KR100648511B1 - System for drive of multi Cold-cathode tub Fluorescent lamp - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multiple cold cathode fluorescent lamp driving system, and more particularly to a driving system for lighting a plurality of fluorescent lamps, comprising: a switching circuit for converting and outputting a DC input voltage into an AC voltage according to external control; A current balance circuit which receives an AC voltage output from the switching circuit and maintains a lamp current balance; A plurality of transformers for amplifying the signal output from the current balancing circuit; A plurality of fluorescent lamps lit by the voltage output from each said transformer; A current sensing circuit for sensing current output from each of the fluorescent lamps; And a control circuit for controlling the switching circuit according to the signal output from the current sensing circuit.

According to the present invention as described above, by using a single feedback loop and a single control circuit, the manufacturing cost is low, the volume is relatively small, and the lamp current can be uniformized when driving multiple lamps.

Cold cathode tube, multiple, driven, current, balanced

Description

System for drive of multi Cold-cathode tub Fluorescent lamp

1 and 2 is a block diagram showing the configuration of a conventional multiple cold cathode fluorescent lamp driving system,

3 is a block circuit diagram showing the configuration of a multiple cold cathode fluorescent lamp driving system according to a first embodiment of the present invention;

4 is an equivalent circuit for explaining the operation of the current balancing circuit of the multiple cold cathode fluorescent lamp driving system according to the first embodiment of the present invention;

5 is a block circuit diagram showing the configuration of a multiple cold cathode fluorescent lamp driving system according to a second embodiment of the present invention;

6 is a block circuit diagram showing the configuration of a multiple cold cathode fluorescent lamp driving system according to a third embodiment of the present invention;

7 is a block circuit diagram showing the configuration of a multiple cold cathode fluorescent lamp driving system according to a fourth embodiment of the present invention;

8 is a block circuit diagram showing a configuration of a multiple cold cathode fluorescent lamp driving system according to a fifth embodiment of the present invention.

<Explanation of symbols on main parts of the drawings>

10: switching circuit 20: current balancing circuit

30: current sensing circuit 40: control circuit

Cb1, CbN, Cp1, CpN: Capacitors L1, L2, LN, Lc: Inductors

Lp1, Lp2, LpN: Fluorescent lamps T1, T2, TN: Transformer

The present invention relates to a multiple cold cathode fluorescent lamp driving system, and more particularly, to a multiple cold cathode fluorescent lamp driving system in a backlight lighting module device of a liquid crystal display device.

Generally, since the LCD does not emit light, the LCD displays information by reflecting extraneous light passing through the LCD panel, or displays an information by installing a separate light source, that is, a backlight module, on the back of the LCD panel. do.

The backlight module includes a discharge lamp used as a light source of a liquid crystal display, a reflector reflecting light emitted from the lamp toward a light guide plate or a diffuser plate, and increasing light efficiency, and electrically connected to the lamp to apply power to the lamp. It includes an inverter.

In recent years, as LCDs and monitors, such as monitors and televisions, the range of use is rapidly expanded, and the size of the LCD is gradually increased, the brightness of the LCD is an important problem. In particular, as the size of the liquid crystal panel increases, more and more lamps are driven, thereby increasing the need for parallel driving of the lamps.

The discharge lamp decreases the lamp voltage as the lamp current increases, and the lamp voltage also shows a large deviation from lamp to lamp. Thus, a circuit for providing power to the lamp, such as an inverter, must have a feedback loop to control the current through the lamp to allow load regulation while ensuring stable operation.

1 shows a multiple lamp drive system (inverter) in a conventional device. The system includes a switching circuit 10 for converting a DC input voltage into an AC voltage, a transformer T1 for boosting the AC output voltage of the switching circuit 10, and a transformer for boosting a drive signal of the drive circuit 10 ( Feedback and control to control the brightness by measuring the current output from the fluorescent lamps Lp1 and Lp2 and the fluorescent lamps Lp1 and Lp2, which are lit by the voltage applied through the transformer T1). Circuit 30.

In such a multiple lamp drive system, the voltage difference of the fluorescent lamp has a great influence on the currents I1 and I2 passing through the lamp, which causes an unbalance in the current distribution. However, the multiple lamp drive system of FIG. 1 only controls the total current of fluorescent lamps Lp1, Lp2, and thus fails to balance the current passing through each fluorescent lamp Lp1, Lp2. This imbalance not only affects the brightness uniformity of the LCD panel because the luminance is insufficient for fluorescent lamps with too small current, but also shortens the life of the lamp and backlight system due to overheating for lamps with too large current. There is.

Thus, in order to solve the above disadvantages, some techniques using several switching circuits and transformers for providing a plurality of feedback and control circuits for current regulation while driving a plurality of lamps have been presented as shown in FIG.

Referring to FIG. 2, the first switching circuit 10, the first transformer T1, the first fluorescent lamp Lp1, the first feedback and control circuit 30 are formed of one channel, and the second The switching circuit 20, the second transformer T2, the second fluorescent lamp Lp2 and the second feedback and control circuit 40 are composed of one other channel.

In this multiple lamp drive system, the lamp currents I1 and I2 are in balance, but each component is used two by one, thereby increasing the manufacturing cost and increasing the volume.

The present invention is to solve the above problems, by using a single feedback loop, a single control circuit, a single switching circuit, the manufacturing cost is low, the volume is relatively small, it is possible to uniformize the lamp current when driving multiple lamps It is an object of the present invention to provide a multiple cold cathode fluorescent lamp driving system.

Features of the present invention for achieving the above object,

A drive system for turning on a plurality of fluorescent lamps, comprising: a switching circuit for converting a DC input voltage into an AC voltage and outputting the same under external control; A current balance circuit which receives an AC voltage output from the switching circuit and maintains a lamp current balance; A plurality of transformers for amplifying the signal output from the current balancing circuit; A plurality of fluorescent lamps lit by the voltage output from each said transformer; A current sensing circuit for sensing current output from each of the fluorescent lamps; And a control circuit for controlling the switching circuit according to the signal output from the current sensing circuit.

Here, the current balancing circuit includes a common inductor connected in series with the output terminal of the switching circuit; And a plurality of inductors connected to a line connected to the common inductor and each of the transformers.

Here, the current balancing circuit further comprises: a common inductor connected in series with the output terminal of the switching circuit; A plurality of inductors connected to a line connected to the common inductor and each of the transformers; And a plurality of capacitors connected in parallel to the output terminal of each transformer.

Here, the current balancing circuit further comprises: a common inductor connected in series with the output terminal of the switching circuit; A plurality of inductors connected on a line connected to the common inductor and each of the transformers; A plurality of first capacitors connected in parallel to the output of each transformer; And a plurality of second capacitors connected in series with the output terminal of each transformer at a rear end of the first capacitor.

Hereinafter, the configuration of a multiple cold cathode fluorescent lamp driving system according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

First Embodiment

3 is a block circuit diagram showing the configuration of a multiple cold cathode fluorescent lamp driving system according to a first embodiment of the present invention.

Referring to FIG. 3, the multiple cold cathode fluorescent lamp driving system according to the first embodiment of the present invention includes a switching circuit 10, a current balancing circuit 20, transformers T1 and T2, and a fluorescent lamp ( Lp1, Lp2, the current sensing circuit 30, and the control circuit 40 are comprised.

The switching circuit 10 converts and outputs a DC input voltage into an AC voltage according to the control of the control circuit to be described below.

The current balancing circuit 20 receives a AC voltage output from the switching circuit 10 and a common inductor Lc connected in series with the output terminal of the switching circuit 10 to maintain the lamp current balance, and the common inductor Lc. And a plurality of inductors L1 and L2 connected on a line connected to each of the transformers T1 and T2, and a plurality of first capacitors Cp1 and Cp2 connected in parallel to the output terminals of the respective transformers T1 and T2. ) And a plurality of second capacitors Cb1 and Cb2 connected in series to the output terminals of the respective transformers T1 and T2 at the rear ends of the respective first capacitors Cp1 and Cp2.

The transformers T1 and T2 are connected to the current balancing circuit 20 to amplify the signal output from the current balancing circuit 20.

The fluorescent lamps Lp1 and Lp2 are connected to the transformers T1 and T2, respectively, and are lit by the voltages output from the respective transformers T1 and T2.

The current sensing circuit 30 senses the current output from each of the fluorescent lamps Lp1 and Lp2.

The control circuit 40 controls the switching circuit 10 according to the signal output from the current sensing circuit 30.

Hereinafter, the operation of the multiple cold cathode fluorescent lamp driving system according to the first embodiment of the present invention will be described in detail with reference to FIGS. 3 and 4.

First, referring to FIG. 3, when the switching circuit 10 converts a DC input voltage into an AC voltage and outputs the AC voltage, the AC voltage output from the switching circuit 10 may be used to determine the common inductor Lc of the current balancing circuit 20. Via a common terminal (a). The voltage applied to the common terminal a is boosted by the transformers T1 and T2 via the inductors L1 and L2, and the fluorescent lamps Lp1 and Lp2 via the second capacitors Cb1 and Cb2 connected in series. Is passed on. At this time, the common inductor Lc, the inductor L1, the transformer T1, the first capacitor Cp1, the second capacitor Cb1, the common inductor Lc, the inductor L2, the transformer T2, The first capacitor Cp2 and the second capacitor Cb2 may mutually resonate to provide the fluorescent lamps Lp1 and Lp2 with voltages of appropriate magnitudes similar to sinusoidal waves.

In addition, the common inductor Lc, the inductor L1, the transformer T1, the first capacitor Cp1, the second capacitor Cb1, the common inductor Lc, the inductor L2, the transformer T2, The resonance circuit formed of the first capacitor Cp2 and the second capacitor Cb2 may reduce the loss by allowing zero voltage switching to the switching circuit 10.

The common inductor Lc and the inductors L1 and L2 constitute the current balancing circuit 20, and the first capacitors Cp1 and Cp2 and the second capacitors Cb1 and Cb2 on the side of the transformers T1 and T2. In this case, when one of the control circuits and one switching circuit is used, the two lamp currents are the same despite the variation of the lamp voltage and the negative impedance characteristic of the lamp. Can be.

4 is an equivalent circuit for explaining the operation of the current balancing circuit of the multiple cold cathode fluorescent lamp driving system according to the first embodiment of the present invention. 4 shows only a resonant circuit for driving one fluorescent lamp Lp1.

Components on the main side of the transformer T1 are equally moved to the side of the transformer T1. In the equivalent circuit of FIG. 4, Lt1 represents the sum of the leakage inductances of the inductor L1 and the transformer T1. Cu1 connected in parallel to the fluorescent lamp Lp1 is a parasitic capacitance equivalently explaining the leakage current of the lamp Lp1. In the equivalent circuit of FIG. 4, the common terminal voltage Vc at the side of the transformer T1 is represented by Equation 1 below.

이다.From here,

to be.

In Equation 1, the common terminal voltage Vc depends on both the lamp voltage VLp1 and the lamp current ILp1, but when the specific condition is met, Equation 1 shows the ramp voltage VLp1. The coefficient becomes zero so that the common terminal voltage Vc does not depend on the ramp voltage.

The main cause of the lamp current unbalance in the parallel operation of the fluorescent lamps Lp1 and Lp2 is that the voltage difference between the lamps or the lamp voltage deviation is reduced when the common terminal voltage Vc does not depend on the lamp voltage because the above mentioned conditions are satisfied. If present, the imbalance between lamp currents is improved.

Second Embodiment

5 is a block circuit diagram showing the configuration of a multiple cold cathode fluorescent lamp driving system according to a second embodiment of the present invention.

Referring to FIG. 5, in the multiple cold cathode fluorescent lamp driving system according to the second embodiment of the present invention, the current balancing circuit 20 maintains a current balance of the voltage output from the switching circuit 10. Common inductor Lc connected in series to the output terminal of the plurality of common inductors Lc and a plurality of inductors L1 and L2 connected on a line connected to each of the transformers T1 and T2, and each transformer ( It is composed of a plurality of capacitors (Cb1, Cb2) connected in series to the output terminal of the T1, T2. The rest of the configuration is the same as in FIG.

Hereinafter, the operation of the multiple cold cathode fluorescent lamp driving system according to the second embodiment of the present invention will be described in detail with reference to FIG. 5.

Referring to FIG. 5, when the switching circuit 10 converts a DC input voltage into an AC voltage and outputs the converted AC voltage, the AC voltage output from the switching circuit 10 is transferred through the common inductor Lc of the current balancing circuit 20. It is provided to the common terminal a. The voltage applied to the common terminal a is boosted by the transformers T1 and T2 through the inductors L1 and L2 and transferred to the fluorescent lamps Lp1 and Lp2 through the capacitors Cb1 and Cb2 connected in series. do. At this time, the common inductor Lc, the inductor L1, the transformer T1, the capacitor Cb1, and the common inductor Lc, the inductor L2, the transformer T2, and the capacitor Cb2 are mutually resonant. To provide fluorescent lamps Lp1 and Lp2 of appropriate magnitude in the shape of sinusoids.

In addition, the resonant circuit formed of the common inductor Lc, the inductor L1, the transformer T1, and the capacitor Cb1, the common inductor Lc, the inductor L2, the transformer T2, and the capacitor Cb2 is switched. The loss can be reduced by enabling zero voltage switching in the circuit 10.

Meanwhile, in the multiple cold cathode fluorescent lamp driving system according to the second embodiment, only a slight change is made in the transformer load-side capacitance Ct1, and when Lt1 is set to satisfy Equation 3 below in response to Ct1, FIG. The same principle described above can improve the current imbalance between lamps.

이다.From here,

to be.

Third Embodiment

6 is a block circuit diagram showing the configuration of a multiple cold cathode fluorescent lamp driving system according to a third embodiment of the present invention.

Referring to FIG. 6, in the multiple cold cathode fluorescent lamp driving system according to the third embodiment of the present invention, the current balancing circuit 20 maintains a current balance of the voltage output from the switching circuit 10. Common inductor Lc connected in series to the output terminal of the plurality of common inductors Lc and a plurality of inductors L1 and L2 connected on a line connected to each of the transformers T1 and T2, and each transformer ( It is composed of a plurality of capacitors (Cp1, Cp2) connected in parallel to the output terminal of T1, T2. The rest of the configuration is the same as in FIG.

Hereinafter, the operation of the multiple cold cathode fluorescent lamp driving system according to the third embodiment of the present invention will be described in detail with reference to FIG. 6.

Although the configuration of the multiple cold cathode fluorescent lamp driving system according to the third embodiment is similar to that of FIG. 3, there is a difference in that capacitors Cb1 and Cb2 connected in series to the fluorescent lamps Lp1 and Lp2 are not used. When the capacitance value of the series-connected capacitor Cb1 of FIG. 3 is set to infinity, it is the same as that of FIG. 6. Therefore, the load-side capacitance Ct1 measured by the common terminal voltage Vc 'and the transformers T1 and T2 is represented by Equation 4 below. Is modified as

이다.From here,

to be.

That is, in the case of the multiple cold cathode fluorescent lamp driving system according to the third embodiment, there is only a slight change in the load-side capacitance Ct1, and the current imbalance between lamps can be improved by the same principle described with reference to FIG. 3.

Fourth Embodiment

7 is a block circuit diagram showing the configuration of a multiple cold cathode fluorescent lamp driving system according to a fourth embodiment of the present invention.

Referring to FIG. 7, in the multiple cold cathode fluorescent lamp driving system according to the third embodiment of the present invention, the current balancing circuit 20 maintains a current balance of the voltage output from the switching circuit 10. And a plurality of inductors L1 and L2 connected on a line connected to the common inductor Lc connected in series to the output terminal of the C1 and a common inductor Lc and the respective transformers T1 and T2. The rest of the configuration is the same as in FIG.

Hereinafter, the operation of the multiple cold cathode fluorescent lamp driving system according to the fourth embodiment of the present invention will be described in detail with reference to FIG. 7.

The fourth embodiment of the present invention has a difference in that neither the second capacitors Cb1 and Cb2 connected in series to the fluorescent lamp and the first capacitors Cp1 and Cp2 connected in parallel to the side of the transformers T1 and T2 are used. .

When the capacitance value of the series-connected capacitor Cb1 of FIG. 3 is set to infinity and the capacitance value of the parallel-connected capacitor Cp1 is set to zero, it is the same as the circuit of FIG. 7, and thus the common terminal voltage Vc ′ and the transformer ( The load-side capacitance Ct1 measured in T1 and T2 is modified as shown in Equation 5 below.

이다.From here,

to be.

That is, in the case of the multiple cold cathode fluorescent lamp driving system according to the fourth embodiment, there is only a slight change in the load-side capacitance Ct1, and the current imbalance between lamps can be improved by the same principle described with reference to FIG. 3.

Fifth Embodiment

8 is a block circuit diagram illustrating a configuration of a multiple cold cathode fluorescent lamp driving system according to a fifth embodiment of the present invention.

In FIG. 8, the multiple cold cathode fluorescent lamp driving system according to the fifth embodiment of the present invention has the same resonant circuit as that of FIG. 3 except that N lamps and N resonant circuits are connected. According to the principle of the lamp current balance described in FIG. 3, the present invention may be applied to driving N lamps as shown in FIG. 8. Although not shown, the circuit composed of two fluorescent lamps is illustrated in FIGS. 5, 6, and 7, but the current balancing principle may be applied to the case of N lamps.

According to the present invention, the multiple cold cathode fluorescent lamp driving system configured as described above, the production cost is low, the volume is relatively small, and the uniformity of the lamp current when driving the multiple lamps by using a single feedback loop and a single control circuit. It can be possible.

Claims (4)

delete A switching circuit for converting and outputting a DC input voltage into an AC voltage according to external control, a current balancing circuit for receiving an AC voltage output from the switching circuit and maintaining a lamp current balance, and a signal output from the current balancing circuit A plurality of transformers for amplifying a plurality of transformers, a plurality of fluorescent lamps lit by voltages output from the respective transformers, a current sensing circuit for sensing currents output from each of the fluorescent lamps, and outputs from the current sensing circuits. In a drive system configured to control the switching circuit in accordance with a signal to light a plurality of fluorescent lamps, The current balance circuit, A common inductor connected in series with the output terminal of the switching circuit; And And a plurality of inductors connected on a line connected to the common inductor and each of the transformers. A switching circuit for converting and outputting a DC input voltage into an AC voltage according to external control, a current balancing circuit for receiving an AC voltage output from the switching circuit and maintaining a lamp current balance, and a signal output from the current balancing circuit A plurality of transformers for amplifying a plurality of transformers, a plurality of fluorescent lamps lit by voltages output from the respective transformers, a current sensing circuit for sensing currents output from each of the fluorescent lamps, and outputs from the current sensing circuits. In a drive system configured to control the switching circuit in accordance with a signal to light a plurality of fluorescent lamps, The current balance circuit, A common inductor connected in series with the output terminal of the switching circuit; A plurality of inductors connected to a line connected to the common inductor and each of the transformers; And Multiple cold cathode fluorescent lamp driving system comprising a plurality of capacitors connected in parallel to the output terminal of each transformer. A switching circuit for converting and outputting a DC input voltage into an AC voltage according to external control, a current balancing circuit for receiving an AC voltage output from the switching circuit and maintaining a lamp current balance, and a signal output from the current balancing circuit A plurality of transformers for amplifying a plurality of transformers, a plurality of fluorescent lamps lit by voltages output from the respective transformers, a current sensing circuit for sensing currents output from each of the fluorescent lamps, and outputs from the current sensing circuits. In a drive system configured to control the switching circuit in accordance with a signal to light a plurality of fluorescent lamps, The current balance circuit, A common inductor connected in series with the output terminal of the switching circuit; A plurality of inductors connected to a line connected to the common inductor and each of the transformers; A plurality of first capacitors connected in parallel to the output of each transformer; And And a plurality of second capacitors connected in series with the output terminal of each transformer at a rear end of the first capacitor.

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