vref2 as the inverting input terminal (-). Four op amps A4. When the output voltage V140 of the converter 140 is greater than the second reference voltage Vref2, a positive output signal is generated, and conversely, the output voltage of the converter 140 When V140 is less than the second reference voltage Vref2, a negative output signal is generated.

The display unit 160 outputs an output signal of the first display unit 161 and the second detection unit 152 to externally indicate whether the return wire is opened by using the output signal of the first detection unit 151. And a second display unit 162 for externally displaying whether the return wire and the reflector are short-circuited.

The first display unit 161 includes a first light emitting diode LED21 and a resistor between an emitter terminal of the first NPN transistor Q21 having a collector terminal connected to a power supply voltage V + and a ground power supply. R23 is connected in series, and is connected between the base terminal of the first NPN transistor Q21 and the output terminal of the first sensing unit 151 and the base terminal of the first NPN transistor Q21 and the emitter terminal. The resistors R21 and R22 are connected to each other.

Therefore, when a positive signal is generated in the first detector 151, the first NPN transistor Q21 is turned on to turn on the first light emitting diode LED21, and conversely, the first detector 151 is turned on. When the negative signal is generated at, the first light emitting diode LED21 is turned off.

The second display unit 162 includes a second light emitting diode LED31 and a resistor R33 in series between a collector terminal of a second NPN transistor Q31 having an emitter terminal connected to a ground power supply and a power supply voltage V +. Connected between the base terminal of the second NPN transistor Q31 and the output terminal of the second sensing unit 152, and the resistors R31 and R32 between the base terminal and the emitter terminal of the second NPN transistor Q31, respectively. Is connected.

Therefore, when a positive signal is generated in the second detector 152, the second NPN transistor Q31 is turned on to turn on the second light emitting diode LED31, and conversely, the second detector 152 is turned on. When the negative signal is generated at, the second NPN transistor Q31 is turned off and the second light emitting diode LED31 is turned off.

The first and second light emitting diodes LED21 and LED31 use diodes of different colors, such as red or green.

In the liquid crystal display, when no error occurs in the backlight unit and a normal tube current flows, the output voltage V140 of the converter unit 140 is between the first reference voltage Vref1 and the second reference voltage Vref2. The first reference voltage Vref1 and the second reference voltage Vref2 are set to have a value.

Therefore, as the control signal Vd for controlling the tube current I is adjusted, the output voltage V140 of the converter 140 is lower than the first reference voltage Vref1 at regular intervals, or the second reference. Since the voltage is higher than the voltage vref2, the first and second light emitting diodes LED21 and LED31 are alternately turned on to indicate that the backlight unit is normally operated.

On the other hand, if an error occurs in the backlight unit and the return wire is opened, the tube current I is greatly reduced, and accordingly, the output voltage V140 of the converter 140 is lower than the first reference voltage Vref1. Therefore, the output signal of the first sensing unit 151 becomes positive, the output signal of the second sensing unit 152 becomes negative, and the first light emitting diode LED21 of the first display unit 161 continues. And the second light emitting diode LED31 is continuously turned off to indicate that the return wire is open.

On the contrary, when the return wire and the reflector are short-circuited, the tube current I rises to the maximum value, so that the output voltage V140 of the converter unit 140 becomes larger than the second reference voltage Vref2. Therefore, the output signal of the first sensing unit 151 becomes negative and the first light emitting diode LED21 is continuously turned off, and the output signal of the second sensing unit 152 becomes positive and the second light emitting diode ( LED31 is continuously lit, indicating a short circuit between the return wire and the reflector.

As described above, in order to display the open of the return wire or the short circuit of the return wire and the reflector to the outside, in addition to the NPN transistor and the light emitting diode as shown in FIG. 3, a MOS transistor or other light emitting device Can be used.

As described in detail above, according to the backlight error detection system of the present invention, a return wire for transmitting a driving signal to the fluorescent lamp constituting the backlight unit is opened, or a short circuit occurs between the return wire and the reflector. Easily detect cases and easily recognize them externally, making it easy to correct errors in products.

In addition, it is possible to detect an error occurring in the backlight unit without a separate test equipment that can test only a short circuit of the conventional return wire, thereby reducing the additional cost, and the time required to check the error of the backlight unit one by one. You can save effort.

Therefore, there is an advantage that the manufacturing time and manufacturing process of the liquid crystal display device can be shortened, and the manufacturing yield can be increased, thereby securing the competitiveness of the product.

Hereinafter, this invention can be implemented in various changes in the range which does not deviate from the summary.

Claims (10)

A backlight unit including a fluorescent lamp for emitting light, a reflector for preventing leakage of light emitted from the fluorescent lamp, and a return wire for transmitting a signal for driving the fluorescent lamp; An inverter for generating a drive signal to the fluorescent lamp; A converter unit connected between a main power supply and the inverter and detecting a tube current flowing to the inverter and converting the tube current into a voltage; A detector configured to determine an open state and a short state of the return wire by using an output voltage of the converter unit, and output a signal corresponding thereto; And a display unit configured to display a state corresponding to the opening of the return wire and the short circuit in accordance with an output signal of the detector. The method of claim 1, wherein the converter unit A sensing resistor connected between the main power source and the inverter; A first amplifier configured to amplify the voltage difference across the sensing resistor including a first OP amplifier; And a second amplifier configured to amplify the output voltage of the first amplifier, including a second OP amplifier. The method of claim 2, wherein the first amplification unit A first resistor coupled between the first node of the sensing resistor and the inverting input terminal of the first OP amplifier to amplify the voltage difference between both nodes of the sensing resistor; A second resistor for feeding back an output signal of the first OP amplifier to an inverting input terminal; A third resistor connected between the second node of the sensing resistor and a non-inverting input terminal of the first OP amplifier, And a fourth resistor connected between the non-inverting input terminal of the first OP amplifier and a ground power source. The method of claim 2 or 3, wherein the second amplification unit The non-inverting input terminal of the second OP amplifier is connected to a ground power source, A fifth resistor connected between the output terminal of the first amplifier and the inverting input terminal of the second OP amplifier, And a sixth resistor for feeding back the output signal of the second op amp to an inverting input terminal. The method of claim 1, wherein the detection unit A first detector for detecting whether a return wire is open by using the output voltage of the converter; And a second detector for detecting whether the return wire and the reflector are short-circuited. The method of claim 5, wherein the first detection unit The output voltage of the converter unit is provided to an inverting input terminal, And an op amp provided with a non-inverting input terminal for a reference voltage to be compared with an output voltage of the converter unit. The method of claim 5, wherein the second detection unit The output voltage of the converter unit is provided to a non-inverting input terminal, And an op amp provided with a reference voltage for comparing the output voltage of the converter unit as an inverting input terminal. The display unit of claim 1 or 5, wherein the display unit A first display unit for externally indicating whether a return wire is opened by using an output signal of the first detector; And a second display unit configured to externally indicate whether the return wire and the reflector are shorted by using the output signal of the second detector. 10. The display device of claim 8, wherein the first display unit An NPN transistor whose collector terminal is connected to a supply voltage, A light emitting diode having an anode terminal connected to an emitter terminal of the NPN transistor; A first resistor connected between the cathode terminal of the light emitting diode and a ground power source; A second resistor connected between the base terminal of the NPN transistor and the output terminal of the first sensing unit; And a third resistor connected between the base terminal and the emitter terminal of the NPN transistor. 10. The display device of claim 8, wherein the second display portion NPN transistors whose emitter terminals are connected to ground power; A light emitting diode having a cathode terminal connected to the collector terminal of the NPN transistor; A first resistor connected between the anode terminal of the light emitting diode and a power supply voltage; A third resistor connected between the base terminal of the NPN transistor and an output terminal of a second sensing unit; And a fourth resistor connected between the base terminal and the emitter terminal of the NPN transistor.

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