JP5117979B2 - Light source device and display device - Google Patents

Description

  The present invention relates to a light source device and a display device that control the brightness of a light source by controlling a current for driving the light source.

FIG. 8 is a diagram illustrating a configuration example of a light source driving circuit 90 according to a conventional technique. The light source driving circuit 90 is a driving circuit that supplies a direct current to the light source element 99 to emit light, and includes a voltage conversion unit 901 and a resistance element 905. The light source element 99 is an LED (Light Emitting
When the applied voltage rises, the flowing current increases and the brightness increases.

  When a DC or AC voltage is input to the input terminal 902, the voltage converter 901 outputs from the output terminal 904 so that the feedback voltage VFB applied to the feedback voltage application terminal 903 is equal to the reference voltage VREF. The voltage VOUT is controlled. The light source element 99 is connected to the ground via a resistance element 905 having one end connected to the output terminal 904 and the other end connected in series. A connection point between the light source element 99 and the resistance element 905 is connected to a feedback voltage application terminal 903. Since the current flowing into the feedback voltage application terminal 903 has a magnitude that can be ignored, if this is “0” (also “0” in the following description), the feedback voltage VFB is: The voltage is a value obtained by multiplying the current value of the current IL flowing through the light source element 99 by the resistance value R1 of the resistance element 905.

  For example, in a state before driving the light source element 99, no voltage is applied to the light source element 99, the current value of the current IL flowing through the light source element 99 is “0”, and the feedback voltage VFB is also “0”. When driving of the light source element 99 is started, the output voltage VOUT gradually increases, the current IL flowing through the light source element 99 also increases, and the feedback voltage VFB also increases. When the feedback voltage VFB becomes equal to the reference voltage VREF, the increase of the output voltage VOUT stops.

  When the current IL is to be decreased from a steady-state current value (hereinafter referred to as “IL steady-state value”) = VREF / R1, the voltage conversion unit 901 increases the output voltage VOUT, and the current IL is a steady-state current value = VREF. When trying to increase from / R1, the voltage conversion unit 901 drops the output voltage VOUT and keeps the current IL constant. Thus, the IL steady value becomes the same value as the value obtained by dividing the reference voltage VREF by the resistance value R1 of the resistance element 905. The feedback voltage application terminal 903 of the voltage conversion unit 901 is connected to the input of the operational amplifier that constitutes the voltage conversion unit 901, and the inflow current to the feedback voltage application terminal 903 is large enough to be ignored as compared with the IL steady state. That's it.

  When driving a plurality of light source elements 99, a form using a plurality of circuit configurations shown in FIG. 8, a form where all the light source elements 99 shown in FIG. 8 are connected in series, for example, a liquid crystal backlight drive described in Patent Document 1 There is a circuit or a form of driving for each of a plurality of light emitting element groups to be connected, for example, a light emitting element driving circuit described in Patent Document 2.

JP 2002-244103 A JP 2007-242477 A

  However, in the embodiment using a plurality of circuit configurations shown in FIG. 8, it is necessary to provide a plurality of voltage conversion units 901, and there is a problem that the cost and the volume of the circuit are increased. In the form in which all the light source elements 99 are connected in series, the output voltage VOUT must be increased in accordance with the number of the light source elements 99. In consideration of restrictions on parts used, for example, withstand voltage and safety, an expensive part There is a problem in terms of economy such as manufacturing costs.

  The light-emitting element driving circuit described in Patent Document 2 is provided with a current driving circuit for each light-emitting element group, and even if there is a variation in each light-emitting element group, the current of the same current value flows. A current drive circuit must be provided for each light emitting element group.

  The objective of this invention is providing the light source device and display apparatus which can control an electric current for every light emitting element group with less cost and circuit volume.

The light source device according to the present invention has an input terminal, an output terminal, and a feedback voltage application terminal, converts an input voltage input from the input terminal to an output voltage based on a first reference voltage, and is converted A voltage converter that outputs an output voltage from the output terminal;
One light source element or a plurality of light source elements connected in series, a plurality of light source element groups connected to the output terminal,
A voltage generator that is connected to the first light source element group of the plurality of light source element groups and the feedback voltage application terminal, and generates a second reference voltage according to a current flowing from the first light source element group;
Provided for each remaining second light source element group excluding the first light source element group among the plurality of light source element groups, and controls the current of each second light source element group based on the second reference voltage A current control unit that
The voltage drop of the first light source element group is larger than the voltage drop of any second light source element group.
A display device according to the present invention includes the light source device.

  According to the light source device of the present invention, an input voltage input from the input terminal based on a reference voltage is converted into an output voltage by a voltage converter having an input terminal, an output terminal, and a feedback voltage application terminal, The converted output voltage is output from the output terminal. One end of each of a plurality of light source element groups composed of one light source element or a plurality of light source elements connected in series is connected to the output terminal. A second reference voltage corresponding to a current flowing from the first light source element group is generated by a voltage generation unit connected to the first light source element group and the feedback voltage application terminal of the plurality of light source element groups. The Based on the second reference voltage, each second light source element is provided by a current control unit provided for each remaining second light source element group excluding the first light source element group among the plurality of light source element groups. The group current is controlled. The voltage drop of the first light source element group is larger than the voltage drop of any second light source element group.

  Therefore, since the current of all the light source terminal groups connected to the output terminal can be controlled by one voltage conversion unit and the current control unit provided for each second light source element group, the cost and circuit can be reduced. The current can be controlled for each light emitting element group by volume.

  Since the display device according to the present invention includes the above-described light source device, the same effect as the above-described effect relating to the light source device can be obtained.

  FIG. 1 is a block diagram showing a circuit configuration of a light source device 1 according to an embodiment of the present invention. The light source device 1 includes a light source driving circuit 10 and light source element groups 17, 27, and 37. The light source drive circuit 10 includes a voltage conversion unit 11, a resistance element 15, and current control units 20 and 30. In FIG. 1, as a combination of the light source element group and the current control unit, a combination of the light source element group 27 and the current control unit 20 and a combination of the light source element group 37 and the current control unit 30 are illustrated as examples. This combination may be one, or three or more.

  The voltage converter 11 includes an input terminal 12, an output terminal 13, and a feedback voltage application terminal 14, and controls the output voltage VOUT output from the output terminal 13 based on the feedback voltage VFB applied to the input terminal 12. That is, the voltage converter 11 compares the reference voltage VREF, which is the first reference voltage, with the feedback voltage VFB applied to the feedback voltage application terminal 14, and outputs the output voltage so that the feedback voltage VFB becomes equal to the reference voltage VREF. Controls VOUT. Specifically, when the feedback voltage VFB is lower than the reference voltage VREF, the output voltage VOUT is increased, and when the feedback voltage VFB is higher than the reference voltage VREF, the output voltage VOUT is decreased. The reference voltage VREF may be generated based on a voltage applied to the input terminal 12, a voltage source that outputs the reference voltage VREF may be used, or may be input from the outside. The feedback voltage VFB corresponds to the second reference voltage.

  Each of the light source element groups 17, 27, and 37 includes one light source element 16 or a plurality of light source elements 16 connected in series. The light source element 16 is a light source in which the flowing current IL decreases when the applied voltage decreases, and the brightness of light emission decreases. For example, a light source such as a light emitting diode (hereinafter referred to as “LED”) or an incandescent light bulb. Consists of. Each light source element 16 causes a voltage drop when the current IL flows. As for the voltage drop, a standard value and a range of variation are determined as specifications.

  The light source element group 17 in the first row, which is the first light source element group, has one end connected to the output terminal 13 and the other end connected to one end of the resistor element 15. The resistance element 15 that is a voltage generation unit is a resistance element having one end connected to the other end of the light source element group 17 and the other end connected to the ground. A connection point between the light source element group 17 and the resistance element 15 is connected to the feedback voltage application voltage 14. Since the current to the feedback voltage application terminal 14 of the voltage conversion unit 11 is negligible compared to the current of the light source element group 17, if this is set to “0” (the same applies to the following description) The feedback voltage VFB, that is, the voltage at the connection point between the light source element group 17 and the resistance element 15 is multiplied by the current value of the current flowing through the light source element group 17 and the resistance value of the resistance element 15. Can be handled as the same value.

  The light source element group 27 in the second row, which is the second light source element group, has one end connected to the output terminal 13 and the other end connected to the current control unit 20. The current control unit 20 includes a resistance element 25, an NPN type transistor (hereinafter referred to as “NPN transistor”) 26, and an operational amplifier 28. The NPN transistor 26 has a collector connected to the other end of the light source element group 27 and an emitter connected to one end of the resistance element 25. The resistance element 25 has one end connected to the emitter of the NPN transistor 26 and the other end connected to the ground. The resistance value of the resistance element 25 is, for example, the same value as the resistance value of the resistance element 15.

  In the operational amplifier 28, the connection point between the light source element group 17 and the resistance element 15 is connected to the non-inverting input, the connection point between the emitter of the NPN transistor 26 and the resistance element 25 is connected to the inverting input, and the output is the NPN transistor 26. Connected to the base. The operational amplifier 28 compares the voltage at the connection point between the light source element group 17 and the resistance element 15, that is, the feedback voltage VFB with the voltage at the connection point between the emitter of the NPN transistor 26 and the resistance element 25, thereby obtaining the light source element. The base current of the NPN transistor 26 is controlled so that the current value of the current IL2 flowing through the group 27 becomes the same value as the current value of the current IL1 flowing through the light source element group 17.

  In the example shown in FIG. 1, the voltage at the connection point between the light source element group 17 and the resistance element 15, that is, the feedback voltage VFB is applied to the non-inverting input of the operational amplifier 28. The voltage VREF may be applied to the non-inverting input of the operational amplifier 28. In the example illustrated in FIG. 1, the current control unit 20 performs control so that a current having the same current value as that of the light source element group 17 in the first column flows to the light source element group 27 in the second column. The current values do not have to be the same, and when currents having different current values are flowed, it is possible to flow currents having different current values by changing the resistance value of the resistance element 25 of the current control unit 20, for example.

  The light source element group 37 in the third row, which is the second light source element group, has one end connected to the output terminal 13 and the other end connected to the current control unit 30. The current control unit 30 includes a resistance element 35, an NPN transistor 36, and an operational amplifier 38. The current control unit 30 has the same components, that is, the resistance element 35, the NPN transistor 36, and the operational amplifier 38, respectively, as the resistance element 25, the NPN transistor 26, and the operational amplifier 28 of the current control unit 20. The description is omitted to avoid it.

  The configuration of each light source element group, specifically, the number of light source element groups and the number of light source elements 16 included in each light source element group are used by the restrictions on the output voltage VOUT of the voltage converter 11 and the light source driving circuit 10. It is determined in consideration of the conversion efficiency and economic efficiency of the light source device 1 as a whole.

  At this time, each light source element group is configured such that the voltage drop VF1 of the light source element group 17 is larger than the maximum voltage drop of the voltage drop VF2 of the light source element group 27 and the voltage drop VF3 of the light source element group 37. The specifications and number of the light source elements 16 are determined. The voltage drop VF of each light source element 16 is generated at both ends of the light source element 16 when a current having a predetermined current value that needs to flow through the light source element 16 in order to cause the light source element 16 to emit light with a predetermined brightness. This is the potential difference that occurs. In other words, it is a voltage to be applied in order to flow a current having a current value that needs to flow through the light source element 16 in order to cause the light source element 16 to emit light with a predetermined brightness.

  The first embodiment in which the voltage drop VF1 of the light source element group 17 is larger than the maximum voltage drop of the voltage drop VF2 of the light source element group 27 and the voltage drop VF3 of the light source element group 37 is the voltage of each light source element 16. Since the drop VF may vary and there may be a difference in the number of light source elements 16 included in each light source element group, the light source element group 17 is within a range of variation and the number of light source elements 16 allowed in each light source element group. Of the light source element group 17 so that the minimum value of the voltage drop VF1 of the light source element group 27 is larger than the maximum voltage drop of the maximum value of the voltage drop VF2 of the light source element group 27 and the maximum value of the voltage drop VF3 of the light source element group 37. The number of light source elements 16 is made larger than the larger one of the number of light source elements 16 in the light source element group 27 and the number of light source elements 16 in the light source element group 37.

  The second embodiment in which the voltage drop VF1 of the light source element group 17 is larger than the maximum voltage drop of the voltage drop VF2 of the light source element group 27 and the voltage drop VF3 of the light source element group 37 is the same as the light source element 16. A plurality of types of light source elements 16 having different specifications of the standard value of the voltage drop when a current value is passed are used. For example, when the number of light source elements 16 that can be used in each light source element group is determined, the standard voltage drop determined by the specifications as the light source elements 16 used in the light source element group 17 is the light source element. By using the light source element 16 having a voltage drop larger than the voltage drop of the light source elements 16 used in the groups 27 and 37, the voltage drop VF1 of the light source element group 17 is changed to the voltage drop VF2 of the light source element group 27 and the light source element group 37. It is set to be larger than the maximum voltage drop in the voltage drop VF3.

  For example, when there are two types of light source elements 16, that is, a 3.5 V light source element 16 and a 3.0 V light source element 16 as specifications of the standard value of the voltage drop of the light source element 16, the light sources used in the light source element group 17 By using the 3.5 V light source element 16 as the element 16 and the 3.0 V light source element 16 as the light source element 16 used in the light source element groups 27 and 37, the voltage drop VF1 of the light source element group 17 is The voltage drop VF2 of the light source element group 27 and the voltage drop VF3 of the light source element group 37 are set larger than the maximum voltage drop.

  In the third embodiment in which the voltage drop VF1 of the light source element group 17 is larger than the maximum voltage drop of the voltage drop VF2 of the light source element group 27 and the voltage drop VF3 of the light source element group 37, A voltage drop when a current of a predetermined current value is passed is measured in advance, and the light source element 16 having a large voltage drop of the actually measured voltage drops is used as the light source element 16 of the light source element group 17. The voltage drop VF1 of the element group 17 is set larger than the maximum voltage drop of the voltage drop VF2 of the light source element group 27 and the voltage drop VF3 of the light source element group 37. The first to third embodiments may be combined.

  As described above, even in one voltage conversion unit 11, by dividing the light source elements 16 into a plurality of light source element groups to which the plurality of light source elements 16 are connected, the output voltage required when all the light source elements 16 are connected in series and driven. It can be driven with an output voltage lower than VOUT. Further, the current can be controlled for each light emitting element group with less cost and circuit volume by one voltage conversion unit 11 and a current control unit provided for each light source element group in the second column and thereafter.

  Further, the voltage drop VF1 of the light source element group 17 is made larger than the maximum voltage drop of the voltage drop VF2 of the light source element group 27 and the voltage drop VF3 of the light source element group 37, and the voltage drop VF1 of the light source element group 17 And the maximum voltage drop of the voltage drops VF2 and VF3 of the light source element group 27 are set to a minimum value, that is, variations in the voltage drop of the light source element 16, selectable light sources In the range of the types of the elements 16 and the number of the light source elements 16 allowed in each light source element group, the potential difference is set to be a value closest to 0 volts.

  The voltage converter 11 outputs an output voltage VOUT for allowing a predetermined current value to flow through the light source element group 17 having the largest voltage drop. The voltage drop in the second and subsequent light source element groups excluding the light source element group 17 in the first column is VFn, for example, the voltage drop VF2 in the light source element group 27 in the second column, and the light source element group 37 in the third column. Voltage drop VF3 and voltage drop VFn of the light source element group in the nth column, the voltage drop VF1 of the light source element group 17 in the first column and each light source element in each light source element group in the second column and thereafter. The voltage difference from the group voltage drop VFn is an excessive voltage, and power Qn = (VF1−VFn) × IL due to this voltage difference is lost power. n is an integer of 2 or more, and IL is a current value of a predetermined current.

  The voltage drop VF1 of the light source element group 17 is made larger than the maximum voltage drop among the voltage drops VFn of each light source element group, and the voltage drop VF1 of the light source element group 17 and the voltage drop VFn of each light source element group are The difference between the maximum voltage drop and the voltage drop is set to the minimum value. That is, since the value of “voltage drop VF1−voltage drop VFn” is set to be larger than 0 and minimized, the above-described loss power can be minimized.

  FIG. 2 is a circuit diagram showing a detailed configuration of the light source device 1. The voltage conversion unit 11 is, for example, a switching step-up voltage conversion circuit, and includes a control unit 111, a switching transistor 112, a choke coil 113, a rectifier diode 114, and smoothing capacitors 115 and 116. The control unit 111 includes, for example, a reference voltage source that generates the reference voltage VREF, an error amplifier that compares the reference voltage VREF and the feedback voltage VFB applied to the feedback voltage application terminal 14, a triangular wave generation circuit that generates a triangular wave, and an error amplifier The output of the triangular wave oscillation circuit is compared with the output of the triangular wave oscillation circuit, and a comparator and an amplifier for generating a switch wave for driving the switching transistor 112 based on the comparison result are included. Many of these components are integrated. It has become. The configurations of the light source element groups 17, 27, and 37 and the current control units 20 and 30 are the same as those shown in FIG. 1, and a description thereof is omitted to avoid duplication.

  When the current value of a predetermined current (hereinafter referred to as “IL steady value”) for causing the light source element 16 to emit light with a predetermined brightness is 10 mA and the reference voltage VREF is 1.0 V, the resistance value R1 of the resistance element 15 is 1.0V / 10 mA = 100Ω. The current value of the current flowing through each light source element group is made the same. That is, the current flowing through the light source element group 17 in the first column is IL1, the current in the light source element group in the nth column is ILn, the resistance value of the resistance element of the light source element group 17 in the first column is R1, and the nth. When the resistance value of the resistance element of the light source element group in the column is Rn, IL1 = ILn, so R1 = Rn. n is an integer of 2 or more, and the potential difference VCE between the collector and the emitter when the switching transistor 112 is saturated (at the time of ON) is approximately 0V.

  The voltage converter 11 shown in FIG. 2 is a switching step-up voltage conversion circuit, but includes a switching step-down voltage conversion circuit, a switching type polarity reversal voltage conversion circuit, a shunt type voltage conversion circuit, or the like. If the converter circuit is a converter circuit that outputs a DC voltage and feedback-controls the output voltage, such as a converter circuit that has a function to convert AC voltage to DC voltage, the method, configuration, and types of parts used are limited. Not.

  For example, the number of light source elements 16 required to obtain a predetermined light emission amount, that is, predetermined brightness is ten, but is included in the light source element group connected in series due to the restriction of the output voltage VOUT of the voltage conversion unit 11. If the maximum number of light source elements 16 that can be handled is nine, it can be dealt with by dividing the ten light source elements 16 into at least two light source element groups.

  In the case of the first embodiment described above, the ten light source elements are divided into two light source element groups, the light source element group 17 and the light source element group 27, and the light source element group 17 is configured by the six light source elements 16, and the light source element group 27 is composed of four light source elements 16, and the specification of the voltage drop VF of the light source element 16 when the IL steady value, that is, the current value is 10 mA, is a standard value of 3.5 V and a variation range of ± 0.5 V. The voltage drop of each light source element group is as shown in Table 1.

  The minimum value 18.0V of the voltage drop VF1 of the light source element group 17 is larger than the maximum value 16.0V of the voltage drop VF2 of the light source element group 27, and the voltage drop VF of the light source element 16 has a variation of ± 0.5V. However, the voltage drop VF1 of the light source element group 17 can always be larger than the voltage drop VF2 of the light source element group 27.

  In the case of the above-described second embodiment, the specification of the standard value of the voltage drop as the light source element 16 of the light source element group 27 in the second column is the voltage drop of the light source element 16 in the light source element group 17 of the first column. A light source element 16 of a type smaller than the standard value specification is used. Furthermore, in the case of the above-described third embodiment, among the actually measured voltage drops VF of the light source elements 16, those having the largest voltage drop VF are assigned to the light source element group 17 in the first column. Alternatively, the light source elements 16 and the first light source element groups 17 and 17 are arranged so that the voltage drop VF1 of the light source element group 17 in the first column is larger than the voltage drop VF2 of the light source element group 27 in the second column. Assigned to the light source element group 27 in the second column.

  When ten light source elements are divided into two light source element groups, the light source element group 17 and the light source element group 27, the voltage of the light source element 16 is also applied when seven light source element groups 17 and three light source element groups 27 are allocated. Even if there is a variation of ± 0.5 V in the drop VF, the voltage drop VF1 of the light source element group 17 can always be larger than the voltage drop VF2 of the light source element group 27. However, when the power loss Q2 of the transistor 26 in the second column is assigned to 7 for the light source element group 17 and 3 for the light source element group 27, Q2 = (VF1−VF2) × IL = (3.5V × 7 −3.5V × 3) × 10 mA = 0.14 W, but when 6 elements are assigned to the light source element group 17 and 4 elements are assigned to the light source element group 27, Q2 = (VF1−VF2) × IL = (3.5V × 6−3.5V × 4) × 10 mA = 0.07 W.

  In other words, when 6 light sources are assigned to the light source element group 17 and 4 light sources are assigned to the light source element group 27, the power loss may be less than when 7 are assigned to the light source element group 17 and 3 are assigned to the light source element group 27. it can. In other words, the potential difference between the voltage drop VF1 of the light source element group 17 in the first column and the voltage drop VF2 of the light source element group 27 in the second column is set to a minimum value, that is, a value closest to the potential difference of 0 volts. By doing so, power loss can be reduced.

  FIG. 3 is a block diagram showing a circuit configuration of a light source device 2 according to another embodiment of the present invention. The light source device 2 includes a light source driving circuit 101 and light source element groups 17, 27, and 37. The light source drive circuit 101 has a circuit configuration in which a resistance element 18 is added to the components of the light source drive circuit 10, and the same components as those of the light source device 1 and the light source drive circuit 10 are denoted by the same reference numerals. The description is omitted to avoid duplication.

  The resistance element 18 is a voltage drop unit connected in series between the light source element group 17 in the first row and the resistance element 15. In the light source device 2 shown in FIG. 3, one resistive element is used as the voltage drop unit. However, any element that causes a voltage drop, such as a diode or a constant voltage diode, may be used, and depending on an element group in which a plurality of elements are combined. It may be configured. The position where the voltage drop unit is added may be added in series between the output terminal 13 and the light source element group 17.

  A voltage drop when an IL steady-state current flows through the resistance element 18 is VR, and a voltage drop due to the light source element array 17 and the resistance element 18 is VFR. The voltage drop VFR is VFR = VF1 + VR.

  In the light source device 2, each voltage drop VFR due to the light source element group 17 and the resistance element 18 is larger than the maximum voltage drop among the voltage drop VF 2 of the light source element group 27 and the voltage drop VF 3 of the light source element group 37. The specifications and number of the light source elements 16 constituting the light source element group are determined. Since the resistance element 18 is added to the first column, the voltage drop VF1 of the light source element group 17 can be reduced by the voltage drop VR of the resistance element 18 as compared with the light source device 1.

  Further, the potential difference between the voltage drop VFR of the light source element group 17 and the resistance element 18 in the first column and the maximum voltage drop among the voltage drops of the light source element groups in the second column and later is set to be the minimum value. Is done. Therefore, the power loss of the transistors in the second and subsequent columns can be reduced.

  As described above, the voltage conversion unit 11 having the input terminal 12, the output terminal 13, and the feedback voltage application terminal 14 receives the input voltage input from the input terminal 12 based on the reference voltage VREF that is the first reference voltage. The output voltage is converted into an output voltage, and the converted output voltage is output from the output terminal 13. A plurality of light source element groups including one light source element 16 or a plurality of light source elements 16 connected in series are connected to the output terminal 13. A voltage generator connected to the light source element group 17 in the first column and the feedback voltage application terminal 14 among the plurality of light source element groups, and a second corresponding to the current flowing from the light source element group 17 in the first column. The reference voltage is generated. Based on the second reference voltage by a current control unit provided for each light source element group in the remaining second column except the light source element group 17 in the first column among the plurality of light source element groups, The current of each second light source element group is controlled. The voltage drop of the light source element group 17 in the first column is larger than the voltage drop of any light source element group in the second column and thereafter.

  Therefore, the current of all the light source terminal groups connected to the output terminal 13 can be controlled by one voltage conversion unit 11 and the current control unit provided for each light source element group in the second column and thereafter. The current can be controlled for each light emitting element group with less cost and circuit volume.

  Further, the light source elements 16 have the same specifications of the standard value and variation of the voltage drop when the same current value is passed, and the number of the light source elements 16 included in the light source element group in the first column is as follows. The minimum value of the voltage drop VF1 of the light source element group in the first column due to variations in each light source element 16 is greater than the number of light source elements 16 in any light source element group in the second column and thereafter. This is a number that is larger than the maximum voltage drop value among the maximum values of the voltage drop VFn of each light source element group in the second and subsequent columns due to the variation of. Therefore, by adjusting the number of light source elements 16 constituting each light source element group, a current having the same current value can be supplied to each light emitting element group.

  Furthermore, the light source element 16 includes a plurality of types of light source elements 16 having different specifications of standard values of voltage drops when currents having the same current value are passed, and the light source elements in the first column due to variations in the light source elements 16 The first value is set such that the minimum value of the voltage drop VF1 of the group 17 is larger than the maximum voltage drop value among the maximum values of the voltage drop of each light source element group in the second and subsequent columns due to variations in the light source elements 16. The type of the light source element 16 included in the light source element group in the column and the type of the light source element 16 included in the light source element group in the second column and thereafter are selected. Therefore, by changing the type of the light source elements 16 constituting each light source element group and selecting them, it is possible to cause a current having the same current value to flow for each light emitting element group.

  Furthermore, the light source element 16 is a light source element in which a voltage drop when a current having the same current value is passed is measured in advance, and the voltage drop VF1 of the light source element group 17 in the first column is the second and subsequent columns. The light source elements 16 included in the light source element group 17 in the first row and the light source element groups 17 in the first row are based on the voltage drop measured in advance of the light source elements 16 so as to be larger than the maximum voltage drop value among the voltage drops of each light source element group. The light source elements 16 included in the light source element groups in the second and subsequent columns are selected. Therefore, by measuring and assigning the voltage drop of the light source elements 16 constituting each light source element group, the current having the same current value can be made to flow for each light emitting element group.

  Further, the difference between the total VFR of the voltage drop VF1 of the light source element group 17 in the first column and the voltage drop VR of the resistor element 18 and the maximum voltage drop among the voltage drops of the light source element groups in the second column and thereafter. Since is a minimum value, power loss can be minimized.

  Further, the current control unit includes an NPN-type transistor whose collector is connected to the light source element group in the second and subsequent columns, a resistance element whose one end is connected to the emitter of the transistor, and whose other end is connected to the ground. The non-inverting input is connected to the connection point between the light source element group 17 in the first column and the resistance element 15 as the voltage generation unit, the inverting input is connected to the connection point between the transistor and the resistance element, and the output is And an operational amplifier connected to the base of the transistor. Therefore, the current control unit can be configured with a circuit configuration according to a conventional technique such as an NPN transistor, a resistance element, and an operational amplifier.

  Furthermore, the voltage conversion unit 11 includes a switching voltage conversion circuit. Therefore, the voltage conversion unit 11 can be realized by a circuit configuration according to a conventional technique such as the control unit 111, the NPN transistor 112, the coil 113, the diode 114, and the capacitor 116.

Further, the resistance element 15 as a voltage generation unit generates a voltage proportional to the current.
Furthermore, since the voltage generation unit is configured by the resistance element 15, the voltage generation unit can be realized using a circuit element that is inexpensive and easily available.
So
Furthermore, since one end of the resistance element 15 is connected to the light source element group 17 in the first column and the other end is connected to the ground, a voltage corresponding to the current is applied to the light source element group 17 in the first column and the resistance. It can be generated at one end connected to the connection point with the element 15.

  FIG. 4 is a circuit diagram showing a detailed configuration of the light source device 2. The configuration of the voltage conversion unit 11 is the same as the configuration of the voltage conversion unit 11 of the light source device 1 shown in FIG. 3, and the description thereof is omitted to avoid duplication by attaching the same reference numerals.

  For example, the number of light source elements 16 required to obtain a predetermined light emission amount, that is, predetermined brightness is ten, but is included in the light source element group connected in series due to the restriction of the output voltage VOUT of the voltage conversion unit 11. If the maximum number of light source elements 16 that can be handled is nine, it can be dealt with by dividing the ten light source elements 16 into at least two light source element groups.

  For example, when the light source device 2 corresponds to the first embodiment described above, ten light source elements are divided into two light source element groups, a light source element group 17 and a light source element group 27, and the light source element group 17 is divided into five light sources. The light source element group 27 is composed of five light source elements 16, and the specification of the voltage drop VF of the light source element 16 when the IL steady value, that is, the current value is 10 mA, is 3.5V ± 0. Assuming 5 V, the voltage drop of each light source element group is as shown in Table 2.

  The minimum value 15.0V of the voltage drop VF1 of the light source element group 17 is smaller than the maximum value 20.0V of the voltage drop VF2 of the light source element group 27, but it is 5 by the resistance element 18 connected in series to the light source element group 17. By causing a voltage drop larger than 0.0 V, even if there is a variation of ± 0.5 V in the voltage drop VF of the light source element 16, the voltage drop VFR due to the light source element group 17 and the resistance element 18 is reduced in the light source element group 27. The voltage drop VF2 can be larger than the voltage drop VF2. The resistance value of the resistance element 18 is a resistance value at which the minimum value of the voltage drop is larger than 5.0 V in consideration of variations in the resistance value in order to cause a voltage drop of 5.0 V or more at the IL steady value. The resistance value is greater than 5.0 V / 10 mA = 500Ω. In the case where a constant voltage diode is used as the voltage drop unit, a diode whose zener voltage is larger than 5.0 V by energization of 10 mA in the temperature range in which the light source device 2 is used is used.

  The light source drive circuit 101 is limited in the number of light source elements 16 constituting the light source element group 17, and the number of light source elements 16 constituting the light source element group 17 is set to the number of light source elements 16 constituting the light source element group 27. Even if it cannot be increased, the voltage drop VFR due to the light source element group 17 and the resistance element 18 can be reduced by connecting a voltage drop unit such as the resistance element 18 in series with the light source element group 17. The voltage drop VF2 can be larger than the voltage drop VF2 of 27.

  As described above, even in one voltage conversion unit 11, by dividing the light source elements 16 into a plurality of light source element groups to which the plurality of light source elements 16 are connected, the output voltage required when all the light source elements 16 are connected in series and driven. It can be driven with an output voltage lower than VOUT. Further, the current can be controlled for each light emitting element group with less cost and circuit volume by one voltage conversion unit 11 and a current control unit provided for each light source element group in the second column and thereafter.

  As described above, the second reference voltage is a voltage at a connection point between the light source element group 17 and the resistor element 15 in the first column, that is, the feedback voltage VFB. Therefore, the reference voltage VREF used in the voltage converter 11 is used. Is not required to be taken out from the voltage converter 11.

  Furthermore, a voltage drop corresponding to the current value of the current flowing through the light source element is generated by the voltage drop unit connected in series to the light source element 16 included in the light source element group 17 in the first row.

  Therefore, the number of the light source elements 16 constituting the light source element group 17 in the first row is limited, and the number of the light source elements 16 constituting the light source element group 17 is changed to the light source element group 27 in the second row and the like. Even if the number of light source elements 16 cannot be increased, the voltage drop unit such as the resistor element 18 is connected to the light source element group 17 in series, so that the light source element group 17 and the resistor element 18 The voltage drop VFR can be made larger than the voltage drop VF2 of the voltage drop VF2 of the light source element group 27.

  Furthermore, since the resistance element 18 that is a voltage drop unit drops in proportion to the current, a voltage drop that is proportional to the current value of the current can be generated.

  Furthermore, since the voltage drop unit is constituted by the resistance element 18, it is possible to realize the voltage generation unit using a cheap and easily obtainable circuit element.

  FIG. 5 is a block diagram showing a circuit configuration of a light source device 3 according to still another embodiment of the present invention. The light source device 3 includes a light source driving circuit 102 and light source element groups 17, 27, and 37. The light source driving circuit 102 replaces the resistive element 15 of the light source driving circuit 10 with the resistive elements 151 and 152 connected in series, and the voltage divided by the resistive element 151 and the resistive element 152 is applied to the non-operational amplifiers. The voltage is applied to the inverting input, and the resistance values of the resistance elements of each current drive circuit, for example, the resistance element 25 and the resistance element 35 are changed. The same constituent elements as those of the light source device 1 and the light source driving circuit 10 are denoted by the same reference numerals, description thereof is omitted to avoid duplication, and differences will be described below. The voltage divided by the resistance element 151 and the resistance element 152 is the second reference voltage.

  The total resistance value of the resistance value R11 of the resistance element 151 and the resistance value R12 of the resistance element 152 is the same as the resistance value of the resistance element 15 of the light source driving circuit 10, and the resistance element of each current driving circuit, for example, the resistance element The resistance values of 25 and the resistance element 35 are set so that a current having the same current value as that of the light source element group 17 in the first column flows through the light source element groups in the second and subsequent columns, for example, the light source element group 27 and the light source element group 37. Further, the resistance value is the same as the resistance value R12 of the resistance element 152.

  A voltage drop when an IL steady-state current flows through the resistance element 151 is VR, and a voltage drop due to the light source element array 17 and the resistance element 151 is VFR. The voltage drop VFR is VFR = VF1 + VR.

  In the light source device 3, each voltage drop VFR due to the light source element group 17 and the resistance element 151 is larger than the maximum voltage drop of the voltage drop VF2 of the light source element group 27 and the voltage drop VF3 of the light source element group 37. The specifications and number of the light source elements 16 constituting the light source element group are determined.

  The light source driving circuit 102 is configured to apply a voltage obtained by dividing the feedback voltage VFB by the resistance element 151 and the resistance element 152 to each operational amplifier, for example, the non-inverting input of the operational amplifier 28 and the operational amplifier 38. The resistance values of the resistance elements, for example, the resistance element 25 and the resistance element 35 are set to a resistance value R12 that is smaller than the resistance value R1 of the resistance element 15 of the light source driving circuit 10, so that the same effect as the light source driving circuit 101 is maintained. Compared to the light source drive circuit 101, the power loss due to the resistance elements 18 connected in series to the light source element group 17 in the first column of the light source drive circuit 101 and the resistance values of the current drive circuits in the second column and thereafter are as follows. It is possible to reduce the power loss corresponding to the reduction.

  FIG. 6 is a circuit diagram showing a detailed configuration of the light source device 3. The configuration of the voltage conversion unit 11 is the same as the configuration of the voltage conversion unit 11 of the light source device 1 shown in FIG. 3, and the description thereof is omitted to avoid duplication by attaching the same reference numerals.

  For example, the number of light source elements 16 required to obtain a predetermined light emission amount, that is, a predetermined brightness is two, but is included in the light source element group connected in series due to the restriction of the output voltage VOUT of the voltage conversion unit 11. When the maximum number of light source elements 16 that can be handled is one, it can be dealt with by dividing the two light source elements 16 into two light source element groups.

  For example, when the light source device 3 corresponds to the first embodiment described above, two light source elements are divided into two light source element groups, a light source element group 17 and a light source element group 27, and the light source element group 17 is divided into one light source. The light source element group 27 is composed of one light source element 16, and the specification of the voltage drop VF of the light source element 16 when the IL steady value, that is, the current value is 10 mA, is a standard value of 3.5 V. Table 3 shows the voltage drop of each light source element group when the variation range is ± 0.3V.

  The minimum value 3.2 V of the voltage drop VF1 of the light source element group 17 is smaller than the maximum value 3.8 V of the voltage drop VF2 of the light source element group 27, but is 0 by the resistance element 151 connected in series to the light source element group 17. By causing a voltage drop larger than .6 V, even if the voltage drop VF of the light source element 16 has a variation of ± 0.3 V, the voltage drop VFR due to the light source element group 17 and the resistance element 151 is reduced. The voltage drop VF2 can be larger than the voltage drop VF2.

  When the resistance value of the resistance element 15 is 100Ω, the resistance value of the resistance element 151 is 70Ω, and the resistance value of the resistance element 152 is 30Ω, the resistance element 151 has a voltage drop of 70Ω × 10 mA = 0.7V at the IL steady value. And the resistance element 152 generates a voltage drop of 30Ω × 10 mA = 0.3V. Therefore, since the light source driving circuit 102 causes a voltage drop of 0.7 V due to the resistance element 151, the voltage drop VFR due to the light source element group 17 and the resistance element 151 is larger than the voltage drop VF2 of the light source element group 27. can do.

  As described above, the voltage generation unit is configured by two second resistance elements connected in series, for example, the resistance element 151 and the resistance element 152, and the second reference voltage is determined by the resistance element 151 and the resistance element 152. The voltage at the connection point. Therefore, the light source driving circuit 102 has a power loss due to the resistance element 18 connected in series to the light source element group 17 in the first column of the light source driving circuit 101 and the second and subsequent columns as compared with the light source driving circuit 101. The power loss can be reduced as the resistance value of the current driving circuit decreases.

  The light source driving circuit 101 shown in FIG. 3 and the light source driving circuit 102 shown in FIG. 5 may be combined. In the light source driving circuit 101 shown in FIG. 3, the light source driving circuit 102 shown in FIG. 5, and the light source driving circuit combining them, the voltage drop VFR due to the light source element group 17 and the resistance element 18, the light source element group 17 and the resistance element The voltage drop VFR due to 151, or the voltage drop VFR due to the light source element group 17, the resistor element 18 and the resistor element 151 is based on the maximum voltage drop among the voltage drop VF2 of the light source element group 27 and the voltage drop VF3 of the light source element group 37. The specifications and number of the light source elements 16 constituting each light source element group are determined so as to increase. Alternatively, the voltage drop VFR becomes larger than the maximum voltage drop of the voltage drop VF2 of the light source element group 27 and the voltage drop VF3 of the light source element group 37, and the voltage drop VFR and the voltage drop VF2 of the light source element group 27 The specifications and the number of light source elements 16 constituting each light source element group are determined so that the difference between the voltage drop of the voltage drop VF3 and the maximum voltage drop becomes a minimum value.

  The voltage converter 11 outputs an output voltage VOUT for allowing a predetermined current value to flow through the light source element group 17 having the largest voltage drop. In each light source element group in the second and subsequent columns, the voltage difference between the voltage drop VFR in the first column and the voltage drop VFn in each light source element group is an excessive voltage, and the power Qn = ( VFR−VFn) × IL is power loss. n is an integer of 2 or more, and IL is a current value of a predetermined current.

  The voltage drop VFR in the first column is made larger than the maximum voltage drop in the voltage drop VFn of each light source element group, and the voltage drop VFR in the first column and the voltage drop VF3n of each light source element group are The difference between the maximum voltage drop and the voltage drop is set to the minimum value. That is, since the value of voltage drop VFR−voltage drop VFn is set to be larger than 0 and minimized, the above-described loss power can be minimized.

  FIG. 7 is a cross-sectional view showing a schematic configuration of the display device 30 according to the embodiment of the present invention. The display device 30 includes a light source device 31, a liquid crystal display panel 32, and a housing 33. The light source device 31 includes a plurality of light source units 311, a light guide 312, a light diffuser 313, a reflector 314, a diffuser plate 315, and a prism 316. Each light source unit 311 includes the light source device 1 illustrated in FIG. 1, the light source device 2 illustrated in FIG. 3, or the light source device 3 illustrated in FIG. 3, and is arranged and provided on one end surface of the light guide 312. ing. The light source device 31 is configured by sequentially laminating a reflector 314 that reflects light, a light diffuser 313 that diffuses light, a light guide 312, a diffuser plate 315 that diffuses light, and a prism 316 from the bottom side.

  The liquid crystal display panel 32 is a panel in which a liquid crystal layer made of liquid crystal is formed between two transparent substrates. The light source device 31 is stacked behind the liquid crystal display panel 32 as a backlight, and is housed in the housing 33 together with the liquid crystal display panel 32.

It is a block diagram which shows the circuit structure of the light source device 1 which is one Embodiment of this invention. 2 is a circuit diagram illustrating a detailed configuration of the light source device 1. FIG. It is a block diagram which shows the circuit structure of the light source device 2 which is other forms of implementation of this invention. 3 is a circuit diagram showing a detailed configuration of a light source device 2. FIG. It is a block diagram which shows the circuit structure of the light source device 3 which is the further another form of implementation of this invention. 3 is a circuit diagram showing a detailed configuration of a light source device 3. FIG. It is sectional drawing which shows the schematic structure of the display apparatus 30 which is one Embodiment of this invention. It is a figure which shows the structural example of the light source drive circuit 90 by a prior art.

Explanation of symbols

1, 2, 3 Light source device 10, 90, 101, 102 Light source drive circuit 11, 901 Voltage converter 12, 902 Input terminal 13, 904 Output terminal 14, 903 Feedback voltage application terminal 15, 905 Resistive element (voltage generator)
16, 99 Light source elements 17 First light source element group 18 Resistive element (voltage drop unit)
20, 30 Current control unit 25, 35, 151, 152 Resistance element 26, 36 NPN transistor 27 Second light source element group 28, 38 Operational amplifier 37 Third light source element group 111 Control unit 112 Switching transistor 113 Choke coil 114 Rectification Diode 115, 116 Smoothing capacitor 311 Light source part 312 Light guide 313 Light diffuser 314 Reflector 315 Diffusion plate 316 Prism

Claims (17)

It has an input terminal, an output terminal, and a feedback voltage application terminal, converts an input voltage input from the input terminal to an output voltage based on a first reference voltage, and outputs the converted output voltage from the output terminal A voltage converter to
One light source element or a plurality of light source elements connected in series, a plurality of light source element groups connected to the output terminal,
A voltage generator connected to a first light source element group of the plurality of light source element groups and the feedback voltage application terminal, and generating a second reference voltage corresponding to a current flowing from the first light source element group; ,
Provided for each remaining second light source element group excluding the first light source element group among the plurality of light source element groups, and based on the second reference voltage, the current of each second light source element group is A current control unit to control,
The light source device, wherein a voltage drop of the first light source element group is larger than a voltage drop of any second light source element group. The light source element has the same specification of the standard value of the voltage drop and the specification of the range of variation when the current of the same current value flows.
The number of light source elements included in the first light source element group is greater than the number of light source elements in any second light source element group, and the minimum voltage drop of the first light source element group due to variations in each light source element 2. The light source device according to claim 1, wherein the value is a number that is greater than a maximum voltage drop value among the maximum voltage drop values of each second light source element group due to variations of the light source elements. The light source element includes a plurality of types of light source elements having different specifications of a standard value of a voltage drop when a current having the same current value flows.
The minimum value of the voltage drop of the first light source element group due to the variation of each light source element is larger than the maximum voltage drop value among the maximum values of the voltage drop of the second light source element group due to the variation of each light source element. As described above, the type of the light source element included in the first light source element group and the type of the light source element included in the second light source element group are selected. The light source element is a light source element in which a voltage drop when a current of the same current value is passed is measured in advance,
Based on the voltage drop measured in advance of the light source element so that the voltage drop of the first light source element group becomes larger than the maximum voltage drop value among the voltage drops of the second light source element groups. The light source device according to claim 1, wherein a light source element included in one light source element group and a light source element included in a second light source element group are selected.   The difference between the voltage drop of the first light source element group and the maximum voltage drop among the voltage drops of the second light source element group is a minimum value. The light source device according to one. The current control unit includes an NPN transistor whose collector is connected to the second light source element group,
A resistive element having one end connected to the emitter of the transistor and the other end connected to ground;
A non-inverting input is connected to a connection point between the first light source element group and the voltage generator, an inverting input is connected to a connection point between the transistor and the resistance element, and an output is connected to a base of the transistor. The light source device according to claim 1, further comprising: an operational amplifier.   The light source device according to claim 1, wherein the voltage conversion unit includes a switching voltage conversion circuit.   The light source device according to claim 1, wherein the voltage generation unit generates a voltage proportional to a current.   The light source device according to claim 8, wherein the voltage generation unit includes a resistance element.   The light source device according to claim 9, wherein one end of the resistance element is connected to the first light source element group and the other end is connected to the ground.   11. The light source device according to claim 1, wherein the second reference voltage is a voltage at a connection point between the first light source element group and the voltage generation unit.   12. A voltage drop unit that is connected in series to a light source element included in the first light source element group and that generates a voltage drop according to a current value of a current flowing through the light source element. The light source device according to any one of the above.   The light source device according to claim 12, wherein the voltage drop unit drops a voltage in proportion to a current.   The light source device according to claim 13, wherein the voltage drop unit includes a resistance element. The voltage generation unit is configured by two second resistance elements connected in series,
11. The light source device according to claim 1, wherein the second reference voltage is a voltage at a connection point of the two resistance elements.   The light source device according to claim 1, wherein the light source element is a light emitting diode.   A display device comprising the light source device according to claim 1.

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