KR100661087B1 - Protection circuit of inverter for lcd back-light - Google Patents

Abstract

The present invention relates to a protection circuit of an LCD backlight inverter, and more particularly, a cathode is connected to an output side of a transformer of an LCD backlight inverter, and an anode is connected to ground to supply a current supplied from a voltage supply terminal at a predetermined level. A Zener diode, which is converted into and outputted from the Zener diode, is divided between the transformer and the cold cathode tube to divide the voltage output from the Zener diode, and a voltage divider comprising a first resistor and a second resistor; and an AC voltage input through the voltage divider. A low pass filter that removes the first switching means, a first switching means switched according to a level of the DC voltage divided by the voltage divider, and an output signal output from the enable signal supply terminal in association with the switching of the first switching means. And second switching means for applying / blocking an enable signal to the cold cathode tube driving IC. And it characterized in that.

Therefore, according to the present invention configured as described above, if the human body contacts the high voltage portion connected to the transformer and the cold cathode tube by detecting it to stop the drive of the inverter due to the high pressure or high power generated in the human body cold cathode tube This damage can be prevented beforehand.

LCD backlight, inverter, cold cathode tube, human body, contact

Description

Protection circuit of inverter for LCD backlight {PROTECTION CIRCUIT OF INVERTER FOR LCD BACK-LIGHT}

1 is a block diagram schematically showing the configuration of a conventional LCD backlight inverter

Figure 2 is a block diagram schematically showing the configuration of the protection circuit of the inverter for LCD backlight according to the present invention

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

1: Cold cathode tube drive IC 2: Transformer

3: cold cathode tube 4: output current detection circuit

5; Open Lamp Protection Circuit 100: Protection Circuit

110: voltage divider 120: low pass filter

C1: capacitor R1, R2: first and second resistor

Q1: FET Q2: Transistor

ZD1: Zener Diode

The present invention relates to an inverter for LCD backlight, and in detail, when the human body is in contact with a high voltage applied to a cold cathode tube, an electric shock is generated in the human body or a high current is inputted into the lamp to prevent the lamp from being damaged. It relates to a protection circuit of an inverter.

In general, an LCD backlight inverter refers to a DC / AC converter that drives a cold cathode tube by generating a high voltage using a transformer after converting DC power to AC power.

The conventional inverter is driven by receiving a constant voltage as shown in FIG. 1 to output a driving signal in the form of a pulse, and also by receiving a feedback of a voltage applied to the cold cathode tube 3 to be described below. A cold cathode tube driving IC 1 for detecting whether or not open and detecting an electric current flowing through the cold cathode tube 3 to regulate the output, and boosting an AC power output in the form of a pulse output from the cold cathode tube driving IC 1 A transformer 2 for outputting a high voltage, a cold cathode tube 3 which is turned on at a high voltage output from the transformer 2, and a current flowing through the cold cathode tube 3 is detected and applied to the cold cathode tube driving IC 1. It consists of an output current detection circuit 4 and an open lamp protection circuit 5 which senses the voltage applied to the cold cathode tube 3 and informs the cold cathode tube drive IC 1 whether the cold cathode tube 3 is open.

Referring to the operation of the inverter schematically, the cold cathode tube driving IC 1 generates a pulse-shaped signal when a constant voltage is applied, and then outputs it to the transformer 2, the transformer 2 boosts it to a high voltage The cold cathode tube 3 is turned on to output to the cold cathode tube 3. At this time, the output voltage of the transformer 2 is about 600Vrms in normal operation, and the current passing through the cold cathode tube 3 is input to the cold cathode tube driving IC 1 through the output current detection circuit 4 to drive the cold cathode tube. The IC 1 checks the state of the cold cathode tube 3.

On the other hand, when the cold cathode tube 3 is opened, the magnitude of the voltage input through the open lamp protection circuit 5 increases, so the cold cathode tube driving IC 1 recognizes that the cold cathode tube 3 is open and stops driving the inverter. .

However, since the inverter continues to operate when a human body contacts a high voltage part connected to a transformer and a cold cathode tube, the conventional inverter may cause electric shock or damage to the cold cathode tube due to high power. have.

Therefore, an object of the present invention is to solve the above problems, by detecting when the human body is in contact with the high-voltage region connected to the transformer and the cold cathode tube by stopping the drive of the inverter by the high pressure or electric shock occurs in the human body Alternatively, the high power is generated to prevent the cold cathode tube from being damaged in advance.

Features of the present invention for achieving the above object,

It is driven according to a cold cathode tube which is turned on at a high voltage and an enable signal output from the enable signal supply terminal, receives a constant voltage, outputs a pulse type driving signal, and feeds back the voltage applied to the cold cathode tube. A cold cathode tube driving IC for detecting an open state and detecting an electric current flowing through the cold cathode tube to adjust an output, and boosting an AC power output from the cold cathode tube driving IC to output a high voltage to the cold cathode tube; An output current detecting circuit for detecting a current flowing through the cold cathode tube and applying a transformer to the cold cathode tube driving IC; and sensing a voltage applied from the transformer to the cold cathode tube to determine whether the cold cathode tube is opened. Inverter for LCD backlight that includes open lamp protection circuit informed by driving IC hurry,

A zener diode having a cathode connected to an output side of the transformer and an anode connected to ground to convert a current supplied from a voltage supply terminal into a DC voltage of a predetermined level, and

A voltage divider connected between the transformer and the cold cathode tube, the voltage divider comprising a first resistor and a second resistor to divide the voltage output from the zener diode;

A low pass filter for removing an AC voltage input through the voltage divider;

First switching means switched according to the level of the DC voltage divided by the voltage divider;

And second switching means for interlocking with the switching of the first switching means to apply / block the enable signal output from the enable signal supply terminal to the cold cathode tube driving IC.

The first switching means,

A gate is connected to a node of the divided resistor, a drain is connected to an enable signal supply terminal, and a source is connected to the ground to be turned on / off by a DC voltage divided from the divided resistor.

In addition, the second switching means,

A base is connected to the drain of the FET, an emitter is connected to the enable signal supply terminal, and a collector is connected to the enable terminal of the cold cathode tube driving IC to supply the enable signal according to on / off of the FET. A transistor for applying / blocking the enable signal output from the stage to the cold cathode tube driving IC.

The low pass filter may include a second resistor of the voltage divider resistor and a capacitor connected in parallel to the front end of the second resistor.

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In addition, the collector of the transistor further includes a noise filter including a resistor and a condenser to remove a signal of noise component among the enable signals supplied from the enable signal supply terminal.

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Hereinafter, the configuration of the protection circuit of the LCD backlight inverter according to the present invention will be described in detail with reference to FIG. In FIG. 2, the same parts as those of the inverter for LCD backlight shown in FIG. 1 are denoted by the same reference numerals as in FIG. 1, and description thereof will be omitted.

2 is a block diagram schematically showing the configuration of a protection circuit of the inverter for LCD backlight according to the present invention.

Referring to FIG. 2, the protection circuit 100 of the LCD backlight inverter according to the present invention includes a zener diode ZD1, a voltage divider 110, a low pass filter 120, a FET Q1, It consists of transistor Q2.

The zener diode ZD1 has a cathode connected to the output side of the transformer 2, an anode connected to the ground, and converts a current supplied from the voltage supply terminal Vcc into a DC voltage of a predetermined level. Here, the buffer resistor Rb is connected between the voltage supply terminal Vcc and the cathode of the zener diode ZD1, and the output of the transformer 2 has a DC voltage mixed with the AC voltage.

The voltage divider 110 is connected between the transformer 2 and the cold cathode tube 3 to divide the voltage output from the output side of the transformer 2, that is, the DC voltage output from the zener diode ZD1. ) And the second resistor R2.

The low pass filter 120 includes a capacitor C1 connected in parallel to the second resistor R2 of the voltage divider resistor 110 and the front end of the second resistor R2 to remove an AC voltage input through the voltage divider resistor 110. It is composed of

The FET Q1 has a gate connected to a node of the divider resistor 110, a drain connected to an enable signal supply terminal ENABLE, and a source connected to ground, divided by a DC voltage divided from the divider resistor 110. On / off. Here, the FET Q1 uses an N-channel type FET. Here, the buffer resistor Rb is also connected between the drain of the FET and the enable signal supply terminal ENABLE.

The transistor Q2 has a base connected to the drain of the FET Q1, an emitter connected to the enable signal supply terminal ENABLE, and a collector connected to the enable terminal ENABLE of the cold cathode tube driving IC 1. Then, the enable signal output from the enable signal supply terminal ENABLE is applied / blocked to the enable terminal of the cold cathode tube driving IC 1 as the FET is turned on or off. Here, a transistor of the PNP type is used as the transistor Q2.

Here, the collector terminal of the transistor Q2 is provided with a noise filter 130 composed of a resistor R3 and a capacitor C2 so as to remove a signal of noise component among the enable signals supplied from the enable signal supply terminal ENABLE. do.

Hereinafter, the operation of the protection circuit of the LCD backlight inverter according to the present invention will be described in detail with reference to FIG.

First of all, the operation of the inverter is similar to the conventional one. In general, the cold cathode tube driving IC 1 generates a pulse-shaped signal when a constant voltage is applied, and then outputs it to the transformer 2, which the transformer 2 receives a high voltage. After the pressure was increased, the cold cathode tube 3 was turned on to be output to the cold cathode tube 3. At this time, the current passing through the cold cathode tube 3 is input to the cold cathode tube driving IC 1 through the output current detecting circuit 4, and the cold cathode tube driving IC 1 checks the state of the cold cathode tube 3. When the cold cathode tube 3 is opened, the magnitude of the voltage input through the open lamp protection circuit 5 increases, and thus the cold cathode tube driver IC 1 recognizes that the cold cathode tube 3 is open and stops driving the inverter. .

On the other hand, when the human body is in contact with the output side of the transformer 2, the human body impedance is about 2 ㏀, the output impedance of the transformer 2 is about 950 to 1000 Ω, the impedance of the cold cathode tube 3 is about 80 ,, and the impedance is equivalent As the resistance value is connected in series with each other, the partial pressure value of the voltage dividing resistor 110 in a state in which the human body does not touch and the partial pressure value when the human body is in contact with each other are different. That is, the resistance value increases when the human body contacts.

Therefore, since the FET Q1 is turned on and the drain is low when the human body is not in contact with the human body, the base of the transistor Q2 is also low, which causes the transistor Q2 to be turned on to enable the signal. The enable signal output from the supply terminal ENABLE is applied to the enable terminal ENABLE of the cold cathode tube driving IC 1 through the collector terminal of the transistor Q2 to operate the cold cathode tube driving IC 1. At this time, the AC output of the transformer 2 is passed to the ground through the low pass filter 120.

In this state, when the human body comes into contact with the output side of the transformer 2, the resistance value of the voltage divider 110 becomes high, the FET Q1 is turned off, and the drain becomes high, so the base of the transistor Q2 becomes high. Transistor Q2 is turned off. As a result, the enable signal that is output from the enable signal supply terminal ENABLE and applied to the enable terminal of the cold cathode tube driving IC 1 is cut off to stop driving of the cold cathode tube driving IC 1 to stop the entire inverter. The drive stops.

Therefore, by stopping the operation of the cold cathode tube driving IC at the contact of the human body, it is possible to block the application of high current to the human body and the cold cathode tube by blocking the application of high pressure from the transformer to the cold cathode tube.

As described above, according to the protection circuit of the inverter for an LCD backlight according to the present invention, when the human body contacts the high voltage region connected to the transformer and the cold cathode tube, it detects this and stops the drive of the inverter, thereby causing electric shock to the human body due to the high pressure. Or high power is generated to prevent the cold cathode tube from being damaged.

Claims (5)

It is driven according to the cold cathode tube which is turned on by the high voltage output from the outside and the enable signal output from the enable signal supply terminal, and is driven by receiving a constant voltage to output a pulse type driving signal, and the voltage applied to the cold cathode tube. A cold cathode tube drive IC detects whether a cold cathode tube is opened, and detects a current flowing through the cold cathode tube to adjust an output, and boosts an AC power output from the cold cathode tube drive IC to boost the cold cathode tube. A transformer for outputting a high voltage to the cathode tube, an output current detection circuit for detecting a current flowing through the cold cathode tube and applying it to the cold cathode tube driving IC, and a connection line between the output of the transformer and the cold cathode tube; Whether the cold cathode tube is opened by sensing a current applied to the cold cathode An inverter for an LCD backlight comprising an open lamp protection circuit informed by a tube driving IC, A zener diode having a cathode connected to an output side of the transformer and an anode connected to ground to convert a current supplied from a voltage supply terminal into a DC voltage of a predetermined level, and A voltage divider connected between the transformer and the cold cathode tube, the voltage divider comprising a first resistor and a second resistor to divide the voltage output from the zener diode; A low pass filter for removing an AC voltage input through the voltage divider; First switching means switched according to the level of the DC voltage divided by the voltage dividing resistor; And second switching means for interlocking with the switching of the first switching means to apply / block the enable signal output from the enable signal supply terminal to the cold cathode tube driving IC. Protection circuit. The method of claim 1, The first switching means, And a gate connected to a node of the divided resistor, a drain connected to an enable signal supply terminal, and a source connected to a ground, the FET being turned on / off by a DC voltage divided from the divided resistor. Protection circuit of inverter. The method of claim 2, The second switching means, A base is connected to the drain of the FET, an emitter is connected to the enable signal supply terminal, and a collector is connected to the enable terminal of the cold cathode tube driving IC to be interlocked with the FET and output from the enable signal supply terminal. And a transistor for applying / blocking the enable signal to the cold cathode tube driving IC. The method of claim 1, The low pass filter, A second resistance of the voltage dividing resistor, The protection circuit of the inverter for LCD backlight, characterized in that consisting of a capacitor connected in parallel to the front end of the second resistor. The method of claim 3, wherein And a noise filter comprising a resistor and a condenser in the collector of the transistor to remove a signal of a noise component among the enable signals supplied from the enable signal supply terminal.

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