KR20020073607A - Mulit-lamp driving system - Google Patents

Abstract

PURPOSE: A system for driving multiple lamps is provided to improve the accuracy of current control by employing a balancing controller for matching an impedance of each lamp path. CONSTITUTION: An inverter(70) generates an AC(Alternating Current) power. A lamp set(80) has a first lamp and a second lamp. A balancing controller(50) is connected to the inverter(70) and the lamp set(80) in order to maintain a constant current flowing through the first lamp and the second lamp and includes first to third loads. The first load is connected to the first lamp and the inverter(70). The second load is connected to the second lamp and the inverter(70). The third load is connected to the first and second loads. An impedance ratio of the third load for the second load is negative.

Description

Multi-lamp drive system {MULIT-LAMP DRIVING SYSTEM}

The present invention relates to a lamp drive system. In particular, the present invention relates to a multiple lamp drive system in a backlight lighting module device of a liquid crystal display device.

Discharge lamps used in backlighting of LCD panels, such as low temperature cathode fluorescent lamps (CCFLs), have terminal voltage characteristics that vary with the instantaneous history and frequency of the stimulus (AC signal) applied to the lamp. The lamp does not flow current with an applied terminal voltage less than the crash voltage until the CCFL crashes or ignites. For example, the terminal voltage should be at least 1500V. If an electric arc occurs within the CCFL, the terminal voltage drops to a drive voltage that is one third of the collision voltage for a relatively wide range of input current. For example, the drive voltage may be 500V in the range of 500 mA to 6 mA for a CCFL having a stimulus voltage of 1500 V. In general, the CCFL is driven by an AC signal having a frequency in the range of 50KHz-100KHz.

The discharge lamp has a negative impedance characteristic in which the equivalent impedance decreases with increasing input power. Thus, circuits for providing power to the lamp, such as inverters, must have a feedback loop and (controllable) AC power source for monitoring the current flowing through the lamp to allow for load regulation while ensuring stable operation.

In Fig. 1, a conventional lamp drive system is shown. The system of FIG. 1 has only one feedback loop used to control the total current flowing through the lamp, but this feedback loop does not control or uniformize the current flowing through each lamp. If the current through one lamp is much greater than the current through the other lamp, the lamp life will be reduced and the brightness uniformity of the LCD panel will be reduced.

In Fig. 2, another conventional lamp drive system is shown. However, the system of FIG. 2 has two sets of control circuits that increase cost and space.

In Figure 3, another conventional drive system is shown. However, the system of FIG. 3 has two transformers which increase cost and space. Moreover, the transformer has a second coil connected in parallel, which is not good for high pressure treatment.

Accordingly, it is an object of the present invention to provide a lamp drive system that controls the equalization of current at the load end, while being widely applicable to systems having a single feedback loop and multiple loads.

Another object of the present invention is to provide a lamp drive system which is inexpensive and takes up less space and is easy to manufacture.

Another object of the present invention is to provide a lamp drive system that accurately controls current equalization.

To achieve the above-mentioned object, the present invention provides a multiple lamp drive system comprising the following components. In other words, the lamp drive system of the present invention comprises: 1) an inverter for generating AC power, 2) a lamp set having a first lamp and a second lamp, and 3) a uniform current through the first lamp and the second lamp. A balance controller connected with the inverter and the lamp set. The balance controller comprises 1) a first load connected with the first lamp and the inverter, 2) a second load connected with the second lamp and the inverter, 3) a third load connected with the first load and the second load, The impedance ratio of the third load to the first load is negative.

Moreover, the present invention provides a multiple lamp drive system including the following parts. That is, the multiple lamp drive system of the present invention is connected to a lamp set and an inverter to 1) an inverter for generating AC power, 2) a lamp set with a plurality of lamps, and 3) a uniform current across the lamps. And a balancing controller. The balance controller comprises 1) a plurality of loads each connected with one of the plurality of lamps and an inverter, and 2) a load choke connected with the plurality of loads to equalize the current through the plurality of lamps.

1 is a diagram of a conventional lamp drive system.

2 is a view of another conventional lamp drive system.

3 is a view of another conventional lamp drive system.

4 shows a preferred first embodiment of a lamp drive system according to the invention.

5 is a view of the balance controller of FIG.

6 is a view of a second preferred embodiment of a lamp drive system according to the invention.

7 shows a third preferred embodiment of a lamp drive system according to the invention;

8 is a view of a fourth preferred embodiment of a lamp drive system according to the invention.

9 is a view of a fifth preferred embodiment of a lamp drive system according to the invention.

10A is a preferred circuit diagram of a balance controller according to the present invention.

10B is another preferred circuit diagram of a balance controller according to the present invention.

10C is another preferred circuit diagram of a balance controller according to the present invention.

(Drawing reference)

10 ... power drive 30 ... PWM controller

50, 50a ... Balance Controller 70 ... Inverter

80 ... lamp set

In Fig. 4 a preferred first embodiment of a lamp drive system according to the invention is shown. In FIG. 4, the lamp drive system includes an inverter 70, a lamp set 80, and a balance controller 50. The inverter 70 is provided with a power drive device 10, a transformer T1, and a PWM controller 30. The lamp set 80 is composed of lamps Lp1, Lp2, and the balance controller is composed of loads Zb, Zc, Zd.

The power drive device 10 is used to convert the DC voltage Vin into an AC voltage. The AC voltage is raised by the transformer T1 and provided to the lamp set 80. The PWM controller 30 controls the power drive device according to the feedback signal generated from the lamp set 80. According to a first preferred embodiment of the invention, a balance controller 50 is used to regulate the current through the lamps Lp1 and Lp2 to be uniform. The loads Za, Zb, Zc, Zd can be resistors, capacitors, inductors, transistors, or a combination of integrated circuits. The operation of the balance controller 50 is based on the impedance adjustment of the loads Zb, Zc, Zd for the uniformity of the load current. Impedance adjustment can be made linearly or digitally.

5 is used to explain the operation of the balance controller 50 of FIG.

Assuming Za = 0, Zb = Zc, Lp1 = Z1, Lp2 = Z2,

V12 = I1Z1-I2Z2, and

(1) Iz = (1 / Zd) (I1Z1-I2Z2)

(2) V0 = I1 (Z1 + Zc) + IzZc

(3) V0 = I2 (Z2 + Zc)-IzZc

From equations (2) and (3),

I1 (Z1 + Zc) + IzZc = I2 (Z2 + Zc)-IzZc

→ I1 (Z1 + Zc) + 2IzZc = I2 (Z2 + Zc)

→ I1 (Z1 + Zc) + (2Zc / Zd) (I1Z1-I2Z2) = I2 (Z2 + Zc)

→ I1 (Z1 + Zc + 2Z1Zc / Zd) = I2 (Z2 + Zc + 2Z2Zc / Zd)

If (Z1 + Zc + 2Z1Zc / Zd) = (Z2 + Zc + 2Z2Zc / Zd), then I1 = I2

→ (2Zc / Zd) (Z1-Z2) = Z2-Z1

→ 2Zc / Zd = (-1)

Thus, I1 = I2 may meet the current equalization request when Zc / Zd is chosen to be (−1/2).

When capacitance C and inductance L are used for loads Zc and Zd at operating frequency ω, respectively,

Zc / Zd = (1 / jωC) / (jωL) = -1 / (ω ² LC) = -1/2

^{→ 1 / LC = ω 2/} 2

If other ^{words, 1 / LC = ω 2/} 2 days, there is a current object of the uniform it can be obtained.

According to the present invention, current matching can be achieved using impedance matching. Additionally, the balance controller 50 of FIG. 4 can be replaced with a combination of capacitor and inductor as shown in FIG. 10A. Moreover, the balance controller 50 may be a combination of capacitor, inductor, and resistor as shown in FIG. 10B. Also, as shown in FIG. 10C, another example of the balance controller 50 may be a combination of an inductor and a capacitor. Thus, when the ratio Zc / Zd is (-1/2), the current through the lamps Lp1, Lp2 is essentially the same.

Moreover, as long as the equivalent impedance ratio Zc / Zd is properly designed to a negative value, the current difference between lamps can be effectively reduced. As an example,

I1 (Z1 + Zc + 2Z1Zc / Zd) = I2 (Z2 + Zc + 2Z2Zc / Zd)

→ I1 / I2 = (Z2 + Zc + 2Z2Zc / Zd) / I1 (Z1 + Zc + 2Z1Zc / Zd)

Assuming Z1 = 10, Z2 = 11, Zc = -10j, Zd = 15j (Zc / Zd = -1 / 1.5),

I1 / I2 = (11-10j + 2 * 11 * (-10j) / 15j) / (10-10j + 2 * 10 * (-10j) / 15j)

= (11-10j-14.67) / (10-10j-13.33)

= (3.67 + 10j) / (3.33 + 10j)

= (10.65∠θ1) / (10.54∠θ2)

Thus, the current error (I1-I2) / I1 can be reduced to 1% (does not consider phase). Therefore, the current difference between lamps can be effectively reduced when the equivalent impedance ratio Zc / Zd is negative.

In Fig. 6 a preferred second embodiment of the lamp drive system according to the invention is shown. The circuit of FIG. 6 is similar to FIG. 5, but with a difference in the current feedback signal provided to the PWM controller 30. In FIG. 5, the feedback signal provided to the PWM controller 30 is for the current passing through the lamp Lp1, while the feedback signal provided to the PWM controller 30 in FIG. 6 is for the current passing through the lamps Lp1, Lp2.

In figure 7, a preferred third embodiment of the lamp drive system according to the invention is shown. In this embodiment, the balance controller 50 is connected between the lamp set 80 and the PWM controller 30.

In Fig. 8 a preferred fourth embodiment of the lamp drive system according to the invention is shown. In this case, load choke 60 is used to adjust the load balance of the entire circuit. According to a fourth embodiment of the invention, the balance controller 50a comprises loads Zp1, Zp2, ..., Zpm and load choke 60. The impedance relationship between the load choke 60 and the loads Zp1, Zp2, ..., Zpm can be found according to the formula as mentioned above.

In Fig. 9 a preferred fifth embodiment of the lamp drive system according to the invention is shown. The load choke 60 of the present invention functions as the load choke 60 of FIG. However, the fifth embodiment can be applied to an inverter having several transformers.

It is an object of the present invention to provide a lamp drive system that controls the equalization of current at the load end, while being widely applicable to systems having a single feedback loop and multiple loads.

Another object of the present invention is to provide a lamp drive system which is inexpensive and takes up less space and is easy to manufacture.

Another object of the present invention is to provide a lamp drive system that accurately controls current equalization.

Claims (17)

As a multiple lamp drive system, The system includes an inverter, a lamp set, a balance controller, The inverter generates AC power, The lamp set has a first lamp and a second lamp, The balance controller is connected with the inverter and the lamp set to equalize the current through the first lamp and the second lamp, the balance controller includes first, second and third loads, The first load is connected to the first lamp and the inverter, The second load is connected to the second lamp and the inverter, And the third load is connected to the first load and the second load, wherein the impedance ratio of the third load to the second load is negative. The method of claim 1, The inverter includes a power drive device, a transformer, a PWM controller, The power drive device converts DC power into the AC power, The transformer is connected to the balance controller and the power drive device; The PWM controller is coupled to the lamp set and the power drive to control the power drive device in accordance with a feedback signal generated from the lamp set. The system of claim 2, wherein the PWM controller is connected to the first lamp. 3. The system of claim 2, wherein the PWM controller is coupled to the first lamp and the second lamp. The system of claim 1, wherein the first and second loads are capacitive loads, and the third load is an inductive load. 6. The system of claim 5, wherein said third load is a combination of a resistor, an inductor, and a capacitor. 2. The system of claim 1, wherein the impedance ratio of the third load to the second load is preferably -2. The method of claim 1, The inverter includes a power drive device, a transformer, a PWM controller, The power drive device converts DC power into the AC power, The transformer is connected to the lamp set and the power drive device, The PWM controller is coupled to the balance controller and the power drive to control the power drive in accordance with a feedback signal generated from the balance controller. 9. The system of claim 8, wherein the PWM controller is coupled to the first load. 9. The system of claim 8, wherein the PWM controller is coupled to the first load and the second load. 9. The system of claim 8, wherein the first load and the second load are charging loads, and the third load is an inductive load. 12. The system of claim 11, wherein said third load is a combination of a resistor, an inductor, and a capacitor. As a multiple lamp drive system, The system includes an inverter, a lamp set, a balance controller, The inverter generates AC power, The lamp set has a plurality of lamps, The balance controller is connected with the inverter and the lamp set to equalize the current through the plurality of lamps, the balance controller includes a plurality of loads and load chokes, Each of the plurality of loads is connected to one of the plurality of lamps and the inverter, And the load choke is coupled with the plurality of loads to equalize the current through the plurality of lamps. 14. The system of claim 13, wherein the plurality of loads are capacitive loads and the load choke is a flow device. The inverter of claim 13, wherein the inverter includes a power driving device, a transformer, a PWM controller, The power drive device converts DC power into the AC power, The transformer is connected to the balance controller and the power drive device; The PWM controller is coupled to the lamp set and the power drive to control the power drive in accordance with a feedback signal generated from the lamp set. 16. The system of claim 15, wherein the PWM controller is coupled to one of the plurality of lamps. The method of claim 13, The inverter includes a power drive device, two or more transformers, a PWM controller, The power drive device converts DC power into the AC power, The two or more transformers are connected in parallel and are respectively connected to the balance controller and the power drive device, The PWM controller is coupled to the lamp set and the power drive to control the power drive in accordance with a feedback signal generated from the lamp set.