KR100631984B1 - Back-light inverter with current detecting function of induction type - Google Patents

Abstract

A back-light inverter having an induction-type current detection function is provided to stably control a lamp current by accurately detecting a current of a lamp through an induction manner and a full-wave rectifying manner. A drive unit(100) is controlled in a PWM(Pulse Width Modulation) mode to generate first and second square wave drive current having different inverted phase. A main transformer(200) transforms the first and second square wave drive current into first and second AC drive current. An auxiliary transformer(300) has a first auxiliary coil and a second auxiliary coil. A full-wave rectifier(400) rectifies the current detected by the auxiliary transformer. A drive controller(500) controls a PWM of the first and second square wave drive current.

Description

BACK-LIGHT INVERTER WITH CURRENT DETECTING FUNCTION OF INDUCTION TYPE}

1 is a configuration diagram of a conventional backlight inverter for large LCD.

2 is a waveform diagram of a driving current of the backlight inverter of FIG. 1.

3 is a block diagram of a backlight inverter for a large LCD according to the present invention.

4 is a waveform diagram of a driving current of the backlight inverter of FIG. 3.

5 is a voltage waveform diagram by the lamp driving current detection circuit of the present invention.

Explanation of symbols on the main parts of the drawings

100: drive unit 200: main transformer

300: auxiliary transformer 400: full-wave rectifier

500: drive control unit PD1, PD2: first and second square wave driving current

L1, L2: Primary and secondary coil UL: Lamp

CL: Current line L21, L22: Primary and secondary auxiliary coils

AD1, AD2: first and second AC drive currents R41, R42: first and second resistors

D41, D42: first and second diode C41: capacitor

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lamp driving current detection circuit applied to LCD backlight inverters such as large LCDs (hereinafter referred to as LCDs) -TVs and large LCD monitors. By implementing the induction method and the full-wave rectification method on the secondary side of the transformer to accurately detect the current of the U lamp, the lamp current can be controlled stably and accordingly, thereby inducing the luminance to be kept constant. It relates to a backlight inverter having a current detection function of the type.

In general, as the LCD-TV and LCD-monitor market gradually enlarges, the number of lamps mounted on the back light unit gradually increases, and as the tube shape of the lamp and the tube length of the lamp gradually increase, The manner in which the lamp is driven is also changing.

According to this trend, a conventional backlight backlight inverter for LCDs is also divided into an inverter applied to a small LCD of about 17 inches and an inverter applied to a large LCD of 17 inches or more, and the inverter applied to the small LCD is approximately A feedback node for generating the 500-800 Vrms lamp driving voltage, detecting the lamp current and stabilizing the lamp current is formed at the cold end of the lamp.

In addition, a relatively long lamp is applied to the backlight inverter applied to the large LCD, rather than a lamp applied to a conventional small LCD backlight inverter, such as a long straight lamp or a U-shaped lamp. Since the driving voltage of about 1KVrms is required, there are various technical problems to be solved even for driving such a long lamp, and one of them is how to detect the current flowing through the lamp and control it in the constant current mode. .

 In particular, a large LCD backlight inverter drives one lamp by using two transformers, and the distinction between a hot end and a cold end is ambiguous, and unlike a small LCD inverter, a current is applied at a cold end of a lamp. Since it is not desirable to sense (Sensing), a method of controlling the lamp current through another root (root) is adopted. One of such conventional backlight inverters is as shown in FIG.

1 is a block diagram of a conventional backlight inverter for LCD.

Referring to FIG. 1, a conventional backlight inverter for a large LCD uses two first and second transformers 21 to drive a U lamp (U-shaped lamp) 30 that requires a high driving voltage of about 1 KVrms. 22, wherein each of the first and second transformers 21 and 22 boosts a square wave signal by the corresponding first and second drivers 21 and 22 and converts the square wave signal into an AC signal, thereby converting the ramp 30 The first and second AC driving currents SD1 and SD2 which are in phase relationship with each other, which are required for the operation of the PDP, are supplied to one side and the other side of the lamp 30.

In order to constantly control the current flowing through the lamp 30, the backlight inverter includes a current detector 40 having a feedback node connected to a ground side of each secondary coil of the first and second transformers 21 and 22. It includes. The current detector 40 detects and feeds back a voltage caused by the current flowing in the secondary of the transformer.

Based on the current detected by the current detector 40, the drive controller 50 controls the corresponding first and second drivers 11 and 12 to control the drive current flowing through the lamp 30 to be a constant current. do.

2 is a waveform diagram of a driving current of the backlight inverter of FIG. 1.

Referring to FIG. 2, the first and second AC driving currents AS1 and AS2 supplied to the lamps 30 from the first and second transformers 21 and 22 are in an antiphase relationship with each other. The driving current flows through the lamp 30 by the first and second AC driving currents AS1 and AS2 having an antiphase relationship.

The current detector 40 for detecting the driving current includes a first resistor R1 connected to the ground side of the secondary coil of the first transformer 21 and a ground of the secondary coil of the second transformer 22. It includes a second resistor (R2) connected to the side.

However, in such a conventional large-size LCD backlight inverter, two transformers are required to operate one U lamp 30, so that the price increases. This disadvantage is limited to the miniaturization and cost reduction of the product, it is an undesired driving method considering the size and price aspects.

According to this disadvantage, a method of driving one U lamp with one transformer has been researched and developed. In this one-trans lamp system, the voltage supplied to the U lamp is set to an arbitrary voltage within the range of approximately 750 to 1000 V. Since the voltage is considerably high, a method of detecting a current flowing through the lamp in the high driving voltage state according to the winding ratio of the primary and secondary auxiliary coils L21 and L22 is required.

The present invention has been proposed to solve the above problems, and an object thereof is to accurately detect a current of a U lamp using an induction method and a full wave rectification method on the secondary side of the main transformer in a one-lamp-one-transmission backlight inverter. The present invention provides a backlight inverter having an inductive current detection function capable of controlling the lamp current in a stable and stable manner, thereby maintaining a constant luminance.

In order to achieve the above object of the present invention, a backlight inverter having a current detection function of the induction method of the present invention, the driving unit for generating the first and second square wave drive current controlled by the PWM method and having an opposite phase to each other; The first and second square wave driving currents from the driving unit are converted into first and second alternating currents according to the winding ratios of the primary coil and the secondary coil, and both ends of the secondary coil are connected to the lamps connected to the ends thereof. A main transformer for outputting the AC drive current; A primary auxiliary coil formed on a current line between the secondary coil of the main transformer and the lamp, and a secondary auxiliary coil inductively coupled to the primary auxiliary coil, the primary and the secondary current being supplied to the lamp. An auxiliary transformer detecting according to a winding ratio of a secondary auxiliary coil; A full-wave rectifier for converting the current detected by the auxiliary transformer into a voltage to perform full-wave rectification; And a driving control unit for controlling the PWM duty of the first and second square wave driving currents of the driving unit based on the detected voltage from the current rectifying unit.

The full wave rectifier may include: a first resistor connected to ground at one end of the secondary auxiliary coil of the auxiliary transformer; A second resistor connected to ground at the other end of the secondary auxiliary coil of the auxiliary transformer; A first diode rectifying the voltage detected by the first resistor; A second diode rectifying the voltage detected by the second resistor; And a capacitor that combines the outputs of the first and second diodes to smooth the full-wave rectified voltage.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings referred to in the present invention, components having substantially the same configuration and function will use the same reference numerals.

3 is a configuration diagram of a backlight inverter for a large LCD according to the present invention.

Referring to FIG. 3, the backlight inverter according to the present invention employs a method of detecting a current flowing through the lamp in an inductive manner and full-wave rectification in a method of driving one lamp with one transformer. The large LCD backlight inverter includes a driver 100, a main transformer 200, an auxiliary transformer 300, a full wave rectifier 400, and a drive controller 500.

Referring to FIG. 3, the driving unit 100 is configured to generate first and second square wave driving currents PD1 and PD2 that are controlled in a PWM manner and have an antiphase with each other under the control of the driving control unit 500. . Here, the first and second square wave driving currents may have any frequency within a range of approximately 40 kHz to 70 kHz.

The main transformer 200 converts the first and second square wave driving currents PD1 and PD2 from the driver 100 according to the winding ratios of the primary coil L1 and the secondary coil L2. It converts into second AC driving currents AD1 and AD2 and outputs the AC driving currents AD1 and AD2 to a lamp UL connected to both ends of the secondary coil L2, respectively. The winding ratios of the primary coil L1 and the secondary coil L2 are different depending on the lamp applied, and are determined according to the current or voltage rating required in the applied lamp.

Here, the type of the lamp to be applied to the inverter of the present invention is not particularly limited, but has been implemented to suit the U-shaped U lamp.

The auxiliary transformer 300 of the present invention includes a primary auxiliary coil L21 formed on a current line CL between the secondary coil L2 of the main transformer 200 and the lamp UL, and the primary coil. Including a secondary auxiliary coil (L22) inductively coupled to the auxiliary coil (L21), it is made to detect the current flowing in the lamp (UL) according to the winding ratio of the primary and secondary auxiliary coils (L21, L22) All. In the case of using such an induction transformer, it is possible to detect a desired current without being affected by the high driving voltage of the lamp.

The full-wave rectifying unit 400 of the present invention is to convert the current detected by the auxiliary transformer 300 into a voltage to full-wave rectification.

In one embodiment of the full-wave rectifying unit 400 of the present invention, the first resistor (R41) connected to the ground at one end of the secondary auxiliary coil (L22) of the auxiliary transformer 300, and the two of the auxiliary transformer 300 The second resistor R42 connected to the ground at the other end of the secondary auxiliary coil L22, the first diode D41 rectifying the voltage detected by the first resistor R41, and the second resistor R42. The second diode D42 rectifies the voltage detected by the second diode, and the capacitor C41 smoothes the full-wave rectified voltage by combining the outputs of the first and second diodes.

The driving controller 500 compares the detected voltage from the current rectifying unit 400 with an internal set voltage, and according to the comparison result, the first and second square wave driving currents PD1, To control the PWM duty of PD2).

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

The backlight inverter of the present invention is suitable for a large LCD TV or LCD monitor to which a U lamp (UL) having high luminous efficiency is applied, which will be described with reference to FIGS. 3 to 5.

Referring to FIG. 3, in the backlight inverter of the present invention, the driving unit 100 generates the first and second square wave driving currents PD1 and PD2 which are controlled in a PWM manner by the driving control unit 500 and have an antiphase with each other. To the main transformer 200. The first and second square wave driving currents PD1 and PD2 are as shown in FIG. 4.

Next, the main transformer 200 controls the first and second square wave driving currents PD1 and PD2 from the driving unit 100 according to the winding ratios of the primary coil L1 and the secondary coil L2. The first and second AC driving currents AD1 and AD2 are converted, and the AC driving currents AD1 and AD2 are outputted to a lamp UL connected at both ends of the secondary coil L2.

Here, a voltage of about 1600 Vrms is applied to both ends of the U lamp UL by the AC driving currents AD1 and AD2 as shown in FIG. 4, and the current flowing through the lamp UK by such a high voltage is applied. Since it is not directly detected by an element such as a resistor, in the backlight inverter of the present invention, as shown in FIG. Detection is performed according to the winding ratio of the auxiliary coils L21 and L22.

4 is a waveform of a driving signal of the backlight inverter of FIG. 3.

Referring to FIG. 4, the first and second square wave driving currents PD1 and PD2 from the driving unit 100 are in an antiphase relationship with each other, and the first and second square wave driving currents PD1 and PD2 are approximately equal to each other. It has a frequency of 40KHz to 70KHz. The first and second square wave driving currents PD1 and PD2 are converted into the AC driving currents AD1 and AD2 by the main transformer.

Referring to the process of detecting the current of the lamp by the induction method, the auxiliary transformer 300 is a current flowing from the secondary coil (L2) of the main transformer 200 to the lamp (UL) is a current line (CL) The secondary auxiliary coil (L21) from the primary auxiliary coil (L21) of the auxiliary transformer 300 formed on the (2), in which the current flowing through the lamp in the primary auxiliary coil (L21) in both directions As a result, current flows in both directions to the secondary auxiliary coil L22.

That is, the current flowing through the lamp UL is induced from the primary auxiliary coil L21 to the secondary auxiliary coil L22. At this time, the secondary auxiliary coil L22 of the auxiliary transformer 300 is induced. The current to be detected in both directions, so that the current in both directions is full-wave rectified by the full-wave rectifier 400 described below.

Next, the full-wave rectifying unit 400 converts the current detected by the auxiliary transformer 300 into a voltage to full-wave rectification and supplies it to the driving control unit 500, which will be described with reference to FIG. 5.

5 is a detection waveform diagram by the lamp driving current detection circuit of the present invention.

3 to 5, the first resistor R41 of the full wave rectifying unit 400 receives a current SC1 flowing from the one end of the secondary auxiliary coil L22 of the auxiliary transformer 300 to ground. The second and second secondary coils L21 and L22 are detected according to the winding ratios, and the second resistor R42 of the full-wave rectifying unit 400 is connected to the secondary auxiliary coil L22 of the auxiliary transformer 300. The current SC2 flowing from the other end to the ground is detected according to the winding ratios of the primary and secondary auxiliary coils L21 and L22.

The voltage VD1 detected by the first resistor R41 is half-wave current by the first diode D41 to form a voltage waveform S1 as shown in FIG. 5. The voltage VD2 detected by the second resistor R42 is half-wave rectified by the second diode D42 to form the voltage waveform S2 shown in FIG. 5. When the voltage waveforms S1 and S2 half-wave rectified by the first and second diodes D1 and D2 are combined, a full-wave rectified voltage is generated as shown in the voltage waveform S3 of FIG. 5. At this time, when the voltage waveform S3 is smoothed by the capacitor C41, the voltage waveform S3 is supplied to the driving controller 500 as a direct current (DC) voltage as shown by the waveform S4 shown in FIG. 5.

When the full-wave rectifier 400 is used together with the auxiliary transformer 300, the voltage detected by the full-wave rectifier 400 becomes larger than the half-wave rectifier, so that the secondary coil of the auxiliary transformer 300 The number of turns can be reduced, allowing the use of a small auxiliary transformer.

Thereafter, the driving controller 500 controls the PWM duty of the first and second square wave driving currents PD1 and PD2 of the driving unit 100 based on the detected voltage from the current rectifying unit 400. According to the control of the driving control unit 500 as described above, the driving unit 100 controls the duty by the PWM method with respect to the first and second square wave driving currents, and this PWM control method is a general technical matter in the art. Description is omitted. Accordingly, the current flowing through the lamp UL is kept constant.

The auxiliary transformer and the full-wave rectifying unit of the present invention can detect a stable DC voltage of the current flowing through the lamp, thereby controlling the drive current of the lamp to a constant current almost unchanged by the drive control unit and the drive unit. Thus, the brightness of the lamp can be maintained at a stable level.

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, but is defined by the claims, and the apparatus of the present invention may be substituted, modified, and modified in various ways without departing from the spirit of the present invention. It is apparent to those skilled in the art that modifications are possible.

According to the present invention as described above, among the LCD backlight inverters such as large LCD-TVs and large LCD monitors, induction lamps and full-wave rectification methods are used on the secondary side of the main transformer in the one-lamp-one-transmission backlight inverter. Therefore, by implementing the current to accurately detect the U lamp, it is possible to control the lamp current constantly and stably, thereby maintaining the luminance constant.

Claims (2)

A driver configured to generate the first and second square wave driving currents controlled by the PWM method and having opposite phases to each other; The first and second square wave driving currents from the driving unit are converted into first and second alternating currents according to the winding ratios of the primary coil and the secondary coil, and both ends of the secondary coil are connected to the lamps connected to the ends thereof. A main transformer for outputting the AC drive current; A primary auxiliary coil formed on a current line between the secondary coil of the main transformer and the lamp, and a secondary auxiliary coil inductively coupled to the primary auxiliary coil, the primary and the secondary current being supplied to the lamp. An auxiliary transformer detecting according to a winding ratio of a secondary auxiliary coil; A full-wave rectifier for converting the current detected by the auxiliary transformer into a voltage to perform full-wave rectification; And A driving control unit for controlling the PWM duty of the first and second square wave driving currents of the driving unit based on the detected voltage from the current rectifying unit; Backlight inverter having a current detection function of the induction method, characterized in that made. According to claim 1, wherein the full-wave rectifying unit A first resistor connected to ground at one end of the secondary auxiliary coil of the auxiliary transformer; A second resistor connected to ground at the other end of the secondary auxiliary coil of the auxiliary transformer; A first diode rectifying the voltage detected by the first resistor; A second diode rectifying the voltage detected by the second resistor; And A capacitor that smoothes the full-wave rectified voltage by combining the outputs of the first and second diodes Backlight inverter having a current detection function of the induction method comprising a.

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