KR100616085B1 - Limited current circuit of eefl inverter - Google Patents

Abstract

The current limiting circuit of the disclosed EEFL inverter includes a first and a second switching unit which performs a switching function using a signal input from a control IC, and receives a signal output from the first and second switching units, and uses an LCD backlight lamp. First and second high voltage generators for generating and outputting high-pressure alternating current capable of driving a voltage, and detecting a rise in voltage output from the first and second high voltage generators, and converting the detected signal into direct current A high comparison detection unit for comparing the rectifying unit to the control signal with a reference signal, and outputting a signal for cutting off the high voltage to the control IC using the comparison result, and a detection signal of the rectifying unit And first and second low comparison detectors for comparing output changes of the first and second high voltage generators, and outputting a signal to the control IC to cut off the high voltage by using the comparison result.

According to the above configuration, even if one of the comparison detection units does not operate in a one point failure state, the other comparison detection unit operates normally and operates stably even in an abnormal state.

LCD, EEFL, current limiting circuit, inverter, high voltage, comparative detection.

Description

Current Limiting Circuit of Inverter for External Electrode Fluorescent Lamp {Limited Current Circuit of EEFL Inverter}

1 is a block diagram of an inverter including a conventional current limiting circuit;

FIG. 2 is a detailed circuit diagram of the current limiting circuit shown in FIG. 1;

3 is a block diagram of an inverter including a current limiting circuit according to an embodiment of the present invention;

4 is a detailed circuit diagram of the current limiting circuit shown in FIG.

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

11,17: switching unit 12,18: high pressure generating unit

13,16: low comparison detection unit 14: high comparison detection unit

15: rectifier 19: lamp

IC2: Control IC

The present invention relates to an inverter for an external electrode fluorescent lamp (EEFL), which is being spotlighted as a backlight power source of a large LCD TV, and more particularly, an accident that may occur due to human body contacting a high voltage output terminal of the inverter. The present invention relates to a limited current circuit that limits the output current and prevents it in advance.

Cold Cathode Fluorescent Lamps (CCFLs) and EEFLs are used as LCD backlight lamps, which are a kind of cold cathode discharge lamps that emit light from the positive or negative glow of glow discharge.

EEFL is used in TFT-LCD applications such as TVs, which require higher brightness because luminance is higher than CCFL. Also, unlike CCFL in which the electrode is in the lamp, it is advantageous to operate in parallel because the electrode is external. It is possible to achieve even luminance by reducing

In addition, adopting EEFL reduces the number of inverters required for each lamp to one, which can significantly reduce the cost of components and significantly reduce the weight of the LCD module.

1 is a block diagram of an inverter including a conventional current limiting circuit.

As shown, the switching unit (1,6) to receive the input DC power for driving the input power (Vin) and the lamp (7) to perform a switching function and the control IC (IC1) for supplying a signal for switching And a high pressure generator (2, 5) for generating high-pressure alternating current using signals input from the switching units (1, 6), a rectifier (3) for detecting and rectifying the rectifier, and the rectifier (3). The comparison detection unit 4 compares the detection signal inputted through the reference signal with the control signal IC1 and outputs the control signal to the control IC IC1.

The switching units 1 and 6 are constituted by a circuit which performs a high-speed switching function therein and receive a driving signal from the control IC IC1 to perform switching.

The alternating current of the high pressure is generated in the high pressure generators 2 and 5 by using the signals generated by the switching units 1 and 6.

The alternating voltage made by the high voltage generators 2 and 5 is used to drive a plurality of lamps 7 fastened to the backlight.

A constant current method and a constant voltage method may be used to drive the lamp 7, and the constant current method is generally used for the LCD backlight lamp 7 so that the lamp 7 is always supplied with a constant current.

When a person contacts the output of the high pressure generator 2, 5, that is, the high voltage output terminal, a human body may be injured or severely cause a shock yarn. Thus, a current control circuit is provided to prevent this.

When a person (human resistance: 2 kΩ or less human body resistance) contacts the high voltage output terminal, since the high voltage output voltage greatly changes on the opposite side of the contact, it is common to use this output voltage as a detection signal. Normally, the resistance rises to about 600V.

The current limiting circuit is constituted by using the rising voltage as a detection signal, and the current control circuit is composed of a rectifying section 3 and a comparison detecting section 4.

FIG. 2 is a detailed circuit diagram of the current limiting circuit shown in FIG.

The output voltage of the high voltage generated in the high voltage generators 2 and 5 is distributed using capacitors C2, C3, C4 and C5 to lower the voltage, and then rectified (converted to direct current) through the rectifier 3 The capacitor C1 in the rectifier 3 and the resistors R2 and R3 are filtered and input to the comparison detector 4.

The comparison detection unit 4 is composed of a comparator 4a and a transistor Q1. A reference voltage (signal) is input to an inverting (-) terminal of the comparator 4a, and a non-inverting (+) terminal of the comparator 4a. In the rectifier 3, a signal converted into DC is filtered, that is, a detection signal is input.

The output varies according to the non-inverting and inverting comparison results of the comparator 4a, and the comparison result signal is applied to the base B of the transistor Q1 to turn on / off the transistor Q1.

The collector C of the transistor Q1 is connected to the enable end of the control IC IC1 and the enable end of the control IC IC1 when the input of the transistor Q1 base is a high voltage. This low voltage becomes a high voltage operation.

That is, when the human body resistance is in contact with the high voltage output terminal, the voltage is increased and the rising voltage becomes a detection signal, and the rising voltage is input to the non-inverting (+) terminal of the comparator 4a.

The comparator 4a compares this with the reference voltage of the inverting (-) terminal and outputs a high voltage to the input of the transistor Q1 base B.

When the input of the base of the transistor Q1 is a high voltage, the enable terminal of the control IC IC1 becomes a low voltage, and the high voltage generators 2 and 5 do not operate, thereby preventing shock.

However, since the conventional high voltage output voltage is used as the detection signal, the current limiting circuit does not operate normally in the case of a one-point failure (one point failure) performed during the certification test of overseas safety standards (UL, CE, etc.). Because of this problem, the test standard of safety standard was not satisfied and the certification of safety standard was not obtained.

To explain this in more detail, the international safety standard has a one-point failer standard that the current limiting circuit should operate normally even if any electronic component in the EEFL inverter fails (including open and short). However, conventional current limiting circuits do not satisfy this standard.

In addition, the current limiting circuit does not operate stably in an abnormal state in which a failure occurs in one electronic component, so that a person may be injured when a person contacts the high-voltage output terminal or may cause a shock yarn in severe cases.

The present invention has been made to solve the above problems, in the current limiting circuit test considering the one-point failer performed in the safety standard certification test in the EEFL inverter for LCD backlight, the portion that could not be implemented by the prior art, a plurality of circuits It is an object of the present invention to provide a current limiting circuit of an inverter for an EEFL that can operate stably in one point abnormal state and can satisfy the safety standard certification test.

In order to achieve the above object, the current limiting circuit of the inverter for EEFL according to an embodiment of the present invention is a control IC for generating a control signal to perform a switch function for the input power source, and the control IC First and second switching unit performing a switching function using a signal input from the output, and the high-pressure alternating current to drive the LCD backlight lamp receives the output signal from the first and second switching unit The first and second high voltage generators, a rectifier that detects an increase in the voltage output from the first and second high voltage generators, converts the detected signal into a direct current, and outputs the DC signal, and a detection signal output from the rectifier. Is compared with a reference voltage (signal), and a high comparison detecting unit for outputting a signal for controlling the occurrence of high voltage to the control IC using the comparison result, and a detection signal of the rectifying unit And first and second low comparison detectors for comparing output changes of the first and second high voltage generators and outputting signals for controlling high voltage generation to the control IC using the comparison result.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the current limiting circuit of the inverter for EEFL according to the present invention.

3 is a block diagram of an inverter including a current limiting circuit according to an embodiment of the present invention.

As shown, the control IC (IC2), the switching units 11 and 17, the high voltage generating units 12 and 18, the rectifying unit 15, the high comparison detection unit 14, the low comparison detection unit ( 13, 16).

The control IC IC2 generates a control signal to perform a switch function with respect to the input power source Vin.

The switching units 11 and 17 perform an actual switching function by using the signal input from the control IC IC2.

The high voltage generators 12 and 18 receive and output the signals output from the switching units 11 and 17 to generate an alternating current having a sufficient high pressure to drive the lamp 18.

The rectifier 15 detects an increase in the voltage output from the high voltage generators 12 and 18 and generates a detection signal.

The high comparison detection unit 14 compares the detection signal input from the rectifying unit 15 with a reference voltage (signal), and outputs a signal for blocking high voltage generation using the comparison result.

The furnace comparison detectors 13 and 16 directly detect and compare the detection signal of the rectifier 15 with the output change of the high voltage, and output a signal for blocking the generation of the high pressure using the comparison result.

4 is a detailed circuit diagram of the current limiting circuit shown in FIG.

The switching units 11 and 17 are preferably configured of FETs (field effect transistors) in order to minimize switching losses even during high-speed switching, and the switching signals generated by the switching units 11 and 17 are used to control the lamp 19. It is input to the high pressure generators 12 and 18 for converting into alternating current of sufficient high pressure to drive.

The high pressure generators 12 and 18 generate a high pressure in such a manner that a transformer is used and the primary side (PRI.) And the secondary side (SEC.) Are separated.

The output voltage of the high voltage is divided by using the capacitors C12, C13, C14 and C15 to lower the voltage value and rectified through the rectifier 15, and then the capacitor C11 and the resistor R14 in the rectifier 15. R15 and R16 are filtered and input to the high comparison detection unit 14.

The high comparison detection unit 14 includes a comparator 14a and a transistor Q12, a reference voltage is connected to an inverting (-) terminal of the comparator 14a, and a rectifying unit 15 to a non-inverting (+) terminal. The filtered signal is converted into DC and input.

The output of the comparator 14a is different depending on the comparison result of the non-inverting and inverting, and the comparison result signal is applied to the base B of the transistor Q12 through the resistor R12 to turn on / off the transistor Q12. Do it.

The collector C of the transistor Q12 is connected to the enable end of the control IC IC2, and when the base B input of the transistor Q12 becomes a high voltage, the enable end of the control IC IC2 is turned off. It operates to prevent high voltage output by becoming low voltage.

In addition, the low comparison detectors 13 and 16 are made up of comparators 13a and 16a and transistors Q11 and Q13, respectively, and the signal filtered after being converted into direct current by the rectifier 15 is non-inverted by the comparators 13a and 16a. The detection signal obtained by detecting the master / slave output voltage is input to the (+) terminal and the inverting (-) terminal, respectively.

The outputs of the comparators 13a and 16a are different according to the results of non-inverting and inverting, and the result of the comparison is applied to the base B of the transistors Q11 and Q13 through the resistors R11 and R13 so that the transistors Q11, Q13) is turned on / off.

The collectors C of the transistors Q11 and Q13 are connected to an enable end of the control IC IC2, so that the enable end of the control IC IC2 becomes high when the input of the transistor base B becomes a high voltage. It is operated so that high voltage output is not generated due to low voltage.

As described above, when the human body resistance is in contact with the output generated by the high-pressure generators 12 and 18, the high comparison detection unit 14 detects that the reference signal is higher than the reference signal, and operates the current limiting circuit. 13 and 16 sense that the output signal of the rectifier 15 becomes the reference voltage and lower than the reference voltage of the rectifier 15 to operate the current limiting circuit.

Therefore, even if one of the comparison detection units does not operate in the one-point fail state, the other comparison detection unit operates normally and the current limiting circuit operates stably even in an abnormal state.

Preferred embodiments of the present invention described above are disclosed for purposes of illustration, and those skilled in the art will be able to make various modifications, changes and additions within the spirit and scope of the present invention. Additions should be considered to be within the scope of the following claims.

As described above, according to the present invention, in the current limiting circuit test considering the one-point failer performed during the safety standard certification test in the EEFL inverter for LCD backlight, a plurality of circuits may be implemented. In this way, the current limiting circuit can operate stably even in abnormal state of the one-point failer, can satisfy the safety standard certification test, and there is no risk of injury if a person touches the high voltage output terminal.

Claims (6)

A control IC for generating a control signal to perform a switch function on an input power source; First and second switching units which perform a switching function using a signal input from the control IC; First and second high voltage generators configured to receive and output a signal output from the first and second switching units to generate an alternating current of high voltage capable of driving an LCD backlight lamp; A rectifier for detecting an increase in the voltage output from the first and second high voltage generators, converting the detected signal into a direct current and outputting the DC signal; A high comparison detection unit for comparing the detection signal output from the rectifying unit with a reference signal, and outputting a signal for blocking high voltage generation to a control IC using the comparison result; And The first and second low comparison detection unit for comparing the detection signal of the rectifying unit and the output change of the first and second high voltage generation unit, and outputs a signal for blocking the high voltage generation to the control IC using the comparison result Current limiting circuit of the inverter for EEFL comprising a. The method of claim 1, And the high comparison detecting unit comprises a comparator and a transistor having an output of the comparator connected to a base and a collector connected to an enable end of a control IC. The method of claim 2, The reference signal is input to the inverting (-) terminal of the comparator and the signal converted to the direct current from the rectifying unit is input to the non-inverting (+) terminal. A current limiting circuit of an EEFL inverter. The method of claim 1, And the first and second furnace comparison detectors each comprise a comparator and a transistor having an output of the comparator connected to a base and a collector connected to an enable end of a control IC. The method of claim 4, wherein The high voltage output from the first and second high voltage generators is input to the inverting (-) terminal of the comparator, and the signal converted into direct current from the rectifier is input to the non-inverting (+) terminal as a reference signal, and the high voltage is higher than the reference signal. A current limiting circuit of an inverter for an EEFL characterized by operating a current limiting circuit in a low case. The method of claim 1, The rectifier divides the voltage generated in the first and second high-voltage generator by the capacitor to receive the input in the state of lowering the voltage, the current limiting circuit of the inverter for EEFL.

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