KR20040103271A - Circuit For Detecting Error in Back Light Device - Google Patents

Abstract

PURPOSE: A circuit for detecting a lamp error in a backlight assembly is provided to enhance precision of the lamp error detection, thereby preventing the brightness unbalance of the backlight assembly due to the undetected lamp error, by generating an alarm signal for informing the lamp error. CONSTITUTION: A circuit for detecting a lamp error in a backlight assembly comprises a signal detector(400) for detecting current of the lamp, a standard signal generator(800), a lamp condition signal generator(900), and a comparator(600). The current of the lamp is detected by the signal detector. The standard signal generator and the lamp condition signal generator are connected to the signal detector to generate the standard signal and the lamp condition signal, respectively. The comparator compares these signals, thereby generating an alarm signal for informing the lamp error in case of detection of any of the lamps.

Description

Circuit For Detecting Error in Back Light Device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abnormality detection circuit of a backlight device, and more particularly, to a circuit for detecting abnormality of a lamp in a backlight device composed of a plurality of lamps.

1 is a circuit diagram for detecting an abnormality of a conventional backlight lamp.

As illustrated in FIG. 1, the circuit diagram has a function of stabilizing lamp current by detecting currents of a plurality of lamps, respectively, and feeding back to a drive control circuit of an inverter.

The detector 40 converts the current flowing through the plurality of lamps 30 into a voltage level of a predetermined signal, and converts the voltage level into an input signal of the c ₁ input terminal of the comparator 50. At this time, an AND circuit is formed between the detector 40 and the c ₁ input terminal. An arbitrary constant reference voltage is connected to the reference input terminal c ₂ of the comparator 50.

In the circuit diagram, a plurality of lamps 30 or transformers 20 are shown, but there is no problem in the inverter for a backlight using a circuit consisting of a single lamp or a single transformer or using two to four lamps or a single transformer. .

However, when an abnormality occurs in at least one lamp among the plurality of lamps and the detection current level drops, the following problem occurs.

The potential change is transmitted to the comparator 50 via the AND circuit. At this time, the reference voltage is set so that the output d of the comparator is inverted.

The output signal of the comparator 50 is inverted to cause the alarm control circuit 60 connected to the output terminal d of the comparator 50 to display a predetermined alarm. For example, the power applied to all lamps 30 is stopped, the power is kept stopped, or an alarm signal is sent to the control circuit to execute a predetermined alarm display (mode A and FIG. See B).

The comparator 50 has been used in anticipation of the change of the current flowing through the lamp 30 from the rated set current to almost zero current.

In the backlight device, since a cold cathode lamp or an external electrode lamp is driven with a high voltage high frequency current, leakage current is generated. For example, even if an abnormality occurs in an arbitrary lamp, if other lamps are normal, their leakage current flows into the detection circuit of the abnormally occurring lamp and the abnormality detection potential does not drop, so that the detection function is not properly operated. In the case of a backlight device used in a denser LCD device, this phenomenon has increased.

When the lamp, which is the light source of the backlight unit, is broken, when the wires connecting the inverter and the lamp are cut off, or when the connector connecting the inverter and the lamp is opened, the brightness of the backlight decreases. There has been a problem that when one or more lamps of the plurality of lamps are turned off, the luminance balance of the backlight is damaged. Therefore, there is an increasing demand for circuit installation that detects an abnormal connection of a lamp on the inverter circuit and turns off all lamps or sends an abnormal signal to sound an alarm.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a backlight device that detects an abnormality in one lamp and sounds an alarm in a backlight device for driving a plurality of lamps. It is to provide a lamp abnormality detection circuit.

In the backlight device according to the first aspect of the present invention for achieving the above object, a lamp abnormality detection circuit detects a current flowing through each of a plurality of lamps and generates the detected current at a voltage level corresponding to each. A reference signal generator for connecting to the detector and generating a reference signal; A lamp status signal generator for connecting the detector to generate the lamp status signal; And a comparator for outputting a predetermined signal when a voltage level of the reference signal and the lamp state signal crosses as a result of comparing the reference signal and the lamp state signal input from the reference signal generator and the lamp state signal generator. Characterized in that it comprises a.

Therefore, according to the present invention, even if one of the lamps used in the backlight device has an error can be made to sound an alarm.

1 is a circuit diagram for detecting an abnormality of a conventional backlight lamp.

FIG. 2 is a time chart of the circuit mode of operation at a given node of the circuit of FIG. 1.

3 illustrates a lamp failure detection circuit in the backlight device according to an embodiment of the present invention.

4A and 4B are time charts of a circuit operating mode at a given node of the circuit shown in FIG.

<Explanation of symbols for the main parts of the drawings>

100: power supply

150: control unit

200: transformer

300 lamp

400: detector

410: capacitor

420: resistance

450: current sensing unit

500: reference voltage

600: comparator

700: alarm control unit

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

3 illustrates a lamp failure detection circuit in a backlight device according to an embodiment of the present invention, and FIGS. 4A and 4B are time charts of a circuit operation mode at a predetermined node of the circuit of FIG. 3.

As illustrated in FIG. 3, the comparator 600 converts a current flowing through the plurality of lamps 300 into a voltage level in the detector 400 and uses a potential connected in an diode array to an OR logic circuit state as a reference voltage. . In this case, the potential is used as a reference voltage by a signal generated by a current fed back through a plurality of lamps 300.

In addition, even when the detection reference potential is changed due to the feedback to all the lamps 300, a signal added from the inverter driving circuit is applied to the comparator 600 so that the detection of the abnormal state signal of one or more lamps is valid.

The input voltage of the inverter, the start and stop of the inverter driving circuit, the on / off and dimming conditions of the lamp 300 and the occurrence of abnormalities, the change of the input signal of the comparator 600, the output of the comparator 600 A mode time chart of FIGS. 4A and 4B will be described below.

The circuit diagram is connected to the power supply unit 100, the transformer 200, a plurality of lamps 300 connected in parallel, the lamp 300 in series to sense the current flowing in the lamp 300 to feed back to the control unit 150 A detector 400 for detecting an error of the lamp 300, a reference voltage 500, a comparator 600, connected in parallel to the current detector 450 and the feedback detector 450. And an alarm control unit 700. In addition, the detector 400 is connected to a reference signal generator 800 configured as an OR circuit and a lamp state signal generator 900 configured as an AND circuit. The reference signal generated from the reference signal generator 800 is introduced into the (+) input terminal of the comparator 600, and the lamp status signal generated from the lamp state signal generator 900 is a ( -) It enters into the input stage.

The reference voltage 500 reduces the influence on noise by biasing the voltage levels of the reference signal and the lamp state signal, which are respectively introduced into the (+) and (-) input terminals of the comparator 600.

The detector 400 includes a capacitor 410 and a resistor 420. The time constant of the capacitor 410 of the detector 400 connected to the negative input terminal of the comparator 600 is the time constant of the capacitor C1 connected to the positive input terminal of the comparator 600. Faster than Therefore, in the comparator 600, the potential input to the negative input terminal is preceded by the potential input to the positive input terminal.

Bias resistors Rb1 to Rb9 correct the potential according to the lamp 300 current, R2 and R3 are resistors necessary for the operation of the OR circuit portion and the AND circuit portion, and R1 corrects the potential input to the comparator 600.

Mode 1 of FIG. 4A is the voltage at nodes A, B, C, D, and E of the circuit when the inverter input voltage rises.

When the voltage is first applied to the inverter, the voltage level input to the negative input terminal of the comparator 600 is ahead of the voltage level input to the positive input terminal, so that an abnormal signal is not generated to the output terminal of the comparator 600. Do not. That is, since no abnormal signal is generated, no signal is input to the alarm controller 700, and thus no alarm is generated.

Mode 2 of FIG. 4A is a voltage at nodes A, B, C, D, and E of the circuit when dimming the lamp current while driving the plurality of lamps.

When the amount of current flowing through the plurality of lamps is adjusted to be small, since both the (−) input terminal and the (+) input terminal are connected to the plurality of lamps 300, the voltage levels input to the plurality of lamps are also lowered simultaneously. Therefore, no abnormal signal is generated from the comparator 600.

Mode 3 of FIG. 4A is a voltage at nodes A, B, C, D, and E of the circuit when the lamp is abnormal at the connection side (low voltage side) while driving the plurality of lamps.

When the wire connected to the low voltage side of one of the plurality of lamps 300 is disconnected, one voltage level of the current sensing unit 450 to be fed back becomes zero (solid line of the graph). Therefore, the voltage level for detecting the error of the lamp falls in the detector 400 connected to the current detector 450. At this time, the dotted line of the graph indicates that the other lamps are operating normally. If the voltage applied to the one detection unit is zero, the one detection unit constitutes an AND circuit, so that the voltage input to the comparator 600 is lower than the reference input terminal, that is, the (+) input terminal. Therefore, the comparator 600 outputs an abnormal signal to generate an alarm.

The reason why the voltage of the negative input terminal does not drop to zero in the mode 3 graph of FIG. 4A is that both the positive input terminal and the negative input terminal of the comparator 600 are biased by the reference voltage. Because.

Mode 4 of FIG. 4A is a voltage at nodes A, B, C, D, and E of the circuit when the lamp is abnormal on the high voltage side while driving the plurality of lamps. When the wire connected to the high voltage side of one of the plurality of lamps 300 is disconnected, the voltage applied to one of the plurality of detection units 400 is lowered. However, as the solid line of the graph shows, the voltage due to the detection current does not drop sufficiently (e.g. to zero) under the influence of leakage current from other normal lamps. At this time, the dotted line of the graph indicates that the other lamps are operating normally.

However, if the voltage applied to the one detection unit is zero, the one detection unit constitutes an AND circuit, so that the voltage input to the comparator 600 is lower than the reference input terminal, that is, the (+) input terminal. Accordingly, the comparator 600 outputs an abnormal signal to the alarm controller 700 to generate an alarm.

Mode 5 of FIG. 4B is a voltage at nodes A, B, C, D, and E of the circuit when there is an error in the low connection side of the lamp in the lamp current control state while driving the plurality of lamps.

Since there is an error in the low connection side of at least one of the plurality of lamps while reducing the amount of current flowing through the plurality of lamps, a graph form similar to that of Mode 3 is shown. Therefore, the abnormal signal is output from the comparator 600.

Mode 6 of FIG. 4B is a voltage at nodes A, B, C, D, and E of the circuit when there is an error on the high voltage side of the lamp in the current control state of the lamp while driving the plurality of lamps.

This is similar to mode 4 because there is an error in the high connection side of at least one of the plurality of lamps while reducing the amount of current flowing through the plurality of lamps. Therefore, the abnormal signal is output from the comparator 600.

Mode 7 of FIG. 4B is a voltage at nodes A, B, C, D, and E of the circuit when all lamps have an error while driving the plurality of lamps.

Referring to the graph illustrating the input voltage of the comparator 600, the potentials introduced into the negative input terminal and the positive input terminal are simultaneously lowered. The low level output signal of the controller 150 is connected to the OR circuit as a reference signal of the comparator 600. Therefore, when an abnormal signal is generated from all lamps, the abnormal signal is output from the comparator 600 by preventing the reference signal from being lower than the abnormal signal, that is, due to the crossing of the voltage levels.

Mode 8 of FIG. 4B is a case in which all the lamps are turned on or off by the ON / OFF operation of the controller 150 while powering the backlight device while driving the plurality of lamps. In the case of operation, it is the voltage at the A, B, C, D, and E nodes of the circuit.

Mode 9 of FIG. 4B is a voltage at nodes A, B, C, D, and E of the circuit when the power is cut off while driving the plurality of lamps and the input voltage of the inverter drops.

In other words, in both modes 8 and 9 of FIG. 4B, an abnormal signal is not output from the comparator 600 because the potentials of the (+) input terminal and the (−) input terminal are simultaneously lowered, that is, no intersection of the potentials occurs.

Referring to the modes 3 to 7, the signal potential input to the comparator 600 intersects when there is an error in the at least one lamp 300, so that the output signal output from the comparator 600 also crosses.

In another normal operation, the potentials of the signals input to the comparator 600 simultaneously change, so that the output signals output from the comparator 600 do not cross each other.

In one embodiment of the present invention, the potential of the current flowing through all the lamps 300 is put in the OR circuit on the reference side of the comparator 600, but the potential of one lamp 300 current per one transformer may be connected. Fully functional.

The output signal of the comparator 600 is inverted and input to the alarm control unit 700 to configure a circuit for stopping or holding all the lamps 300, transmitting an alarm signal to the main body, or displaying an alarm. It can be easily implemented by.

The present invention is effective for all inverter circuits used for backlight applications consisting of two or more lamps.

As described above in detail, according to the lamp failure detection circuit in the backlight device of the present invention, an error can be detected until there is an error in one of a plurality of lamps connected in parallel. In addition, the luminance unbalance of the backlight device, which is generated by not detecting an abnormality in a few lamps among the plurality of lamps, may be eliminated.

Embodiment of the present invention is only one embodiment, of course, many modifications and variations of the components of the present invention without departing from the gist of the present invention, of course, the present invention is not limited to the embodiment. .

Claims (5)

A reference signal generator for detecting a current flowing through each of the plurality of lamps and generating a reference signal by connecting to a detector for generating the detected current at a corresponding voltage level; A lamp status signal generator for connecting the detector to generate the lamp status signal; And And a comparator for outputting a predetermined signal when a voltage level between the reference signal and the lamp state signal crosses as a result of comparing the reference signal and the lamp state signal inputted from the reference signal generator and the lamp state signal generator. The lamp abnormality detection circuit in the backlight apparatus characterized by the above-mentioned. The method of claim 1, wherein the reference signal generator is A lamp abnormality detection circuit in a backlight device, comprising: an OR circuit to generate a reference signal even if only one current of a plurality of lamps is detected. 3. The lamp of claim 1 or 2, wherein the lamp status signal generator The lamp abnormality detecting circuit of a backlight device, comprising: an AND circuit to generate a lamp status signal indicating an error even if only one current of a plurality of lamps is not detected. The method of claim 1, wherein the detection unit Lamp abnormality detection circuit in a backlight device, characterized in that consisting of a parallel connection of a capacitor and a resistor. The method of claim 4, wherein The reference signal and the lamp state signal input to the comparator are biased to a voltage level having a predetermined magnitude, The lamp abnormality detecting circuit according to claim 1, wherein the lamp status signal is a predetermined time ahead of the reference signal.