KR100382158B1 - The driving circuit of the plasma discharge type flat backlight - Google Patents

Abstract

An object of the present invention is to adjust the duty and pulse width of the pulse applied to the power transformer driving power switching transistor according to the variation of the power transformer input current of the backlight driving inverter circuit to stabilize the input of the power transformer, high power, high efficiency The present invention provides a driving circuit of a plasma discharge type backlight for driving LCD that can stabilize the brightness of the backlight under the condition of.

Inverter circuit of the present invention is a main controller 50 for generating a pulse for adjusting brightness by receiving the input current variation of the power transformer as a voltage value and comparing it to a reference value; A sub-control unit 60 receiving a luminance control output pulse from the main controller and generating a duty and timing-controlled driving pulse and generating first and second pulse outputs for power transistor switching using the driving pulse; A step-up inverter unit 20 driving the first and second pulse outputs of the sub-control unit to generate a control signal for switching the input current of the power transformer; An output unit 30 outputting a high voltage of a high frequency for driving an LCD backlight according to the switching power output of the step-up inverter unit; The feedback unit 40 converts an input current variation detected by the sensing resistance of the step-up inverter unit 20 into a voltage and provides the feedback unit 40 to the main controller 50.

Description

The driving circuit of the plasma discharge type flat backlight}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit of a plasma discharge type flat backlight. In particular, the main control unit compares a signal fed back from the power transformer primary side of the backlight driving circuit output with a set value to sense a change in the amount of current due to the backlight discharge. By generating PWM (Pulse Width Modulation) signal for brightness control, the sub-control unit adjusts the pulse generation and adjusts the power transformer primary current at the output of the driving circuit, thereby maintaining high power and high efficiency without using a DC / DC converter. The present invention relates to a driving circuit of a plasma discharge type flat backlight capable of controlling stable luminance.

In general, the driving circuit of the CCFL (Cold Cathode Fluorescent Lamp) backlight used in the LCD uses an inverter unit for converting DC to AC and a DC / DC converter, that is, two power converters for adjusting the brightness of the CCFL. The CCFL was driven and the brightness adjusted. An example of such a conventional CCFL backlight driving circuit is shown in FIG. 1.

1 is a block diagram of a conventional CCFL backlight driving circuit.

As shown in the figure, the CCFL backlight driving circuit switches an AC adapter 1 for converting and supplying AC power to DC power, a battery 8 for supplying DC power when AC power is not supplied, and an input DC power switch. DC / DC converter 2 for outputting a switched signal through a regulator, and a DC / AC inverter for converting the signal output from the DC / DC converter 2 into an AC signal and boosting it to drive a cold cathode fluorescent lamp. (3), a CCFL (4) driven by the DC / AC inverter (3), an on / off control key (5) for turning off driving of the CCFL (4), and the DC / AC inverter A brightness controller 6 which receives the signal output from the signal 3 and adjusts the brightness of the CCFL 4, and a feedback unit which feeds the output signal of the brightness controller 6 to the DC / DC converter 2; 7)

The operation of the CCFL backlight driving circuit configured as described above is as follows.

First, the DC power output from the AC adapter 1 to the DC / DC converter 2 is converted into a pulse voltage by the DC / DC converter 2 made of a switching regulator and then output to the DC / AC inverter 3. .

The signal input to the DC / AC inverter 3 is divided into a positive value and a negative value through a power transformer in the DC / AC inverter 3, and in the case of a negative signal, is output to the CCFL 4 so as to be output to the CCFL 4. Is driven, and if it is positive, it is output to the brightness controller 6.

The output signal of the brightness adjusting unit 6 is passed through the feedback unit 7 to the DC / DC converter 2 again to adjust the duty ratio of the switching regulator, so that the current flowing to the CCFL 4 is always Make it constant.

In addition, when the user adjusts the brightness through the brightness controller 6 while the CCFL 4 is driven, the output signal of the brightness controller 6 is input to the DC / DC converter 2 again, so that the duty of the switching regulator is maintained. By adjusting the ratio, the brightness of the CCFL 4 is adjusted.

As described above, the driving circuit of the conventional CCFL backlight samples the current flowing to the secondary side of the power transformer of the DC / AC inverter 3 to adjust the brightness and passes the feedback to the duty of the switching element of the DC / DC converter 2 via the feedback circuit. The ratio was adjusted, and as a result, the brightness was adjusted by varying the voltage level.

However, the conventional driving circuit of the CCFL backlight as described above is possible to the backlight such as CCFL, but in the case of the flat backlight using the plasma discharge method when driving with the conventional CCFL discharge driving circuit unstable discharge when dimming (Dimming) There is a possibility. That is, in the plasma type discharge tube, driving below the discharge voltage is very unstable, so there is a problem in using the existing method. In addition, the conversion loss of the circuit itself is increased by passing through two power converters, a DC / DC converter and a DC / AC inverter.

Therefore, such a conventional driving circuit method is not suitable in the case of requiring high efficiency with a structure that can not only lose the circuit because it passes through two power converters. In particular, when driving a plasma discharge type flat backlight, it is difficult to obtain stable discharge characteristics and to adjust luminance. The voltage at which the backlight discharges completely is called the firing voltage. Especially in the case of the flat type backlight, high voltage and high power are required, and if it is not satisfied, snaking and flicker may occur. There is a problem that can appear relatively more than the CCFL.

An object of the present invention for solving the above problems is to compare the signal fed back from the input side of the backlight drive circuit power transformer with a reference set value to detect a change in the amount of current change according to the change in backlight brightness value and accordingly PWM for brightness adjustment By regenerating the signal to adjust the width of the pulse for driving the power transistor, the input current of the power transformer is automatically adjusted in conjunction with the load (backlight) change, so that a high output, high efficiency backlight driving and stable without a conventional DC / DC converter The present invention provides a driving circuit of a plasma discharge type flat backlight which can adjust brightness.

1 is a block diagram of a conventional CCFL backlight driving circuit;

2 is a block diagram of a plasma discharge type backlight driving circuit according to the present invention;

3 is a detailed circuit diagram of a plasma discharge type backlight driving circuit according to the present invention;

4 is a front view of the secondary side high pressure bobbin of the power transformer at the output of FIG.

5 is a side view of the primary side low pressure bobbin of the power transformer at the output of FIG.

6 is a side view of the bobbin of the power transformer at the output of FIG.

7 is a cross-sectional view of the section of the high-pressure bobbin of the power transformer at the output of FIG.

8 is a view showing a state in which the primary and secondary bobbin of the power transformer is coupled to the output of FIG.

※ Explanation of symbols about main part of drawing ※

10: line filter unit 20: step-up inverter unit

30: output unit 40: feedback unit

50: main controller 51: main controller

60: sub-control unit 61: sub-controller

70: DC power supply 71: regulator

101: high pressure bobbin 102: section

103: fixing pin 104: winding fixing terminal

105: winding outlet 106: low pressure bobbin

107: high-voltage winding fixing pin 108: insulating liquid injection port

109 Barrier

The LCD backlight driving inverter circuit of the present invention to achieve the above object is to receive a voltage value corresponding to the input current variation of the inverter circuit when the LCD drive control signal is generated in the LCD controller, and compare it to the reference voltage value for brightness control A main controller for generating a pulse, a sub-control unit for generating a duty and timing-controlled driving pulse by receiving an output pulse for luminance adjustment from the main controller, and generating first and second pulse outputs for power transistor switching using the driving pulse; A step-up inverter for driving the first and second pulse outputs of the sub-control unit to generate a control signal for input current switching of a power transformer; and a high voltage of a high frequency for driving backlight for an LCD according to the switching power output of the step-up inverter. Output voltage and an input current variation detected by the sensing resistor of the step-up inverter unit as a voltage; Conversion is characterized in that it comprises feedback unit for providing the main control unit.

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

2 shows a schematic block diagram of a plasma discharge backlight driving circuit for backlighting an LCD display device according to the present invention.

As referred to here, the LCD backlight driving inverter circuit receives a voltage value corresponding to the input current variation of the inverter circuit when the driving control signal of the LCD 83 is generated by the LCD controller 81 and receives the reference voltage value. Compared to the main control unit 50 for generating a pulse for adjusting the brightness, the sub-control unit 60 for receiving the output pulse for adjusting the brightness from the main control unit for generating a duty and timing-controlled driving pulse, and the pulse output of the sub-control unit A step-up inverter unit 20 for driving, an output unit 30 for driving the LCD flat backlight 82 with a high-voltage high-voltage high output in accordance with the switching power output of the step-up inverter unit, and the step-up inverter unit ( A feedback part 40 for providing the main control part 50 with an input current component detected by the current detection sensing resistance of the controller 20, and the step-up inverter part included in the input current to be applied. And a line filter unit 10 for filtering noise.

3 shows a specific circuit block diagram of the present invention.

As referred to herein, the DC power supply 70 includes a regulator 71.

The main controller 50 is configured to distribute the Vcc voltage output from the regulator to generate a reference voltage and a main controller 51 which is activated when the LCD driving control signal is generated by the LCD controller 81 to generate a PWM signal for brightness adjustment. It comprises a distribution resistor (R52, R53), a filter capacitor (C52) for removing noise included in the signal input through the feedback unit, a timing capacitor (C53) and a timing resistor (R54) for setting the frequency. .

The sub-control unit 60 receives a sub-controller 61 for generating a bipolar transistor driving pulse by receiving a PWM pulse for adjusting the brightness of the main controller 51 of the main controller and a timing for adjusting the frequency of the driving pulse output from the sub-controller. A capacitor C61 and a variable resistor VR1, a capacitor C62 for stabilizing an input voltage of the sub-controller, a resistor R61 for adjusting the duty ratio to a reference voltage of the sub-controller, and the NPN Regulates the collector current of the totem pole for driving the series bipolar transistor buffer and the pulse transformer T1 for generating the first and second drive pulse outputs by switching the input current according to the switching of the series and PNP type series bipolar transistors. It consists of a resistor (R63).

The step-up inverter unit 20 includes push-pull switching power MOSFETs Q3 and Q4, resistors R21 and R22 for regulating an input current of a pulse transformer input to the gate of the power MOSFET, and a power transformer ( The current sensing resistor R23 is provided on the common grounding line of the power MOSFETs Q3 and Q4 to detect the current flowing to the input side of T2). In addition, a capacitor C23 is inserted to the input side of the power transformer T2 so as to form an LC resonant circuit together with the inductance of its winding.

The output unit 30 includes a power transformer T2, and the input current of the power transformer T2 is configured to be switched and supplied to both sides through a center tap that divides the first and second input terminals. On the output side of the transformer T2, a ballast capacitor C _BAL is inserted to limit the current flowing in the backlight.

The DC input supplied to the center tap of the power transformer T2 of the output unit 30 is filtered after being applied through the L / C line filter unit 10 for preventing current saturation of the power transformer and removing ripple components. Connect and configure.

In particular, a waveform correction capacitor C63 is inserted between the output terminal of the bipolar transistors Q1 and Q2 in the sub-control unit 60 and the input terminal of the pulse transformer T1.

The feedback unit 40 divides the voltage component detected by the sensing resistor R23 at a constant rate and removes the noises R41 and R42, the capacitors C40 and C41, and the variable resistor VR2 for input control. And a condenser C43.

The operation of the plasma discharge backlight driving circuit for LCD backlighting configured as described above is as follows.

First, when the LCD 83 driving control signal generated by the LCD controller 81 is generated, an active signal for generating pulses is applied to the main controller 51 in the main controller 50. Therefore, the main controller 50 generates PWM pulses having an integer value by the resistor R54 and the capacitor C53 under the given basic condition, and outputs them to the sub-control unit 60.

Accordingly, the sub control unit drives the pulse transformer T1 to drive the step-up inverter unit 20 so that the high voltage is output from the output unit 30.

That is, when the line filter 10 filters the DC power of the DC power supply 24V supply unit 70 and supplies it to the step-up inverter unit 20, the high-voltage is generated by the step-up inverter unit 20 and the output unit 30. A high output AC voltage is generated, which provides the backlight driving voltage for backlighting when the LCD is driven.

At this time, the feedback unit 40 reads the current flowing through the input side of the power transformer T2 of the output unit 30 through the sensing resistor R23, converts it into a voltage, and converts the converted signal into a main control unit ( 50).

The main controller 50 compares the input feedback signal in the main controller 51 with a reference voltage set value determined by the resistors R52 and R53 in the comparator to sense a change in the amount of current due to backlight discharge and to adjust brightness. This will reset the PWM signal. The reset luminance control signal is output to the sub controller 60.

The sub-control part 60 processes the drive pulse provided from the main control part 50 side, and adjusts the output frequency. This is determined by the timing capacitor C61 and the variable resistor VR1 for setting the frequency of the pulse signal.

In addition, the capacitor C62 serves to stabilize the voltage input to the sub-controller 61.

The resistors R61 and 62 allow the duty ratio of the pulses to be adjusted using the reference voltage generated at the sub controller 61.

The sub-controller 61 adjusted as described above drives NPN and PNP type transistors Q1 and Q2 by the output and applies a switching voltage to the input side of the pulse transformer T1. At this time, the capacitor C63 plays a role of resonance and waveform correction. On the output side of the pulse transformer T1, first and second pulse outputs appear according to an input voltage switching alternate operation of the two bipolar transistors Q1 and Q2.

The first and second pulse outputs of the sub-control unit 60 are supplied to the gate side of the power MOSFETs Q3 and Q4 of the step-up inverter unit 20 through current limiting resistors R21 and R22.

Input current by the DC voltage supplied through the line filter 10 in accordance with the switching operation of the first and second power MOSFETs Q3 and Q4 on the first and second input sides of the power transformer T2 of the output unit 30, respectively. Will flow alternately. The switching frequency at this time is determined by the L value of the input winding of the capacitor C23 and the power transformer T2.

As the high-frequency switching input voltage is supplied to the first and second input sides of the power transformer T2, a high-voltage high-voltage output is generated at the output side thereof so that an operating voltage is applied to the backlight for driving the LCD and the light is turned on.

At this time, the secondary output voltage of the power transformer can be more than 10KV, the capacitor (C _BAL ) plays a role of limiting the current through the resonance.

The input current of the power transformer T2 may be read by the sensing resistor R23 inserted into the common grounding line of the power MOSFETs Q3 and Q4 of the step-up inverter unit 20. The voltage between both ends according to the change of the current flowing through the sensing resistor R23 is processed by the feedback unit 40 and fed back to the main control unit 50, where it is compared with the reference voltage and the value. The brightness control according to the comparison result is as described above.

In the output unit 30, the power transformer T2 needs a core cross-sectional area that can apply a high voltage and a sufficient winding space to accommodate the winding in the case of an inverter requiring high voltage and high power, such as a flat backlight. . In addition, it is necessary to ensure sufficient insulation space between the primary and secondary and to increase the coupling ratio between the terminals.

Accordingly, the power transformer T2 in the output unit 30 wraps the cylindrical high pressure bobbin provided with a plurality of section type partition walls to maintain the interlayer insulation on the secondary side where the high voltage is output, and the outer diameter of the high pressure bobbin. It is preferable to manufacture using a cylindrical low pressure bobbin that is slidingly coupled.

In order to better maintain the insulation gap between the low pressure bobbin and the high pressure bobbin, a plurality of pins for maintaining the insulation gap and the high-voltage winding may be provided on the outer circumference of the high pressure bobbin, and further, the expansion of insulation may be provided between the high pressure bobbin and the low pressure bobbin. Insulation such as epoxy resin may be filled.

4 shows the front structure of the secondary side high pressure bobbin of the power transformer T2 of the output unit 30.

As referred to in this figure, the high-pressure bobbin 101 is arranged with a plurality of sections 102 to maintain an insulation gap with the primary bobbin, the output terminal for fixing the winding in the lower section of the one end portion 104 ) Is installed, and a fixing pin 103 for fixing when coupled with the primary bobbin is installed.

5 is a cross-sectional view of a section of the secondary high pressure bobbin of the power transformer.

On the outer circumference of the section 102 of the high-pressure bobbin, a plurality of insulation interval maintaining pins 107 are provided. The pin 107 functions as a pin for fixing a high voltage winding.

FIG. 6 is a side view of the secondary side high pressure bobbin of the power transformer, and a winding outlet 105 for discharging the high pressure winding when winding the bobbin body and a winding fixing terminal 104 for fixing the power transformer are installed at one side of the bobbin body. .

By fixing the high-voltage winding by using the same projection as the pin 107 of FIG. 5 when winding by the above structure, it is extracted to the outside through the winding outlet 105 and fixed to the external terminal by the winding fixing terminal 104. Let's go.

7 is a side view of the primary low pressure bobbin of the power transformer.

One side of the low-pressure bobbin 106 is provided with a barrier (109) for maintaining the insulating gap is provided with an injection hole 108 for injecting the insulating liquid (epoxy) to maintain the insulating gap with the secondary winding outlet. have.

8 is a view showing a state in which the primary and secondary bobbin of the power transformer is coupled.

As shown in the figure, the coupling method of the primary and secondary bobbin is made of a type of fitting the primary low pressure bobbin 106 on the secondary high pressure bobbin 101 in a sliding manner, the coupling and fixing between the bobbin for fixing The pins 103, 107 are joined and secured and can always maintain a constant insulation gap.

In addition, an insulating material such as an epoxy resin may be inserted into the insulating space to increase the breakdown voltage between the high voltage windings.

The power transformer bobbin having the above structure accommodates an EER type ferrite core that is used in general use in a switching mode power supply (SMPS). It is also possible to apply a core of EE or EI type.

As described above, the present invention can drive the plasma discharge type backlight stably at a constant luminance value while reducing the power loss because a DC / DC converter is unnecessary.

In addition, the present invention may adjust the brightness of the backlight by artificially adjusting the pulse width of the sub-control unit as necessary.

In addition, the present invention can improve the structure of the power transformer to output a high voltage of a high frequency, it is possible to increase the efficiency and compactness of the backlight drive inverter.

Claims (10)

A main controller 50 which receives a voltage value corresponding to an input current variation of an inverter circuit when the LCD driving control signal is generated in the LCD controller, and compares it with a reference voltage value to generate a pulse for adjusting brightness; A sub-control unit 60 receiving a luminance control output pulse from the main controller and generating a duty and timing-controlled driving pulse and generating first and second pulse outputs for power transistor switching using the driving pulse; A step-up inverter unit 20 driving the first and second pulse outputs of the sub-control unit to generate a control signal for switching the input current of the power transformer; An output unit 30 including a power transformer T2 for outputting a high voltage of a high frequency for driving the backlight for the LCD according to the switching power output of the step-up inverter unit; And a feedback unit 40 which converts the input current variation detected by the sensing resistance of the step-up inverter unit 20 into a voltage component and provides it to the main controller 50. Driving circuit. The input current of the power transformer T2 in the output unit 30 is configured to be switched and supplied to both input sides through a center tap that divides the first and second input terminals. And a ballast capacitor (C _BAL ) inserted into the output side to limit the current flowing in the backlight. The L / C line according to claim 1 or 2, wherein the L / C line prevents current saturation of the power transformer and removes ripple components on the DC input line supplied to the center tap of the power transformer T2 of the output unit 30. The drive circuit of the plasma discharge type flat backlight, characterized in that the filter unit 10 is inserted. 2. The step-up inverter unit 20 according to claim 1, wherein the step-up inverter unit 20 applies currents flowing to the input side of the power input T2 and the gate input current adjusting resistors R21 and R22 of the push-pull switching power MOSFETs Q3 and Q4. A sensing resistor R23 provided on a common grounding line of the power MOSFETs Q3 and Q4 for detection, and a capacitor C23 provided on an input side of the power transformer T2 to form an LC resonance circuit. A driving circuit of the plasma discharge type flat backlight, characterized in that. The main controller (50) of claim 1, wherein the main controller (50) is activated when an LCD drive control signal is generated by the LCD controller (81), and outputs from a regulator to generate a reference voltage and a main controller (51) for generating a PWM signal for brightness adjustment. Distribution resistors R52 and R53 for distributing the Vcc voltage, a filter capacitor C52 for removing noise included in a signal input through the feedback unit, a timing capacitor C53 and a timing resistor for setting the frequency. (R54), the driving circuit of the plasma discharge type flat backlight. According to claim 1, wherein the sub-control unit 60 receives a PWM pulse for adjusting the brightness of the main controller 51 of the main control unit sub-controller 61 for generating a bipolar transistor driving pulse, and the driving pulse output from the sub-controller A timing capacitor C61 and a variable resistor VR1 for adjusting the frequency, a capacitor C62 for stabilizing the input voltage of the sub-controller, and a resistor for adjusting the duty ratio with a reference voltage of the sub-controller ( R61), a pulse transformer T1 for generating first and second driving pulse outputs by switching supply of an input current according to switching of the NPN type and PNP type series bipolar transistors, and for driving the series bipolar transistor buffer. And a resistor (R63) for adjusting the collector current of the totem pole. 7. The driving circuit of the plasma discharge type flat backlight according to claim 6, wherein a waveform correction capacitor (C63) is inserted between the output terminal of the bipolar transistors (Q1, Q2) and the input terminal of the pulse transformer (T1). The method of claim 1, wherein the power transformer T2 in the output unit 30 is a cylindrical high-pressure bobbin 101 is provided with a plurality of section type barrier ribs to maintain the high-voltage interlayer insulation of the secondary side, and The driving circuit of the plasma discharge type flat backlight, characterized in that it is manufactured by using a cylindrical low-pressure bobbin 106 that is sliding coupled around the outer circumference. [9] The plasma discharge type flat backlight of claim 8, wherein a plurality of insulation intervals and high-voltage winding fixing pins 107 are provided on the outer periphery of the high-pressure bobbins to maintain the insulation intervals of the low-voltage bobbins and the high-voltage bobbins. Driving circuit. 10. The driving circuit for a plasma discharge type flat backlight according to claim 8 or 9, wherein an insulating material such as an epoxy resin is filled between the high pressure bobbin and the low pressure bobbin to increase the insulation.