KR20080045488A - Driving system for fluorescent lamp and backlight unit having the same - Google Patents

Abstract

A fluorescent lamp driving system and a backlight unit having the system are provided to convert a sine wave voltage generated by an inverter to a DC voltage and generate a square wave from the DC voltage through a switching operation and drive a fluorescent lamp using the square wave so as to improve the efficiency of the fluorescent lamp. A fluorescent lamp driving system(200) includes an inverter(210), a rectifier(230), and a switching unit(240). The inverter controls an input DC voltage to output a sine wave AC signal. The rectifier is connected to the secondary side of a transformer(220) of the inverter and rectifies an output signal of the inverter to generate a DC voltage. The switching unit generates a square wave from the DC voltage generated by the rectifier.

Description

A driving system of a fluorescent lamp and a backlight unit including the same {DRIVING SYSTEM FOR FLUORESCENT LAMP AND BACKLIGHT UNIT HAVING THE SAME}

1 is an exemplary circuit diagram of a drive system for supplying a sine wave.

2 is an exemplary circuit diagram of a drive system for supplying square waves.

Figure 3 is a perspective view showing the appearance of a flat fluorescent lamp.

4 is a schematic representation of a drive system of the present invention.

5 is an exemplary circuit diagram of a drive system of the present invention.

6 is an equivalent circuit of a switching unit including a fluorescent lamp.

7 is a graph showing a pulse wave according to the operation of the drive system of the present invention.

8 is a graph showing a square wave according to the operation of the drive system of the present invention.

*** Explanation of symbols for the main parts of the drawing ***

200: drive system 210: inverter

220: transformer 222: center tap

230: rectifier 240: switching unit

250: lamp

The present invention relates to a driving system of a fluorescent lamp and a backlight unit including the same, and to a driving system generating a square wave and advantageous for thinning, and a backlight unit including the same.

Unlike other light emitting displays, a liquid crystal display does not emit light by itself, and thus requires a separate backlight.

A variety of light sources are used for the backlight used in the liquid crystal display, and a cold cathode fluorescent lamp (CCFL) with a cold cathode inside the tubular bulb, a hot cathode fluorescent lamp (HCFL) with a hot cathode instead of a cold cathode, and a plurality of tubular types External electrode fluorescent lamps (EEFL) employing a common electrode outside the valve, and the like. In recent years, flat fluorescent lamps in which discharge spaces are formed of flat substrates instead of tubular bulbs have been proposed.

The backlight light source should have low power consumption and excellent luminous efficiency, and should have high brightness and uniform brightness.

In recent years, as the size of liquid crystal displays increases, a large area surface light source is required as a backlight. As the size of liquid crystal displays increases, the size of the surface light source is also increasing. Accordingly, an inverter circuit having a large power capacity is required for the backlight.

In general, an inverter circuit having a large power capacity can be realized by increasing the boosting transformer and its driving circuit, but an inverter circuit having high efficiency is required because an inverter circuit having a large power capacity causes large heat generation even with a small power loss.

In the inverter circuit for a surface light source having a large power capacity, the most costly circuit is a boost transformer and a drive circuit. In a large area light source device requiring a high voltage, a large power of the boosting transformer of the inverter circuit is required, but when the power of the boosting transformer is increased, the size thereof is also enlarged, which inevitably causes an increase in thickness.

1 is an exemplary circuit diagram of a driving system for generating an AC output voltage by a DC input voltage using a conventional inverter 10. The waveform applied to the lamp 15 through the transformer 12 is an output voltage in the form of a sine wave. to be. In general, the circuit configuration of the inverter is a push-pull, half-bridge type is applied to apply the AC waveform to the load through the resonance.

In driving a fluorescent lamp for a backlight, a driving voltage in the form of a square wave is more advantageous for implementing various operations of the backlight such as pulse dimming (PWM dimming) than a driving voltage in the form of a sine wave.

2 is an exemplary circuit diagram of a drive system for applying a square wave to a lamp. The AC input, which is a commercial power source, is converted into a DC voltage of about 380 V to 395 V through the rectifier 20 and the DC converter 22, and a square wave is applied to the lamp 28 through the switch 24. Since the voltage applied to the lamp is a high voltage, the step-up transformer 26 is used to change the output voltage of 380 V to 395 V to high voltage. In order to meet the capacity and withstand voltage characteristics of the transformer for high voltage output, increasing the transformer size is inevitable. Since the backlight for a liquid crystal display device requires a large area and a thinness, it is preferable that the thickness of the step-up transformer of the driving system is as thin as possible.

In addition, the driving system of FIG. 2 generates an overcurrent according to dt / dv when FET or IGBT is applied at the time of switching on / off the bridge diode of the transformer primary side, and also when the fluorescent lamp is connected to the load, the inductance of the secondary transformer Since resonance occurs due to the capacitance of the fluorescent lamp, it is difficult to implement a desired square wave waveform.

It is an object of the present invention to provide a drive system for a fluorescent lamp that generates a drive voltage of a stable square wave.

Another object of the present invention is to provide a slim driving system suitable for a thin backlight.

The present invention relates to a drive system for applying a pulsed square wave for improving the efficiency of a fluorescent lamp. The sine wave output voltage generated by the inverter is converted into a direct current voltage, and finally a square wave is generated by switching to drive a fluorescent lamp.

Specifically, the present invention, an inverter for controlling the input DC voltage to output a sinusoidal AC signal, a rectifier connected to the transformer secondary side of the inverter to rectify the output signal of the inverter to generate a DC voltage, from the DC voltage of the rectifier It provides a drive system of a fluorescent lamp comprising a switching unit for generating a square wave.

The rectifier may include two sub rectifiers receiving an output voltage having the same phase from the transformer, and in this case, each western rectifier may include a bridge diode unit and a capacitor.

The switching unit includes a switching circuit for generating a pulse waveform or a square waveform from the DC voltage output from the rectifier.

The present invention also provides a backlight unit including a fluorescent lamp, a drive system for applying a driving voltage to the fluorescent lamp, and a case for physically supporting the fluorescent lamp.

In the present invention, the transformer primary side circuit of the inverter may be changed in various forms such as push-pull, half bridge and full bridge circuit, but the transformer secondary side output is separated Two high voltages are generated through the wiring. To this end, the transformer secondary side of the inverter preferably includes a center tap for inducing two output voltages of the same phase.

According to the present invention, it is possible to solve the problem of thinning due to the size of the transformer and the heat generation caused by the high capacity of the transformer when the boost type transformer is used. The drive system provided by the present invention can apply a thin transformer to the inverter as it is, contributing to the thinning of the backlight and the liquid crystal display device employing the same.

FIG. 3 shows a flat fluorescent lamp that is one of surface light sources as an example of a fluorescent lamp. The fluorescent lamp 100 includes a light source body 110 and electrode portions 160 provided on outer surfaces of both edges of the light source body 110.

The light source body 110 may include a first substrate and a second substrate disposed to face each other at a predetermined interval. A plurality of partitions 140 are disposed inside the light source body to divide the discharge space inside the light source body into a plurality of discharge channels 120. The discharge channel 120 and the partition wall 140 may be formed by, for example, forming a first substrate, or may be formed by molding a second substrate instead of the first substrate. A sealing member 130 is disposed between the edges of the first substrate and the second substrate to isolate the discharge channels 120 from the outside. Discharge gas is injected into the discharge space 150 inside the discharge channel 120. Although not shown, the discharge channel 120 may further include a fluorescent layer and a protective layer, and a reflective layer may be formed inside the light source body.

In order to drive the fluorescent lamp, a pair of electrode units 160 having a band shape are formed on a surface of the light source body 110. When a voltage is applied to the electrode unit 160 using an inverter (not shown), gas injected into the discharge space 150 in the discharge channel is discharged.

In a fluorescent lamp using an external electrode, a voltage is applied to the internal discharge space through the electrode, and in terms of circuits, the lamp itself may be equivalent to a capacitor.

For convenience, the present invention describes the driving system according to the present invention by taking the flat fluorescent lamp of FIG. 3 as an example. In addition, other types of fluorescent lamps, for example, cold cathode fluorescent lamps (CCFL) and external electrode type tubular fluorescent lamps The drive system of the present invention can also be applied to a lamp EEFL, a hot cathode fluorescent lamp HCHC, and the like.

The operation of the drive system according to the present invention includes a DC input process converted from a commercial power source, oscillation and control process in an inverter, a boosting process through a transformer, a rectifying process of an AC output voltage (DC conversion process), and a final square wave generation process. It is composed.

To this end, the drive system of the present invention has a configuration as shown in FIG. The DC generator may be included outside the fluorescent lamp, for example, a power supply unit of the liquid crystal display. The remaining inverters, transformers, rectifiers and switching units may be packaged into one module and wired to the fluorescent lamp. In some cases, the transformer, the rectifier and the switching unit may be formed in one inverter device. The driving system according to the present invention may be included in a backlight unit together with a fluorescent lamp, for example, a flat fluorescent lamp, a cold cathode fluorescent lamp, an external electrode fluorescent lamp, a hot cathode fluorescent lamp, and the like shown in FIG. 3.

5 is an exemplary circuit diagram of a proposed system for applying a square wave to a fluorescent lamp.

A DC voltage is input to the inverter 210 through a DC generator (not shown) for generating a DC from a commercial power supply. The DC input voltage generates a voltage of a sine wave, which is an AC output, and passes through a transformer 220 through Changed to voltage.

Various forms of means can be applied to generate the initial DC voltage input to the inverter. For example, a method of using a PFC output voltage via a commercial power AC input via a PFC circuit, or converting a PFC output voltage into a 24V or other DC voltage using a DC-DC converter may be used as an input voltage of an inverter. .

The inverter may typically include a DC-DC conversion oscillator, a controller, a driver, and the like, and the transformer primary side circuit of the inverter may be applied to various topologies such as push-pull, half-bridge, and full-bridge.

A boosted AC type output voltage is generated on the secondary side of the transformer. The output voltage is converted into direct current by the rectifying unit 230 through a rectifying process. In the present invention, the AC voltage is rectified using the first bridge diode BD1 and the second bridge diode BD2 connected to the transformer secondary side, respectively. The rectified voltage is converted into a DC voltage through the first capacitor C1 and the second capacitor C2.

In the case of using only one output voltage without using the center tap 222 in the output voltage of the inverter as shown in FIG. 5, the bridge diode unit and the rectifier capacitor may be configured as one block. The stress on each part of the is increased. In order to reduce this disadvantage, in the present invention, the rectifier for converting the output of the inverter into a direct current is separated into two bridge diode parts and two capacitors, and the secondary side of the inverter is separated so that the in-phase AC output voltage is separated from each other. The center tap 222 was placed in the transformer.

The first capacitor C1 and the second capacitor C2 of the rectifier are connected in series to generate a high voltage DC output voltage. The potential across the first capacitor C1 becomes almost twice that of the potential across the second capacitor C2. The potential difference between the first capacitor and the second capacitor is equal to the potential difference between the second capacitor and the transformer secondary side GND.

If the output voltage peak of the inverter is 1 KV, the bridge diode and capacitor will maintain the DC 1 KV voltage in the ideal case. In practice, the DC voltage is below 1 KV due to the bridge diode's on-resistance, output capacitance, equivalent series resistance (ESR), tangent loss, and other parasitic components of the capacitor. Assuming an ideal case, the voltage across the first capacitor C1 charges 1 KV of direct current, and the first capacitor C2 also charges 1 KV of direct current.

The voltage applied across the first capacitor C1 and the second capacitor C2 in the rectifying capacitor is applied with a voltage corresponding to the peak value of the output voltage of the inverter, and the DC voltage applied to the switching unit 240 is a rectifying capacitor. The total voltage stored in the first capacitor C1 and the second capacitor C2 is applied.

A square wave is finally generated through the switching unit 240 using the DC voltage as an input, and the generated square wave is applied to the fluorescent lamp 250 to cause discharge. In the present invention, the full bridge switch (SW1, SW2, SW3, SW4) circuit is used as the switching unit.

Referring to FIG. 6, an equivalent circuit including the full bridge switch is illustrated by equalizing a fluorescent lamp with a capacitor. An example of a drive waveform applied to a fluorescent lamp by the operation of the drive system according to the present invention will be described with reference to FIGS. 7 and 8.

As shown in FIG. 7, the driving waveform is determined according to the pulse wave driving according to the on / off of the switches S1 to S4.

First, in the section A, the switches S2 and S4 are turned on, and OV is applied to both ends of the lamp so that the lamp does not discharge. Next, in the section B, the switches S1 and S4 are turned on to apply V _in voltage across the lamp, and the lamp discharges. Then, in the interval C, the switches S2 and S4 are turned on so that OV is applied across the lamp, and the lamp does not discharge. Finally, in the D section, the switches S2 and S3 are turned on to apply a −V _in voltage having a phase difference of 180 degrees from the voltage applied at the section B across the lamp, and the lamp is discharged again.

The driving waveform of FIG. 7 corresponds to a pulse wave driving in which waveforms from section A to section D are periodically repeated and a dead voltage is present.

Next, referring to the square wave driving shown in FIG. 8, first, in the F section, the switches S1 and S4 are turned on to apply the V _in voltage across the lamp, and the lamp discharges. Next, in the G section, the switches S2 and S3 are turned on to apply -V _in voltage across the lamp, and the lamp is discharged.

In the driving waveform of FIG. 8, the waveforms from the F section to the G section are repeated periodically, and the square wave driving is performed without a specific voltage application time.

The voltage waveform applied to the lamp may be determined as, for example, a pulse wave and a square wave according to the driving method of the full bridge switch.

In the above, it has been described with reference to preferred embodiments of the present invention, but those skilled in the art or those skilled in the art from the spirit and scope of the invention described in the claims to be described later Various modifications and variations can be made in the present invention without departing from the scope thereof.

According to the present invention, a novel drive system suitable for square wave driving without using a large sized high capacity transformer is provided. Therefore, problems such as heat generation of the boost type transformer and inhibition of slimming of the backlight unit due to the increase in the size of the driving system can be solved.

Claims (10)

An inverter for controlling the input DC voltage to output a sinusoidal AC signal, A rectifier connected to the transformer secondary side of the inverter to rectify an output signal of the inverter to generate a DC voltage; It includes a switching unit for generating a square wave from the DC voltage of the rectifier Driving system of fluorescent lamps. The driving system of claim 1, wherein the rectifier comprises two sub rectifiers receiving an output voltage having the same phase from the transformer. 3. The driving system of claim 2, wherein the rectifier comprises two bridge diode units and two capacitors connected to a transformer secondary side of the inverter. 4. The driving system of claim 3, wherein the two capacitors are connected in series with each other. The driving system of claim 1, wherein the switching unit comprises a full bridge switch generating a pulse waveform or a square waveform from a DC voltage output from the rectifying unit. The driving system of claim 1, wherein the transformer secondary side of the inverter includes a center tap for inducing two output voltages of the same phase. The driving system of the fluorescent lamp of claim 1, wherein a DC voltage is applied to the inverter via a PFC circuit. The driving system of claim 1, wherein the transformer primary side circuit of the inverter is any one of a push-pull, a half bridge, and a full bridge circuit. With fluorescent lamps, A drive system for applying a drive voltage to the fluorescent lamp, and A case for physically supporting the fluorescent lamp, The drive system includes an inverter for controlling the input DC voltage to output a sinusoidal AC signal, a rectifier connected to the transformer secondary side of the inverter to rectify the output signal of the inverter to generate a DC voltage, and a square wave from the DC voltage of the rectifier. Including a switching unit for generating Backlight unit. The backlight unit of claim 9, wherein the fluorescent lamp is any one selected from a cold cathode fluorescent lamp, an external electrode fluorescent lamp, a flat fluorescent lamp, and a hot cathode fluorescent lamp.

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