TW201352066A - LED device with simultaneous open and short detection function and method thereof - Google Patents

Abstract

An LED device with simultaneous open and short detection function includes a plurality of LED strings, a voltage converter, a current driving unit, a loop control unit, an open and short detector. The open and short detector is utilized for performing LED open and LED short detection on the plurality of LED strings according to negative electrode voltages of the plurality of LED strings and a level variation trend of a second voltage.

Description

Light-emitting diode device with simultaneous detection of open circuit and short circuit function and method thereof

The present invention relates to a light emitting diode device and a method thereof, and more particularly to a light emitting diode device and a method thereof for simultaneously detecting open circuit and short circuit functions.

The use of light-emitting diodes (LEDs) as illumination sources is becoming more and more popular. For example, a backlight module of a conventional liquid crystal display panel is a cold cathode fluorescent lamp (CCFL) as a light source. Nowadays, as the luminous efficiency of the light-emitting diode is continuously increased and the cost is decreasing, the light-emitting diode has a tendency to gradually replace the cold cathode fluorescent tube as a backlight module light source.

In the conventional light-emitting diode driving circuit, if the LED series is open (LED open), since the corresponding output channel of the driving circuit is in a floating state, the driving circuit may have leakage. It affects the conversion efficiency of the overall circuit or causes abnormal operation of the voltage conversion loop. In addition, if the LEDs are short-circuited (LED short), that is, the voltage across the LEDs is zero, the headroom voltage of the current-driving element is correspondingly increased, resulting in current consumption. The power consumption of the driving element is increased to lower the conversion efficiency of the overall circuit. Therefore, the LED driving circuit needs a mechanism and method for detecting open circuit and short circuit.

Please refer to FIG. 1 , which is a schematic diagram of a conventional LED driving circuit 10 . The LED driving circuit 10 is used to drive a LED module 11. As shown in Figure 1, The LED module 11 includes parallel LED dipoles C1 to Cm, and each LED array is composed of a plurality of serially connected LEDs. The LED driving circuit 10 includes a voltage converter 12, a current driving unit 13, and a loop control unit 14. The voltage converter 12 is configured to convert an input voltage V1 into an output voltage V2 according to a voltage control signal VCTRL to drive the LED module 11. The current driving unit 13 is configured to draw the driving currents Id1 to Idm having a constant current magnitude from the LED module 11. The loop control unit 14 controls the voltage conversion operation of the voltage converter 12 according to the difference between the anode voltages VHR1 VVHRm of the LED series and a predetermined reference voltage VREF to stabilize the level of the output voltage V2.

The loop control unit 14 further includes a voltage selector 142, an error amplifier 144 and a conversion controller 146. The voltage selector 142 is coupled to the LED series C1 to Cm for selecting a minimum voltage as the feedback voltage VFB from the negative voltages VHR1 VVHRm of the LED series. The error amplifier 144 is coupled to the voltage selector 142 and the reference voltage VREF for generating an error voltage signal VERR according to the difference between the feedback voltage VFB and the reference voltage VREF. The conversion controller 146 is coupled to the error amplifier 144 and the voltage converter 12 for generating a voltage control signal VCTRL according to the error voltage signal VERR.

In this way, the LED driving circuit 10 can pass through the loop control unit 14 to connect the anode voltages VHR1 VVHRm of the LEDs (ie, the head space voltage of the current driving component) and the output voltage V2 of the voltage converter. Locked in a reasonable voltage range.

In this case, the LED driving circuit 10 further includes an open circuit detector 15 and a short circuit detector 16 for performing open circuit detection and short circuit detection on the LED series C1 to Cm, respectively. Since the head space voltage of the current driving element is pulled to a low level when the LED array is open, the open circuit detector 15 can be lower than one according to the negative voltage VHR1~VHRm of the LED series. Specific low threshold voltage to determine the LED series C1~Cm is No open circuit occurred. Of course, the above-mentioned low threshold voltage cannot be higher than the head space voltage of the current driving element under normal operation, so as to avoid misjudgment under normal conditions. Conversely, when the short circuit of the LED array is short-circuited (ie, the voltage across the LED is zero), since the head space voltage of the current driving element is correspondingly increased, the short-circuit detector 16 can be illuminated according to the light. Whether the negative voltage VHR1~VHRm of the diode series is greater than a specific high threshold voltage determines whether the LED series C1~Cm are in a short circuit state. Similarly, the above high threshold voltage cannot be lower than the head space voltage of the current driving element under normal operation to avoid misjudgment under normal conditions.

However, when the light-emitting diode series C1 to Cm are simultaneously opened and short-circuited, the light-emitting diode driving circuit 10 may be short-circuited. For example, when the LED array C1 is open, since the head space voltage of the current driving element is pulled to a low potential (for example, zero potential), the voltage selector 142 selects the LED string. The negative voltage VHR1 of the column C1 is used as the feedback voltage VFB, and the output voltage V2 of the voltage converter 12 is raised. In this case, since the cross-voltage of the light-emitting diode is fixed, the negative voltage VHR2~VHRm of the other LED series will increase with the output voltage V2, which is greater than the above-mentioned specific high threshold voltage, which will cause a short circuit. The detector 16 is misjudged.

In other words, when the open-circuit detection and the short-circuit detection are performed on the LED series at the same time, the conventional technology may immediately cause a short-circuit misjudgment after detecting an open circuit of the LED array.

Accordingly, it is an object of the present invention to provide a light emitting diode device and method thereof for simultaneously detecting open and short circuits.

The invention further discloses a light-emitting diode device having simultaneous detection of open circuit and short circuit functions. The light emitting diode device comprises a plurality of light emitting diodes, a voltage converter, and an electric The flow drive unit, the primary circuit control unit, and an open circuit and short circuit detector. Each of the plurality of LED arrays has a positive electrode and a negative electrode. The voltage converter is coupled to the anode of the plurality of LED arrays for converting a first voltage to a second voltage according to a voltage control signal. The current driving unit is coupled to the anode of the plurality of LED arrays for providing a plurality of driving currents to the plurality of LED arrays. The loop control unit is coupled to the plurality of LED arrays and the voltage converter for generating the voltage control signal according to the anode voltage of the plurality of LED arrays. The open circuit and short circuit detector are coupled to the plurality of LED arrays, the loop control unit and the voltage converter for determining a negative voltage and the second voltage according to the plurality of LED strings The change trend of the level is to perform open circuit detection and short circuit detection on the plurality of LED arrays.

The invention further discloses a method for detecting an open circuit and a short circuit by a light emitting diode device. The LED device includes a plurality of LED arrays and a voltage converter. Each of the plurality of LED arrays has a positive electrode and a negative electrode. The voltage converter is coupled to the anode of the plurality of LED arrays for converting a first voltage to a second voltage according to a voltage control signal. The method includes generating a voltage control signal according to the anode voltage of the plurality of LED arrays, and according to a change trend of the anode voltage and the second voltage level of the plurality of LED arrays, The plurality of LEDs are connected in series for open circuit detection and short circuit detection.

10‧‧‧Lighting diode drive circuit

11‧‧‧Lighting diode module

C1~Cm, Cx‧‧‧LED Diodes

12, 21, 51‧‧‧ voltage converter

13, 22, 52‧‧‧ Current drive unit

14, 23, 53‧‧‧ loop control unit

VCTRL‧‧‧ voltage control signal

V1, V2‧‧‧ voltage

Id1~Idm‧‧‧ drive current

VHR1~VHRm, VHRx‧‧‧negative voltage

VREF‧‧‧reference voltage

142, 232, 532‧‧ ‧ voltage selector

144, 234, 534‧‧‧ error amplifier

146, 236, 536‧‧‧ conversion controller

VFB‧‧‧ feedback voltage

VERR‧‧‧ error voltage signal

15, 24‧‧‧ Open circuit detector

16, 25‧‧‧ Short-circuit detector

20, 50‧‧‧Lighting diode device

26‧‧‧Voltage Detector

RST‧‧‧Reset signal

30, 60‧‧‧ Process

300~330, 600~630‧‧ steps

54‧‧‧Open and short circuit detectors

FIG. 1 is a schematic diagram of a conventional LED driving circuit.

FIG. 2 is a schematic diagram of a light-emitting diode device having a function of simultaneously detecting an open circuit and a short circuit according to a first embodiment of the present invention.

FIG. 3 is a schematic diagram of a process for simultaneously detecting an open circuit and a short circuit for a light emitting diode device according to an embodiment of the present invention.

FIG. 4 illustrates a case where the light-emitting diode short-circuit detection is restarted after the LED series is opened in the embodiment of the present invention.

FIG. 5 is a schematic diagram of a light-emitting diode device having a function of simultaneously detecting an open circuit and a short circuit according to a second embodiment of the present invention.

FIG. 6 is a schematic diagram of a process for simultaneously detecting an open circuit and a short circuit for a light emitting diode device according to an embodiment of the present invention.

Figure 7 illustrates the trend of the level of the output voltage of the negative voltage and voltage converter when the LED array is open or shorted.

Please refer to FIG. 2, which is a schematic diagram of a light-emitting diode device 20 having a function of simultaneously detecting an open circuit and a short circuit according to a first embodiment of the present invention. The LED device 20 includes parallel LEDs C1~Cm, a voltage converter 21, a current driving unit 22, a loop control unit 23, an open detector 24, and a short circuit detector. 25 and a voltage detector 26. The voltage converter 21 is coupled to the anode of the LED array C1~Cm for converting a first voltage V1 into a second voltage V2 according to a voltage control signal VCTRL, as a light-emitting diode series C1. ~Cm stable drive voltage. The current driving unit 22 is coupled to the negative electrodes of the LED arrays C1 to Cm for supplying the driving currents Id1 to Idm with a fixed current to the LEDs C1 to Cm. The loop control unit 23 is coupled to the LED arrays C1 to Cm and the voltage converter 21 for generating a voltage control signal VCTRL according to the anode voltages VHR1 VVHRm of the LED arrays C1 to Cm. The open circuit detector 24 is coupled to the LED series C1 to Cm and the loop control unit 23 for illuminating the LEDs according to the negative voltages VHR1 VVm of the LEDs C1 to Cm. ~Cm for open circuit detection. The short-circuit detector 25 is coupled to the LED series C1 to Cm and the loop control unit 23 for illuminating the LEDs according to the negative voltages VHR1 VVm of the LEDs C1 to Cm. ~Cm for short circuit detection. The voltage detector 26 is coupled to the open circuit detector 24, the short circuit detector 25 and the voltage converter 21 for open circuit detection. When detecting that the LED series C1~Cm is open, the device 24 generates a reset signal RST to the short-circuit detector 25 according to the change of the second voltage V2 to restart the LED array. Short circuit detection of C1~Cm.

Therefore, when the LED device 20 performs open-circuit detection and short-circuit detection on the LED series C1 to Cm at the same time, if the LED series C1 to Cm are open, the embodiment of the present invention may be The level change of the two voltages V2 generates a reset signal RST to the short-circuit detector 25 to restart the short-circuit detection of the LED series C1~Cm. In this way, the embodiment of the present invention can avoid the situation in which the short circuit misjudgment occurs immediately after the light emitting diode is opened.

Preferably, the loop control unit 23 further includes a voltage selector 232, an error amplifier 234, and a conversion controller 236. The voltage selector 232 is coupled to the LED series C1 to Cm for selecting a minimum voltage as the feedback voltage VFB from the negative voltages VHR1 VVHRm of the LED series C1 to Cm. The error amplifier 234 is coupled to the voltage selector 232 and a reference voltage VREF for generating an error voltage signal VERR according to the difference between the feedback voltage VFB and the reference voltage VREF. The conversion controller 236 is coupled to the error amplifier 234 and the voltage converter 21 for generating a voltage control signal VCTRL according to the error voltage signal VERR to control the voltage conversion operation of the voltage converter 21. For details on the operation of the light-emitting diode device 20, please continue to refer to the following description.

Please refer to FIG. 3 , which is a schematic diagram of a flow 30 for detecting an open circuit and a short circuit simultaneously for the LED device 20 according to an embodiment of the present invention. The process 30 is used to implement an operation flow of the above-mentioned LED device 20, which comprises the following steps:

Step 300: Start.

Step 310: Perform open-circuit detection and short-circuit detection on the LED series C1~Cm according to the negative voltages VHR1~VHRm of the LEDs C1~Cm.

Step 320: When an open circuit of the LED series C1~Cm is detected, the short circuit detection of the LED series C1~Cm is restarted according to the level of the second voltage V2.

Step 330: End.

According to the process 30, in the embodiment of the present invention, the open-circuit detection and the short-circuit detection are performed on the LED series C1~Cm according to the negative voltages VHR1~VHRm of the LEDs C1~Cm. When the LEDs C1 to Cm are detected to be open, the embodiment of the present invention further restarts the short-circuit detection of the LEDs C1 to Cm according to the change of the second voltage V2. A short-circuit misjudgment occurs immediately after the light-emitting diode is opened.

As described in the prior art, when the LED array is opened, the negative voltage of the LED array (ie, the head space voltage of the current driving element) is pulled to a low potential (eg, zero potential). Therefore, the open circuit detector 24 can determine whether the LED series C1 to Cm are open according to whether the negative voltage VHR1 VVm of the LED series C1 to Cm is lower than a first threshold voltage. Conversely, when the short circuit of the LED array is short-circuited, the anode voltage of the LED array is correspondingly increased. Therefore, the short-circuit detector 25 can be based on the negative voltage VHR1 of the LED series C1 to Cm. Whether VHRm is greater than a second threshold voltage to determine whether the light-emitting diode series C1 to Cm are short-circuited by the light-emitting diode. Of course, the first threshold voltage cannot be higher than the head space voltage of the current driving element under normal operation, and the second threshold voltage cannot be lower than the head space voltage of the current driving element under normal operation to avoid under normal conditions. Produce misjudgment.

In addition, since the voltage selector 232 selects the negative voltage of the LED series in which the open circuit is generated as the feedback voltage VFB, the output voltage V2 of the voltage converter 21 is raised. Therefore, the embodiment of the present invention can use the voltage detector 26 to detect whether the level of the second voltage V2 is greater than a third threshold to generate the reset signal RST, and restart the short circuit detection of the LED series. .

For example, please refer to FIG. 4, which illustrates a case where the LED short-circuit detection is restarted after the LED C1 is opened in the embodiment of the present invention. As shown in FIG. 4, when the light-emitting diode series C1 is open, since the negative voltage VHR1 is pulled to a low potential (for example, zero potential), the voltage selector 232 selects its negative voltage VHR1 as a back. The voltage VFB is applied, and the output voltage V2 of the voltage converter 21 is raised. When the output voltage V2 is higher than the third threshold, the voltage detector 26 immediately generates a reset signal RST to restart the short-circuit detection of the LED. At the same time, the loop control unit 23 also overvoltage protects the output voltage to maintain the output voltage V2 within a reasonable voltage range.

Of course, the process 30 of the embodiment of the present invention further includes the following steps: when detecting that the light-emitting diode series C1~Cm is open, cutting off the electrical properties of the open-circuit LED array and the loop control unit 23 And when the short circuit of the LED series C1 to Cm is detected to be short-circuited, the short-circuited LED array is electrically connected to the current driving unit 22. The above operations are well known to those of ordinary skill in the art and will not be further described herein.

In short, when the open-circuit detection and the short-circuit detection are performed on the LED series at the same time, the embodiment of the present invention can change according to the level of the second voltage V2 if an open circuit of the LED array is detected. , restart the short-circuit detection of the LEDs C1~Cm in series to avoid short-circuit misjudgment. As a result, the embodiments of the present invention can improve the shortcomings that the prior art cannot simultaneously perform open circuit detection and short circuit detection on the LED array.

Please refer to FIG. 5. FIG. 5 is a schematic diagram of a light emitting diode device 50 having a function of simultaneously detecting open circuit and short circuit according to a second embodiment of the present invention. The LED device 50 includes parallel LEDs C1 to Cm, a voltage converter 51, a current driving unit 52, a loop control unit 53, and an open circuit and short circuit detector 54. The voltage converter 51, the current driving unit 52, and the loop control unit 53 are similar to the voltage converter 21, the current driving unit 22, and the circuit in FIG. The control unit 23 will not be described here. The open circuit and short circuit detector 54 is coupled to the LED series C1 to Cm, the loop control unit 53 and the voltage converter 51 for using the negative voltage VHR1~VHRm of the LED series C1~Cm and the first The trend of the voltage of the two voltages V2 is open circuit detection and short circuit detection of the LED series C1~Cm.

Since the cross-voltage of the light-emitting diode is constant, under normal operation (ie, no light-emitting diode is open or short-circuited), the negative voltage VHR1~VHRm of the LED series C1~Cm will be converted with voltage. The output voltage V2 of the device 51 has the same tendency to change in level. In this case, when the anode voltages VHR1 VVHRm of the light-emitting diode series C1 to Cm are different from the second voltage V2, the embodiment of the present invention can perform the open circuit of the light-emitting diode series. Detection and short circuit detection. As a result, the embodiments of the present invention can also improve the shortcomings of the prior art that the open-circuit detection and the short-circuit detection of the LED array are not simultaneously performed. For details on the operation of the light-emitting diode device 50, please continue to refer to the following description.

Please refer to FIG. 6. FIG. 6 is a schematic diagram of a process 60 for simultaneously detecting open circuit and short circuit of the LED device 50 according to an embodiment of the present invention. The process 60 is used to implement an operation flow of the LED device 50, which includes the following steps:

Step 600: Start.

Step 610: Generate a voltage control signal VCTRL according to the negative voltages VHR1 VVHRm of the LED series C1 to Cm.

Step 620: Perform open-circuit detection and short-circuit detection on the LED series C1~Cm according to the change trend of the negative voltages VHR1~VHRm and the second voltage V2 of the LED series C1~Cm.

Step 630: End.

According to the process 60, the embodiment of the present invention firstly according to the LED series C1~Cm The negative voltage VHR1~VHRm generates a voltage control signal VCTRL. Then, in the embodiment of the present invention, the open-circuit detection and short circuit of the LED series C1~Cm can be performed according to the change trend of the negative voltages VHR1~VHRm and the second voltage V2 of the LED series C1~Cm. Detection.

In other words, after the voltage conversion loop is established, the embodiment of the present invention can detect whether the polarization trends of the negative voltages VHR1 VVHRm and the second voltage V2 of the LED series C1 to Cm are the same. The polar body series C1~Cm performs open circuit detection and short circuit detection. For example, please refer to FIG. 7. FIG. 7 illustrates the negative voltage VHRx of the LED series Cx and the output voltage V2 of the voltage converter when the LED series Cx is open or shorted. Bit change trend. As described above, when the LED series Cx is open, its negative voltage VHRx is pulled to a low potential (for example, zero potential), and the voltage selector 532 selects its negative voltage VHRx as the feedback voltage VFB. And the output voltage V2 of the voltage converter 51 is raised. Conversely, when the light-emitting diode series Cx is short-circuited, that is, the cross-voltage of some of the light-emitting diodes in the light-emitting diode series Cx is zero, so that the negative electrode voltage VHRx thereof is thereby increased.

Therefore, when it is detected that the negative voltage VHRx corresponding to the LED series Cx falls and the level of the second voltage V2 rises, the open circuit and short circuit detector 54 can determine that the LED series Cx is open. . Conversely, when it is detected that the negative voltage VHRx corresponding to the LED series Cx rises and the level of the second voltage V2 does not change, the open circuit and short circuit detector 54 can determine the LED array. A short circuit occurs in Cx. In this way, the embodiment of the present invention can also improve the shortcomings of the prior art that the open-circuit detection and the short-circuit detection of the LED series can not be simultaneously performed.

Of course, the process 60 of the embodiment of the present invention also includes the following steps: when detecting that the light-emitting diode series C1~Cm is open, the electrical connection of the open-circuit LED array and the loop control unit 53 is cut off. Linking; and short-circuiting when a short circuit occurs in the LED series C1~Cm detected The electrical connection of the light-emitting diodes of the circuit to the current driving unit 52, etc., is well known to those skilled in the art and will not be further described herein.

In summary, the present invention provides a method for simultaneously performing open-circuit detection and short-circuit detection in a light-emitting diode device to avoid the occurrence of a short-circuit misjudgment after the open circuit of the light-emitting diode.

C1~Cm‧‧‧Light Diodes

51‧‧‧Voltage Converter

52‧‧‧ Current drive unit

53‧‧‧Circuit Control Unit

VCTRL‧‧‧ voltage control signal

V1, V2‧‧‧ voltage

Id1~Idm‧‧‧ drive current

VHR1~VHRm‧‧‧Negative voltage

VREF‧‧‧reference voltage

532‧‧‧Voltage selector

534‧‧‧Error amplifier

536‧‧‧Transition controller

VFB‧‧‧ feedback voltage

VERR‧‧‧ error voltage signal

50‧‧‧Lighting diode device

54‧‧‧Open and short circuit detectors

Claims (11)

A light-emitting diode device having a function of simultaneously detecting an open circuit and a short circuit, wherein the light-emitting diode device comprises: a plurality of light-emitting diode series, each light-emitting diode series having a positive electrode and a negative electrode; The voltage converter is coupled to the anode of the plurality of LED strings for converting a first voltage into a second voltage according to a voltage control signal; and a current driving unit coupled to the plurality of LEDs a cathode of the diode series for providing a plurality of driving currents to the plurality of LED strings; a loop control unit coupled to the plurality of LED arrays and the voltage converter Generating the voltage control signal according to the negative voltage of the plurality of LEDs; and an open circuit and short circuit detector coupled to the plurality of LED arrays, the loop control unit, and the voltage The converter is configured to perform open circuit detection and short circuit detection on the plurality of LED arrays according to a trend of a change in a voltage between the negative voltage of the plurality of LED strings and the second voltage. The light-emitting diode device of claim 1, wherein the open-circuit and short-circuit detector detects a decrease in a negative voltage corresponding to a first light-emitting diode series in the plurality of light-emitting diode series When the level of the second voltage rises, it is determined that the first LED array is open. The light-emitting diode device of claim 2, wherein the open-circuit and short-circuit detector is further configured to cut off the first light-emitting diode series when the first light-emitting diode series is opened The electrical connection of the loop control unit. The illuminating diode device of claim 1, wherein the open circuit and short circuit detector detects a negative voltage corresponding to a second illuminating diode series in the plurality of illuminating diode strings When the level of the second voltage is constant, it is determined that the second LED array is short-circuited. The light-emitting diode device of claim 4, wherein the open-circuit and short-circuit detector is further configured to cut off the second light-emitting diode series when the second light-emitting diode series is short-circuited The current drive unit is electrically connected. The illuminating diode device of claim 1, wherein the loop control unit comprises: a voltage selector coupled to the illuminating diode module for arranging from the plurality of illuminating diodes In the negative voltage, a minimum voltage is selected as a feedback voltage; an error amplifier is coupled to the voltage selector and a reference voltage for generating an error voltage signal according to the difference between the feedback voltage and the reference voltage And a conversion controller coupled to the error amplifier and the voltage converter for generating the voltage control signal according to the error voltage signal. A method for detecting an open circuit and a short circuit by a light emitting diode device, the light emitting diode device comprising a plurality of light emitting diode series and a voltage converter, each of the plurality of light emitting diodes A light-emitting diode series has a positive electrode and a negative electrode, and the voltage converter is coupled to the positive electrode of the plurality of light-emitting diodes for converting a first voltage into a second according to a voltage control signal Voltage, the method includes: generating the voltage control signal according to the negative voltage of the plurality of LED strings; and changing the voltage of the negative voltage and the second voltage according to the plurality of LED strings The trend is to perform open circuit detection and short circuit detection on the plurality of LED arrays. The method of claim 7, wherein the plurality of LED arrays are open-circuited and short-circuited according to a change trend of the anode voltage of the plurality of LED strings and the second voltage level The detection step includes: Determining the first light-emitting diode string when detecting a decrease in a negative voltage corresponding to a first light-emitting diode series in the plurality of light-emitting diode strings, and raising a level of the second voltage The column has an open circuit. The method of claim 8, wherein the LED device further includes a loop control unit coupled to the plurality of LED arrays and the voltage converter for determining the plurality of LEDs according to the plurality of LEDs The voltage of the negative voltage of the body string is generated to generate the voltage control signal, and the method further comprises: cutting off the first light emitting diode series and the circuit of the loop control unit when the first light emitting diode series is open circuited Sexual links. The method of claim 7, wherein the plurality of LED arrays are open-circuited and short-circuited according to a change trend of the anode voltage of the plurality of LED strings and the second voltage level The detecting step includes: detecting a rise in a negative voltage corresponding to a second LED array in the plurality of LED arrays, and when the second voltage level is unchanged, It is determined that the second LED array is short-circuited. The method of claim 10, wherein the LED device further comprises a current driving unit coupled to the cathode of the plurality of LED arrays for providing a plurality of driving currents to the plurality of LEDs In the diode array, the method further includes: electrically disconnecting the second LED array and the current driving unit when the second LED array is short-circuited.