KR20080071411A - Current balancing circuit for driving led backlight light source - Google Patents

Abstract

A current balancing circuit for driving an LED(Light Emitting Diode) backlight source is provided to increase brightness uniformity of the plurality of LED arrays. A current balancing circuit for driving an LED backlight source includes a plurality of transformers(11) corresponding to a plurality of LED arrays(21). Primary sides of the plurality of transformers are connected between a power input terminal(Vin) and a ground in series. Secondary sides(11-2) of the plurality of transformers are connected to a plurality of first electrodes(21-1) of the LED arrays corresponding to one ends, respectively. The other ends are connected to the ground in common.

Description

CURRENT BALANCING CIRCUIT FOR DRIVING LED BACKLIGHT LIGHT SOURCE}

In order to more fully understand the drawings used in the detailed description of the invention, a brief description of each drawing is provided.

1 is a circuit diagram of a current balancing circuit according to a first embodiment of the present invention.

2 is a circuit diagram of a current balancing circuit to which a protection circuit is added.

3A to 3E are circuit diagrams showing various modifications in which a compensation circuit for compensating for leakage current is added.

4 is a circuit diagram of a current balancing circuit according to a second embodiment of the present invention.

5 is a circuit diagram of a current balancing circuit according to a third embodiment of the present invention.

6 is a circuit diagram of a current balancing circuit according to a fourth embodiment of the present invention.

The present invention relates to an LED backlight light source, and more particularly, to a current balancing circuit for driving an LED backlight light source for more uniform brightness of the LED backlight light source.

Passive display devices such as liquid crystal display devices employed in televisions, computer monitors, and the like require a back light unit (BLU) for irradiating light from the rear end as a non-light emitting device. The backlight unit may be classified into a direct light emission method and an edge light emission method according to the position of the light source. As the display size increases, direct light emission is mainly used. In the direct emission method, a plurality of discharge lamps are arranged in parallel to form a surface light source. Currently, a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), or the like is used as a discharge lamp.

Recently, use of a backlight light source using a light emitting diode (LED) has been proposed. LED backlight light sources are known to be eco-friendly and have high-speed response speeds of several nanoseconds, which are effective for video signal streams, have very high color reproducibility, and high flexibility for arbitrarily changing brightness and color temperature. This LED backlight light source uses a plurality of LED arrays. The LED array may have low luminance and overall luminance uniformity because voltage and current deviations occur in each LED element and the corresponding array. In order to overcome this problem, a constant current driver for driving a plurality of LED arrays with a constant current is used. However, in the drive current detection method for the constant current drive, there is a space in the series of signal detection, and thus there is a problem that it is difficult to accurately maintain the output current because it is difficult to accurately detect.

It is an object of the present invention to provide a current balancing circuit for driving an LED backlight light source that can drive a plurality of LED arrays in parallel more efficiently in parallel, and can further increase the luminance uniformity of the plurality of LED arrays.

One aspect of the present invention for achieving the above technical problem relates to a current balancing circuit for driving the LED backlight light source. A current balancing circuit for driving an LED backlight light source of the present invention includes: a plurality of transformers corresponding to a plurality of LED arrays, the primary side of the plurality of transformers being connected in series between a power input terminal and a ground; The secondary side is respectively connected to the first electrode of the corresponding LED array and the other end is commonly connected to the ground.

In one embodiment, the primary side and secondary side of the plurality of transformers have the same phase, and the second electrodes of the plurality of LED arrays are commonly connected to ground.

In one embodiment, the primary side and the secondary side of the plurality of transformers have a 180 degree phase difference, and the second electrodes of the plurality of LED arrays are commonly connected to a power input terminal.

In one embodiment, further comprising a power split circuit for generating a constant voltage and a negative voltage from the power input through the power input terminal, the constant voltage is input to the first primary side of the plurality of transformers, the negative voltage of the plurality of LED arrays It is commonly input to the second electrode.

In one embodiment, a protection circuit is connected to both ends of each primary side of the plurality of transformers.

In one embodiment, the protection circuit is composed of a varistor.

In one embodiment, the protection circuit is composed of a constant voltage diode.

In one embodiment, a compensation circuit for compensating for leakage current of the plurality of transformers is included.

The plurality of LED arrays may include a plurality of switching elements included in the plurality of LED arrays, the plurality of LED arrays having a configuration connected in parallel and switching elements for switching on / off unit LED cells included in each LED array. And a controller for controlling the on / off switching operation of the devices.

DETAILED DESCRIPTION In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the embodiments of the present invention, reference should be made to the accompanying drawings which illustrate preferred embodiments of the present invention and the contents described in the accompanying drawings. The embodiments of the present invention may be modified in various forms, and the scope of the present invention should not be construed as being limited by the embodiments described below. This embodiment is provided to more completely explain the present invention to those skilled in the art. Accordingly, the shape of the elements in the drawings and the like are exaggerated to emphasize a clearer description. In understanding the drawings, it should be noted that like parts are intended to be represented by the same reference numerals as much as possible. And detailed description of known functions and configurations that are determined to unnecessarily obscure the subject matter of the present invention is omitted.

(Example)

Hereinafter, with reference to the accompanying drawings illustrating a preferred embodiment of the present invention, a current balancing circuit for driving the LED backlight light source of the present invention will be described in detail.

1 is a circuit diagram of a current balancing circuit according to a first embodiment of the present invention.

Referring to FIG. 1, the current balancing circuit 10 according to the first embodiment of the present invention drives the plurality of LED arrays 21 in parallel. The plurality of LED arrays 21 is composed of a plurality of LED cells connected in series. The current balancing circuit 10 includes a plurality of transformers 11 corresponding to the plurality of LED arrays 21. The primary side 11-1 of the plurality of transformers 11 is connected in series between the power input terminal Vin and ground. Secondary sides 11-2 of the plurality of transformers 11 are respectively connected to the first electrode 21-1 of the LED array corresponding to one end thereof, and the other end thereof is commonly connected to the ground. The second electrodes 21-2 of the plurality of LED arrays 21 are commonly connected to the ground. The plurality of transformers 11 have a phase in phase between the primary side and the secondary side. And the winding ratio of primary side and secondary side basically has 1: 1 but can be changed to other ratio.

When power is input to the power input terminal Vin, the plurality of transformers 11 of the current balancing circuit 10 divide the voltage between the power input terminal Vin and the ground into a plurality of uniformly, and the divided voltages are divided into a plurality of LED arrays. The first electrodes 21-1 of 21 are respectively input.

Since the primary side 11-1 of the plurality of transformers 11 is connected in series between the power input terminal Vin and the ground, the impedance of any one of the plurality of LED arrays 21 is changed to change the amount of current. Is generated, the plurality of transformers 11 of the current balancing circuit 10 interact with each other to achieve current balancing. This current balancing operation is continuously and continuously automatic adjustment while the plurality of LED arrays 11 are driven. Thus, the plurality of LED arrays 21 has a uniform luminance.

2 is a circuit diagram of a current balancing circuit to which a protection circuit is added.

Referring to FIG. 2, the current balancing circuit 10 may further include a protection circuit 12 for preventing an excessive voltage from being increased in the plurality of transformers 11. The protection circuit 12 is, for example, a varistor connected to both ends of the primary side 11-1 of the plurality of transformers 11. Or it may be composed of a constant voltage diode such as a control diode. The protection circuit 12 prevents overcurrent from occurring and damage to the transformer 11 when the LED array 21 is electrically opened.

3A to 3E are circuit diagrams showing various modifications in which a compensation circuit for compensating for leakage current is added.

3A to 3E, since a plurality of transformers 11 of the current balancing circuit 10 may generate a loss due to leakage current, it may be desirable to configure a compensation circuit for leakage current appropriately. For example, as shown in FIG. 3A, the compensation circuit is a leakage compensation capacitor 40 configured at a power supply input Vin. Alternatively, as shown in FIG. 3B, the compensation circuit is a leakage compensation capacitor 41 configured between ground and the second electrodes 21-2 of the plurality of LED arrays 21. Alternatively, as illustrated in FIG. 3C, the compensation circuit may be provided between one end of each secondary side 11-2 of the plurality of transformers 11 and the first electrode 21-1 of the plurality of LED arrays 21, respectively. A plurality of leakage compensation capacitors 42 are configured. Alternatively, as shown in FIG. 3D, the compensation circuits are a plurality of leakage compensation capacitors 43 respectively configured between ground and the second electrodes 21-1 of the plurality of LED arrays 21. Alternatively, as shown in FIG. 3E, the compensation circuits are a plurality of leakage compensation capacitors 44 respectively configured across the primary side 11-1 of the plurality of transformers 11 of the current balancing circuit 10.

4 is a circuit diagram of a current balancing circuit according to a second embodiment of the present invention.

Referring to FIG. 4, the current balancing circuit 10 according to the second embodiment of the present invention has the same configuration as the first embodiment described above. In addition, a power split circuit 30 is added between the power input terminal Vin and the current balance circuit 10. The power divider circuit 30 receives power through a power input terminal Vin, divides the power into a constant voltage and a negative voltage, and outputs the divided power. The constant voltage is applied to the primary side of the first transformer of the plurality of transformers 11 of the current balancing circuit 10, and the negative voltage is commonly applied to the second electrodes of the plurality of LED arrays 21.

The power split circuit 30 can be configured using the transformer 31. The primary side 31-1 of the transformer 31 is connected between the power input terminal Vin and ground, and the secondary side 31-2 has a grounded intermediate tab 32. Based on the grounded intermediate tap 32 of the secondary side 31-2, a constant voltage is output to one end and a negative voltage is output to the other end. Although the winding ratio of the primary side 31-1 and the secondary side 31-2 of the transformer 31 is set to 1: 1, other ratios can be set. The ratio of the constant voltage and the negative voltage is determined according to the position of the intermediate tap 32. For example, the intermediate tap 31-2 may be installed so that the ratio of the constant voltage and the negative voltage is 1: 2, and in this case, the current balance circuit 10 may supply the total power for driving the plurality of LED arrays 21. The current balance is performed in the power capacity range of about 1/3 of the capacity.

5 is a circuit diagram of a current balancing circuit according to a third embodiment of the present invention.

Referring to FIG. 5, the current balancing circuit 10a according to the third embodiment of the present invention drives the plurality of LED arrays 21 in parallel. The current balancing circuit 10a includes a plurality of transformers 11a corresponding to the plurality of LED arrays 21. The primary side 11a-1 of the plurality of transformers 11a is connected in series between the power supply input Vin and ground. Secondary sides 11a-2 of the plurality of transformers 11a are respectively connected to the first electrode 21-1 of the LED array corresponding to one end thereof, and the other end thereof is commonly connected to the ground. The second electrodes 21-2 of the plurality of LED arrays 21 are commonly connected to the power input terminal Vin. The plurality of transformers 11a have a 180 degree phase difference between the primary side and the secondary side. And the winding ratio of primary side and secondary side basically has 1: 1 but can be changed to other ratio.

When power is input to the power input terminal Vin, a constant voltage is applied to the second electrodes 21-2 commonly connected to the plurality of LED arrays 21. The plurality of transformers 11a of the current balancing circuit 10a uniformly divide the voltage between the power supply input Vin and the ground, and the divided voltages of the plurality of LED arrays 21 are inverted by 180 degrees. The first electrodes 21-1 are respectively input.

Since the primary side 11a-1 of the plurality of transformers 11a is connected in series between the power input terminal Vin and the ground, when one of the plurality of LED arrays 21 changes in impedance and a change in current amount occurs, The plurality of transformers 11a of the current balancing circuit 10a interact with each other to achieve current balance. This current balancing operation is continuously and continuously automatically adjusted while the plurality of LED arrays 11a are driven. Therefore, the plurality of LED arrays 11a have uniform luminance.

In the case of the current balancing circuit of the third embodiment of the present invention, a protection circuit and a compensation circuit for leakage compensation may be added as illustrated in the above-described embodiments. Repeated description thereof will be omitted.

6 is a circuit diagram of a current balancing circuit according to a fourth embodiment of the present invention.

Referring to FIG. 6, in the fourth exemplary embodiment of the present invention, the plurality of LED arrays 21a have a configuration connected in parallel, and a plurality of switching elements for switching on / off unit LED cells included in each LED array. (22) is provided. The controller 23 is provided to control the on / off switching operation of the plurality of switching elements 22 included in the plurality of LED arrays 21a. The controller 23 controls on / off of the unit LED cells of the plurality of LED arrays 21a for brightness control. The luminance control of the controller 23 may be performed based on the image signal or based on the brightness of the surrounding environment.

The embodiment of the current balancing circuit for driving the LED backlight light source of the present invention described above is merely exemplary, and those skilled in the art to which the present invention pertains various modifications and other equivalent embodiments therefrom. You can see that examples are possible. Therefore, it is to be understood that the present invention is not limited to the specific forms mentioned in the above description. Therefore, the true technical protection scope of the present invention should be defined by the technical spirit of the appended claims, and the present invention is intended to cover all modifications, equivalents, and substitutes within the spirit and scope of the present invention as defined by the appended claims. It should be understood to include.

According to the current balancing circuit for driving the LED backlight light source of the present invention as described above, it is possible to drive a plurality of LED arrays in parallel more efficiently and to improve the uniformity of the luminance of the plurality of LED arrays. In addition, since a protection circuit for protecting the overcurrent of the plurality of transformers and a compensation circuit for compensating for the leakage current are provided, the protection against the overcurrent and the compensation for the leakage current are provided, thereby providing a more stable current balancing circuit. In addition, the circuit configuration for parallel driving of a plurality of LED arrays can be simplified as compared with the prior art, thereby lowering the manufacturing cost.

Claims (9)

In the current balancing circuit for driving the LED backlight light source: Having a plurality of transformers corresponding to the plurality of LED arrays, The primary side of the multiple transformers is connected in series between the power input and ground, The secondary side of the plurality of transformers, one end is connected to each of the first electrode of the corresponding LED array and the other end is connected to the ground in common, the current balancing circuit for driving the LED backlight light source. The current balance of claim 1, wherein the primary side and the secondary side of the plurality of transformers have the same phase, and the second electrodes of the plurality of LED arrays are commonly connected to ground. Circuit. The method of claim 1, wherein the primary side and the secondary side of the plurality of transformers have a phase difference of 180 degrees, and the second electrodes of the plurality of LED arrays are commonly connected to a power input terminal. Current balancing circuit. The power supply circuit of claim 1, further comprising a power split circuit configured to generate a constant voltage and a negative voltage from a power source input through a power input terminal. Constant voltage is input to the first primary side of the plurality of transformers, The negative voltage is commonly input to the second electrodes of the plurality of LED arrays, wherein the current balancing circuit for driving the LED backlight light source. The current balancing circuit according to any one of claims 1 to 4, further comprising a protection circuit connected to both ends of each primary side of the plurality of transformers. 6. The current balancing circuit of claim 5, wherein the protection circuit comprises a varistor. 6. The current balancing circuit of claim 5, wherein the protection circuit is composed of a constant voltage diode. The current balancing circuit according to any one of claims 1 to 4, comprising a compensation circuit for compensating for leakage currents of the plurality of transformers. The LED array device of claim 1, wherein the plurality of LED arrays includes a configuration connected in parallel and a switching element for switching on / off unit LED cells included in each LED array. And a controller for controlling an on / off switching operation of the plurality of switching elements included in the plurality of LED arrays.

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