KR102050440B1 - Back light unit and mehtod for driving the same - Google Patents

Abstract

The present invention relates to a backlight unit capable of accurately detecting an abnormality of a light emitting diode in a light source array and protecting a constant current switching device from an overvoltage, and a method of driving the same. First to m th light source arrays individually connected to each node (m is a natural number greater than 1); And determining whether to float each of the first to mth nodes based on the signals from the first to mth nodes, and driving the driving based on the lowest voltage among the voltages of the remaining nodes other than the floated node. It characterized in that it comprises a light source control unit for controlling the magnitude of the voltage.

Description

BACK LIGHT UNIT AND MEHTOD FOR DRIVING THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit, and more particularly, to a backlight unit capable of accurately detecting an abnormality of a light emitting diode in a light source array and protecting a constant current switching element from overvoltage.

Since the liquid crystal display uses a liquid crystal that is a non-light emitting element, a backlight unit for generating light is required.

The backlight unit includes a plurality of light source arrays provided with a plurality of light emitting diodes. These light source arrays are connected in parallel to one driving voltage transmission line to which a driving voltage is applied. When an abnormality occurs in any one light source array, the driving current may not flow through the light source array. The conventional backlight unit sets the driving voltage based on the driving current detected from the light source array in which the abnormality is generated. As described above, when the driving current of the light source array approaches almost zero, the driving voltage is maximum. Is raised. In such a case, overvoltage may be applied to the constant current switching elements that are in charge of controlling the driving current of the remaining normal light source arrays. If the overvoltage is maintained for longer than the constant current switching elements can withstand, they may be damaged. As such, the conventional backlight unit has a problem in that constant current switching devices cannot be protected from overvoltage when an abnormality of the light source array occurs.

The present invention has been made to solve the above-mentioned conventional problems, it is determined whether the light source array is abnormal on the basis of the base current of the constant current switching device, the remaining nodes other than the node is connected to the light source array is generated It is an object of the present invention to provide a backlight unit and a driving method thereof which can protect the constant current switching elements from overvoltage by controlling the magnitude of the driving voltage based on the smallest voltage of each individual voltage.

The backlight unit according to the present invention for achieving the above object, the first to the first to the m-th node (m is a natural number greater than 1) is supplied with a driving voltage from the driving voltage transmission line, respectively m light source arrays; And determining whether to float each of the first to mth nodes based on the signals from the first to mth nodes, and driving the driving based on the lowest voltage among the voltages of the remaining nodes other than the floated node. It characterized in that it comprises a light source control unit for controlling the magnitude of the voltage.

The light source controller may include first to mth constant current controllers to individually control each of the driving currents supplied to each of the first to mth light source arrays; First to m-th node detectors respectively sensing signals from the first to m-th nodes and outputting a detection signal according to the detection result; A node controller determining whether to float each of the first to mth nodes based on the detection signals from the first to mth node detectors; A minimum voltage detector detecting a smallest voltage among the voltages of the first to mth nodes; And a driving voltage controller configured to control the magnitude of the driving voltage based on the voltage detected by the minimum voltage detector.

The kth constant current controller (k is any one of 1 to m) includes: a constant current switching element connected to the kth node via a collector terminal; A sense resistor connected between the emitter terminal and the ground terminal of the constant current switching element; And a first comparator comparing the preset first reference voltage with the voltage applied to the emitter terminal, and adjusting the magnitude of the control signal based on the comparison result and outputting the control signal to the base terminal of the constant current switching device. It features.

The kth node detection unit includes: a detection resistor connected in series between an output terminal of the first comparator included in the kth constant current control unit and a base terminal of the constant current switching element; And comparing the voltage detected from the output terminal of the first comparator included in the k-th constant current controller with the preset second reference voltage, and adjusting the magnitude of the detected signal based on the comparison result to supply the node to the node controller. 2 comparators.

The node controller is configured to float the k-th node by turning off the constant current switching element belonging to the k-th constant current control unit when the detection signal from the k-th node detector is maintained at a value greater than a threshold value for a preset time. It is characterized by making a state.

The node controller may turn off the constant current switching device by dropping the first reference voltage applied to the first comparator belonging to the k-th constant current control unit to 0 [V].

The minimum voltage detector may include first to mth diodes connected between the first to mth nodes and a common node; A pull-up resistor connected between the common node and a voltage source for outputting a power supply voltage; The anode terminal of the k th diode is connected to the common node, and the cathode terminal is connected to the k th node.

The driving voltage controller controls the magnitude of the driving voltage based on the voltage from the common node.

The light source controller further includes first to mth switches; The k th switch is connected between the k th node and the collector terminal of the constant current switching element belonging to the k th constant current control unit.

The node controller may turn the k-th switch into a floating state by turning off the k-th switch when the second control signal from the k-th node detector is maintained at a value greater than a reference value for a preset time. It is done.

The kth node detection unit includes: a detection resistor connected in series between an output terminal of the first comparator included in the kth constant current control unit and a base terminal of the constant current switching element; A voltage detector detecting a voltage across both ends of the detection resistor; An amplifier for amplifying the voltage from the voltage detector; And a second comparator for comparing the voltage from the voltage detector with a preset second reference voltage and adjusting the magnitude of the second control signal based on the comparison result to supply the node to the node controller.

In addition, the driving method of the backlight unit according to the present invention for achieving the above object, is supplied with a driving voltage from the driving voltage transmission line and is individually connected to each of the first to m-th node (m is a natural number greater than 1) A method of driving a backlight unit including light source arrays, the method comprising: determining whether to float each of the first to mth nodes based on the signals from the first to mth nodes, and remaining nodes other than the floated node. And controlling the magnitude of the driving voltage based on the smallest voltage of each individual voltage.

The first step may include steps 1-A for individually controlling each of the driving currents supplied to each of the first to m th light source arrays; Step 1-B of individually sensing the signals from the first to m-th nodes and generating a detection signal according to the detection result; Determining whether to float each of the first to m th nodes based on the detection signals; Detecting the smallest voltage among the voltages of the first to mth nodes; And step 1-E of controlling the magnitude of the driving voltage based on the voltage detected from the step 1-D.

The backlight unit and the driving method thereof according to the present invention have the following effects.

First, it is possible to accurately find a specific light source array in which an abnormality has occurred.

Second, since the abnormality is determined based on the base current, the abnormality of the light source array can be accurately determined even in the dimming method in which the emitter voltage is low.

Third, when an abnormality occurs in the light source array, the base current is always set to a constant value (the maximum output value of the first comparator) regardless of the magnitude of the driving current, so that the reliability of the abnormal detection is high.

1 is a view showing a backlight unit according to a first embodiment of the present invention;
2 is a diagram illustrating that a first comparator, a second comparator, a detection resistor, a pull-up resistor, a node controller, and a driving voltage controller corresponding to one channel are formed in one integrated circuit.
3 is a view for explaining the operation of the backlight unit according to the first embodiment of the present invention;
4 illustrates a backlight unit according to a second embodiment of the present invention.
5 is a diagram illustrating that a first comparator, a second comparator, a detection resistor, a pull-up resistor, a node controller, and a driving voltage controller corresponding to one channel are formed in one integrated circuit.
6 is a view for explaining the operation of the backlight unit according to the second embodiment of the present invention;
7 is a view showing still another configuration of the node detection unit
8 is a diagram showing the emitter voltage and the base current of the constant current switching device in a normal environment, and the emitter voltage and the base current of the constant current switching device in an abnormal environment in which an error occurs in the light emitting diode of one light source array.

1 is a view showing a backlight unit according to a first embodiment of the present invention.

As shown in FIG. 1, the backlight unit according to the first embodiment of the present invention determines the first to m th light source arrays LA1 to LAm and whether the light source arrays are abnormal. And a light source controller (a component including all the components except for the light source array in FIG. 1) for controlling the operation of the light sources based on the above.

The first to m th light source arrays LA1 to LAm (m is a natural number greater than 1) are connected in parallel to the driving voltage transmission line DVL. Specifically, the first to m th light source arrays are commonly connected to the driving voltage transmission line DVL and individually connected to each of the first to m th nodes N1 to Nm. Each light source array LAk includes a plurality of light emitting diodes LEDs connected in series with each other. One light source array LAk (k is any one of 1 to m) may be viewed as one channel. As shown in FIG. 1, if the number of light source arrays is m, there may be m channels.

The light source controller determines whether to float each of the first to mth nodes N1 to Nm based on the signals from the first to mth nodes N1 to Nm, and excludes the floated node. The magnitude of the driving voltage is controlled based on the smallest voltage among the individual voltages of the remaining nodes. For example, when one of the light emitting diodes LED included in the first light source array LA1 is damaged and the electrical connection between the driving voltage transmission line DVL and the first node N1 is broken, the light source The control unit makes the floating state of the first node N1 so that the voltage of the first node N1 is not detected to the minimum value, and then the smallest of the voltages of the second to mth nodes N2 to Nm. The voltage is detected as the minimum value, and the magnitude of the driving voltage VLED is adjusted based on the detected minimum value.

That is, when a specific light emitting diode is damaged, the driving voltage VLED is abnormally increased due to the decrease in the voltage of the node to which the specific light emitting diode is connected, and accordingly, overvoltage is increased to normal constant current controllers connected to other nodes. The light source control unit according to the present invention accurately detects whether or not such a specific light emitting diode is damaged, and adjusts the driving voltage (VLED) on the basis of the result to suppress the occurrence of overvoltage. Even when an abnormality occurs in a specific light emitting diode, the constant current switching elements included in each constant current controller may be safely protected from overvoltage. To this end, the light source control unit according to the present invention, as shown in Figure 1, the first to m-th constant current control unit (CC1 to CCm), the first to m-th node detection unit (NS1 to NSm), the node control unit ( NC), the minimum voltage detector MIN, and the driving voltage controller DC may be included. Specifically, the listed components will be described below.

Constant current controller

The first to m th constant current controllers CC1 to CCm individually control each of the driving currents supplied to each of the first to m th light source arrays LA1 to LAm. That is, the first to m th constant current controllers CC1 to CCm are always of constant size as the first to m th light source arrays LA1 to LAm regardless of their size increase or decrease even when the driving voltage VLED increases or decreases. The magnitude of the drive currents is controlled so that the drive current flows.

In FIG. 1, m constant current controllers CC1 to CCm are shown. The k-th constant current controller, which is one of them, controls the driving current supplied to the k-th light source array. For example, the first constant current controller CC1 controls the driving current supplied to the first light source array LA1, and the second constant current controller CC2 controls the driving current supplied to the second light source array LA2. The m-th constant current controller CCm controls the drive current supplied to the m-th light source array LAm. To this end, each of the constant current controllers CC1 to CCm includes a constant current switching element BT, a sensing resistor Rs, and a first comparator COM1 as shown in FIG. 1. Each of the constant current controllers CC1 to CCm is connected to the light source arrays of different channels, and all have the same configuration. Therefore, the constant current switching element BT, the sensing resistor Rs, and the first resistor of the kth constant current controller are provided. 1 Comparator COM1 will be described representatively.

The constant current switching device BT provided in the k-th constant current control unit includes a base terminal, a collector terminal, and an emitter terminal, and the base terminal thereof is connected to the output terminal of the first comparator COM1 through the detection resistor Rd. The collector terminal is connected to the k-th node, and the emitter terminal is connected to the sensing resistor Rs. As the constant current switching element BT, a bipolar transistor may be used.

The sensing resistor Rs provided in the k-th constant current control unit is connected between the emitter terminal and the ground terminal of the constant current switching element BT. The voltage at the emitter terminal is generated by this sense resistor Rs.

The first comparator COM1 included in the k-th constant current control unit compares the preset first reference voltage VR1 with a voltage applied to the emitter terminal (a sensing voltage generated by the sensing resistor Rs). Based on the comparison result, the control signal is adjusted in magnitude and output to the base terminal of the constant current switching element BT. To this end, the first reference voltage VR1 is applied to the non-inverting terminal (+) of the first comparator COM1, and the sensing voltage generated from the emitter terminal is applied to the inverting terminal (−) thereof.

The first comparator COM1 compares the sensing voltage sensed through the sensing resistor Rs with the first reference voltage VR1, and if the sensing voltage is less than the first reference voltage VR1, the sensing voltage is set to zero. The output current (control signal) is increased until it becomes equal to the first reference voltage VR1 so that the constant current switching element BT can flow more driving current, while the detected voltage is higher than the first reference voltage VR1. If large, the output current (control signal) is reduced until the detection voltage is equal to the first reference voltage VR1, so that the constant current switching element BT can flow less driving current.

The value of the first reference voltage VR1 is set such that the constant current switching element BT can flow a predetermined predetermined driving current. The first reference voltages VR1 in all the constant current controllers may have the same value, or may all have different values.

Node detection unit

The first to m th node detection units NS1 to NSm separately detect each of the signals from the first to m th nodes N1 to Nm, and output a detection signal according to the detection result.

In FIG. 1, m node detection units NS1 to NSm are shown. The k-th node detection unit, which is one of them, detects a signal from the k-th node and outputs a detection signal according to the detection result. For example, the first node detection unit NS1 detects a signal from the first node N1 and outputs a detection signal, and the second node detection unit NS2 outputs a signal from the second node N2. The sensing signal is outputted, and the ... m th node detecting unit NSm detects a signal from the m th node Nm and outputs a sensing signal.

That is, each node detection unit NS1 to NSm directly detects a change in the base current of the constant current switching element BT to indirectly detect a change in signal of each node. Accordingly, each node detection unit NS1 to NSm may determine whether the LED is abnormal based on the base current change of the constant current switching element BT. To this end, each node detection unit NS1 to NSm includes a detection resistor Rd and a second comparator COM2 as shown in FIG. 1. Since each node detection unit is connected to light source arrays of different channels and all have the same configuration, the detection resistor Rd and the second comparator COM2 included in any one k-th node detection unit will be described.

The detection resistor Rd included in the k-th node detection unit is connected in series between the output terminal of the first comparator COM1 belonging to the k-th constant current control unit and the base terminal of the constant current switching element BT belonging to the k-th constant current control unit. Connected. The voltage corresponding to the current (base current) flowing through the base terminal is detected by this detection resistor Rd. Accordingly, the voltage detected from the detection resistor Rd included in the k-th node detection unit reflects the signal change of the k-th node. That is, the current or voltage change of the k-th node affects the base current of the constant current switching element BT connected to the k-th node, and the change of the base current is dependent on the voltage generated by the detection resistor Rd. Give effect.

The second comparator COM2 included in the k-th node detection unit compares the voltage detected from the output terminal of the first comparator COM1 belonging to the k-th constant current control unit with the preset second reference voltage VR2. Based on the comparison result, the sensing signal is adjusted in magnitude and supplied to the node controller NC. To this end, the voltage (detection voltage) generated by the detection resistor Rd is applied to the non-inverting terminal (+) of the second comparator COM2, and the second reference voltage VR2 is applied to the inverting terminal (-) of the second comparator COM2. Is approved.

When the detection voltage is greater than the second reference voltage VR2, the second comparator COM2 increases the size of the detection signal so as to have a value greater than a preset threshold value, and outputs the detected signal as the second reference voltage ( When smaller than or equal to VR2), the magnitude of the detection signal is reduced and output so as to have a value smaller than the threshold value.

Node control unit NC )

The node controller NC determines whether to float each of the first to mth nodes N1 to Nm based on the detection signals from the first to mth node detection units NS1 to NSm.

At this time, the node controller NC can make the k-th node in a floating state by turning off the constant current switching element BT belonging to the k-th constant current controller, for example, the detection from the k-th node detector. This can be done by turning off the constant current switching element BT belonging to the k-th constant current control unit when the signal is maintained at a value greater than the threshold for a preset reference time. In other words, even when a detection signal higher than a threshold is input, the node controller NC does not immediately convert the node into a floating state, but starts counting the time from the moment when the detection signal exceeds the threshold and the detection signal. The node will be floated only when the holding time (time remaining at the value exceeding the threshold value) exceeds the reference time described above.

Here, in order to float the node, the node controller NC drops the first reference voltage VR1 applied to the first comparator COM1 belonging to the k-th constant current controller to 0 [V] so that the constant current switching device BT ) Can be turned off.

On the other hand, the reason for the reference time as described above is that when the voltage of a node suddenly drops for a while due to noise from the outside, the node controller NC incorrectly recognizes this as an abnormality in the light emitting diode. To prevent it. Since most of the noise occurs for a short time and then disappears, as described above, the voltage of the node which has dropped sharply by the noise is restored to its original value.

Minimum voltage detector MIN )

The minimum voltage detector MIN detects the smallest voltage among the voltages of the first to m th nodes N1 to Nm. To this end, the minimum voltage detector MIN includes first to m th diodes D1 to Dm and a pull-up resistor Rp as shown in FIG. 1.

The first to m th diodes D1 to Dm are connected between the first to m th nodes N1 to Nm and the common node CN. That is, the anode terminal of each of the first to mth diodes D1 to Dm is commonly connected to the common node CN, while the cathode terminal of each of the first to mth diodes D1 to Dm is connected. The first to m th nodes N1 to Nm are individually connected. In other words, the anode terminal of the k th diode is connected to the common node CN, and the cathode terminal is connected to the k th node.

The pull-up resistor Rp is connected between the voltage source for outputting the power supply voltage VCC and the common node CN.

Since the voltage drop degree of each light source array may be different according to the characteristics of the light emitting diode in the light source array, each node N1 to Nm may have a different voltage according to the voltage drop degree. The higher the voltage drop, the smaller the voltage on that node. The minimum voltage detector MIN detects the voltages of the first to m th nodes N1 to Nm to detect the lowest voltage, and applies the detected voltage to the common node CN. For example, if the first light source array LA1 has the highest resistance value among the first to mth light source arrays LA1 to LAm, and the voltage drop caused by the first light source array LA1 is the highest, Since the lowest voltage is applied to the first node N1 among the first to mth nodes N1 to Nm, the voltage of the first node N1 is detected as the minimum value by the minimum voltage detector MIN.

Driving voltage control unit DC )

The driving voltage controller DC controls the magnitude of the driving voltage based on the voltage from the common node CN. In other words, the driving voltage control unit DC adjusts the magnitude of the driving voltage in accordance with the light source array having the largest voltage drop. Although the voltage drop degree may be different for each light source array as described above, since one driving voltage VLED is applied thereto, the driving voltage control unit DC is based on the light source array having the largest voltage drop. The driving voltage is set.

Meanwhile, one integrated circuit IC of the first comparator COM1, the second comparator COM2, the detection resistor Rd, the pull-up resistor Rp, the node controller NC, and the driving voltage controller DC in FIG. 1. ) May be formed. This will be described in detail with reference to FIG. 2.

FIG. 2 illustrates that a first comparator COM1, a second comparator COM2, a detection resistor Rd, a pull-up resistor Rp, a node controller NC, and a driving voltage controller DC corresponding to one channel are connected to one channel. As shown in the figure formed in the integrated circuit (IC), the components listed above may be integrated in one integrated circuit (IC).

Here, the common node CN is connected to the diode D1 through a first pin P1, and the detection resistor Rd is connected to the base terminal of the constant current switching element BT through the second pin P2. The inverting terminal (−) of the first comparator COM1 is connected to the emitter terminal of the constant current switching element BT through the third pin P3.

The first comparator COM1, the second comparator COM2, the detection resistor Rd, the pull-up resistor Rp, the node controller NC and the driving voltage controller DC corresponding to the other channels are also integrated circuits IC. Can be integrated into the device.

The detection resistor Rd may be formed outside the integrated circuit IC.

Hereinafter, the operation of the backlight unit according to the first embodiment of the present invention will be described with reference to FIG. 3.

3 is a view for explaining the operation of the backlight unit according to the first embodiment of the present invention.

For example, as shown in FIG. 3, when the light emitting diode in the first light source array LA1 is damaged and the electrical connection between the driving voltage transmission line DVL and the first node N1 is lost, the first connection is performed. As the current at node N1 decreases rapidly, the voltage at this first node N1 drops to nearly zero. As a result, the voltage at the emitter terminal of the constant current switching element BT (enclosed by a circular dotted line) also drops. Then, the first comparator COM1 that senses the decrease in the voltage of the emitter voltage increases its output current (detection signal) to compensate for the dropped voltage. In the situation as shown in FIG. 3, since the emitter voltage drops to a considerably low value, the output current from the first comparator COM1 becomes maximum. Therefore, the current (base current) of the base terminal of the constant current switching element BT increases rapidly. Then, the detection voltage generated through the detection resistor Rd is rapidly increased, and the second comparator COM2 supplied with the detection voltage outputs a detection signal having a value higher than the threshold. Thereafter, the detection signal is input to the node controller NC, and the node controller NC determines whether the detection signal is maintained at a value greater than the threshold for the reference time. When the magnitude of the detection signal is kept longer than the reference time while the magnitude of the detection signal exceeds the threshold value, the node controller NC receives the first reference voltage VR1 (enclosed by a circular dotted line) supplied to the first comparator COM1. To 0 [V]. As a result, the output current (detection signal) of the first comparator COM1 becomes 0, and the constant current switching element BT is turned off, thereby the first node N1 is in a floating state.

The minimum voltage detector MIN detects the smallest value among the voltages of the second to mth nodes N2 to Nm other than the floating first node N1 as the minimum value. Here, as described above, since the first node N1 and the driving voltage transmission line DVL are electrically disconnected, the first node N1 has the smallest voltage, but the first node N1 is floated. Accordingly, from the standpoint of the minimum voltage detector MIN, the first node N1 no longer exists in a circuit. However, the voltage of the first node N1 may be maintained at almost zero for a short time before the first node N1 is floated. In this case, the voltages of the first node N1 may be different from those of the normal nodes N2 to other ones. Since it is smaller than the voltages of Nm, the voltage of this first node N1 can be detected to a minimum value. Then, the driving voltage VLED may increase abnormally sharply for a while by the abnormal voltage of the first node N1. However, as soon as the first node N1 is in a floating state, the minimum voltage detector MIN selects the smallest value among the voltages of the normal second to m nodes except the first node N1. This driving voltage VLED may again have a normal value. As described above, according to the present invention, the floating light source array is connected to the floating node so that the node connected to the light source array is not visible in circuit, so that the magnitude of the driving voltage can be normally set by the voltages of the remaining normal nodes. Therefore, occurrence of overvoltage due to an abnormal driving voltage is suppressed, and thus, even when an abnormality occurs in the light source array, the constant current switching elements BT connected to the first to mth nodes N1 to Nm can be safely protected from overvoltage. have.

4 is a diagram illustrating a backlight unit according to a second embodiment of the present invention.

As shown in FIG. 4, the backlight unit according to the second exemplary embodiment of the present invention may check whether the first to m th light source arrays LA1 to LAm and the light source arrays LA1 to LAm are abnormal. And a light source controller (a component including all components except for the light source array in FIG. 4) for determining and controlling the operation of the light sources based on the determination.

As shown in Fig. 4, the light source control unit according to the second embodiment of the present invention further includes first to mth switches SW1 to SWm as compared to that in the above-described first embodiment.

The kth switch is connected between the kth node and the collector terminal of the constant current switching element BT belonging to the kth constant current control unit. For example, the first switch SW1 is connected between the first node N1 and the collector terminal of the constant current switching element BT belonging to the first constant current control unit CC1, and the second switch SW2 is connected to the second terminal SW2. It is connected between the node N2 and the collector terminal of the constant current switching element BT belonging to the second constant current control unit CC2, and the m th switch SWm is the m th node Nm and the m th constant current. It is connected between the collector terminals of the constant current switching element BT belonging to the control part CCm.

The first to mth constant current controllers CC1 to CCm, the first to mth node detectors NS1 to NSm, the minimum voltage detector MIN, and the driving voltage controller included in the light source controller according to the second embodiment of the present invention. Since DC) is the same as those of the above-described first embodiment, the description thereof refers to the above-described first embodiment.

However, the node controller NC according to the second embodiment is different from the node controller NC of the first embodiment in the following points.

That is, the node controller NC according to the second embodiment controls the first to m th switches SW1 to SWm instead of the first reference voltage VR1 of each first comparator COM1. For example, when an error occurs in the light source array of one channel, the node controller NC selectively turns off only the switch connected to the channel to make the node connected to the channel into a floating state.

Meanwhile, in FIG. 4, the first comparator COM1, the second comparator COM2, the detection resistor Rd, the pull-up resistor Rp, the node controller NC, and the driving voltage controller DC are one integrated circuit ( IC). This will be described in detail with reference to FIG. 5.

FIG. 5 illustrates that the first comparator COM1, the second comparator COM2, the detection resistor Rd, the pull-up resistor Rp, the node controller NC, and the driving voltage controller DC corresponding to one channel are connected to one channel. As shown in the figure formed in the integrated circuit (IC), the components listed above may be integrated in one integrated circuit (IC).

Here, the common node CN is connected to the diode D1 through the first pin P1, and the node controller NC is connected to the first switch through the second pin P2 and the detection resistor Rd. Is connected to the base terminal of the constant current switching device BT through the third pin P3, and the inverting terminal (-) of the first comparator COM1 is connected to the constant current switching device BT through the fourth pin P4. Is connected to the emitter terminal of.

The first comparator COM1, the second comparator COM2, the detection resistor Rd, the pull-up resistor Rp, the node controller NC and the driving voltage controller DC corresponding to the other channels are also integrated circuits IC. Can be integrated into the device.

The detection resistor Rd may be formed outside the integrated circuit IC.

Hereinafter, the operation of the backlight unit according to the second embodiment of the present invention will be described with reference to FIG. 6.

6 is a view for explaining the operation of the backlight unit according to the second embodiment of the present invention.

For example, as shown in FIG. 6, one of the light emitting diodes LED in the first light source array LA1 is damaged, so that the electrical connection between the driving voltage transmission line DVL and the first node N1 is lost. When disconnected, the current of the first node N1 decreases rapidly, and thus the voltage of the first node N1 drops to almost zero. As a result, the voltage at the emitter terminal of the constant current switching element BT (enclosed by a circular dotted line) also drops. Then, the first comparator COM1 that senses the decrease in the voltage of the emitter voltage increases its output current (detection signal) to compensate for the dropped voltage. In the situation as shown in Fig. 6, since the emitter voltage drops to a considerably low value, the output current from the first comparator COM1 becomes maximum. Therefore, the current of the base terminal of the constant current switching element BT increases rapidly. Then, the detection voltage generated through the detection resistor Rd is rapidly increased, and the second comparator COM2 supplied with the detection voltage outputs a detection signal having a value higher than the threshold. Thereafter, the detection signal is input to the node controller NC, and the node controller NC determines whether the detection signal is maintained at a value greater than the threshold for the reference time. When the magnitude of the detection signal is kept longer than the reference time while the magnitude of the detection signal exceeds the threshold value, the node controller NC supplies the switch control signal to the first switch SW1 to turn the first switch SW1 on. -Turn it off. Then, the first node N1 is in the floating state.

The minimum voltage detector MIN detects the smallest value among the voltages of the normal second to mth nodes N2 to Nm other than the floating first node N1 as the minimum value. Here, as described above, since the first node N1 and the driving voltage transmission line DVL are electrically disconnected, the first node N1 has the smallest voltage, but the first node N1 is floating. This first node N1 is no longer considered to be circuitally present. Therefore, the driving voltage may be abnormally sharply increased by the smallest voltage detected from the first node N1 for a while, but since the first node N1 is in a floating state, the minimum voltage detection unit MIN ) Selects the smallest value among the voltages of the normal second to mth nodes N2 to Nm except for the first node N1, and thus the driving voltage VLED may have a normal value again. . As described above, according to the present invention, the floating light source array is connected to the floating node so that the node connected to the light source array is not visible in circuit, so that the magnitude of the driving voltage can be normally set by the voltages of the remaining normal nodes. Therefore, occurrence of overvoltage due to an abnormal driving voltage is suppressed, and thus, even when an abnormality occurs in the light source array, the constant current switching elements BT connected to the first to mth nodes N1 to Nm can be safely protected from overvoltage. have.

7 is a view showing another configuration of the node detection unit.

As illustrated in FIG. 7, the k-th node detector (eg, NS1) may include a detection resistor Rd, a voltage detector, an amplifier, and a second comparator COM2.

Since the detection resistor Rd and the second comparator COM2 in FIG. 7 are the same as those in the above-described first embodiment, the description thereof will be referred to the first embodiment.

The voltage detection unit VD detects a voltage across the detection resistor Rd. The voltage detector calculates a difference voltage between the voltage applied to one side of the detection resistor Rd and the voltage applied to the other side of the detection resistor Rd, and outputs the calculated difference voltage as the detection voltage.

The amplifier APM amplifies the detected voltage from the voltage detector VD at a predetermined ratio.

The node detecting unit shown in FIG. 7 may be applied to both the first and second embodiments described above.

8 is a diagram illustrating an emitter voltage and a base current of the constant current switching device BT in a normal driving environment, and an emitter voltage and a base current of the constant current switching device BT in an abnormal driving environment.

As shown in FIG. 8A, the base current represents about 200 [uA] in a normal environment. However, if any one of the light emitting diodes is damaged and one node is cut off from the driving voltage transmission line DVL, the base current rapidly increases.

Specifically, FIG. 8A illustrates the emitter voltage V_E and the base current I_B when the driving voltage is applied to the light source arrays in a state where there is no abnormality in the light emitting diodes in all the light source arrays. Accordingly, the emitter voltage V_E represents about 1.9 [V] and the base current I_B represents about 200 [uA].

FIG. 8B shows the emitter voltage V_E and the base current I_B before and after applying the driving voltage to the light source arrays in a state in which one light emitting diode artificially belonging to one light source array is removed. It is a change. Here, the period before the lighting time Ton refers to a period before the driving voltage is applied to the light source arrays as described above, and the period after the lighting time Ton indicates the driving voltage to the light source arrays as described above. It means the period after authorization. As shown in (b) of FIG. 8, the emitter voltage V_E is almost unchanged when compared with before and after the lighting time Ton. That is, under normal circumstances, the emitter voltage V_E should rise to the size as shown in FIG. In other words, it can be seen that in the abnormal driving environment, the emitter voltage V_E does not rise but remains sharply low. If the light emitting diode is damaged during driving, the emitter voltage V_E is rapidly changed from the state as shown in FIG. 8A to the state as shown in FIG. 8B (after ON). Will fall. On the other hand, it can be seen that the base current I_B rises significantly after the lighting time V_E. This is because, as described above, the output of the first comparator COM1 sensing the emitter voltage V_E becomes the maximum.

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, and it is common in the art that various substitutions, modifications, and changes can be made without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

VLED: Drive voltage LA #: # # light source array
VCC: Power Voltage LED: Light Emitting Diode
D: Diode DVL: Drive Voltage Transmission Line
MIN: Minimum voltage detector Rp: Pullup resistor
N #: Node # CN: Common Node
DC: drive voltage controller NC: node controller
CC #: constant current controller NS #: node # node detection unit
COM #: # comparator VR #: # # reference voltage
Rd: detection resistance Rs: detection resistance
BT: constant current switching element

Claims (13)

First to mth light source arrays, each of which is supplied with a driving voltage from the driving voltage transmission line and individually connected to each of the first to mth nodes (m is a natural number greater than 1);
First to mth constant current controllers individually controlling each of the driving currents supplied to each of the first to mth light source arrays;
First to m-th node detectors respectively sensing signals from the first to m-th nodes and outputting a detection signal according to the detection result;
Constant current belonging to the k-th constant current controller when the detection signal from the k-th node (k is any one of 1 to m) among the first to m-th node detectors is maintained at a value greater than a threshold value for a predetermined time. A node controller which makes the k-th node in a floating state by turning off a switching element;
A minimum voltage detector detecting a smallest voltage among the voltages of the first to mth nodes; And
And a driving voltage controller configured to control the magnitude of the driving voltage based on the voltage detected by the minimum voltage detector. delete The method of claim 1,
Kth constant current control unit,
A constant current switching element connected to the k-th node through a collector terminal;
A sense resistor connected between the emitter terminal and the ground terminal of the constant current switching element; And
And a first comparator comparing the preset first reference voltage with the voltage applied to the emitter terminal and adjusting the magnitude of the control signal based on the comparison result and outputting the control signal to the base terminal of the constant current switching device. Backlight unit. The method of claim 3, wherein
K-th node detection unit,
A detection resistor connected in series between an output terminal of the first comparator included in the k-th constant current control unit and a base terminal of the constant current switching element; And,
A second comparator that compares the voltage detected from the output terminal of the first comparator included in the k-th constant current controller with the preset second reference voltage and adjusts the magnitude of the detection signal to supply to the node controller based on the comparison result; Backlight unit comprising a. delete The method of claim 3, wherein
The node control unit,
And turning off the constant current switching device by dropping the first reference voltage applied to the first comparator belonging to the k-th constant current control unit to 0 [V]. The method of claim 1,
The minimum voltage detection unit,
First to mth diodes connected between the first to mth nodes and a common node; And,
A pull-up resistor connected between the common node and a voltage source for outputting a power supply voltage; And,
And an anode terminal of the kth diode is connected to the common node, and a cathode terminal of the kth diode is connected to the kth node. The method of claim 7, wherein
And the driving voltage controller controls the magnitude of the driving voltage based on the voltage from the common node. The method of claim 4, wherein
And first to mth switches connected between each of the first to mth nodes and a collector terminal of each of the constant current switching elements belonging to the first to mth constant current controllers. The method of claim 9,
The node control unit,
And turning off the k-th switch when the second control signal from the k-th node detector is maintained at a value greater than a reference value for a preset time, thereby bringing the k-th node into a floating state. The method of claim 3, wherein
K-th node detection unit,
A detection resistor connected in series between an output terminal of the first comparator included in the k-th constant current control unit and a base terminal of the constant current switching element;
A voltage detector detecting a voltage across both ends of the detection resistor;
An amplifier for amplifying the voltage from the voltage detector; And,
And a second comparator comparing the voltage from the voltage detector with a preset second reference voltage, and adjusting the magnitude of the second control signal based on the comparison result and supplying the second control signal to the node controller. delete delete

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