JP2011113684A - Light emitting device, and lighting system and display device with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED light emitting device in which unnecessary power consumption is reduced and heat generation in a constant current drive unit is suppressed.
[Solution]
A plurality of light emitting element units (LED arrays) 101a and 101b; a booster circuit 11 that boosts the input voltage Vin and supplies the boosted voltage Vout to each of the light emitting element units; constant current drive units 23a and 23b; And a boost control unit that generates a boost control signal for controlling the circuit 11. The light-emitting device is connected in parallel to each LED of the light-emitting element unit, and individually controls turning off and lighting of each LED. And a bypass switch control unit 100 for controlling on / off of the bypass switch. When the output terminal voltage Vda (Vdb) of the light emitting element unit is higher than the input voltage, the constant value connected to the light emitting element unit is provided. The output terminal of the current driver 23a (23b) (one end of the constant current circuit 26a (26b)) is connected to the input side of the booster circuit 11.
[Selection] Figure 3

Description

  The present invention relates to a light-emitting device, and more particularly, to a light-emitting device that includes a circuit that adjusts the current of a drive current that drives a light-emitting element, reduces power consumption, and a lighting device and a display device that include the light-emitting device.

  Conventionally, in a backlight unit such as an illumination device or a liquid crystal display device, a fluorescent lamp or an incandescent lamp is used as a light source. On the other hand, technological development is currently underway for using LEDs (light emitting diodes), which have features of longer life and lower power consumption than conventional light sources, as illumination or display light sources.

  When such LEDs are used in lighting devices, etc., in order to ensure sufficient brightness, a number of LEDs connected in series and a plurality of LED rows connected in series are further connected in parallel and arranged in the device as an aggregate of LEDs. To do. In addition, Patent Document 1 discloses a light emitting device including a constant current element (transistor) that makes a current flowing in an LED array constant in order to make the brightness of LEDs uniform.

  When a transistor is used as the constant current element, the remaining voltage obtained by subtracting the voltage drop due to the LED string from the anode voltage of the LED string is applied between the emitter and collector of the transistor. In a light emitting device in which a plurality of LED strings are connected in parallel, when a difference occurs in the amount of voltage drop due to the LED string for each LED string, a voltage applied between the emitter and collector of each transistor also varies for each LED string. A high voltage may be applied between the emitter and collector of the transistor. As a result, 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 the problem is how to dissipate the heat generated by the transistor. When the heat generation of the transistor is large, there is a risk that the deterioration of the transistor is accelerated and the reliability of the device is impaired.

  In Patent Document 2, in order to reduce power loss caused by a constant current element that supplies a predetermined current to an LED array, the cathode voltage of each LED array connected in parallel is monitored in a time-sharing manner, and the LED array to be driven A light emitting device is disclosed in which the power loss in the constant current drive unit is reduced by switching the voltage applied to the constant current element in a time-sharing manner every time. In addition, the cathode voltage of each LED string monitored in a time-sharing manner is fed back to the input voltage of the DC / DC converter (boost circuit), so that the output of the booster circuit is increased to the voltage necessary for driving each LED string. The voltage is boosted and the constant current element is operated stably.

JP 2007-42758 A JP 2007-220855 A Japanese Patent No. 4177022

  Since the light-emitting device shown in Patent Document 2 controls the LED row to be driven in a time-sharing manner, there is only one LED row in which a current flows through the constant current element at one time, and the constant current driving unit Power loss can be reduced, but the amount of light emitted by the LED is sacrificed accordingly.

  Further, in the light emitting device disclosed in Patent Document 2, there is only one LED row to be monitored at one time, and since a plurality of LED rows are driven simultaneously, a plurality of cathode voltages are simultaneously monitored. The output voltage of the booster circuit is not boosted to a voltage necessary to drive all the LED strings. In other words, in the configuration of Patent Document 2, when the time-division switching control of the voltage applied between the emitter and collector of the transistor of the constant current element is stopped, the driving current can be made to flow to a plurality of LED arrays at the same time. When the cathode voltage of the LED row to be monitored is the lowest (that is, the voltage drop due to the LED row to be monitored is the largest), a problem arises because the voltage necessary for driving is supplied to the LED row that is not to be monitored. If not, for example, when the cathode voltage of the LED row to be monitored is the highest (that is, the voltage drop due to the LED row to be monitored is the smallest), the output voltage of the booster circuit is combined with the cathode voltage. If it is controlled, it becomes impossible to supply a voltage necessary for driving in another LED string that requires a higher driving voltage.

  As a solution to the above problem, as disclosed in Patent Document 3, the lowest cathode voltage among the cathode voltages of all the LED strings is detected, and the detected voltage and the constant current element perform a constant current operation. And a method of comparing a low voltage (reference voltage) that can be controlled and controlling the output of the booster circuit based on the detected voltage. However, in this method, the cathode voltage of the LED strings other than the LED string having the lowest cathode voltage is higher than the minimum voltage required for the constant current driving unit to flow a predetermined current, and is not necessary for the constant current element. Since a high voltage is applied, extra power is lost in the constant current drive unit.

  FIG. 5 shows a configuration example of the light emitting device described in Patent Document 3. In FIG. 5, the lowest cathode voltage is detected from the cathode voltages Vdr, Vdg, Vdb of the LED rows 12r, 12g, 12b corresponding to red (r), green (g), and blue (b), respectively, and the detected voltage is detected. Is compared with the reference voltage Vref, and based on the comparison result, the boost controller 14 controls the output voltage Vout of the booster circuit 11 so that the detected voltage becomes equal to the reference voltage Vref. Here, the reference voltage Vref is a voltage necessary for the constant current circuits 16r, 16g, and 16b of the constant current drive units 13r, 13g, and 13b to stably operate at a constant current.

  For example, each LED of the red LED row 12r, each LED of the green LED row 12g, and each LED of the blue LED row 12b is made to emit light with a predetermined luminance, so that Ir (= 40 mA) and Ig (= 50 mA), respectively. ), And the constant current drive units 13r, 13g, and 13b are controlled so that a drive current of Ib (= 35 mA) flows. Further, the voltages necessary for driving the red, green, and blue LEDs are Vfr (= 2.3 V), Vfg (= 3.5 V), and Vfb (= 3.6 V), respectively, for each LED. At this time, the voltage drop generated in each LED row is Vfr × 4 = 9.2 V for the red LED row, Vfg × 4 = 14 V for the green LED row, and Vfb × 4 for the blue LED row, respectively. = 14.4V. In this case, the LED column to be controlled by the boost control unit 14 is the blue LED column 12b having the largest voltage drop and the lowest cathode voltage as a result. The boost control unit 14 determines from the output voltage Vout of the boost circuit 11. The output voltage Vout of the booster circuit is controlled so that the remaining cathode voltage Vdb obtained by subtracting the voltage drop (= 14.4V) in the blue LED row 12b becomes equal to the reference voltage Vref (= 1V). That is, the boost control unit 14 controls the boost circuit 11 so that Vout = 15.4V.

  However, in this case, the constant current circuits connected to the red and green LED strings 12r and 12g that are not controlled by the boost control unit 14 have Vout−Vfr × 4 = 6.2V and Vout−Vfg × 4 = 1. Since a voltage of 4V is applied and an originally unnecessary high voltage is applied, it causes unnecessary power consumption.

  As a solution to the above problem, as shown in FIG. 6, for each cathode voltage Vdr, Vdg, Vdb of the monitored LED string, a booster controller 14r, 14g, 14b and a booster circuit to be applied to the anode side of the LED string By providing 11r, 11g, and 11b one by one, it is conceivable to control the voltages VoutR, VoutG, and VoutB applied to the anode side of each LED row independently for each LED row. As many as these are required, which increases the manufacturing cost.

  The present invention has been made in view of the problems associated with the above-described prior art, and an object thereof is to have a plurality of LED strings and output voltage of a booster circuit based on the lowest cathode voltage among the plurality of LED strings. A light-emitting device that controls heat generation in the constant-current drive unit is reduced by reducing unnecessary power consumption in the constant-current drive unit of LED columns other than the LED column having the lowest cathode voltage. And a low power consumption lighting device and display device including the light emitting device.

  In order to achieve the above object, a light-emitting device according to the present invention includes a plurality of light-emitting element portions each having one light-emitting element or a plurality of light-emitting elements connected in series, and the input voltage is boosted and boosted. A step-up circuit that supplies a voltage to each of the plurality of light emitting element units; and the light emitting element unit that is connected to each of the plurality of light emitting element units and supplies a drive current to the light emitting element of the light emitting element unit; Detect the lowest first voltage among the same number of constant current drive units and the output terminal voltage of the light emitting element unit, compare the first voltage with a reference voltage, and control the booster circuit based on the comparison result A boosting control unit that generates a boosting control signal for performing, and among the light emitting element units, provided for each of the light emitting elements of at least one first light emitting element unit in which a plurality of the light emitting elements are connected in series, Connected in parallel with the light emitting element A bypass switch that bypasses a current flowing through the light emitting element, and a bypass switch control unit that controls on / off of the light emitting element of the first light emitting element unit for each light emitting element by controlling on / off of the bypass switch; And the output terminal of the booster circuit is connected to the input terminal of each of the plurality of light emitting element units, and the output terminal of the light emitting element unit is connected to the input terminal of the corresponding constant current driving unit. Calculating a voltage drop amount in each first light emitting element unit based on the number of lighting of the light emitting elements in each first light emitting element unit derived from the on / off state of the bypass switch in the first light emitting element unit. Then, the voltage at the output terminal of each of the first light emitting element units is calculated, and at least one of the constant current driving units connected to the first light emitting element unit is an output of the first light emitting element unit. When the voltage at the end is higher than the input voltage by the reference voltage or more, a current path is formed in which at least a part of the drive current supplied by the constant current drive unit flows to the input side of the booster circuit, and When the voltage at the output terminal of the light emitting element unit is not higher than the reference voltage than the input voltage, at least a part of the driving current supplied by the constant current driving unit is a predetermined fixed potential lower than the input voltage The first feature is that the first constant current driving unit is configured to form a current path flowing through the first constant current driving unit.

  Furthermore, in the light emitting device according to the present invention, in addition to the first feature described above, the bypass switch control unit is configured so that each of the first light emitting element units includes a light emitting element. By calculating the voltage drop amount, the voltage at the output terminal of each first light emitting element unit is calculated, the calculated voltage at the output terminal of each first light emitting element unit is compared with the input voltage, Forming a current path that flows to the input side of the booster circuit of the driving current supplied by the first constant current driving unit connected to the first light emitting element unit, and the first connecting to the first light emitting element unit A second feature is that a switching control signal for controlling formation of a current path that flows in the fixed potential of the driving current supplied by a constant current driving unit is generated.

  Further, in the light emitting device according to the present invention, in addition to the first or second feature, the first constant current driving unit is connected to the first constant current driving unit. A voltage path is higher than the input voltage by the reference voltage or more, a third current path forms a current path through which all of the drive current supplied by the first constant current drive unit flows to the input side of the booster circuit. Features.

  Furthermore, in the light emitting device according to the present invention, in addition to any of the first to third features, the first constant current driving unit is connected to the first constant current driving unit. When the output terminal voltage is lower than the input voltage, a fourth feature is that a current path is formed in which all of the drive current supplied by the first constant current drive unit flows to the fixed potential.

  Furthermore, in addition to any of the first to fourth features, the light emitting device according to the present invention compares the voltage of the output terminal of the first light emitting element section with the input voltage, by comparing each of the first light emitting devices. In addition to comparing the voltage at the output end of the first light emitting element unit calculated based on the number of lighting of the light emitting elements in the element unit with the input voltage, the voltage at the actual output end of the first light emitting element unit And the actual input voltage is referred to as a fifth feature.

  Furthermore, in the light emitting device according to the present invention, in addition to any of the first to fifth features, the first constant current driving unit includes a plurality of constant current circuits and one end of the plurality of constant current circuits. Each of the constant current circuits connected to each of the plurality of constant current circuits, the input terminals being connected to the other ends of the plurality of constant current circuits, and at least one of the output terminals being an input of the booster circuit. The output terminal not connected to the input side of the booster circuit is connected to the fixed potential, and the voltage at the output terminal of the first light emitting element unit connected to the first constant current drive unit is the input voltage. Higher than the constant current circuit, the constant current circuit has one end connected to the input side of the booster circuit and the other end connected to the output end of the first light emitting element unit. Activating the circuit, the voltage of the output terminal of the first light emitting element unit and the input Based on the difference between the pressure, the sixth feature of said drive current amount flowing to the constant current circuit of each is controlled.

  Further, in the light emitting device according to the present invention, in addition to the sixth feature, the voltage at the output terminal of the first light emitting element connected to the first constant current driver is higher than the reference voltage by the reference voltage. The seventh characteristic is that all of the constant current circuits whose one ends are not connected to the input side of the booster circuit among the constant current circuits of the first constant current drive unit are inactivated. .

  Furthermore, in addition to any of the first to seventh features, the light-emitting device according to the present invention includes the light-emitting element unit in which the boost control unit detects the first voltage among the plurality of light-emitting element units. When the constant current driver connected to the first constant current driver is the first constant current driver, a current path is formed in which all of the drive current supplied by the first constant current driver flows to the fixed potential. Eight features.

  Furthermore, in the light emitting device according to the present invention, in addition to any one of the first to eighth features, the bypass switch control unit combines on / off of the bypass switch with a target luminance of the light emitting element to be bypassed. The ninth feature is that the PWM control is performed.

  An illumination device according to the present invention includes the light emitting device having any one of the first to ninth characteristics.

  A display device according to the present invention includes the light emitting device having any one of the first to ninth characteristics.

  According to the light emitting device of the present invention, at least one first constant current driving unit among the constant current driving units has a voltage (cathode voltage) at the output end of the light emitting element unit (LED array) connected to its own input end. ) Is higher than the input voltage Vin of the booster circuit by a reference voltage or higher, the output terminal of itself is connected to the input side of the booster circuit. Thereby, a current path of a drive current that returns from the booster circuit to the input side of the booster circuit through the light emitting element unit (LED array) and the first constant current driver unit is formed. As a result, since the voltage applied to the constant current circuit of the first constant current drive unit is suppressed, the power consumed by the constant current circuit is reduced, and a light emitting device in which heat generation in the constant current drive unit is suppressed is provided. can do. Furthermore, the power consumption can be reduced by collecting a part of the driving current of the LED of the light emitting element portion as the input current of the booster circuit. In addition, since there is no need to provide a plurality of booster circuits as in the configuration example shown in FIG. 6, the effect of reducing power consumption can be obtained without increasing the manufacturing cost.

  Furthermore, the light-emitting device of the present invention is configured such that, among the light-emitting element units driven by the first constant current driving unit, each of the light-emitting elements of at least one first light-emitting element unit is connected in parallel with the light-emitting element. A bypass switch for bypassing a current flowing through the element is provided, and the bypass switch control unit controls turning on and off of each light emitting element for each light emitting element by controlling on / off of the bypass switch. With such a configuration, it is possible to control lighting / extinguishing for each light emitting element in accordance with the required target luminance, and based on the number of lighting of the light emitting elements of each first light emitting element unit, The difference of the voltage drop amount in each first light emitting element part can be calculated, and the voltage at the output terminal of each first light emitting element part can be calculated. Thus, the voltage at the output terminal of each light emitting element part and the input voltage Vin Can be obtained. Thus, it is possible to switch the output terminal of the first constant current driving unit to be connected to the input side of the booster circuit using the switching control signal from the bypass switch control unit.

  Therefore, by providing the light-emitting device of the present invention in a lighting device or a display device, a lighting device and a display device with low power consumption can be realized.

The circuit block diagram of the light-emitting device which concerns on 1st Embodiment of this invention. The figure which shows the circuit structure of a light emitting element part provided with a bypass switch, and a drive control method. The circuit block diagram of the light-emitting device which concerns on 2nd Embodiment of this invention. The circuit block diagram of the light-emitting device which concerns on 3rd Embodiment of this invention. The circuit block diagram of the light-emitting device which concerns on a prior art. The circuit block diagram of the light-emitting device which concerns on a prior art.

<First Embodiment>
FIG. 1 shows a configuration example of a light emitting device 1 according to an embodiment of the present invention (hereinafter, referred to as “the present device 1” as appropriate). As shown in the circuit configuration diagram of FIG. 1, the device 1 of the present invention includes a booster circuit 11, a bypass switch control unit 100, light emitting element units 101a and 101b, constant current drive units 13a and 13b, a boost control unit 14, and It consists of determination circuits (comparison units) 18a and 18b.

  The booster circuit 11 boosts the input voltage Vin (here, 5 V) from the power supply 10 based on the control signal 41 from the boost control unit 14, and the boosted voltage Vout and the output load current Iout are converted into the light emitting element units 101a, 101a, It supplies to each of 101b. If the drive currents flowing through the light emitting element portions 101a and 101b are Ia and Ib, respectively, the relationship of Iout = Ia + Ib is established. Assuming that the current flowing through the input terminal of the booster circuit 11 is Iin, the input power Pin is Pin = Vin × Iin, and the output power Pout is Pout = Vout × Iout. The efficiency α of the booster circuit is expressed by α = Pout / Pin.

  The light emitting element portions 101a and 101b, which are the first light emitting element portions, are each composed of an LED array in which one or more light emitting elements (here, four white LEDs) are connected in series, and the anode side of each LED array Since the output terminal of the booster circuit 11 is connected to the input terminal, the boosted output voltage Vout is supplied to each of the input terminals. On the other hand, the cathode side output end of each LED row is connected to the input end of the corresponding constant current drive unit (any one of 13a and 13b). Here, the output terminal voltages on the cathode side of each LED row connected to the constant current drive unit 13a or 13b are set to Vda and Vdb, respectively.

  The light emitting element portions 101a and 101b are further connected in parallel with the light emitting element of the light emitting element portion, and are provided with a bypass switch for bypassing the current flowing through the light emitting element. By controlling on / off for each light emitting element, the light emission and lighting of each light emitting element are controlled for each light emitting element together with the required target luminance. The bypass switch control unit 100 generates control signals 48a and 48b for controlling on / off of the bypass switch for each light emitting element.

  Below, with reference to FIG. 2, the specific circuit structure of a light emitting element part provided with a bypass switch and operation | movement of a bypass switch control part are demonstrated.

  The bypass switch control unit 100 is a PWM for controlling lighting and extinguishing of the light emitting elements LED01 to LED04 connected in series in the first light emitting element unit (here, 101a) in accordance with required target luminance. The signal 48a is generated and used as an input signal to the bypass switches SW1 to SW4, thereby switching the bypass switches SW1 to SW4 on and off. When the bypass switch is on, the current flowing through the LED connected in parallel to the bypass switch is bypassed and the LED is turned off. On the other hand, when the bypass switch is in the OFF state, the LEDs connected in parallel to the bypass switch are lit.

  FIG. 2A shows an example of a timing chart of the input signal 48a from the bypass switch control unit 100 to the bypass switch. In the present embodiment, the corresponding bypass switch is turned off when the input signal 48a is at a high level. In this case, since the bypass switches SW1 and SW3 are in the on state and the bypass switches SW2 and SW4 are in the off state at a certain time t1, as shown in FIG. 2B, the LED 01 and the LED 03 are turned off, and the LED 02 LED04 is turned on, and a current path is formed which flows from the anode side input end of the light emitting element portion to the cathode side output end via the bypass switches SW1, LED02, bypass switches SW3, LED04.

  At time t1, the number of light-emitting elements that are lit in the first light-emitting element unit 101a is two, LED02 and LED04. The bypass switch control unit 100 controls on / off of the bypass switch connected in parallel with the light emitting element of each first light emitting element unit, and at the same time uses information on the number of lighting of the light emitting elements of each first light emitting element unit. By calculating the amount of voltage drop due to lighting of the light emitting element of one light emitting element unit, switching control signals 47a and 47b for switching the current path returning to the input side of the booster circuit are generated. To 18b.

  The constant current driving unit 13a is a first constant current driving unit including a constant current circuit 16a and a changeover switch 17a, and the constant current driving unit 13b is a first constant current driving unit including a constant current circuit 16b and a changeover switch 17a. A drive current necessary for driving the light emitting element is supplied to either 101a or 101b. One end of the constant current circuit 16a is connected to the changeover switch 17a, and the other end is connected to the cathode side output terminal of the LED row of the light emitting element portion 101a. On the other hand, one end of the constant current circuit 16b is connected to the changeover switch 17b, and the other end is connected to the cathode side output terminal of the LED row of the light emitting element portion 101b.

  Each of the changeover switches 17a and 17b has one end connected to one end of a constant current circuit, and the other end connected to a predetermined fixed potential (here, based on control signals 46a and 46b from a determination circuit 18a or 18b described later). Then, it can be switched to either one of the input side of GND and the booster circuit 11. By connecting the other end of the changeover switch 17a to the input side of the booster circuit 11, the drive current returning from the booster circuit 11 to the input side of the booster circuit 11 via the light emitting element unit 101a and the constant current driver unit 13a. The current path or the other end of the changeover switch 17b is connected to the input side of the booster circuit 11, so that the input of the booster circuit 11 from the booster circuit 11 via the light emitting element unit 101b and the constant current drive unit 13b. A current path of the drive current returning to the side is formed. Here, the current driven by the constant current circuit 16a is Ia, and the current driven by the constant current circuit 16b is Ib.

  The step-up control unit 14 includes an output voltage Vda on the cathode side of the LED row of the light emitting element unit 101a connected to the constant current driving unit 13a, and a cathode side of the LED row of the light emitting element unit 101b connected to the constant current driving unit 13b. Output terminal voltage Vdb as an input, detects the lowest voltage (first voltage) of Vda and Vdb, compares the first voltage with the reference voltage Vref, and boosts the voltage based on the comparison result. A control signal 41 for controlling the output voltage Vout of the circuit 11 is generated. Here, the reference voltage Vref is a voltage necessary for the constant current circuits 16a and 16b to stably operate at a constant current, and is 1 V here. Although the reference voltage Vref varies depending on the configuration of the constant current circuit, it is desirable to set the reference voltage Vref as low as possible as long as the constant current operation can be stably performed. Further, the boost control unit 14 does not form a current path of the drive current that returns to the input side of the boost circuit 11 for any one of the constant current drive units 13a and 13b connected to the light emitting element unit in which the first voltage is detected. Control signals 44a and 44b to be output are output to determination circuits 18a and 18b, respectively.

  The determination circuits 18a and 18b determine the relationship between the output terminal voltages Vda and Vdb on the cathode side of the LED rows of the light emitting element portions 101a and 101b and the voltage of the input voltage Vin, respectively, and either Vda or Vdb. Is higher than the input voltage Vin by the reference voltage Vref or higher, the first constant current driving unit connected to the light emitting element unit in which the output terminal voltage higher than the input voltage Vin is detected by the reference voltage is used. Control signals 46a and 46b for switching the connection destination of the constant current circuit in the current driver to the input side of the booster circuit 11 are output to the changeover switches 17a and 17b.

  Here, for comparison between the cathode-side output terminal voltages Vda and Vdb and the input voltage Vin, information on the number of light-emitting elements of each first light-emitting element unit from the bypass switch control unit 100 can be used. Since the voltage Vf applied to the light emitting element of each first light emitting element unit is known, the voltage drop generated in the LED row of each first light emitting element unit is calculated based on the number of lighting of the light emitting elements of each first light emitting element unit. Can be calculated. On the other hand, the voltage drop that occurs in the LED string of the light emitting element unit that does not include the bypass switch is also known, and the output voltage on the cathode side of the LED string in which the lowest first voltage is detected is the output terminal voltage. Is controlled by the step-up control unit 14 so as to be equal to the sum of the fixed potential (GND) and the reference voltage Vref, whereby the output terminal voltage on the cathode side of the LED row of each first light emitting element unit can be calculated. . The bypass switch control unit 100 calculates, for example, a difference voltage between the cathode side output terminal voltage and the input voltage Vin of the LED row of each first light emitting element unit, and uses the determination circuit 18a and the switching control signals 47a and 47b, respectively. To 18b.

  Specifically, the determination circuit 18a determines whether the output terminal voltage Vda and the input voltage Vin of the first light emitting element unit 101a are high or low based on the switching control signal 47a, Vda is higher than Vin by the reference voltage Vref, and the first When the voltage does not correspond to the voltage, a control signal 46a for switching the connection destination of one end of the constant current circuit 16a to the input side of the booster circuit 11 is output to the changeover switch 17a. Further, the determination circuit 18a receives a control signal 44a from the boost control unit, and when Vda corresponds to the first voltage, control for switching the connection destination of one end of the constant current circuit 16a to a fixed potential (GND). The signal 46a is output to the changeover switch 17a.

  Similarly, the determination circuit 18b determines the magnitude of the output terminal voltage Vdb and the input voltage Vin of the first light emitting element unit 101b based on the switching control signal 47b, and Vdb is higher than Vin by the reference voltage and corresponds to the first voltage. If not, a control signal 46b for switching the connection destination of one end of the constant current circuit 16b to the input side of the booster circuit 11 is output to the changeover switch 17b. In addition, the determination circuit 18b receives a control signal 44b from the boost control unit, and when Vdb corresponds to the first voltage, control for switching the connection destination of one end of the constant current circuit 16b to a fixed potential (GND). The signal 46b is output to the changeover switch 17b.

  Here, as an example, for each light emitting element of the light emitting element unit 101a and each light emitting element of the light emitting element unit 101b, prescribed currents Ia (= 20 mA) and Ib are obtained in order to obtain a predetermined light emission amount at the time of lighting. (= 20 mA) is controlled by the constant current drive units 13a and 13b, which are first constant current drive units, so that a drive current flows, to drive each light emitting element of the light emitting element unit 101a and each light emitting element of the light emitting element unit 101b. For example, it is assumed that the necessary voltage Vf is about 3.6 V for each light emitting element. Further, the voltage drop in the ON state of each bypass switch is 1V.

  At a certain time t1, when two bypass switches of the light emitting element unit 101a are turned on, two light emitting elements are lit, all bypass switches of the light emitting element unit 101b are off, and four light emitting elements are lit. Then, the voltage drop generated in each LED row is 3.6V × 4 = 14.4V in the case of the light emitting element portion 101b and 3.6V × 2 + 1.0V × 2 = 9.2V in the case of the light emitting element portion 101a, respectively. Become. Therefore, the first voltage detected by the boost control unit 14 is the voltage Vdb on the cathode side of the LED column of the light emitting element unit 101b in which the voltage drop generated in the LED column is the largest and as a result the cathode voltage is the lowest. Therefore, the light emitting element portion 101b is subjected to boost control, and the boost control portion 14 determines that the remaining voltage Vdb obtained by subtracting the voltage drop (= 14.4V) in the light emitting element portion 101b from the output voltage Vout of the booster circuit is a fixed potential. The output voltage Vout of the booster circuit 11 is controlled to be equal to the sum of (GND) and the reference voltage Vref (= 1V). In other words, the boost control unit 14 outputs the control signal 41 for boosting to the booster circuit 11 so that Vout becomes 15.4 V obtained by adding the reference voltage to the voltage drop. As a result, the output terminal voltages on the cathode side of the LED rows of the respective light emitting element portions 101a and 101b are Vda = 15.4V−9.2V = 6.2V and Vdb = 1.0V (= Vref).

  Thus, the determination circuit 18a receives the switching control signal 47a from the bypass switch control unit 100 and the control signal 44a from the boost control unit, and Vda is higher than the reference voltage by more than Vin and does not correspond to the first voltage. A control signal 46a for switching the connection destination of the constant current circuit 16a of the current driver 13a to the input side of the booster circuit 11 is output to the changeover switch 17a. On the other hand, the determination circuit 18b is based on the switching control signal 47b from the bypass switch control unit 100 and the control signal 44b from the boost control unit, and Vdb corresponds to the first voltage. A control signal 46b for switching the connection destination of the circuit 16b to a fixed potential (GND) is output to the changeover switch 17b.

  As a result, all of the drive current supplied by the constant current drive unit 13a flows to the input side of the booster circuit 11, and from the booster circuit 11 to the input side of the booster circuit 11 through the light emitting element unit 101a and the constant current drive unit 13a. A return current path is formed. Here, since Vin = 5V, Vdr−Vin> Vref, and the constant current characteristic of the constant current circuit 16a is maintained.

  Further, by connecting the constant current driving unit 13a to the input side of the booster circuit 11, the voltage applied between the input and output terminals of the constant current circuit 16a is greatly reduced from 6.2V to 1.2V, and the constant current Power consumption in the circuit 16a is reduced, and heat generation in the constant current drive unit 13a is suppressed.

  Here, in order to simplify the calculation, assuming that the efficiency of the booster circuit is α = 1.0 (100%), the output power Pout of the booster circuit 11 is Pout = Vout × Iout = Vout × (Ia + Ib) = 15. 4V × (20 mA + 20 mA) = 616 mW. On the other hand, since the input power Pin of the booster circuit 11 is Pin × α = Pout, the input current Iin of the booster circuit 11 is Iin = Pout / Vin = 123 mA, but the current Ia is supplied from the constant current circuit 16a. Therefore, the power supply 10 only needs to supply an input current of Iin−Ia = 103 mA.

  Therefore, the input power viewed from the power source 10 is Pin ′ = Vin × (Iin−Ia) = 515 mW, which is Pin ′ / Pin as compared with the configuration of the related art in which all constant current circuits are connected to the fixed potential GND. = 515 mW / 616 mW = 0.836, and a power reduction effect of about 16% is obtained as compared with the prior art.

Second Embodiment
FIG. 3 shows a configuration example of a light emitting device 2 according to an embodiment of the present invention (hereinafter referred to as “the present device 2” as appropriate). As shown in the circuit configuration diagram of FIG. 3, the device 2 of the present invention includes a booster circuit 11, a bypass switch control unit 100, light emitting element units 101 a and 101 b that are first light emitting element units, constant current driving units 23 a and 23 b, The boosting control unit 14 and determination circuits (comparing units) 28a and 28b are configured. The device 2 of the present invention is different from the device 1 of the present invention in the configuration of the constant current drive unit. That is, each of the constant current driving units 23a and 23b has a plurality (two) of constant current circuits with different connection destinations therein, and the plurality of constant current drivers 23a and 23b are based on switching signals from the determination circuits 28a and 28b. This is a first constant current drive unit configured to be able to control the amount of drive current flowing in each of the current circuits. The configurations of the booster circuit 11, the bypass switch control unit 100, the light emitting element units 101a and 101b, and the boost control unit 14 are the same as those of the device 1 of the present invention according to the first embodiment, and thus description thereof is omitted.

  The constant current driving unit 23a includes constant current circuits 26a and 27a, and the constant current driving unit 23b includes constant current circuits 26b and 27b, each having two constant current circuits. One ends of the constant current circuits 26a and 26b are connected to the input side of the booster circuit 11, and one ends of the constant current circuits 27a and 27b are connected to a predetermined fixed potential (here, GND). On the other hand, the other ends of the constant current circuits 26a and 27a are the cathode side output ends of the LED rows of the light emitting element portion 101a, and the other ends of the constant current circuits 26b and 27b are the cathode side output ends of the LED rows of the light emitting element portion 101b. Each is connected in parallel. As a result, the current path of the drive current returning from the booster circuit 11 to the input side of the booster circuit 11 through the light emitting element unit 101a and the constant current circuit 26a of the constant current driver unit 23a, and the constant current circuit from the booster circuit 11 to the light emitting element unit 101b. It is possible to form a current path of a drive current that returns to the input side of the booster circuit 11 through the constant current circuit 26b of the current driver 23b.

  Furthermore, the constant current drive unit 23a receives control signals 42a and 43a from a determination circuit 28a described later, thereby controlling the amount of current flowing through the constant current circuits 26a and 27a of the constant current drive unit 23a. Similarly, the constant current drive unit 23b receives control signals 42b and 43b from a determination circuit 28b described later, thereby controlling the amount of current flowing through the constant current circuits 26b and 27b of the constant current drive unit 23b. Here, the current driven by the constant current circuit 26a is Ia1, the current driven by the constant current circuit 27a is Ia2, the current driven by the constant current circuit 26b is Ib1, and the current driven by the constant current circuit 27b is Ib2. Then, the drive current Ia flowing through the light emitting element portion 101a is Ia = Ia1 + Ia2, the drive current Ib flowing through the light emitting element portion 101b is Ib = Ib1 + Ib2, and the total current Ia flowing through the constant current circuits 26a and 27a is constant and constant. The currents Ia1, Ib1, Ia2, and Ib2 driven by the individual constant current circuits 26a, 26b, 27a, and 27b are controlled so that the total current Ib flowing through the current circuits 26b and 27b is constant in the stable state. Is done.

  The determination circuits 28a and 28b determine the relationship between the output terminal voltages Vda and Vdb on the cathode side of the LED rows of the first light emitting element portions 101a and 101b and the input voltage Vin, and any of Vda and Vdb is determined. Is higher than the input voltage Vin, the first constant current drive unit is connected to the first constant current drive unit connected to the first light emitting element unit in which the output voltage higher than the input voltage Vin is detected. Among the constant current circuits, a control signal is output that enables use of a constant current circuit having one end connected to the input side of the booster circuit 11.

  Specifically, the determination circuit 28 a determines whether the output terminal voltage Vda and the input voltage Vin of the first light emitting element unit 101 a are high or low based on the switching control signal 47 a from the bypass switch control unit 100, and outputs from the boost control unit 14. Control signal 42a that enables use of constant current circuit 26a of constant current drive unit 23a, which is the first constant current drive unit, when Vda is higher than Vin and does not correspond to the first voltage by calculation with control signal 44a. Is output to the constant current drive unit 23a. Further, when Vda is higher than Vin and does not correspond to the first voltage, but Vda is not higher than Vin by a reference voltage or higher, the constant current circuit 26a alone cannot supply a current necessary for driving the light emitting element portion 101a. Therefore, the control signal 43a for compensating for the insufficient drive current using the constant current circuit 27a is output to the constant current drive unit 23a, and the constant current required for driving is supplied by the constant current circuits 26a and 27a. To do. On the other hand, when Vda is lower than Vin, the determination circuit 28a outputs a control signal 42a that disables the constant current circuit 26a to the constant current driving unit 23a, and is connected to a fixed potential. A constant current required for driving is supplied using only 27a. Further, the determination circuit 28a receives the control signal 44a from the boost control unit 14, and when Vda corresponds to the first voltage, the determination circuit 28a inactivates the constant current circuit 26a of the constant current drive unit 23a, and constant current circuit 27a. The control signals 42a and 43a using only the current are output to the constant current drive unit 23a.

  Similarly, the determination circuit 28b determines the magnitude of the output terminal voltage Vdb and the input voltage Vin of the first light emitting element unit 101b based on the switching control signal 47b from the bypass switch control unit 100, and the control signal from the boost control unit 14 44b, when Vdb is higher than Vin and does not correspond to the first voltage, a control signal 42b for making the constant current circuit 26b of the constant current drive unit 23b, which is the first constant current drive unit, available. It outputs to the constant current drive part 23b. Further, when Vdb is higher than Vin and does not correspond to the first voltage, but Vdb is not higher than Vin by a reference voltage or higher, the constant current circuit 26b alone cannot supply a current necessary for driving the light emitting element portion 101b. Therefore, the control signal 43b for compensating for the insufficient driving current using the constant current circuit 27b is output to the constant current driving unit 23b, and the constant current required for driving is supplied by the constant current circuits 26b and 27b. To do. On the other hand, when Vdb is lower than Vin, the determination circuit 28b outputs a control signal 42b that disables the constant current circuit 26b to the constant current driving unit 23b, and is connected to a fixed potential. A constant current required for driving is supplied using only 27b. In addition, the determination circuit 28b receives the control signal 44b from the boost control unit 14, and when Vdb corresponds to the first voltage, the determination circuit 28b inactivates the constant current circuit 26b of the constant current drive unit 23b, and constant current circuit 27b. The control signals 42b and 43b using only the current are output to the constant current driving unit 23b.

  Thus, when Vda is higher than Vin and does not correspond to the first voltage, the drive returns from the booster circuit 11 to the input side of the booster circuit 11 through the light emitting element unit 101a and the constant current circuit 26a of the constant current drive unit 23a. When the current path of the current or Vdb is higher than Vin and does not correspond to the first voltage, the booster circuit 11 passes through the light emitting element unit 101b and the constant current circuit 26b of the constant current drive unit 23b. Current paths for driving currents returning to the input side are formed.

  Here, as in the first embodiment, as an example, for each LED of the light emitting element unit 101a and each LED of the light emitting element unit 101b, a predetermined current Ia ( = 20 mA) and Ib (= 20 mA) are controlled by the constant current driving units 13a and 13b so that the driving current flows, and the voltages necessary for driving the LEDs of the light emitting element unit 101a and the LEDs of the light emitting element unit 101b Assume that Vf is about 3.6 V per LED, for example. Further, the voltage drop amount in the ON state of each bypass switch is set to 1V. At a certain time t1, when two bypass switches of the light emitting element unit 101a are turned on, two light emitting elements are lit, all bypass switches of the light emitting element unit 101b are off, and four light emitting elements are lit. Then, the voltage drop generated in each LED row is 3.6V × 4 = 14.4V in the case of the light emitting element portion 101b and 3.6V × 2 + 1.0V × 2 = 9.2V in the case of the light emitting element portion 101a, respectively. Become. Therefore, the light emitting element unit 101b is subjected to boost control, and the boosting control unit 14 fixes the remaining voltage Vdb obtained by subtracting the voltage drop (= 14.4V) in the light emitting element unit 101b from the output voltage Vout of the booster circuit. The output voltage Vout of the booster circuit 11 is controlled so as to be equal to the sum of the potential (GND) and the reference voltage Vref (= 1V). That is, the boost control unit 14 outputs the control signal 41 for boosting to the booster circuit 11 so that Vout = 15.4V. As a result, the output terminal voltages on the cathode side of the LED rows of the respective light emitting element portions 101a and 101b are Vda = 15.4V−9.2V = 6.2V and Vdb = 1.0V (= Vref).

  In this case, the determination circuit 28a receives the switching control signal 47a from the bypass switch control unit and the control signal 44a from the boost control unit, and since Vda is higher than Vin and does not correspond to the first voltage, the constant current driving unit 23a The control signal 42a for enabling the constant current circuit 26a is output to the constant current drive unit 23a. On the other hand, the determination circuit 28b receives the switching control signal 47b from the bypass switch control unit and the control signal 44b from the boost control unit, and Vdb corresponds to the first voltage, so that the constant current circuit 26b of the constant current drive unit 23b is changed. The control signals 42b and 43b that are deactivated and use only the constant current circuit 27b are output to the constant current drive unit 23b.

  As a result, at least a part of the drive current supplied by the constant current drive unit 23a flows to the input side of the booster circuit 11, and from the booster circuit 11 through the light emitting element unit 101a and the constant current circuit 26a of the constant current drive unit 23a. A current path returning to the input side of the booster circuit 11 is formed.

  At this time, the current driven by the constant current circuit 27a is such that the sum of the current Ia1 driven by the constant current circuit 26a and the current Ia2 driven by the constant current circuit 27a is Ia1 + Ia2 = 20 mA (= Ia). It is controlled by the control signal 43a. Now, since Vin = 5V, Vda−Vin> Vref, the constant current circuit 27a connected to the fixed potential (GND) is not used, is deactivated, and is connected to the input side of the booster circuit 11 Even if only 26a is used, the constant current characteristic of the constant current circuit 26a can be maintained. For this reason, the determination circuit 28a outputs a control signal 43a for inactivating the constant current circuit 27a of the constant current drive unit 23a to the constant current drive unit 23a.

  As a result, the constant current circuit 26a of the constant current drive unit 23a is connected to the input side of the booster circuit 11, and the constant current circuit 27a is deactivated so that the voltage applied to the constant current circuit 26a is 6.2V. To 1.2V, the power consumption in the constant current drive unit 23a is reduced, and heat generation is suppressed.

  Further, a part of the current necessary for driving the light emitting element (here, Ia1 (= Ia)) is returned to the input side of the booster circuit 11 and used as a part of the input current Iin of the booster circuit 11, thereby providing a power source. The input power viewed from 10 is reduced, and as in the inventive device 1 according to the first embodiment, a power reduction effect of about 16% is achieved as compared with the configuration of the prior art in which all constant current circuits are connected to GND. can get.

  Furthermore, the device 2 of the present invention according to the above embodiment includes a constant current circuit having one end connected to the fixed potential and a constant current circuit having one end connected to the input side of the booster circuit for each of the constant current driving units 23a and 23b. And the amount of current driven by each constant current circuit is controlled by a control signal. By doing so, the potential at one end of each constant current circuit is always maintained at a constant value of either the fixed potential or the input voltage. As a result, the constant current circuit becomes a problem when the constant current circuit is configured as a source follower circuit, as compared with the device 1 of the present invention that switches and controls the output destination of one end of one constant current circuit for each constant current drive unit. It is possible to avoid fluctuations in the source potential accompanying switching of the output destination at one end of the current circuit, and the constant current driving unit can perform stable constant current operation.

<Third Embodiment>
FIG. 4 shows a configuration example of a light emitting device 3 according to an embodiment of the present invention (hereinafter, appropriately referred to as “present invention device 3”). As shown in the circuit configuration diagram of FIG. 4, the device 3 of the present invention includes a booster circuit 11, a bypass switch control unit 100, light emitting element units 101a and 101b that are first light emitting element units, and a first constant current driving unit. The constant current drive units 23a and 23b, the boost control unit 14, and the comparison units 35a and 35b each including a determination circuit and a comparator. In addition to the features of the inventive device 2 according to the second embodiment, the inventive device 3 compares the actual output terminal voltage on the cathode side of the LED columns of the light emitting element portions 101a and 101b with the actual input voltage Vin. Comparators 39a and 39b are further provided.

  The comparison units 35a and 35b are each composed of a determination circuit 38a and a comparator 39a, a determination circuit 38b and a comparator 39b, and output terminal voltages Vda and Vdb and input voltages on the cathode side of the LED rows of the respective light emitting element portions 101a and 101b. A constant current connected to the light emitting element portion in which an output terminal voltage higher than the input voltage Vin is detected is determined when the voltage relationship with Vin is determined and either Vda or Vdb is higher than the input voltage Vin. A control signal that enables use of a constant current circuit having one end connected to the input side of the booster circuit 11 among the constant current circuits in the constant current drive unit is output to the drive unit.

  Specifically, the comparator 39a refers to the actual output terminal voltage on the cathode side of the LED array of the first light emitting element unit 101a and the actual input voltage Vin. When Vda is higher than Vin, the comparator 39a is a constant current circuit. A control signal 45a enabling the use of 26a is output to the determination circuit 38a. Then, the determination circuit 38a calculates Vda higher than Vin by calculation of the control signal 45a from the comparator 39a, the switching control signal 47a from the bypass switch control unit, and the control signal 44a from the boost control unit 14. When the voltage does not correspond to one voltage, the control signal 42a for enabling the constant current circuit 26a of the constant current drive unit 23a is output to the constant current drive unit 23a. When Vda is higher than Vin and does not correspond to the first voltage, but Vda is not higher than Vin by a reference voltage or more, the determination circuit 38a is necessary for driving the light emitting element portion 101a only by the constant current circuit 26a. Since a constant current cannot be supplied, a control signal 43a for compensating for an insufficient drive current using the constant current circuit 27a is output to the constant current drive unit 23a, and the constant current required for driving by the constant current circuits 26a and 27a is output. To supply. On the other hand, the determination circuit 38a outputs a control signal 42a that disables the use of the constant current circuit 26a to the constant current drive unit 23a when Vda is lower than Vin, and is connected to a fixed potential. A constant current required for driving is supplied using only 27a. Further, when Vda corresponds to the first voltage, the determination circuit 38a deactivates the constant current circuit 26a of the constant current drive unit 23a and sets the control signals 42a and 43a using only the constant current circuit 27a to the constant current circuit 27a. It outputs to the current drive part 23a.

  Similarly, the comparator 39b refers to the actual output terminal voltage on the cathode side of the LED row of the first light emitting element unit 101b and the actual input voltage Vin. When Vdb is higher than Vin, the comparator 39b sets the constant current circuit 26b. A control signal 45b that can be used is output to the determination circuit 38b. Then, the determination circuit 38b calculates Vdb higher than Vin by calculation of the control signal 45b from the comparator 39b, the switching control signal 47b from the bypass switch control unit, and the control signal 44b from the boost control unit 14, and When the voltage does not correspond to one voltage, the control signal 42b for enabling the constant current circuit 26b of the constant current drive unit 23b is output to the constant current drive unit 23b. Further, when Vdb is higher than Vin and does not correspond to the first voltage, but Vdb is not higher than Vin by a reference voltage or more, the determination circuit 38b is necessary for driving the light emitting element unit 101b only by the constant current circuit 26b. A constant current required for driving by the constant current circuits 26b and 27b is output to the constant current drive unit 23b by supplying a control signal 43b for compensating for the insufficient drive current using the constant current circuit 27b. To supply. On the other hand, when Vdb is lower than Vin, the determination circuit 38b outputs a control signal 42b that disables the constant current circuit 26b to the constant current drive unit 23b, and is connected to a fixed potential. A constant current required for driving is supplied using only 27b. Further, when Vdb corresponds to the first voltage, the determination circuit 38b deactivates the constant current circuit 26b of the constant current drive unit 23b, and sets the control signals 42b and 43b using only the constant current circuit 27b. It outputs to the current drive part 23b.

  Other booster circuit 11, bypass switch control unit 100, light emitting element units 101a and 101b, constant current drive units 23a and 23b, constant current circuits 26a, 26b, 27a and 27b in the constant current drive unit, and boost control unit 14 Since the configuration is the same as that of the device 2 of the present invention according to the second embodiment described above, the description thereof is omitted.

  As described above, the cathode-side output terminal voltages Vda and Vdb can be calculated from the number of lighting of the light emitting elements of the first light emitting element units by the switching control signals 47a and 47b from the bypass switch control unit 100. However, the voltage Vf applied to each light-emitting element has a characteristic variation at the time of manufacture, and also fluctuates due to a characteristic change or deterioration due to temperature. Therefore, only the switching control signal from the bypass switch control unit is used. And voltage comparison with the input voltage Vin may not be performed correctly.

  In the device 3 of the present invention, as a result of turning on and off the bypass switch, the difference in the number of light emitting elements of the first light emitting element portions 101a and 101b decreases, and the voltage difference between the output terminals on the cathode side of each LED row decreases. In addition, a voltage comparison result between the actual output voltage Vda or Vdb on the cathode side and the input voltage Vin of the actual booster circuit by the comparators 39a and 39b is used to control the control signal 45a from the comparator 39a and the comparator 39b. The constant current drive units 23a and 23b are controlled using the control signal 45b from As a result, even if the forward voltage Vf of each LED has a characteristic variation, or the forward voltage Vf fluctuates due to a characteristic change or deterioration due to temperature, the switching determination of the constant current circuit is stably performed. It can be carried out.

  On the other hand, when the difference in the number of lighting of the light emitting elements of the first light emitting element portions 101a and 101b increases and the voltage difference between the cathode side output terminals of each LED row increases, there is a relationship between the voltage levels of the output terminals. When it is clear that the switching is not performed, the switching control signal 47a from the bypass switch control unit 100 is referred to without referring to the actual output voltage Vda or Vdb on the cathode side and the input voltage Vin of the actual booster circuit. , 47b only, switching determination of the constant current circuit can be performed.

  Therefore, the device 3 of the present invention has the characteristic variation of the forward voltage Vf of each LED in the light emitting element portions 101a and 101b at the time of manufacture, the fluctuation of the forward voltage Vf due to the characteristic change or deterioration due to the temperature, and the boosting. The constant current circuit can be switched stably in consideration of the fluctuation of the input voltage Vin of the circuit, and the cost for selecting the characteristics of the LED can be reduced.

  The above-described embodiment is an example of a preferred embodiment of the present invention. The embodiment of the present invention is not limited to this, and various modifications can be made without departing from the gist of the present invention.

  <1> In the first to third embodiments described above, the configuration in which two light emitting element portions (LED arrays) 101a and 101b in which four white light emitting elements are connected in series is connected in parallel has been described as an example. The number of light emitting element units connected in parallel with the output terminal of the booster circuit 11, and the number and color of light emitting elements in each light emitting element unit are only examples, and two parallel, four series connected, white LEDs It is not limited to this configuration. For example, as shown in FIG. 5, a plurality of light emitting element portions 12r in which a plurality of red light emitting elements are connected in series, a light emitting element portion 12g in which a plurality of green light emitting elements are connected in series, and a plurality of blue light emitting elements. The present invention is applied to a configuration in which the light emitting element portions 12b connected in series are connected in parallel to the output terminal of the booster circuit 11, and a light emitting device with reduced power consumption can be realized.

  <2> In the first to third embodiments described above, since the first light emitting element portion connected in parallel to the output terminal of the booster circuit 11 is two, 101a and 101b, the input side of the booster circuit 11 The first constant current driver that can be connected to the first light emitting element is connected to the first light emitting element having the higher output voltage of Vda and Vdb. However, when there are three or more first light emitting element units connected in parallel with the output terminal of the booster circuit 11, the output terminal voltage of the first light emitting element unit is higher than Vin and lowest. If the voltage does not correspond to the first voltage, further power reduction effect can be expected by connecting the output terminals of the plurality of constant current driving units connected to the first light emitting element unit to the input side of the booster circuit 11 respectively. .

  <3> In the third embodiment described above, the comparator 39a and 39b are used to refer to the actual output voltage Vda or Vdb on the cathode side and the input voltage Vin of the actual booster circuit, and from the bypass switch control unit 100 Although the configuration for performing the switching determination of the constant current circuit is disclosed together with the switching control signals 47a and 47b, the same configuration is also possible for the inventive device 1 according to the first embodiment. That is, the determination circuits 18a and 18b receive the voltage comparison result between the actual cathode-side output terminal voltage Vda or Vdb and the actual booster circuit input voltage Vin as a control signal for switching determination. Even when the forward voltage Vf has a characteristic variation or the forward voltage Vf fluctuates due to a characteristic change or deterioration due to temperature, the switching determination of the constant current circuit can be performed stably.

  <4> In the first to third embodiments described above, the bypass switch control unit 100 calculates the voltage drop amount in each first light emitting element unit based on the number of lighting of the light emitting elements in each first light emitting element unit, and The configuration of calculating the voltage at the output terminal of the first light emitting element unit and outputting the difference voltage from the input voltage as the switching control signal is illustrated. However, the bypass switch control unit 100 turns on the light emitting element of each first light emitting element unit. It is also possible to output the number information as a switching control signal, and another circuit such as a determination circuit calculates the voltage at the output terminal of each first light emitting element unit and determines the level of the voltage with respect to the input voltage. .

  The present invention can be used for a light-emitting device using a plurality of LEDs as a light source, and can be used for an illumination device and a display device including the light-emitting device.

1-3: Light-emitting device 10 according to the present invention: Power supply 11, 11r, 11g, 11b: Booster circuit 12r, 12g, 12b, 101a, 101b: Light-emitting element unit (LED array)
13r, 13g, 13b, 13a, 23a, 23b: constant current drive units 14, 14r, 14g, 14b: boost control units 16r, 16g, 16b, 26a, 26b, 27a, 27b: constant current circuits 17a, 17b: changeover switches 18a, 18b, 28a, 28b, 38a, 38b: determination circuits 35a, 35b: comparison units 39a, 39b: comparators 41, 42a, 42b, 43a, 43b, 44a, 44b, 45a, 45b, 46a, 46b: control signals 47a, 47b: switching control signals 48a, 48b from the bypass switch control unit: control signals (PWM signals)
100: Bypass switch control unit Iin: Input current Iout of the booster circuit: Output currents Ir, Ig, Ib, Ia, Ia1, Ia2, Ib1, Ib2: LED drive currents SW1 to SW4: Bypass switches Vdr, Vdg, Vdb , Vda: Voltage on the cathode side of the LED string Vin: Input voltages Vout, VoutR, VoutG, VoutB of the booster circuit: Output voltage of the booster circuit

Claims (11)

A plurality of light emitting element units each having one light emitting element or a plurality of light emitting elements connected in series;
A boosting circuit that boosts an input voltage and supplies the boosted voltage to each of the plurality of light emitting element units;
A plurality of light emitting element units connected to each of the light emitting element units, and the same number of constant current driving units as the light emitting element units for supplying a driving current to the light emitting elements of the light emitting element units;
The lowest first voltage among the voltages at the output terminals of the light emitting element part is detected, the first voltage is compared with a reference voltage, and a boost control signal for controlling the booster circuit is generated based on the comparison result A boost control unit that
Among the light emitting element units, a plurality of the light emitting elements are provided for each light emitting element of at least one first light emitting element unit connected in series, and connected in parallel with one light emitting element, A bypass switch for bypassing the flowing current;
A bypass switch control unit that controls on / off of the light emitting element of the first light emitting element unit for each light emitting element by controlling on / off of the bypass switch;
An output terminal of the booster circuit is connected to each input terminal of the plurality of light emitting element units,
The output ends of the light emitting element portions are connected to the input ends of the corresponding constant current drive portions, respectively.
A voltage drop amount in each first light emitting element unit is calculated based on the number of lighting of the light emitting elements of each first light emitting element unit derived from the on / off state of the bypass switch in each of the first light emitting element units. Thus, the voltage at the output terminal of each first light emitting element unit is calculated,
At least one of the constant current driving units connected to the first light emitting element unit is:
When the voltage at the output terminal of the first light emitting element unit is higher than the input voltage by the reference voltage or more, at least a part of the driving current supplied by the constant current driving unit flows to the input side of the booster circuit Form a pathway,
When the voltage at the output terminal of the first light emitting element unit is not higher than the reference voltage than the input voltage, at least a part of the driving current supplied by the constant current driving unit is lower than the input voltage. A light-emitting device, wherein the light-emitting device is a first constant-current drive unit configured to form a current path that flows to a fixed potential. The bypass switch control unit
By calculating the voltage drop amount in each first light emitting element unit based on the number of lighting of the light emitting elements in each first light emitting element unit, the voltage at the output terminal of each first light emitting element unit is calculated,
Comparing the calculated voltage of the output terminal of each first light emitting element unit with the input voltage;
Forming a current path that flows to the input side of the booster circuit of the drive current supplied by the first constant current driver connected to the first light emitting element, and the first connected to the first light emitting element. The light-emitting device according to claim 1, wherein a switching control signal for controlling formation of a current path that flows in the fixed potential of the driving current supplied by one constant current driving unit is generated. The first constant current driving unit includes:
When the voltage at the output terminal of the first light emitting element connected to the first constant current driver is higher than the input voltage by the reference voltage or more, all of the drive current supplied by the first constant current driver The light emitting device according to claim 1, wherein a current path that flows to an input side of the booster circuit is formed. The first constant current driving unit includes:
When the voltage at the output terminal of the first light emitting element connected to the first constant current driver is lower than the input voltage, all of the drive current supplied by the first constant current driver is the fixed potential. The light-emitting device according to any one of claims 1 to 3, wherein a current path that flows through the current path is formed.   The voltage of the output terminal of the first light emitting element unit calculated by comparing the voltage of the output terminal of the first light emitting element unit and the input voltage based on the number of lighting of the light emitting element of each first light emitting element unit. 5 is performed with reference to the actual output voltage and the actual input voltage of the first light-emitting element section together with the comparison with the input voltage. The light emitting device according to one item. The first constant current driving unit includes:
A plurality of constant current circuits, and the same number of output terminals as the constant current circuits respectively connected to one end of each of the plurality of constant current circuits,
An input end is connected to each of the other ends of the plurality of constant current circuits,
At least one of the output terminals is connected to an input side of the booster circuit;
The output terminal not connected to the input side of the booster circuit is connected to the fixed potential,
When the voltage at the output terminal of the first light emitting element connected to the first constant current driving unit is higher than the input voltage,
Among the constant current circuits of the first constant current driving unit, one end is connected to the input side of the booster circuit, and the other end is activated to the constant current circuit connected to the output end of the first light emitting element unit,
6. The drive current amount flowing through each of the constant current circuits is controlled based on a difference between an output terminal voltage of the first light emitting element unit and the input voltage. The light emitting device according to one item. When the voltage of the output terminal of the first light emitting element unit connected to the first constant current driving unit is higher than the reference voltage than the input voltage,
7. The constant current circuit of the first constant current drive unit is deactivated for all the constant current circuits whose one ends are not connected to the input side of the booster circuit. Light-emitting device.   Among the plurality of light emitting element units, when the constant current driving unit connected to the light emitting element unit in which the boosting control unit detects the first voltage is the first constant current driving unit, the first constant current driving is performed. The light emitting device according to claim 1, wherein a current path in which all of the driving current supplied by the unit flows to the fixed potential is formed.   The light-emitting device according to any one of claims 1 to 8, wherein the bypass switch control unit performs PWM control on and off of the bypass switch in accordance with a target luminance of the light-emitting element to be bypassed.   An illuminating device comprising the light emitting device according to claim 1.   A display device comprising the light-emitting device according to claim 1.

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