JP2011018868A - Light emitting element driving device, and surface lighting device or display device with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting element driving device that performs supply voltage control respectively optimal for a case when cathode voltages of all light emitting elements are low and a case when the cathode voltage of a light emitting element only at one place is low.SOLUTION: The light emitting element driving device includes: a voltage control circuit 1; a plurality of light emitting element arrays constituted of a plurality of light emitting elements 2 to 7 which emit light in accordance with levels of supplied currents; and constant-current drive control parts 8 to 10 connected to the light emitting element arrays in series respectively. The respective light emitting element arrays are further connected to a plurality of gm amplifiers 11 to 13, and comparisons with a reference voltage 14 are made. When the gm amplifiers 11 to 13 output currents based on the voltage errors, in accordance with the composite current of the output currents of the gm amplifiers 11 to 13, the voltage control circuit 1 adjusts an output voltage VOUT output to the light emitting elements 2 to 7.

Description

  The present invention relates to a light emitting element driving device, and more particularly, to a light emitting element driving device including a circuit for adjusting a current of a driving current for driving a light emitting element, and a planar illumination device or display device including the same.

  Conventionally, fluorescent lamps, incandescent lamps, and the like are used as light sources in lighting apparatuses, display apparatuses, and the like. On the other hand, technical development for using an LED (light emitting diode) having features of a long life and low power consumption as compared with a conventional light source as a light source for illumination or display has been performed.

  When such an LED is used in a lighting device or the like, in order to ensure sufficient brightness, a large number of LEDs are connected in series or in parallel and arranged in the device as an aggregate of LEDs. Moreover, in order to make the brightness of each LED uniform, an LED driving device including a constant current element that makes a current flowing through each LED constant is disclosed (see Patent Document 1).

  Further, in the LED driving device as in Patent Document 1, for example, a transistor is used as the constant current element, and the total current flowing through the LEDs connected in parallel flows through such a transistor. For this reason, the power loss caused by the voltage applied between the emitter and collector of the transistor and the current flowing through the collector increases, and it becomes a problem how to dissipate the heat generated by the transistor. In particular, when the heat generation of the transistor is large, the lifetime of the transistor may be deteriorated and the reliability of the device may be impaired.

  In view of this problem, the voltage applied between the emitter and collector of the transistor is monitored in a time-sharing manner in order to reduce the power loss that occurs in the constant current element that supplies a predetermined current to the LED. Has been disclosed (see Patent Document 2).

Japanese Unexamined Patent Publication No. 2007-42758 (released on February 15, 2007) JP 2007-220855 A (published August 30, 2007)

  However, in the light emitting element driving apparatus as in Patent Document 2, the cathode voltage of the light emitting element monitored is only one place, and the light emission lower than the minimum voltage necessary for the constant current drive control unit to flow a predetermined current. Since it is not possible to determine whether the device has only one cathode voltage or a plurality of devices, the control is the same when the cathode voltage of the light-emitting device is low and when the cathode voltage of all the light-emitting devices is low. There is a problem of end.

  The present invention has been made in view of such circumstances, and when the voltage supplied to the light emitting elements is very low and the cathode voltage of all the light emitting elements is low, the voltage input to the light emitting elements is Light-emitting element driving device capable of gradually increasing the supply voltage when the voltage supplied to the light-emitting element is rapidly increased and the cathode voltage of the light-emitting element is low by only one place, and the driving device It aims at providing a planar illuminating device or a display apparatus provided with.

  In order to solve the above-described problems, a light-emitting element driving device according to the present invention includes a voltage control circuit, a plurality of light-emitting elements that are supplied with a voltage from the voltage control circuit and emit light according to a current, and are applied to the light-emitting elements. And a constant current drive control unit configured to make a constant current a constant current, wherein the plurality of light emitting elements form a plurality of light emitting element rows each having at least one light emitting element. The constant current drive control unit is provided as a plurality of constant current drive control units connected in series to each of the light emitting element arrays, and further applied to each constant current drive control unit. A voltage error is detected by comparing a voltage with a reference voltage, and a plurality of detection units that output a current according to the detection result are provided, and the voltage control circuit is based on a combined output of the plurality of detections, The light emitting element It is characterized by controlling the that voltage.

  According to the above configuration, when the control voltage output from the voltage control circuit is very low and the applied voltages to the constant current drive control units connected to the light emitting element arrays are all below the reference voltage, It can be detected that the voltage error is large in the plurality of detection units. Since the voltage control circuit controls the voltage applied to the light emitting element based on the combined output of the plurality of detections, the voltage control circuit can rapidly increase the control voltage. On the other hand, when the control voltage is relatively high and part of the voltage applied to the constant current drive control unit connected to each light emitting element array is below the reference voltage, the voltage error is large only in some of the detection units. Is detected. For this reason, the control of increasing the control voltage gradually becomes possible.

  Further, in the light emitting element driving apparatus, the plurality of detection units are set to absolute values of output currents output from one detection unit to which an applied voltage to the constant current drive control unit equal to or lower than the reference voltage is input. On the other hand, the absolute value of the output combined current output when the applied voltage to the constant current drive control unit input to all the detection units other than the detection unit is equal to or higher than the reference voltage can be configured to be smaller. .

  According to the above configuration, even when the applied voltage in some constant current drive control units is equal to or lower than the reference voltage and the applied voltage in some other constant current drive control units is equal to or higher than the reference voltage. The control for the constant current drive control unit below the reference voltage is dominant, and the lowest applied voltage is controlled to be the reference voltage.

  Further, in the light emitting element driving device, with respect to the change of the applied voltage to the constant current drive control unit, the output of the detection unit to which the voltage is input is the voltage difference when the applied voltage is lower than the reference voltage. A current that changes according to the current is started, and when the applied voltage is higher than a reference voltage, a constant current is drawn.

  Further, in the light emitting element driving apparatus, an abnormality determination circuit that compares each applied voltage applied to the constant current drive control unit with an arbitrary abnormality determination voltage and determines that an applied voltage that is equal to or lower than the abnormality determination voltage is abnormal. And a switch circuit that separates the applied voltage determined to be abnormal by the abnormality determination circuit from the detection unit.

  Alternatively, in the light emitting element driving apparatus, an abnormality determination circuit that compares each applied voltage applied to the constant current drive control unit with an arbitrary abnormality determination voltage and determines that an applied voltage that is equal to or lower than the abnormality determination voltage is abnormal. And a switch circuit that separates the output of the detection unit connected to the applied voltage determined to be abnormal by the abnormality determination circuit from the output of another commonly connected detection unit.

  According to the above configuration, even if there is a light emitting element array to which a voltage higher than the reference voltage is not applied due to a defect such as short or open, the light emitting element array in which the defect is generated is detected by the abnormality determination circuit, and the detection unit Detached from. For this reason, the problem that the control voltage is continuously raised by the voltage control circuit can be avoided.

  The light emitting element driving device may further include a function that does not validate the output of the abnormality determination circuit until the output of the voltage control circuit rises to an arbitrary voltage.

  The light emitting element driving device further includes a function of not enabling the output of the abnormality determination circuit until the voltage applied to at least one constant current drive control unit rises to an arbitrary voltage. be able to.

  In the light emitting element driving device, the reference voltage connected to each of the plurality of detection units may be a different reference voltage in each detection unit.

  Further, in the light emitting element driving apparatus, a driving current value controlled to a constant current by the constant current driving control unit is different for each light emitting element column to which each constant current driving control unit is connected, and The reference voltage can be configured to be a value set based on the drive current value of each connected constant current drive control unit.

  According to said structure, even if it drives with the constant current which changes for every light emitting element row | line | column, the control voltage which a voltage control circuit outputs can be optimally controlled.

  The light emitting element driving device further includes a current-voltage conversion unit that converts a combined current of output currents of the plurality of detection units into a voltage, and the voltage control circuit is converted by the current-voltage conversion unit. The voltage applied to the light emitting element can be controlled based on the voltage.

  In the light emitting element driving device, the voltage control circuit may be a DC-DC converter.

  Moreover, the light-emitting element driving device of the present invention is a planar illumination device including any of the above-described light-emitting element driving devices.

  The display device of the present invention is a display device including any of the light-emitting element driving devices described above.

  In the light emitting element driving device of the present invention, when the voltage supplied to the light emitting elements is very low and the cathode voltage of all the light emitting elements is low, the voltage input to the light emitting elements is rapidly increased. On the other hand, when the voltage supplied to the light-emitting element is relatively high and the cathode voltage of the light-emitting element is low by one place, it is possible to perform control such that the supply voltage is gradually increased.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates an embodiment of the present invention and is a circuit diagram illustrating a configuration of a main part of a light emitting element driving device according to a first embodiment. FIG. 6 is a circuit diagram illustrating a configuration of a main part of a light emitting element driving device according to Embodiment 2. 6 is a circuit diagram illustrating a case where an open defect has occurred in the light emitting element driving device according to Embodiment 2. FIG. It is a circuit diagram which shows the modification of the light emitting element drive device which concerns on Embodiment 2, and shows the case where the open defect has arisen. FIG. 10 is a circuit diagram illustrating a configuration in which an abnormality detection start determination circuit is provided, showing a modification of the light emitting element driving device according to Embodiment 2. It is a circuit diagram which shows the modification of the light emitting element drive device which concerns on Embodiment 2, and shows the other structure which provided the abnormality detection start determination circuit. FIG. 5 is a circuit diagram illustrating a configuration of a main part of a light emitting element driving device according to Embodiment 3. It is a graph which shows the relationship between the setting electric current value and required voltage in a constant current drive control part.

[Embodiment 1]
Hereinafter, the present invention will be described with reference to the drawings illustrating embodiments thereof. FIG. 1 is a circuit diagram showing a main configuration of the light emitting element driving apparatus according to the first embodiment. The light emitting element driving device includes a voltage control circuit 1, light emitting elements 2 to 7, constant current drive control units 8 to 10, gm amplifiers 11 to 13, a reference voltage 14, and a current-voltage conversion unit 17. . The present invention can be applied to a planar illumination device that drives a plurality of light emitting elements arranged in a planar shape by the light emitting element driving device, a display device that uses the planar illumination device as a backlight, and the like.

  The voltage control circuit 1 is a DC-DC converter that supplies a control voltage VOUT to the light emitting elements 2 to 7 and supplies a predetermined constant current to the entire light emitting elements 2 to 7 connected in series and in parallel. Note that the number of light-emitting elements illustrated in FIG. 1 is an example, and is not limited to two series or three parallels as illustrated. It suffices to have at least two parallel light emitting element arrays, and each light emitting element array only needs to have at least one light emitting element.

  Constant current drive control units 8 to 10 are connected to the cathodes of the light emitting elements 3, 5 and 7, respectively. As a result, a constant current driving circuit for supplying a constant current (for example, about 10 to 100 mA) to the entire light emitting elements 2 to 7 is configured.

  One end of each of the gm amplifiers 11 to 13 is connected to each cathode of the light emitting elements 3, 5, and 7, and the other end of the gm amplifier is connected to the reference voltage 14. The gm amplifiers 11 to 13 compare the input cathode voltages of the light emitting elements 3, 5, and 7 with the reference voltage, and output a current according to the voltage difference. The outputs of the gm amplifiers 11 to 13 are connected in common.

  A current-voltage conversion unit 17 is connected to the outputs of the gm amplifiers 11 to 13 connected in common. FIG. 1 shows a configuration in which a current-voltage conversion resistor 15 is connected to a bias voltage 16 as an embodiment of the current-voltage conversion unit. The current-voltage conversion unit 17 is an example, and the present invention is not limited to this circuit.

  The voltage VEO converted from the current by the current-voltage converter 17 is input to the voltage control circuit 1, and the voltage control circuit 1 adjusts the control voltage VOUT according to the input voltage.

  Next, the operation of the light emitting element driving device according to the first embodiment will be described.

  When the current flowing through the constant current drive control units 8 to 10 is Id and the cathode voltages of the light emitting elements 3, 5, and 7 are V3, V5, and V7, respectively, with the light emitting elements 2 to 7 being lit, constant current drive control is performed. The unit 8 generates a power loss of W = Id × V3, the constant current drive control unit 9 generates a power loss of W = Id × V5, and the constant current drive control unit 10 generates a power loss of W = Id × V7. In order to light each light emitting element 2 to 7 with a required brightness, the current Id flowing through the constant current drive control unit must be set to a required value, and the constant current drive control unit 8 to In order to reduce the power loss at 10, the cathode voltages V3, V5 and V7 of the light emitting elements 3, 5 and 7 need to be lowered.

  In order to reduce the cathode voltages V3, V5, and V7 of the light emitting elements 3, 5, and 7, the control voltage VOUT may be lowered. However, the constant current drive control units 8 to 10 have a minimum voltage VDRV_min required to flow a predetermined current, and when the cathode voltages V3, V5, and V7 of the light emitting elements 3, 5, and 7 become the minimum required voltage VDRV_min or less. The predetermined current cannot flow.

  The gm amplifiers 11 to 13 compare the cathode voltages V3, V5, and V7 of the light emitting elements 3, 5, and 7 with the reference voltage 14, and the cathode voltages V3, V5, and V7 of the light emitting elements 3, 5, and 7 and the reference voltage 14 are compared. Control is performed so that the current value of the output current is increased or decreased according to the magnitude of the difference.

  For example, when the cathode voltage V3 of the light emitting element 3 is compared with the reference voltage 14, and the cathode voltage V3 of the light emitting element 3 is lower than the reference voltage 14, and the difference is relatively small, the gm amplifier 11 has a relatively small value. Is supplied to the current-voltage converter 17. When the cathode voltage V3 of the light emitting element 3 is lower than the reference voltage 14 and the difference is relatively large, the gm amplifier 11 sends a relatively large value of current to the current-voltage conversion unit 17.

  On the other hand, when the cathode voltage V3 of the light emitting element 3 is higher than the reference voltage 14 and the difference is relatively small, the gm amplifier 11 draws a relatively small value of current from the current-voltage conversion unit 17. Similarly, when the cathode voltage V3 of the light emitting element 3 is higher than the reference voltage 14 and the difference is relatively large, the gm amplifier 11 draws a relatively large value of current from the current-voltage conversion unit 17.

  As a result, when the cathode voltages V3, V5, V7 of the light emitting elements 3, 5, 7 are lower than the reference voltage, the voltage VEO converted by the current-voltage conversion unit 17 becomes high, and the cathodes of the light emitting elements 3, 5, 7 When the voltages V3, V5 and V7 are higher than the reference voltage, VEO is low.

  The voltage VEO converted by the current-voltage conversion unit 17 is input to the voltage control circuit 1, and the voltage control circuit 1 increases the control voltage VOUT when the voltage VEO converted by the current-voltage conversion unit 17 increases. And when the voltage VEO converted by the current-voltage converter 17 becomes lower, the control voltage VOUT is lowered.

  By these controls, the control voltage VOUT is adjusted in accordance with the difference between the cathode voltages V3, V5, V7 of the light emitting elements 3, 5, and 7 and the reference voltage 14, and the constant current drive control unit sets the reference voltage 14 to a predetermined current. The cathode voltage V3, V5, V7 of the light emitting elements 3, 5, and 7 can be optimized (minimum necessary) by setting the voltage VDRV_min that is the minimum necessary for the current to flow.

  Moreover, it is desirable that the current flowing capacity of the outputs of the gm amplifiers 11 to 13 is sufficiently larger than the current drawing capacity.

  In light-emitting elements that are actually used, the forward voltage VF varies greatly. Therefore, the cathode voltages V3, V5, and V7 of the light emitting elements 3, 5, and 7 vary widely, and some of the cathode voltages may be lower than the reference voltage, and some of the other cathode voltages may be higher than the reference voltage. .

  In such a state, some of the gm amplifiers draw current, and some of the other gm amplifiers draw current. However, if the current flowing capacity is sufficiently increased, the output of the gm amplifier is increased. In the combined current, current will flow out. That is, the voltage control circuit increases the control voltage VOUT, and is controlled so that the lowest voltage among the cathode voltages V3, V5, and V7 of the light emitting elements 3, 5, and 7 becomes the reference voltage 14.

  For example, when three gm amplifiers are connected in common as shown in FIG. 1, it is necessary to make the current flow capability of the gm amplifier more than twice the current drawing capability.

  Further, the output of the gm amplifier generates current when the cathode voltage of the light emitting element is lower than the reference voltage 14, and does not draw current when the cathode voltage is higher than the reference voltage 14, so that the cathode voltage of the light emitting elements 3, 5, and 7 is obtained. Regardless of the above, the same control can be performed by adopting a configuration in which a constant current is drawn from a commonly connected node of the gm amplifier.

  By connecting the outputs of the gm amplifiers 11 to 13 in common, the cathode voltages V3, V5, and V7 of the light emitting elements 3, 5, and 7 have one node lower than the reference voltage 14 and a plurality of nodes. Then, the combined current of the output of the gm amplifier is different, and the combined current is larger in a plurality of cases than in the case of one place.

  By doing so, when the control voltage VOUT is very low and the cathode voltages of the light emitting elements are all below the reference voltage 14, the voltage control circuit 1 rapidly increases the control voltage VOUT, and the control voltage VOUT is relatively high. Thus, when only one portion of the cathode voltage of the light emitting element becomes equal to or lower than the reference voltage 14, it is possible to perform control such that the control voltage VOUT is gradually increased.

[Embodiment 2]
FIG. 2 is a circuit diagram showing a main configuration of the light emitting element driving apparatus according to the second embodiment. The light emitting element driving device shown in FIG. 2 has a configuration similar to that of the light emitting element driving device according to the first embodiment in FIG. 1, but further includes an abnormality detection circuit 21, a switch circuit 22, and a pull-up voltage 23. It is configured with. In the light emitting element driving apparatus of FIG. 2, the same reference numerals as those in FIG. 1 are assigned to the same configurations as those of the light emitting element driving apparatus of FIG.

  The abnormality detection circuit 21 is connected to these cathode voltages so as to detect each of the cathode voltages V3, V5, V7 of the light emitting elements 3, 5, 7, and outputs an abnormality detection result to the switch circuit 22. The switch circuit 22 is arranged in front of the gm amplifiers 11 to 13 and includes a plurality of switches. Depending on the result output from the abnormality detection circuit 21, any one of the gm amplifiers 11 to 13 is connected to the cathode voltage V3. Disconnect from V5 and V7 and connect to pull-up voltage 23 instead.

  In the configuration of FIG. 1, when one of the cathodes of the light emitting element is short-circuited to GND or when there is a problem that the light-emitting element is open, no matter how much the control voltage VOUT is increased, it is shorted to GND. Since the voltage of the node (the input side node of the constant current drive control unit 10) does not rise above the reference voltage 14 (mainly remains at 0V), the voltage control circuit 1 continues to raise the control voltage.

  In the light emitting element driving device according to the second embodiment, when there is no problem such as short circuit or open circuit, as shown in FIG. 2, each switch of the switch circuit 22 includes each of the gm amplifiers 11 to 13. Since it is connected to the cathode voltages V3, V5 and V7, the same operation as that of the light emitting element driving device in the first embodiment can be performed.

  On the other hand, for example, as shown in FIG. 3, when a problem occurs in which the cathode of the light emitting element 7 is open, this problem is detected by the abnormality detection circuit 21, and the abnormality detection circuit 21 sends the abnormality detection result to the switch circuit 22. Output. The switch circuit 22 switches a switch connected to the gm amplifier 13 and connects the gm amplifier 13 to the pull-up voltage 23. The abnormality detection circuit 21 compares the cathode voltage of each light emitting element array with the abnormality determination voltage, and determines that the light emitting element array that is equal to or lower than the abnormality determination voltage is abnormal.

  In the light emitting element driving apparatus according to the second embodiment, even when there is a light emitting element array in which an abnormality due to a short circuit or an open occurs due to the above control, voltage control is performed only by information other than the light emitting element array determined to be abnormal. The circuit 1 can control the control voltage VOUT. That is, it is possible to prevent the voltage control circuit 1 from continuously increasing the control voltage VOUT.

  FIG. 4 shows a modification of the light emitting element driving device shown in FIG. 2. Instead of the switch circuit 22 and the pull-up voltage 23, a switch circuit 24 arranged after the gm amplifiers 11 to 13 is provided. Have. The switch circuit 24 disconnects any of the outputs of the gm amplifiers 11 to 13 from the node that commonly connects the outputs of the gm amplifiers 11 to 13 in accordance with the result output from the abnormality detection circuit 21.

  FIG. 4 also illustrates a case where a problem that the cathode of the light emitting element 7 is open occurs. This malfunction is detected by the abnormality detection circuit 21, and the abnormality detection circuit 21 outputs an abnormality detection result to the switch circuit 24. The switch circuit 22 disconnects the output of the gm amplifier 13 from the node that commonly connects the outputs of the gm amplifiers 11 to 13. Also with this configuration, the voltage control circuit 1 can control the control voltage VOUT only by information other than the light emitting element row determined to be abnormal, and the same effect as the light emitting element driving device of FIG. 2 can be obtained.

  FIG. 5 shows a circuit example in which an abnormality detection start determination circuit 25 is added to the light emitting element driving device shown in FIG. In the abnormality detection circuit 21 of FIG. 4, the determination that the light emitting element array is abnormal is made by detecting that the cathode voltage of each light emitting element array is equal to or lower than the abnormality determination voltage. However, even if there is no abnormality in the light-emitting element array, when the control voltage VOUT is low, the cathode voltage of the light-emitting element array may be equal to or lower than the abnormality determination voltage, which causes erroneous detection of the light-emitting element array.

  The abnormality detection start determination circuit 25 in FIG. 5 detects that the control voltage VOUT has become equal to or higher than a certain voltage, and when it exceeds a certain arbitrary voltage, the abnormality detection circuit 21 starts detecting abnormality in each light emitting element array. Control to do. In this way, until the output of the voltage control circuit 1 rises to an arbitrary voltage, the function of not enabling the output of the abnormality determination circuit 21 is further provided, so that abnormality detection is performed only when the control voltage VOUT is sufficiently high. Thus, erroneous detection of abnormalities in the light emitting element array can be prevented.

  FIG. 6 shows a circuit example in which an abnormality detection start determination circuit 26 is added to the light emitting element driving device shown in FIG. The abnormality detection start determination circuit 26 monitors the cathode voltage of each light emitting element array, and when any cathode voltage becomes equal to or higher than the abnormality detection start determination voltage, the abnormality detection circuit 21 starts detecting abnormality of each light emitting element array. To control. If this abnormality detection start determination voltage is set to a voltage equal to or higher than the maximum variation of the light-emitting element array, when any one of the cathode voltages exceeds this voltage, a sufficient voltage is applied to all the cathode voltages. I can judge. In this way, the control voltage VOUT is sufficiently high by further providing a function that does not enable the output of the abnormality determination circuit 21 until the voltage applied to at least one constant current drive control unit rises to an arbitrary voltage. Abnormality detection can be performed only at times, and erroneous detection of abnormalities in the light emitting element array can be prevented.

[Embodiment 3]
FIG. 7 is a circuit diagram showing a main configuration of the light emitting element driving apparatus according to Embodiment 3. In FIG. The light emitting element driving apparatus shown in FIG. 7 has a configuration similar to that of the light emitting element driving apparatus according to the first embodiment in FIG. 1, but the gm amplifiers 11 to 13 are connected to different reference voltages 31 to 33, respectively. 1 is different from FIG. In the light emitting element driving apparatus of FIG. 7, the same reference numerals as those in FIG. 1 are given to the same configurations as those of the light emitting element driving apparatus of FIG.

  The operation of the light emitting element driving apparatus according to Embodiment 3 will be described below.

  The constant current drive control units 8 to 10 have a voltage VDRV_min necessary for flowing a predetermined current. When the cathode voltages V3, V5, and V7 of the light emitting elements 3, 5, and 7 become the minimum required voltage VDRV_min or less, the predetermined current is supplied. Is the same as in the first embodiment.

  When the same constant current drive circuit is used, the minimum required voltage VDRV_min increases as the set current value of the constant current drive unit is increased as shown in FIG. Therefore, when the current values driven by the constant current drive control units 8 to 10 are different, the minimum required voltage VDRV_min for the constant current drive control units 8 to 10 to drive the current as set is different.

  In the light emitting element driving apparatus of FIG. 7, by setting the reference voltages 31 to 33 to different values, it is possible to cope with cases where the current values driven by the constant current drive control units 8 to 10 are different. That is, in the configuration of FIG. 7, the reference voltage 31 is the minimum necessary voltage of the constant current drive control unit 8, the reference voltage 32 is the minimum necessary voltage of the constant current drive control unit 9, and the reference voltage 33 is the minimum voltage of the constant current drive control unit 10. Use the required voltage. In this way, the control voltage VOUT is adjusted according to the difference between the cathode voltages V3, V5, V7 of the light emitting elements 3, 5, 7 and the reference voltages 31, 32, 33. As a result, even when the necessary minimum voltages of the constant current drive control units are different, the cathode voltages V3, V5, V7 of the light emitting elements 3, 5, 7 can be optimized (minimum necessary).

  The light emitting element driving apparatus according to the third embodiment is effective in, for example, backlight driving of a color liquid crystal display apparatus using three types of LEDs (that is, red, green, and blue). That is, in the case of using a red LED, a blue LED, and a green LED as light emitting elements and adjusting the luminance and chromaticity of each color LED by the current flowing through each LED, a white light source is configured for each LED of each color. The set current is often different. For this reason, it is preferable to use the circuit configuration of the second embodiment in order to connect LEDs of the same color in series, arrange LED columns of different colors in parallel, and drive each column with a different constant current. Thereby, the cathode voltage of each LED row can be optimized, and the power loss in the constant current drive control unit can be minimized.

  As described above, in the light emitting element driving device according to the present invention, power loss in the constant current drive control unit can be reduced, and heat generation in the constant current drive control unit can be suppressed. Further, heat generation can be prevented and reliability can be improved. Further, if the heat generation is reduced, it is not necessary to take a heat dissipation measure such as providing a heat dissipation member for the constant current drive control unit, the structure of the apparatus can be simplified, and the size can be reduced.

  The present invention can be applied to a light emitting element driving device including a circuit that adjusts a driving current for driving a light emitting element, and can be used for a planar illumination device or a display device including the circuit.

DESCRIPTION OF SYMBOLS 1 Voltage control circuit 2-7 Light emitting element 8-10 Constant current drive control part 11-13 gm amplifier (detection part)
14, 31 to 33 Reference voltage 15 Resistor 16 Bias voltage 17 Current-voltage converter 21 Abnormality detection circuit 22, 24 Switch circuit 23 Pull-up voltage

Claims (13)

A voltage control circuit; a plurality of light emitting elements which are supplied with a voltage from the voltage control circuit and emit light according to a current; and a constant current drive control unit configured to make the current applied to the light emitting elements constant. A light emitting element driving device,
The plurality of light emitting elements form a plurality of light emitting element rows, each row having at least one light emitting element,
The constant current drive control unit is provided as a plurality of constant current drive control units connected in series to each of the light emitting element rows,
In addition, a voltage error is detected by comparing the voltage applied to each of the constant current drive control units with a reference voltage, and a plurality of detection units for outputting a current according to the detection result are provided.
The voltage control circuit controls a voltage applied to the light emitting element based on a combined output of the plurality of detections. The plurality of detection units are:
The absolute value of the output current output from one detection unit to which the applied voltage to the constant current drive control unit below the reference voltage is input is input to all detection units other than the detection unit 2. The light emitting element driving device according to claim 1, wherein the absolute value of the output combined current output when the voltage applied to the constant current drive control unit is equal to or higher than the reference voltage is smaller.   In response to a change in the applied voltage to the constant current drive control unit, the output of the detection unit to which the voltage is input passes a current that changes according to the voltage difference when the applied voltage is lower than a reference voltage. However, the light emitting element driving device according to claim 1, wherein when the applied voltage is higher than a reference voltage, a constant current is drawn. An abnormality determination circuit that compares each applied voltage applied to the constant current drive control unit with an arbitrary abnormality determination voltage and determines that an application voltage that is equal to or lower than the abnormality determination voltage is abnormal,
4. The light emitting element driving device according to claim 1, further comprising a switch circuit that disconnects an applied voltage determined to be abnormal by the abnormality determination circuit from the detection unit. 5. An abnormality determination circuit that compares each applied voltage applied to the constant current drive control unit with an arbitrary abnormality determination voltage and determines that an application voltage that is equal to or lower than the abnormality determination voltage is abnormal,
2. The switch circuit according to claim 1, further comprising a switch circuit that disconnects an output of the detection unit connected to an applied voltage determined to be abnormal by the abnormality determination circuit from an output of another commonly connected detection unit. 4. The light emitting element driving device according to any one of 3.   6. The light emitting element driving device according to claim 4, further comprising a function of not enabling the output of the abnormality determination circuit until the output of the voltage control circuit rises to an arbitrary voltage.   6. The method according to claim 4, further comprising a function of not enabling the output of the abnormality determination circuit until an applied voltage to at least one constant current drive control unit rises to an arbitrary voltage. The light emitting element drive device of description.   The light-emitting element driving device according to claim 1, wherein a reference voltage connected to each of the plurality of detection units is a different reference voltage in each detection unit. The drive current value controlled to a constant current by the constant current drive control unit is different for each light emitting element row to which each constant current drive control unit is connected,
The light-emitting element driving device according to claim 8, wherein the reference voltage is a value set based on a driving current value of each constant current driving control unit connected thereto. A current-voltage conversion unit that converts a combined current of output currents of the plurality of detection units into a voltage;
10. The light emitting device according to claim 1, wherein the voltage control circuit controls a voltage of a current applied to the light emitting device based on a voltage converted by the current-voltage conversion unit. Drive device.   The light-emitting element driving device according to claim 1, wherein the voltage control circuit is a DC-DC converter.   A planar illumination device comprising the light emitting element driving device according to claim 1.   A display device comprising the light emitting element driving device according to claim 1.

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