KR20100121816A - Led driving circuit and method for operating the same - Google Patents

Abstract

PURPOSE: An LED driving circuit and a method for operating the same are provided to improve the power factor and the efficiency factor of an apparatus including an LED device at the same time by controlling the LED device included in a string. CONSTITUTION: A bridge circuit part(200) comprises four diodes(D5~D8). The bridge circuit part is inputted with the AC voltage supplied from a power supply(100) and offers the rectified driving voltage to a string(400). A current controller(300) comprises a plurality of unit current controllers. A string is connected with a plurality of LED elements applied with the driving voltage.

Description

LED driving circuit and driving method thereof {LED DRIVING CIRCUIT AND METHOD FOR OPERATING THE SAME}

The present invention relates to a driving circuit having a light emitting diode (LED) and a driving method thereof.

The LED device is a diode having a PN junction structure manufactured by using a semiconductor manufacturing process, and the device emits extra energy as light when electrons and holes combine in the PN junction. The wavelength of light output from the LED device varies depending on the type of material constituting the LED device and impurities added in the manufacturing process.

LED devices are smaller than conventional light sources, have a long life, have good efficiency, and have fast response characteristics. The LED device has recently been used as a backlight light source of a flat panel display device having a liquid crystal display device due to the aforementioned advantages. A flat panel display device using an LED element as a backlight light source has more advantages in color reproducibility and lifespan than in the case of using a fluorescent lamp as a backlight light source.

Recently, LED devices have been used in lighting devices by taking advantage of high brightness, low power consumption, and long lifespan of LED devices. One LED device can be used to make an LED lighting device, or a plurality of LED devices can be connected in series or in parallel to make an LED lighting device.

When the lighting device is configured using one or a relatively small number of LED elements, the power factor characteristic representing the ratio of the active power and the apparent power in the AC circuit is improved, but how much light can be output to the supplied electric energy. The efficiency characteristic indicating whether there is any worsens. On the other hand, when the lighting is configured using a string in which a relatively large number of LED elements are connected in series, the power factor characteristic becomes relatively poor and the efficiency characteristic becomes better.

The present invention provides an LED driving circuit and a driving method thereof capable of improving both efficiency and power factor.

The present invention includes at least two LED elements, the string driven by the main drive current in the first voltage section of the drive voltage; And a current controller for allowing the LED element selected from the LED elements of the string to be driven by the auxiliary drive current in the second voltage section of the drive voltage.

In addition, the present invention provides a method of driving a LED drive circuit for driving a string connected to a plurality of LED elements, the method comprising the steps of: driving a selected LED element of the string in the first voltage section of the drive voltage as an auxiliary drive current; And driving the string with a main driving current in a second voltage section of the driving voltage.

According to the present invention, both the power factor and the efficiency characteristics of the device including the LED element can be improved. In particular, it is possible to improve both the power factor and the efficiency characteristics of the lighting apparatus having a large number of LED elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, in order to facilitate a person skilled in the art to easily carry out the technical idea of the present invention. do.

1 is a circuit diagram showing an LED driving circuit for explaining the present invention.

Referring to FIG. 1, the LED driving circuit includes a bridge circuit 20, a current limiting device 30, and a string 40 in which a plurality of LED devices are connected in series. The bridge circuit unit 20 includes four diodes D1 to D4 to receive the AC voltage provided from the power supply unit 10 to provide the rectified voltage to the string 40. The current limiting element 30 is intended to provide a constant amount of current to the string 40. As shown below in FIG. 1, the current limiting device 30 may be implemented as a resistor, a capacitor, a bipolar transistor, or a MOS transistor. The string 40 has a plurality of LED elements connected in series. The type and number of LED elements provided in the string 40 are determined according to the amount or color of light to be output by the LED driving circuit.

FIG. 2 is a waveform diagram showing the operation of the LED driving circuit shown in FIG. In particular, it shows a section in which the AC voltage provided from the power supply unit 10 represents a positive value. 3 is a diagram showing the characteristics of the LED driving circuit shown in FIG.

When the input voltage VIN output by the bridge circuit unit 20 changes, the driving current flowing in the string 40 may include a first case C1 and a second case C2. The first case C1 is a case where the number of LED elements provided in the string 40 is relatively large, and the second case C2 is a case where the number of LED elements provided in the string 40 is relatively small. In the case of the first case C1, since there are many LED elements included in the string 40, a driving current flows in the string 40 in the first section X that is greater than or equal to a relatively large voltage Vb. Light is emitted from the string 40 in one section X. In the case of the second case C2, since there are few LED elements included in the string 40, a driving current flows in the string 40 in the second section Y, which is greater than or equal to a relatively small voltage Va. Light is emitted from the string 40 in two sections (Y).

Factors used in determining the performance of lighting devices are power factor and efficiency. Power factor refers to the active power against the supplied apparent power. Efficiency represents how much light can be output for the supplied electrical energy. When the number of LED elements included in the string is large, that is, in the first case, the power factor is bad and the efficiency is good. As shown in FIG. 3, when the LED element is used in the string 40 like the first case C1, the current limiting element 30 takes a relatively small voltage compared to the string 40 and the string 40. The efficiency characteristic is good because a large voltage is applied. However, when there are many LED elements in the string 40, there is a large phase difference between the input voltage VIN and the driving current flowing through the string 40, so that the power factor characteristic is deteriorated.

As shown in FIG. 3, when fewer LED elements are used in the string 40 as in the second case, the voltage is greater than the current limiting element 30 compared to the string 40, and the voltage is applied to the string 40. Although the efficiency characteristic is not good because it is applied small, the power factor characteristic is good because the phase difference is relatively small between the input voltage VIN and the drive current flowing through the string 40.

As described above, when the LED driving device is decorated as shown in FIG. 1, when the power characteristic is increased, the power factor characteristic deteriorates, and when the power factor characteristic is increased, the efficiency characteristic deteriorates. In order to solve this problem, the present invention proposes an LED driving circuit and a driving method thereof capable of simultaneously improving power factor and efficiency characteristics.

4 is a circuit diagram showing an LED driving circuit according to a first preferred embodiment of the present invention.

Referring to FIG. 4, the LED driving circuit according to the present exemplary embodiment includes a bridge circuit 200, a current controller 300, a string 400, and a main current limiting device 500. The bridge circuit unit 200 includes four diodes D5 to D8 to receive the AC voltage provided from the power supply unit 100 to provide the rectified driving voltage VIN to the string 400. The current controller 300 includes a plurality of unit current controllers 300_1 to 300_n. The string 400 is connected in series with a plurality of LED elements to which the driving voltage VIN is applied. The main current limiting element 500 is disposed between the string 400 and the ground voltage supply terminal VSS such that the string 400 is driven by the main current I2. The main current limiting element 500 causes a main driving current I2 having a predetermined amount to flow from the string 400 to the ground voltage supply terminal VSS. The main current limiting element 500 may be implemented as a resistor, a capacitor, a bipolar transistor, or a MOS transistor.

The plurality of unit current controllers 300_1 to 300_n are connected to the LED elements provided in the string 400, respectively, and each unit current control unit 300_1 to 300_n is a predetermined driving current in a predetermined section. To be driven. Here, the plurality of unit current controllers 300_1 to 300_n are configured to correspond to the plurality of LED elements provided in the string 400 in a 1: 1 manner. However, in some cases, a plurality of LED elements included in the string 400 may be grouped, and the unit current controllers 300_1 to 300_n may be configured to correspond to each group 1: 1.

FIG. 5 is a waveform diagram showing the operation of the LED driving circuit shown in FIG.

As shown in FIG. 5, in the LED driving circuit, a plurality of auxiliary driving currents I_1 to I_n are generated by the unit current controllers 300_1 to 300_n when the driving voltage VIN changes, and the main current limiting element ( The main driving current I2 is generated by 500. In order to maintain the efficiency and improve the power factor, the main driving current I2 has a larger amount of current than the auxiliary driving currents I_1 to I_n. The string 400 is driven by the main driving current I2 in the first voltage section T1 of the driving voltage VIN, and the current controller 300 drives a voltage having a lower voltage level than the first voltage section T1. The corresponding LED device is driven by the auxiliary driving currents I_1 to I_n in the second voltage section T2 of the voltage VIN.

The plurality of unit current controllers 300_1 to 300_n may be grounded in an LED device corresponding to a predetermined current (for example, I_1) in each of the sections a, b, and c having different voltage levels among the second voltage sections T2. It can flow to the voltage supply terminal (VSS) respectively. At this time, the amount of current flowing in each section (a, b, c) has a different value, in particular, the current flows from the first connected LED device from the string 400 to the last connected LED device by the corresponding unit current controller The amount of current increases further.

The plurality of unit current controllers 300_1 to 300_n may preferably allow the plurality of auxiliary driving currents I_1 to I_n to have the most optimal amount of current within a range in which the driving voltage VIN changes. To this end, as shown in FIG. 5, when the driving voltage VIN changes in a semicircular shape, the values of the plurality of auxiliary driving currents I_1 to I_n gradually increase as the driving voltage VIN increases. Increasingly, the shapes of the plurality of auxiliary driving currents I_1 to I_n and the main driving current I2 are matched with the shape of the driving voltage VIN as much as possible. The power factor characteristics are improved when the shapes of the plurality of auxiliary driving currents I_1 to I_n and the main driving current I2 match the shape of the driving voltage VIN as much as possible. However, the plurality of auxiliary driving currents I_1 to I_n may be configured such that the plurality of auxiliary driving currents I_1 to I_n have a constant value or decrease as the driving voltage VIN increases as necessary.

FIG. 6 is a waveform diagram showing operating characteristics of the LED driving circuit shown in FIG.

As shown in FIG. 6, the LED driving circuit according to the present embodiment does not follow the current generation pattern P1 of the LED driving circuit of FIG. 1 while the driving voltage VIN is changed, and the current has improved power factor. It operates along the generation pattern P2. This is because the LED driving circuit according to the present embodiment is a section other than the section in which all the LED elements of the string 400 operate in the section in which the driving voltage VIN changes (see section T1 in FIG. 5) (T2 section in FIG. 5). This is because a plurality of current control units 300_1 to 300_n are provided to operate for each LED element. For reference, the current generation pattern P3 represents a case where the power factor is 100%.

The LED driving circuit of the present invention can be configured such that the power factor can be substantially 100% by properly configuring the current controllers 300_1 to 300_n. In addition, the unit current controllers 300_1 to 300_n may be configured to satisfy the required power factor according to the situation in which the LED driving circuit is applied.

FIG. 7 is a block diagram illustrating an exemplary embodiment of the unit current controller illustrated in FIG. 4.

Referring to FIG. 7, the first unit current controller 300_1 includes an auxiliary current limiting device 310, a first switch unit 320, and a second switch unit 330. The auxiliary current limiting device 310 is for flowing the auxiliary driving current I_1. The first switch unit 320 allows the auxiliary driving current I-1 to flow from the corresponding LED element to the auxiliary current limiting device 310 at the first voltage level V1 of the driving voltage VIN. The second switch unit 330 controls the first switch unit 310 to prevent the auxiliary driving current I_1 from flowing at the second voltage level V2 of the driving voltage VIN. In FIG. 7, the unit current control unit includes the first switch unit 320, the second switch unit 330, and the auxiliary current limiting device 310. If the amount of current flowing through is appropriately adjusted, it is also possible to configure the auxiliary current limiting element 310 without using it.

FIG. 8 is a waveform diagram illustrating the operation of the current control unit shown in FIG. 7.

As shown in FIG. 8, the first switch unit 320 is activated at the first voltage level V1 within a period in which the driving voltage VIN is input and increases, and the auxiliary current limiting device 310 is activated from the corresponding LED device. Auxiliary drive current I-1 flows. The second switch unit 330 deactivates the first switch unit 320 at the second voltage level V2 so that the auxiliary driving current I_1 no longer flows. In addition, the second switch unit 330 activates the first switch unit 320 to allow the auxiliary drive current I_1 to flow at the second voltage level V2 within the section in which the driving voltage VIN is input and decreases. . The first switch unit 320 is deactivated at the first voltage level V1 so that the auxiliary driving current I-1 no longer flows.

9 is a circuit diagram of an example of the unit current controller of FIG. 4.

Referring to FIG. 9, the first switch unit 320 may include a first voltage divider 321 for distributing the driving voltage VIN based on the reference node O, and a voltage level of the reference node O. The first transistor T1 is turned on to allow current to flow from the auxiliary current limiting device 310 to the ground voltage supply terminal VSS. The first voltage divider 321 includes resistors R1 and R2. In addition, although the first transistor T1 is implemented as a bipolar transistor, in some cases, the first transistor T1 may be implemented as a MOS transistor. The first switch unit 320 includes a zener diode Z1 between the base terminal of the first transistor T1 and the ground voltage supply terminal VSS to stabilize the voltage applied to the base terminal of the first transistor T1. do.

The second switch unit 330 may include a second voltage divider 331 for distributing the driving voltage VIN, and a reference node O and ground in response to the voltage divided by the second voltage divider 331. A second transistor T2 is provided for selectively connecting the voltage supply terminal VSS. In addition, although the second transistor T2 is implemented as a bipolar transistor, in some cases, the second transistor T2 may be implemented as a MOS transistor. The second switch unit 330 includes a zener diode Z2 between the base of the second transistor T2 and the ground voltage supply terminal VSS to stabilize the voltage applied to the base terminal of the second transistor T2. do.

In FIG. 9, the unit current controller includes the first switch unit 320, the second switch unit 330, and the auxiliary current limiting device 310, but according to a practical case, the first transistor T1 is used. By appropriately adjusting the amount of current flowing by, it is possible to configure without the auxiliary current limiting element 310. In this case, the amount of current flowing through the transistor T1 provided in the first switch unit 320 can be appropriately controlled to allow a desired current to flow at a desired timing.

9, when the driving voltage VIN is increased, a voltage is applied to the reference node O by the first voltage divider 321 of the first switch unit 320, and the level is constant. When abnormal, the first transistor T1 is turned on. When the first transistor T1 is turned on, the auxiliary driving current I-1 flows from the auxiliary current limiting device 130 to the ground voltage supply terminal VSS. This current causes the LED element corresponding to the auxiliary current limiting element 130 to operate. When the driving voltage VIN continues to increase, the second transistor T2 is turned on by the voltage distributed by the second voltage divider 331. When the second transistor T2 is turned on, the first transistor T1 is turned off. Therefore, the auxiliary driving current I-1 no longer flows.

When the driving voltage VIN increases further in this state, all the LED elements of the string 400 are turned on, and thus, the main driving current I2 flows through the string 400. At this time, all the LED elements provided in the string 400 are operated. When the driving voltage VIN is lowered and the voltage divided by the second voltage dividing unit 331 falls below a predetermined level, the second transistor T2 is turned off. As a result, the first transistor T1 is turned on, and the auxiliary driving current I-1 flows again. When the driving voltage VIN decreases further, the level of the voltage distributed by the first voltage divider 321 falls below a predetermined level, and the first transistor T1 is turned off to turn off the auxiliary driving current I−. 1) no longer flows.

FIG. 9 illustrates one of the unit current controllers (for example, 300_1) shown in FIG. 4. The timing at which the plurality of unit current controllers in the current controller 300 operates is eventually provided with transistors (for example, T1). It is determined by the turn-on and turn-off timing of T2). Here, the turn-on and turn-off timings of the transistors T1 and T2 are determined by the resistance values of the resistors R1 to R4. As an embodiment for obtaining the current waveform shown in FIG. 5, the resistance value of the resistors R1 to R4 included in the unit current controller of the current controller 300 increases as the number of nodes LED_1 to LED_n increases. Can be used.

As described above, the LED driving circuit according to the present embodiment connects a relatively large number of LED elements to the string 400 in series, and the unit current controllers 300_1 to 300_n corresponding to each LED element correspond to the corresponding LED elements. Allow auxiliary drive current to flow. All the LED elements provided in the string 400 are driven by the main driving current I2 flowing by the main current limiting element 500, and each LED element is further driven by the corresponding unit current controller. It is driven by (I_1 to I_n). At this time, since the auxiliary drive current is relatively smaller than the main drive current, the efficiency characteristics are not substantially affected. In addition, the auxiliary drive current flows in addition to the main drive current in the process of changing the driving voltage VIN, thereby increasing the power factor of the LED driving circuit. Characteristics are improved. In addition, since the LED driving circuit according to the present embodiment is provided with a large number of LED elements in the string 400, the LED driving circuit having the string 400 can expect good efficiency characteristics. In conclusion, the LED driving circuit according to the present embodiment can expect good efficiency characteristics and good power factor characteristics due to the relatively large number of LED elements and unit current control units connected to each LED element.

10 is a circuit diagram showing an LED driving circuit according to a second preferred embodiment of the present invention.

As shown in Fig. 10, the LED driving circuit according to the second embodiment includes a bridge circuit portion 200A including four diodes forming a bridge circuit portion, a string 400A including a plurality of LED elements, Control unit for controlling the auxiliary current limiting device (IS1 ~ ISn), the main current limiting device (500A), and the auxiliary current limiting device (IS1 ~ ISn) corresponding to each of the plurality of LED elements provided in the string 400 ( 300A). The controller 300A controls each current limiting device IS1 to ISn so that the auxiliary driving current flows from each current limiting device IS1 to ISn to the ground voltage supply terminal VSS according to the voltage level of the driving voltage VIN. To control.

The LED driving circuit according to the second embodiment also basically operates to allow a driving current of the form as shown in FIG. 5 to flow. The current limiting elements IS1 to ISn may correspond 1: 1 to the plurality of LED elements provided in the string 400A. In some cases, the plurality of LED elements provided in the string 400A may be grouped and grouped in each group. It may correspond to 1: 1. The auxiliary current limiting devices IS1 to ISn may use any of the current limiting devices shown in FIG. Whether the control unit 300A activates each of the auxiliary current limiting devices IS1 to ISn at which voltage level of the driving voltage VIN depends on the case where the LED driving circuit is applied, that is, which current waveform is required. Can be.

Fig. 11 is a circuit diagram showing an LED driving circuit according to a third preferred embodiment of the present invention.

As shown in Fig. 11, the LED driving circuit according to the third embodiment includes a bridge circuit portion 200B, a current controller 300B, a string 400B, and a main current limiting element 500B. Each component of the LED driving circuit shown in FIG. 12 performs substantially the same operation as the component shown in FIG. 4, but the LED elements shown in the string 400B are grouped (G1, G2, G3), The unit current control unit corresponding to each group is connected. Here, two LED elements are grouped into one group, but in some cases, various numbers of LED elements may be grouped into one group. In addition, the number of LED elements included in all groups may be the same or different. For example, from the first LED device in the string to the last LED device, the number of LED devices in the group can be increased. In addition, the current control unit 300B may have a configuration as shown in FIG. 4, or may use a method as shown in FIG. 10.

12 is a circuit diagram showing an LED driving circuit according to a fourth preferred embodiment of the present invention.

As shown in FIG. 12, the LED driving circuit according to the fourth embodiment includes a bridge circuit 200C, a first current controller 300C, a first string 400C, and a first main current limiting device 500C, A second current controller 300D, a second string 400D, and a second main current limiting device 500D are included. The LED driving circuit according to the fourth embodiment basically performs the same operation as the LED driving circuit shown in FIG. 4 and shows a case where two strings are connected in parallel. Although two strings are connected in parallel here, in some cases, more strings may be connected in parallel. In addition, although all the LED elements provided in the two strings are shown as being individually driven, only some selected LED elements can be controlled to flow the auxiliary driving current. In addition, the current controllers 300C and 300D may have a configuration as shown in FIG. 4 or may have a configuration as shown in FIG. In addition, the current controllers 300C and 300D may control the LED device in the same manner as shown in FIG. 11.

Fig. 13 is a circuit diagram showing an LED driving circuit according to a fifth preferred embodiment of the present invention.

As shown in FIG. 13, the LED driving circuit according to the fifth embodiment includes the first string 400E, the second string 400F, the first current controller 300E, the second current controller 300F, and the first string. A main current limiting element 500E, and a second main current limiting element 500F. In the LED driving circuit according to the fifth embodiment, the first string 400E, the first current controller 300E, and the first main current limiter operating when the AC voltage supplied from the power supply unit 100 is a positive value. 500E, a second string 400F, a second current controller 300F, and a second main current limiting device 500F that operate when the AC voltage provided from the power supply unit 100 is negative. have.

Since the LED driving circuit according to the fifth embodiment has both a region that operates when the AC voltage has a positive value and a region that operates when the AC voltage has a negative value, a bridge circuit unit that serves to rectify the AC voltage (FIG. Does not have 200). The method of operating the first string 400E, the first current controller 300E, and the first main current limiting element 500E is substantially the same as that of the LED driving circuit in FIG. 4, the second string 400F, The waveform of the drive current generated by the second current control unit 300F and the second main current limiting element 500F is as if the current waveform in FIG. 5 is symmetrically symmetrical.

Each of the first current controller 300E and the second current controller 300F includes a plurality of unit current controllers so as to flow auxiliary driving currents to the corresponding LED elements, respectively. The first current controller 300E and the second current controller 300F may include a unit current controller corresponding to all the LED elements provided in the string, group all the LED elements provided in the string, and correspond to each group. The unit current controller may be provided. In addition, the first current controller 300E and the second current controller 300F may control the LED elements in the string, as shown in FIGS. 10 to 12.

As described above, the LED driving circuit according to the present invention can improve both power factor and efficiency characteristics by controlling the LED elements provided in the string. The various LED driving circuits described above may be implemented as an independent lighting device using the LED elements provided in the string, or may be applied to other devices in which the LED elements are used. In addition, the LED driving circuit according to the present embodiment is applicable to the case of driving a general diode instead of the LED element. For example, even in the case of a flat panel display equipped with an LED device, when driving a plurality of LED devices as in the method provided by the present invention, a device having both good power factor and efficiency characteristics can be implemented.

Although the present invention has been described in detail with reference to exemplary embodiments above, those skilled in the art to which the present invention pertains can make various modifications to the above-described embodiments without departing from the scope of the present invention. Will understand. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by the scope of the appended claims, as well as the appended claims.

1 is a circuit diagram showing an LED drive circuit for explaining the present invention.

FIG. 2 is a waveform diagram showing the operation of the LED driving circuit shown in FIG.

3 is a diagram showing the characteristics of the LED driving circuit shown in FIG.

4 is a circuit diagram showing an LED driving circuit according to a first preferred embodiment of the present invention.

Fig. 5 is a waveform diagram showing the operation of the LED driving circuit shown in Fig. 4;

Fig. 6 is a waveform diagram showing the operating characteristics of the LED driving circuit shown in Fig. 4;

FIG. 7 is a block diagram showing an embodiment of a unit current controller shown in FIG. 4; FIG.

FIG. 8 is a waveform diagram illustrating the operation of the unit current controller shown in FIG. 7; FIG.

FIG. 9 is a circuit diagram of an example of a unit current controller shown in FIG. 4; FIG.

10 is a circuit diagram showing an LED driving circuit according to a second preferred embodiment of the present invention.

Fig. 11 is a circuit diagram showing an LED driving circuit according to a third preferred embodiment of the present invention.

Fig. 12 is a circuit diagram showing an LED driving circuit according to a fourth preferred embodiment of the present invention.

Fig. 13 is a circuit diagram showing an LED driving circuit according to a fifth preferred embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

100: AC power supply 200: bridge circuit

300: current controller 400: string

500: main current limiting element

Claims (18)

A string having at least two LED elements and driven by a main driving current in a first voltage section of the driving voltage; And A current controller for driving the LED element selected from the LED elements of the string to be driven by the auxiliary driving current in the second voltage section of the driving voltage; LED driving circuit having a. The method of claim 1, LED driving circuit further comprises a main current limiting element for limiting the amount of current of the main drive current of the string. The method of claim 1, The current amount of the auxiliary drive current is smaller than the current amount of the main drive current LED drive circuit. The method of claim 1, LED driving circuit further comprises a bridge circuit for rectifying the input AC voltage to provide the drive voltage. The method of claim 1, The current controller A first switch unit configured to allow the auxiliary driving current to flow through the selected LED element at a first voltage level which is one threshold value of the second voltage section; And And a second switch unit for controlling the first switch unit to allow the auxiliary driving current to flow at a second voltage level which is the other limit value of the second voltage section. The method of claim 5, The current controller And an auxiliary current limiting element connected to said selected LED element for flowing said auxiliary driving current from said selected LED element to said first switch section. The method of claim 6, The first switch unit A first voltage divider for distributing the driving voltage based on a reference node; And And a first transistor turned on according to the voltage level of the reference node to flow the auxiliary drive current from the auxiliary current limiting element to a ground voltage supply terminal. The method of claim 7, wherein The second switch unit A second voltage divider for distributing the driving voltage; And And a second transistor for selectively connecting the reference node and a ground voltage supply terminal in response to the voltage distributed by the second voltage divider. The method of claim 1, The current controller And a plurality of unit current controllers configured to receive the driving voltages so that corresponding LED elements among the LED elements of the string are driven by predetermined auxiliary driving currents. The method of claim 9, And the second voltage section has a different voltage range for each of the plurality of unit current controllers. The method of claim 9, Each of the auxiliary driving currents controlled by the plurality of current controllers has a different amount of current LED driving circuit. The method of claim 9, The amount of current of each auxiliary driving current controlled by the plurality of current controllers is increased from the first LED device connected to the string toward the last LED device connected. The method of claim 9, The plurality of unit current controllers correspond to the plurality of LED elements provided in the string 1: 1 LED driving circuit. The method of claim 9, The plurality of current control unit groups a plurality of LED elements provided in the string, LED driving circuit, characterized in that corresponding to each group 1: 1. The method of claim 9, An additional string disposed in a direction opposite to the string based on the voltage polarity of the driving voltage and including at least two LED elements and driven by the first driving current in a third voltage section in which the driving voltage becomes a negative period; And And an additional current controller for causing the LED device selected from the LED elements of the additional string to be driven by a second driving current in a fourth voltage section in which the driving voltage becomes a negative section. In the driving method of the LED driving circuit for driving a string connected to a plurality of LED elements, Driving the selected LED elements of the string with an auxiliary driving current in a first voltage section of a driving voltage; And Driving the string to a main driving current in a second voltage section of the driving voltage; Driving method of the LED driving circuit comprising a. The method of claim 16, The current amount of the auxiliary drive current is lower than the current amount of the main drive current driving method of the LED drive circuit. The method of claim 16, Driving the LED element selected from the strings with the auxiliary driving current in the first voltage section of the driving voltage And driving each of a plurality of LED elements selected from the strings in a plurality of different first voltage sections with a plurality of auxiliary driving currents.

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