LED driver and display device

Abstract

To provide an LED driver capable of light emission control of an LED backlight while saving circuit scale and current consumption.SOLUTION: An LED driver includes: an external terminal configured to be connectable to a light-emitting diode; a first transistor having one end connected to the external terminal, and controlled to be on and off based on a comparison result of comparing a voltage applied to the external terminal with a first voltage; a second transistor connected to the other end of the first transistor, controlled to be on and off by receiving application of a driving control voltage, and for generating output current according to the driving control voltage and leading it to a voltage supply line of a reference voltage when the transistor itself is in on-state and the first transistor is in on-state; and a control circuit for receiving an indication signal for indicating turn on or off of the light-emitting diode, and generating the driving control voltage which controls the second transistor to on-state if the indication signal indicates turn on, and controls the second transistor to off-state if the indication signal indicates turn off.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an LED driver and a display device. [Background technology]

[0002] In recent years, liquid crystal display devices using LEDs (Light Emitting Diodes) as backlight sources have come into use. When LEDs are used as backlight sources for large-screen displays, a constant current must be supplied to a large number of LEDs connected in series. Therefore, LED drivers for driving LED backlights have been proposed that apply feedback control to an output transistor that generates a current to be passed through a group of LEDs so that the output current remains constant (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-53139 Summary of the Invention [Problem to be solved by the invention]

[0004] The output circuit of the LED driver has an output terminal connected to the LED backlight. When the LED backlight is off (not emitting light), a high voltage corresponding to the voltage level of the high power supply voltage (e.g., 18V) is applied to this output terminal. For this reason, the output circuit must be composed of high-voltage elements (hereinafter referred to as HV elements).

[0005] The output circuit of an LED driver is equipped with an amplifier circuit consisting of a differential stage, a current mirror stage, and an output stage. In the differential stage and current mirror stage, precision is required for the transistors that make up each stage to suppress variations in the current flowing through the LEDs. As mentioned above, since the output circuit of an LED driver is made up of HV elements, the size of the transistors that make up the amplifier circuit must be increased in order to increase their precision.

[0006] On the other hand, when turning on (emitting light from) an LED backlight, the output circuit of the LED driver is required to operate at high speed with a large current of several tens of milliamperes. This means that the amplifier circuit needs to be driven by a high power supply voltage while also flowing a large steady-state current, which poses the problem of high power consumption.

[0007] The present invention has been made in view of the above problems, and has an object to provide an LED driver and a display device that can reduce the circuit size and current consumption. [Means for solving the problem]

[0008] The LED driver according to the present invention is characterized in comprising: an external terminal connectable to a light-emitting diode; a first transistor having one end connected to the external terminal and controlled to be turned on and off based on a comparison result between a voltage applied to the external terminal and a first voltage; a second transistor connected to the other end of the first transistor and controlled to be turned on and off in response to a drive control voltage applied thereto, the second transistor generating an output current corresponding to the drive control voltage when the first transistor is in an on state and the first transistor is in an on state and directing the output current to a voltage supply line of a reference voltage; and a control circuit receiving an instruction signal instructing the light-emitting diode to be turned on or off, and controlling the second transistor to be turned on when the instruction signal instructs the light-emitting diode to be turned on, and controlling the second transistor to be turned off when the instruction signal instructs the light-emitting diode to be turned off.

[0009] Further, a display device according to the present invention is a display device including: a liquid crystal display panel having a plurality of data lines and a plurality of gate lines, and a plurality of pixel units provided in a matrix at each intersection of the plurality of data lines and the plurality of gate lines; a gate driver that supplies gate signals to the plurality of gate lines; a source driver that receives a video data signal that includes a series of a plurality of pixel data pieces and indicates an image to be displayed on the liquid crystal display panel, and supplies grayscale voltage signals to the plurality of pixel units via the plurality of data lines based on the video data signal; a backlight panel that is disposed on a rear surface of the liquid crystal display panel and includes first to rth light emitting diodes (r is an integer of 2 or more) connected in series with each other; and an LED driver that drives the first to rth light emitting diodes, wherein the LED driver drives at least one of the first to rth light emitting diodes connected in series. a first transistor having one end connected to the external terminal and controlled to be turned on and off based on a comparison result of a voltage applied to the external terminal and a first voltage; a second transistor connected to the other end of the first transistor and controlled to be turned on and off in response to a drive control voltage applied thereto, the second transistor generating an output current according to the drive control voltage when the first transistor is in an on state and the first transistor is in an on state and directing the output current to a voltage supply line of a reference voltage; and a control circuit receiving an instruction signal instructing the light-emitting diode to be turned on or off, and controlling the second transistor to be turned on when the instruction signal instructs the light-emitting diode to be turned on, and controlling the second transistor to be turned off when the instruction signal instructs the light-emitting diode to be turned off, and generating the drive control voltage. [Effects of the Invention]

[0010] The LED driver according to the present invention makes it possible to control the light emission of an LED backlight while reducing the circuit size and current consumption. [Brief explanation of the drawings]

[0011] [Figure 1]1 is a block diagram showing a configuration of a display device according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a circuit diagram showing the internal configuration of an LED driver. [Figure 3] FIG. 2 is a circuit diagram showing the internal state of the LED driver when the light-emitting diode is lit. [Figure 4] FIG. 2 is a circuit diagram showing the internal state of the LED driver when the light-emitting diode is turned off. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail. In the following description of the embodiments and the accompanying drawings, substantially the same or equivalent parts are designated by the same reference numerals.

[0013] 1 is a block diagram showing the configuration of a display device 100 according to an embodiment of the present invention. The display device 100 is an active matrix liquid crystal display device. The display device 100 includes a display panel 11, a display controller 12, a gate driver 13, a source driver 14, a backlight panel 15, and an LED driver 20.

[0014] The display panel 11 is composed of a semiconductor substrate on which a plurality of pixel units P11 to Pnm and pixel switches M11 to Mnm (n is an integer of 2 or greater, and m is an integer of 2 or greater and a multiple of 3) are arranged in a matrix of n rows and m columns. The display panel 11 has n gate lines GL1 to GLn which are horizontal scanning lines, and m data lines DL1 to DLm which are arranged orthogonally to intersect the gate lines GL1 to GLn. The pixel units P11 to Pnm and pixel switches M11 to Mnm are provided at the intersections of the gate lines GL1 to GLn and the data lines DL1 to DLm, and are arranged in a matrix.

[0015] The pixel switches M11 to Mnm are controlled to be on or off in response to gate signals Vg1 to Vgn supplied from the gate driver 13. The pixel units P11 to Pnm are supplied with grayscale voltage signals Vd1 to Vdm corresponding to video data from the source driver 14. When the pixel switches M11 to Mnm are respectively on, the grayscale voltage signals Vd1 to Vdm are applied to the pixel electrodes of the pixel units P11 to Pnm, and each pixel electrode is charged. The brightness of the pixel units P11 to Pnm is controlled in response to the grayscale voltage signals Vd1 to Vdm at the pixel electrodes of the pixel units P11 to Pnm, and display is performed.

[0016] The display controller 12 receives the video signal VD and supplies a scan timing signal GS indicating the timing for applying a horizontal scan pulse to each scan line in response to the video signal VD to the gate driver 13. Furthermore, based on the video signal VD, the display controller 12 generates a video digital signal DVS including various control signals and a series of display data fragments indicating the luminance level of each pixel, and supplies this to the source driver 14.

[0017] The gate driver 13 sequentially applies gate signals Vg1 to Vgn, which include horizontal scanning pulses synchronized with the scanning timing signal GS supplied from the display controller 12, to the gate lines GL1 to GLn of the display panel 11, respectively.

[0018] In response to the digital video signal DVS, the source driver 14 first takes in a series of display data fragments corresponding to each pixel included in the digital video signal DVS, in units of the number of data lines, that is, m fragments. Next, the source driver 14 converts each of the taken-in m display data fragments into a drive signal having an analog voltage value corresponding to the luminance level indicated by the display data fragment, and supplies the obtained m drive signals to the data lines DL1 to DLm of the display panel 11 as grayscale voltage signals Vd1 to Vdm.

[0019] The backlight panel 15 includes a light guide plate and a plurality of light emitting diodes (LEDs) as light sources, which are installed on the back surface of the display panel 11. The backlight panel 15 irradiates light generated by each of the plurality of light emitting diodes toward the image display area of ​​the display panel 11 via the light guide plate.

[0020] The LED driver 20 drives a plurality of light-emitting diodes included in the backlight panel 15. Specifically, the LED driver 20 receives an illuminance signal ILD, generates an output current that causes the light-emitting diodes to emit light at the illuminance indicated by the illuminance signal ILD, and passes this output current to the plurality of light-emitting diodes included in the backlight panel 15. The LED driver 20 also receives a first on / off control signal SW1 and a second on / off control signal SW2 that instruct the light-emitting diodes to "turn on" or "turn off," and generates the output current described above when these signals instruct "turn on," but stops generating the output current when these signals instruct "turn off."

[0021] FIG. 2 is a circuit diagram showing the internal configuration of the LED driver 20 and the connection state of a plurality of light-emitting diodes included in the backlight panel 15.

[0022] The backlight panel 15 includes light emitting diodes LE1 to LEr (r is an integer of 2 or more) connected in series. A power supply voltage is applied to the anode terminal of the light emitting diode LE1 in the first stage of the light emitting diodes LE1 to LEr, and the cathode terminal of the light emitting diode LEr in the last stage is connected to an external terminal tm of the LED driver 20.

[0023] The LED driver 20 is composed of a first circuit section 20A and a second circuit section 20B. The first circuit section 20A is a circuit section composed of low-voltage elements (hereinafter referred to as LV elements) that can be driven at a low power supply voltage VL (e.g., 3V). The second circuit section 20B is a circuit section composed of high-voltage elements (hereinafter referred to as HV elements) that can be driven at a high power supply voltage VH (e.g., 18V).

[0024] The first circuit section 20A includes a ladder resistor 21, a digital-to-analog converter (DAC) 22, a differential amplifier 23, a transistor 24, a transistor 25, and a resistor .

[0025] The ladder resistor 21 receives a first potential and a second potential lower than the first potential, and divides a voltage between the first potential and the second potential into a plurality of different voltages. The ladder resistor 21 supplies the plurality of voltages generated by this voltage division to the digital-analog converter 22 as a voltage group VX.

[0026] The digital-to-analog converter 22 receives an illuminance signal ILD, which represents, as a digital value, the illuminance at which the light-emitting diodes LE1 to LEr are caused to emit light. The digital-to-analog converter 22 selects, from the voltage group X supplied from the ladder resistor 21, a voltage having a value corresponding to the illuminance indicated by the illuminance signal ILD, and supplies the amplified voltage signal Vin to the non-inverting input terminal of the differential amplifier 23.

[0027] The differential amplifier 23 is set to ON or OFF in response to the supply of a first on / off control signal SW1. The first on / off control signal SW1 is a signal for instructing the LED driver 20 to control the "on" or "off" of the backlight panel 15 depending on its signal level. The first on / off control signal SW1 has a voltage level of the first voltage V1 when instructing "on" and a voltage level of the reference voltage VSS when instructing "off." In this embodiment, the reference voltage VSS is the ground potential.

[0028] The differential amplifier 23 is turned on (operating state) when the first on / off control signal SW1 is at the first voltage V1, and turned off (non-operating state) when it is at the reference voltage VSS. In the on state (i.e., operating state), the differential amplifier 23 receives a feedback voltage VF at its inverting input terminal and generates a drive control voltage VG having a voltage value corresponding to the difference between the feedback voltage VF and a voltage signal Vin input to its non-inverting input terminal. The differential amplifier 23 supplies the generated drive control voltage VG from its output terminal via node n1 to the drain of transistor 24 and the gate of transistor 25 serving as an output transistor. In the off state (non-operating state), the output terminal of the differential amplifier 23 is in a high impedance (HiZ) state.

[0029] The transistor 24 is configured by an N-channel MOSFET. The drain of the transistor 24 is connected to the node n1. The source of the transistor 24 is connected to the supply line of the reference voltage VSS.

[0030] The transistor 24 is controlled to be on or off by receiving a second on / off control signal SW2 at its gate (control terminal). The second on / off control signal SW2 is a signal for instructing the LED driver 20 to control the "on" or "off" of the backlight panel 15 depending on its signal level. The second on / off control signal SW2 has a voltage level of the reference voltage VSS when instructing "on" and a voltage level of the first voltage V1 when instructing "off." The transistor 24 is turned off when the second on / off control signal of the reference voltage VSS instructing "on" is applied to its gate. On the other hand, the transistor 24 is turned on when the second on / off control signal of the first voltage V1 instructing "off" is applied to its gate. As a result, the reference voltage VSS is applied to the node n1.

[0031] The transistor 25 is composed of an N-channel MOSFET. The source of the transistor 25 is connected to one end of the resistor 26 via the node n2. The drain of the transistor 25 is connected to the source of the transistor 28. The gate (control end) of the transistor 25 is connected to the output end of the differential amplifier 23 via the node n1. The transistor 25 is turned on when the voltage difference between the drive control voltage VG received at its gate and the voltage at its source is higher than its own threshold voltage, and outputs an output current of a magnitude corresponding to the drive control voltage VG (for example, several tens of mA) to the supply line of the reference voltage VSS via the resistor 26.

[0032] One end of the resistor 26 is connected to the node n2, and the other end is connected to the supply line of the reference voltage VSS. With this configuration, the current flowing through the resistor 26 is converted into a voltage, and the voltage generated at one end of the resistor 26 is supplied to the inverting input terminal of the differential amplifier 23 via the node n2 as a feedback voltage VF.

[0033] The second circuit section 20B includes a comparator circuit 27 and a transistor .

[0034] The comparator circuit 27 is a voltage comparison circuit that compares a voltage input to a first input terminal, which is a positive input terminal, with a voltage input to a second input terminal, which is a negative input terminal. The first input terminal of the comparator circuit 27 is connected to the cathode of the light-emitting diode LEr included in the backlight panel 15 via an external terminal tm. The second input terminal of the comparator circuit 27 is connected to a voltage supply line of the low power supply voltage VL.

[0035] The comparator circuit 27 receives the voltage Vout of the external terminal tm at a first input terminal and the low power supply voltage VL at a second input terminal, and outputs a voltage according to the comparison result as a control voltage nghv from an output terminal. Specifically, the comparator circuit 27 outputs a control voltage nghv having a voltage level of the low power supply voltage VL when the voltage Vout is greater than the low power supply voltage VL (hereinafter referred to as a case where Vout>VL), and having a voltage level of the high power supply voltage VH when the voltage Vout is equal to or less than the low power supply voltage VL (hereinafter referred to as a case where Vout≦VL).

[0036] In this embodiment, the low power supply voltage VL is a power supply voltage having a voltage level of approximately 3 V. On the other hand, the high power supply voltage VH is a voltage that is much higher than 3 V, and has a voltage level of approximately 18 V in this embodiment.

[0037] The transistor 28 is composed of an N-channel MOSFET. The drain of the transistor 28 is connected to the cathode of the light-emitting diode LEr included in the backlight panel 15 via the external terminal tm. The source of the transistor 28 is connected to the drain of the transistor 25. The gate of the transistor 28 is connected to the output terminal of the comparator circuit 27.

[0038] The transistor 28 is in a fully-on state (completely on state) when the control voltage nghv applied to the gate is sufficiently large (in this embodiment, when the gate-source voltage Vgs is 15 V or higher). As described above, when the control voltage nghv output from the comparator circuit 27 is at the voltage level of the high power supply voltage VH, a voltage of approximately 18 V is applied to the gate of the transistor 28, and the transistor 28 is in a fully-on state. When the transistor 28 is fully on, the output current of the light-emitting diodes LE1 to LEr flows between the drain and source of the transistor 28 and is led to the supply line of the reference voltage VSS through the node n3, the drain-source of the transistor 25, the node n2, and the resistor 26.

[0039] On the other hand, when the control voltage nghv applied to the gate of transistor 28 is at the voltage level of the low power supply voltage VL (3V), VL-Vt (where Vt is the threshold voltage of transistor 28) is applied to node n3, which is the connection node between the source of transistor 28 and the drain of transistor 25.

[0040] Next, the internal operation of the LED driver 20 will be described separately for when the light-emitting diodes LE1 to LEr are turned on and when they are turned off. In the following description, an example of the internal operation of the LED driver 20 will be described assuming that the high power supply voltage VH=18V, the low power supply voltage VL=3V, the first voltage V1=3V, and the reference voltage VSS=0V.

[0041] [When lit] FIG. 3 is a circuit diagram showing the internal state of the LED driver 20 when the light-emitting diodes LE1 to LEr are turned on (emitting light).

[0042] First, a first on / off control signal SW1 of 3V indicating "on" is supplied to the differential amplifier 23. This causes the differential amplifier 23 to turn on and output the drive control voltage VG. Also, a second on / off control signal SW2 of 0V indicating "on" is supplied to the gate of the transistor 24. This causes the transistor 24 to turn off.

[0043] The transistor 25 receives at its gate the drive control voltage VG from the differential amplifier 23 and turns on, thereby generating an output current Iout having a current value corresponding to the drive control voltage VG, which is then output via the resistor 26 to the voltage supply line of the reference voltage VSS.

[0044] At this time, the voltage Vout applied to the external terminal tm is equal to or lower than 3 V. Since the voltage Vout input to the first input terminal of the comparator circuit 27 is equal to or lower than the low power supply voltage VL (voltage value 3 V), which is the voltage input to the second input terminal, the comparator circuit 27 outputs a control voltage nghv with a voltage value of 18 V. This causes the transistor 28 to enter a fully on state.

[0045] When the transistor 28 and the transistor 25 are both turned on, an output current Iout flows from the light-emitting diodes LE1 to LEr included in the backlight panel 15 through the transistors 28, 25 and the resistor 26, as shown by the arrows in Fig. 3. This causes the light-emitting diodes LE1 to LEr to emit light at an illuminance indicated by the illuminance signal ILD.

[0046] [Lights off] FIG. 4 is a circuit diagram showing the internal state of the LED driver 20 when the light-emitting diodes LE1 to LEr are turned off (not emitting light).

[0047] First, a first on / off control signal SW1 of 0V indicating "lights off" is supplied to the differential amplifier 23. This causes the differential amplifier 23 to turn off. Also, a second on / off control signal SW2 of 3V indicating "lights off" is supplied to the gate of the transistor 24. This causes the transistor 24 to turn on, and the potential of the node n1 becomes the voltage level of the reference voltage VSS, i.e., 0V. The transistor 25 receives 0V at its gate and turns off.

[0048] A voltage Vout having a voltage value (for example, 18 V) sufficiently greater than 3 V is applied to the external terminal tm. The comparator circuit 27 outputs a control voltage nghv having a voltage value of 3 V because the voltage Vout input to the first input terminal is greater than the low power supply voltage VL (voltage value 3 V) which is the voltage input to the second input terminal.

[0049] As a result, a voltage (3V-Vt) obtained by subtracting the threshold voltage Vt of the transistor 28 from the control voltage nghv (=3V) is applied to the node n3 connected to the source of the transistor 28.

[0050] In this embodiment, the transistor 28 functions as a clamp circuit that limits the voltage applied to the second circuit section 20B. That is, if the voltage Vout at the external terminal tm is large (for example, 18 V), the voltage Vout would be applied directly to the second circuit section 20B (specifically, to node n3) if the transistor 28 were not present. In contrast, in the configuration of this embodiment, the presence of the transistor 28 limits the voltage applied to node n3 to (3 V - Vt).

[0051] Therefore, in the LED driver 20 of this embodiment, the second circuit section 20B can be configured using LV elements (low-voltage elements). The differential amplifier 23 of the second circuit section 20B, in particular, includes a differential stage, a current mirror, and an output stage, each of which is composed of transistors. The transistors constituting the differential stage and current mirror must have a certain level of precision. Generally, LV elements have better transistor precision than HV elements (high-voltage elements). To achieve a certain level of precision with HV elements, the transistors must be large. If the differential amplifier is configured with HV elements and the transistors are small, the offset voltage (the voltage difference between the input voltage and the feedback voltage) of the differential amplifier increases, which can cause variations in the current flowing through the LEDs and adversely affect the image quality of the image displayed on the display panel 11.

[0052] In contrast, in the LED driver 20 of this embodiment, the transistors that make up the differential stage and current mirror of the differential amplifier 23 can be constructed using LV elements, so the size can be kept smaller than when these are constructed using HV elements.

[0053] Furthermore, the transistor 25 constituting the second circuit section 20B is required to operate at high speed by passing a large current of several tens of mA when the LED is emitting light. In this case, if the differential amplifier 23 and the transistor 25 were made of HV elements, power consumption would be large.

[0054] In contrast, in the LED driver 20 of this embodiment, the differential amplifier 23 and the transistor 25 are configured as LV elements, and the differential amplifier 23 is configured to be driven by a low power supply voltage, making it possible to keep power consumption low.

[0055] Therefore, the LED driver 20 of this embodiment makes it possible to control the light emission of the LED backlight while suppressing the circuit size and current consumption.

[0056] It should be noted that the present invention is not limited to the above-described embodiments. For example, in the above-described embodiments, the high power supply voltage VH=18V, the low power supply voltage VL=3V, the first voltage V1=3V, and the reference voltage VSS=0V (ground potential) are described as examples, but the voltage values ​​of each voltage are not limited to these. It is sufficient that the high power supply voltage VH has a voltage value sufficiently higher than the low power supply voltage VL, and the first voltage V1 has a voltage value approximately the same as that of the low power supply voltage VL.

[0057] In the above embodiment, the transistors 24, 25 and 28 are all N-channel MOSFETs, but they may be P-channel MOSFETs.

[0058] Furthermore, in the above embodiment, the LED driver 20 that drives light-emitting diodes LE1 to LEr (loads) was used as an example of a load driving circuit, and its configuration and operation when lit (driven) and when extinguished (not driven) were explained, but the load to be driven is not limited to light-emitting diodes. [Explanation of symbols]

[0059] 100 display device 11 Display panel 12 Display Controller 13 Gate Driver 14 Source Driver 15 Backlight Panel 20 LED drivers 21 Ladder Resistor 22 Digital-to-analog converter 23 Differential Amplifier 24 transistors 25 transistors 26 Resistance 27 Comparator Circuit 28 transistors

Claims

1. an external terminal configured to be connectable to a light emitting diode; a first transistor, one end of which is connected to the external terminal and which is controlled to be turned on and off based on a comparison result obtained by comparing a voltage applied to the external terminal with a first voltage; a second transistor connected to the other end of the first transistor, and controlled to be turned on and off in response to application of a drive control voltage, and when the second transistor is in an on state and the first transistor is in an on state, generates an output current corresponding to the drive control voltage and outputs the output current to a voltage supply line of a reference voltage; a control circuit that receives an instruction signal instructing the light-emitting diode to be turned on or off, and controls the second transistor to be in an on state when the instruction signal instructs the light-emitting diode to be turned on, and generates the drive control voltage that controls the second transistor to be in an off state when the instruction signal instructs the light-emitting diode to be turned off; An LED driver comprising:

2. 2. The LED driver according to claim 1, wherein the first transistor is made of a semiconductor element having a higher breakdown voltage than a semiconductor element constituting the second transistor.

3. a comparator circuit configured by the high-voltage semiconductor element, receiving an input of the voltage of the external terminal at a first input terminal and the first voltage at a second input terminal, and outputting a control voltage having a voltage level of the first voltage when the voltage of the external terminal is higher than the first voltage, and outputting a control voltage having a voltage level of a high power supply voltage higher than the first voltage when the voltage of the external terminal is equal to or lower than the voltage level of the first voltage; the first transistor receives the control voltage at a control end thereof, and is controlled to an ON state when the control voltage is at a voltage level of the high power supply voltage, and is controlled to an OFF state when the control voltage is at a voltage level of the first voltage; 3. The LED driver of claim 2.

4. The control circuit a resistor provided in a current path of the output current led from the second transistor to a voltage supply line of the reference voltage, the resistor converting the output current into a voltage; a differential amplifier that receives a voltage signal specifying a current value of the output current by a voltage value, and outputs a difference between the voltage signal and the voltage converted by the resistor as the drive control voltage to a control terminal of the second transistor via a first node; a third transistor that receives the instruction signal at a control end thereof and is controlled to be turned on or off, and applies the reference voltage to the first node when in an on state; 2. The LED driver of claim 1, comprising:

5. a liquid crystal display panel having a plurality of data lines and a plurality of gate lines, and a plurality of pixel units provided in a matrix at each intersection of the plurality of data lines and the plurality of gate lines; a gate driver that supplies gate signals to the plurality of gate lines; a source driver that receives a video data signal that includes a series of a plurality of pixel data pieces and indicates an image to be displayed on the liquid crystal display panel, and supplies a grayscale voltage signal to the plurality of pixel units through the plurality of data lines based on the video data signal; a backlight panel disposed on the rear surface of the liquid crystal display panel and including first to rth (r is an integer of 2 or more) light emitting diodes connected in series with each other; an LED driver that drives the first to rth light emitting diodes; A display device comprising: The LED driver an external terminal configured to be connectable to the cathode of the last stage light emitting diode among the first to rth light emitting diodes connected in series; a first transistor, one end of which is connected to the external terminal and which is controlled to be turned on and off based on a comparison result obtained by comparing a voltage applied to the external terminal with a first voltage; a second transistor connected to the other end of the first transistor, and controlled to be turned on and off in response to application of a drive control voltage, and when the second transistor is in an on state and the first transistor is in an on state, generates an output current corresponding to the drive control voltage and outputs the output current to a voltage supply line of a reference voltage; a control circuit that receives an instruction signal instructing the light-emitting diode to be turned on or off, and controls the second transistor to be in an on state when the instruction signal instructs the light-emitting diode to be turned on, and generates the drive control voltage that controls the second transistor to be in an off state when the instruction signal instructs the light-emitting diode to be turned off; A display device comprising:

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