JP2011253957A - Light-emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize change of loss for variation of power supply voltage and to simplify the circuitry.SOLUTION: When the power supply voltage Vs varies (drops), a driving current Iflowing to a light source 1 decreases. However, as the variation of the power supply voltage Vs (droppage for a rated voltage) increases, control means 4 controls selection means 2 to increase the number of light-emitting diodes LDi selected (short-circuited) not to feed the driving current Iand to decrease the number of light-emitting diodes LDj selected to feed the driving current I. In other words, the light-emitting device according to an embodiment utilizes a resistance component existing in the light-emitting diode LD as a current limit element and decreases the number of light-emitting diodes LDj through which the driving current Iflows according to variation of an input voltage (power supply voltage Vs). Consequently, change (increase) of loss for variation of the power supply voltage Vs is minimized and the circuitry can be simplified.

Description

  The present invention relates to a light emitting device using a solid light emitting element such as a light emitting diode as a light source.

  Conventionally, various types of light emitting devices using light emitting diodes, which are one type of solid state light emitting elements, as light sources have been provided. For example, Patent Literature 1 describes an LED display device that lights and displays a battery capacity. In this conventional device, a series circuit of a plurality of light emitting diodes is connected between the positive and negative electrodes of a battery, and a switch is connected between the positive electrode of the battery and the cathode of each light emitting diode, and the number of switches that are simultaneously turned on is determined. The battery capacity is displayed by switching and increasing / decreasing the number of light emitting diodes. In Patent Document 1, instead of providing a power supply circuit for stabilizing the battery voltage, a current limiting resistor is connected in series to a series circuit of light emitting diodes, thereby stabilizing the current flowing through the light emitting diodes. Embodiments that are intended to be disclosed are also disclosed.

Japanese Patent Laying-Open No. 2004-279668 (see paragraphs 0049 to 0053 and FIG. 4)

  However, the conventional device described in Patent Document 1 requires a power supply circuit and a current limiting resistor in order to stabilize the current (drive current) that flows through the light emitting diode. In recent years, the drive current has been increasing as the output of light emitting diodes has increased, and as the drive current has increased, electronic components used in power circuits (especially passive components such as inductors and transformers) have become larger. In addition, there is a problem that the circuit configuration of the power supply circuit becomes complicated, and a loss of the current limiting resistor greatly changes due to power supply voltage fluctuation.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a light emitting device capable of suppressing a change in loss with respect to fluctuations in power supply voltage and simplifying a circuit configuration.

  The light-emitting device of the present invention comprises a light source comprising a plurality of solid-state light-emitting elements connected in series, a solid-state light-emitting element that causes a driving current to flow in the light source, and a selection unit that selects a solid-state light-emitting element that does not pass the driving current; A detection unit that detects a state of the light source; a solid-state light-emitting element that controls the selection unit so as to suppress a change in the detection result when a change occurs in the detection result of the detection unit; And a control means for selecting a solid state light emitting element that does not pass a driving current.

  In the light emitting device, it is preferable that the detection unit detects the drive current, and the control unit controls the selection unit so as to suppress fluctuations in the drive current detected by the detection unit.

  In this light-emitting device, it is preferable that the detection unit detects a light output of the light source, and the control unit controls the selection unit so as to suppress a variation in the light output detected by the detection unit.

  In this light emitting device, the detection means detects an input voltage input to the light source, and the control means controls the selection means so as to suppress fluctuations in the input voltage detected by the detection means. Is preferred.

  In the light emitting device, the detection unit detects input power input to the light source, and the control unit controls the selection unit so as to suppress fluctuations in the input power detected by the detection unit. Is preferred.

  In this light-emitting device, the selection means has one or more switch elements for short-circuiting both ends of the solid-state light-emitting element, and the control means controls on / off of the switch elements to flow a driving current. It is preferable to select a solid light-emitting element and a solid light-emitting element that does not pass the driving current.

  In this light emitting device, it is preferable that the switch element is provided for every solid light emitting element.

  In this light-emitting device, the selection unit includes one or more switch elements that are connected to one end of the light source and one end of the solid-state light-emitting element and short-circuit both ends of the solid-state light-emitting element, and the control unit includes the control unit It is preferable to select a solid-state light-emitting element that allows a drive current to flow by controlling on / off of the switch element and a solid-state light-emitting element that does not flow the drive current.

  The light-emitting device includes an inductor connected in series with the light source, and the selection unit includes one or more switch elements that collectively short-circuit the plurality of solid-state light-emitting elements connected in series. It is preferable that the means select a solid light-emitting element that allows a drive current to flow by controlling on / off of the switch element and a solid light-emitting element that does not flow the drive current.

  In this light-emitting device, the number of the solid-state light-emitting elements constituting the light source is preferably a number that makes the total forward voltage of the solid-state light-emitting elements larger than the maximum value of the input voltage.

  In this light emitting device, the number of the solid state light emitting elements that are collectively short-circuited by the switch element is preferably such that the total forward voltage of the solid state light emitting elements is larger than the fluctuation value of the input voltage.

  In this light-emitting device, the solid-state light-emitting element includes a mounting substrate on which the solid-state light-emitting element is mounted, the solid-state light-emitting element that is collectively short-circuited by the switch element, and the solid-state light-emitting element that is not short-circuited collectively by the switch element It is preferable that the mounting surfaces of the mounting substrate are arranged substantially evenly.

  In this light emitting device, it is preferable that the inductor includes a plurality of inductance elements connected in series with the solid state light emitting element.

  In the light emitting device, it is preferable that the control unit performs on / off control of the plurality of switch elements in a time division manner.

  In the light emitting device, it is preferable that the control unit performs on / off control so that a sum of ON periods of the plurality of switch elements is substantially constant.

  In this light emitting device, it is preferable that the switch element is turned on / off by an optical signal output from the control means.

  In this light emitting device, it is preferable that the control means controls an on-duty ratio of the switch element.

  In this light emitting device, it is preferable that the control means sequentially replaces the switch elements to be turned on / off.

  In this light emitting device, it is preferable that the control means randomly switches the switch elements to be turned on / off.

  In the light emitting device, it is preferable that the control unit performs on / off control so that a sum of ON periods of the plurality of switch elements is substantially constant.

  In this light-emitting device, it is preferable that the control means obtains an operating power source from both ends of the one or more solid-state light-emitting elements via rectifier elements.

  This light-emitting device preferably includes voltage conversion means for converting a power supply voltage of an external power supply into an input voltage of the light source.

  In this light emitting device, the voltage converting means includes one or more capacitors charged by the external power source, a switching element that opens and closes a charging path to the capacitor and a discharging path from the capacitor, and the switching element. It is preferable that an open / close control means for performing open / close control is provided, and a discharge voltage of the capacitor is used as an input voltage of the light source.

  In this light emitting device, the voltage converting means includes one or more capacitors charged by the external power source, a switching element that opens and closes a charging path to the capacitor and a discharging path from the capacitor, and the switching element. It is preferable that an open / close control means for performing open / close control is provided, and a voltage obtained by superimposing a discharge voltage of the capacitor on a power supply voltage of the external power supply is used as an input voltage of the light source.

  In this light emitting device, the capacitor is preferably connected in series with the light source with respect to the external power source during charging.

  The light-emitting device of the present invention has an effect of suppressing a change in loss with respect to a fluctuation in power supply voltage and simplifying a circuit configuration.

1 shows Embodiment 1 of the present invention, where (a) is a circuit configuration diagram, and (b) is a circuit configuration diagram of a control unit. It is a truth table for demonstrating operation | movement of the control part in the same as the above. It is a circuit block diagram containing the selection means of another structure same as the above. It is a circuit block diagram containing the selection means of another structure same as the above. It is explanatory drawing for demonstrating operation | movement of the control part in the same as the above. It is a circuit block diagram which shows Embodiment 2 of this invention. It is a circuit block diagram containing the selection means of another structure same as the above. It is a circuit block diagram which shows Embodiment 3 of this invention. It is a circuit block diagram which added the inductor to the same as the above. It is a circuit block diagram which shows Embodiment 4 of this invention. It is a circuit block diagram which added the inductor to the same as the above. It is a circuit block diagram which shows Embodiment 5 of this invention. It is a circuit block diagram which added the inductor to the same as the above.

  Hereinafter, an embodiment using a light emitting diode as a solid state light emitting device will be described. However, the solid state light emitting element constituting the light source is not limited to the light emitting diode, and may be, for example, an organic EL element.

(Embodiment 1)
As shown in FIG. 1A, the light emitting device of the present embodiment includes a light source 1 composed of a plurality of light emitting diodes LD1, LD2,..., LDn-1, LDn connected in series, and a driving current I _LD in the light source 1. LED i (i = 1, 2,..., N−1, n) and a light emitting diode LDj (j = 1, 2,..., N−1, n not flowing the drive current I _LD , i + selection means 2 for selecting j ≦ n), detection means 3 for detecting the state of the light source 1, and selection means 2 so as to suppress fluctuations in the detection results 3 when fluctuations occur in the detection results of the detection means 3. by controlling the, and a control unit 4 for selecting the light emitting diode LDj not shed light emitting diode LDi the drive current I _LD flowing a drive current I _LD.

  In the light source 1, the anode of the light emitting diode LDn at one end is connected to the positive electrode of the external power source PS composed of a DC power source, and the cathode of the light emitting diode LD1 at the other end is connected to the negative electrode of the external power source PS. However, it is desirable to use all the light emitting diodes LD1 to LDn having the same rating. The external power supply PS is created by rectifying and smoothing a commercial AC power supply, for example, and the power supply voltage Vs fluctuates as the power supply voltage of the commercial AC power supply fluctuates.

  The selection means 2 includes a plurality (four in the illustrated example) of switch elements S1 to S4 for short-circuiting both ends (anode and cathode) of the plurality of (four in the illustrated example) light emitting diodes LD1 to LD4. Yes. Note that the switch elements S1 to S4 in the present embodiment are configured by phototransistors and are turned on / off by an optical signal output from the control means 4 as will be described later.

The detection means 3 detects the magnitude of the drive current I _LD flowing through the light source 1 and is constituted by a small resistance (not shown) inserted between the negative electrode of the external power source PS and the light source 1, for example. Has been. That is, since a voltage drop proportional to the magnitude of the drive current I _LD occurs at both ends of the resistor, the detection means 3 outputs the voltage drop to the control means 4 as a detection voltage.

  The control means 4 includes a control unit 40 and a plurality (four in the illustrated example) of light emitting elements (light emitting diodes) 41 that are controlled to blink by the control unit 40. These four light emitting elements 41 are optically coupled to the switch elements S1 to S4 of the selection means 2, respectively.

  As shown in FIG. 1B, the control unit 40 includes an amplifier that amplifies the detection voltage of the detection means 3, a microcontroller (hereinafter abbreviated as a microcomputer) MC, and a plurality of (four in the illustrated example) logic circuits. (And gates) G1 to G4. The amplifier is an inverting amplifier composed of an operational amplifier OP and resistors R1 and R2. The detection voltage amplified by the amplifier is input to the input port P0 of the microcomputer MC. One input terminals of AND gates G1 to G4 are connected to the output ports P1 to P4 of the microcomputer MC, respectively. Further, the timer output port P5 of the microcomputer MC is connected to the other input terminals of the AND gates G1 to G4, and the light emitting element 41 is connected to the output terminals of the AND gates G1 to G4, respectively. That is, the light emitting element 41 does not emit light when the outputs of the AND gates G1 to G4 are L level, and the light emitting element 41 emits light only when the outputs of the AND gates G1 to G4 are H level. Light emitted from the light emitting element 41 is input as an optical signal to the switch elements S1 to S4, and the switch elements S1 to S4 to which the optical signal is input are turned on to short-circuit both ends of the light emitting diodes LD1 to LD4.

  Next, the control operation of the control unit 4 according to the detection result (detection voltage) of the detection unit 3 will be described.

In the light emitting device of this embodiment, when the power supply voltage Vs of the external power supply PS decreases, the input voltage of the light source 1 also decreases. As a result, the drive current I _LD flowing through the light source 1 decreases and the detection voltage of the detection means 3 Also decreases. Here, the detection voltage of the detection means 3 when the power supply voltage Vs of the external power supply PS is equal to the rated voltage is V0, and the detected voltage becomes V1, V2, V3, as the power supply voltage Vs fluctuates and falls below the rated voltage. It is assumed that the voltage drops to V4 (however, V0>V1>V2>V3> V4). When the detection voltage of the detection unit 3 decreases, the control unit 4 turns on the number of switch elements S1 to S4 corresponding to the degree of decrease. Specifically, as shown in the truth table of FIG. 2, the microcomputer MC of the control means 4 sets all output ports P1 to P4 to L level when the detection voltage is V0, and outputs when the detection voltage is V1. When only port P1 is at H level, when detection voltage is V2, output ports P1, P2 are at H level, when detection voltage is V3, output ports P1, P2, P3 are at H level, and detection voltage is V4 Sets all the output ports P1 to P4 to the H level.

Thus, when the power supply voltage Vs fluctuates (decreases), the drive current I _LD flowing through the light source 1 decreases. As described above, the control means increases as the fluctuation amount of the power supply voltage Vs (decrease amount with respect to the rated voltage) increases. 4 increases the number of light emitting diodes LDi selected (short-circuited) by the selection means 2 so that the driving current I _LD does not flow, and decreases the number of light emitting diodes LDj selected to flow the driving current I _LD . In other words, in the light emitting device of the present embodiment, the resistance component inherent in the light emitting diode LD is utilized as a current limiting element, and the light emission in which the drive current I _LD flows according to the amount of change in the input voltage (power supply voltage Vs) as described above. Since the number of diodes LDj is reduced, a change (increase) in loss with respect to fluctuations in the power supply voltage Vs can be suppressed and the circuit configuration can be simplified.

In this embodiment, the switch elements S1 to S4 of the selection means 2 are controlled to be turned on / off by the optical signal output from the control means 4, and the selection means 2 and the control means 4 are electrically insulated. Therefore, it is possible to prevent the occurrence of the problem that the drive current I _LD flows into the control means 4 by mistake and the microcomputer MC is destroyed.

  By the way, the selection means 2 in the present embodiment is selected by connecting the switch elements S1 to S4 to only a part of the light emitting diodes LD1 to LDn (four light emitting diodes LD1 to LD4) constituting the light source 1. . However, as shown in FIG. 3, the switch elements S1 to Sn may be connected to all the light emitting diodes LD1 to LDn constituting the light source 1. As described above, when the selection unit 2 selects all the light emitting diodes LD1 to LDn, it is possible to cope with a larger power supply voltage fluctuation.

  Further, the selection means 2 in the present embodiment selects whether or not to short-circuit each light emitting diode LDi in a one-to-one correspondence with the switch element Si and the light emitting diode LDi. However, in this configuration, in order to short-circuit the plurality of light emitting diodes LDi, the same number of switch elements Si must be kept on. Therefore, as shown in FIG. 4, one end of the switch elements S1 to S4 is connected to one end of the light source 1 (the cathode of the light emitting diode LD1), and the other end of the switch elements S1 to S4 is connected to the anode of the light emitting diodes LD1 to LD4, respectively. You may connect. With this configuration, even when a plurality of light emitting diodes LDi are short-circuited, only one of the switch elements S2 to S4 needs to be turned on, so that the power consumption in the control means 4 and the selection means 2 can be reduced. is there.

  By the way, in the case where the switch element Si of the selection means 2 is separately connected to both ends (between the anode and the cathode) of the plurality of light emitting diodes LDi as shown in FIG. When the two switch elements Si are turned on according to the detected voltage 3, the switch elements Si that are turned on every predetermined time (for example, several seconds) may be changed. That is, after the switch elements S1 and S2 are first turned on, when the predetermined time elapses, the switch elements S3 and S4 are turned on instead of the switch elements S1 and S2, and each time the predetermined time elapses, the switch element S5 , S6, S7, S8,... In this way, it is possible to suppress variations in lifetime between the light emitting diodes LDi and between the switch elements Si. Instead of sequentially turning on the switch elements Si as described above, the switch elements Si to be turned on may be switched at random according to a random number generated by the microcomputer MC. However, instead of replacing the switch element Si that is turned on every predetermined time, the switch element Si that is turned on at an arbitrary time is replaced, and the sum of the periods during which the switch element Si is turned on per unit time is substantially constant. As described above, the control unit 4 may perform on / off control of the selection unit 2.

Furthermore, the on-duty ratio of the switch element Si may be controlled by the control means 4. For example, as shown in FIG. 5, when the horizontal axis is the detection voltage and the vertical axis is the on-duty ratio of the timer output port P5, the on-duty ratio of the timer output port P5 is increased as the detection voltage decreases. What is necessary is just to lengthen the period when the element Si is turned on and the drive current I _LD does not flow through the light emitting diode LDi. In this way, it is possible to finely adjust the drive current I _LD according to the on-duty ratio of the switch element Si, compared to the case where the switch element Si is simply turned on.

  Here, if the operation power supply of the microcomputer MC constituting the control means 4 is obtained from both ends of one or a plurality of light emitting diodes LDi via rectifier elements, there is no need to provide a separate operation power supply, and the circuit configuration can be reduced. It can be simplified.

(Embodiment 2)
The light emitting device of this embodiment is characterized in that it includes an inductor L connected in series with the light source 1 as shown in FIG. However, since the basic configuration of the present embodiment is almost the same as that of the first embodiment, the same reference numerals are given to the common components, and description and illustration will be omitted as appropriate.

  As shown in FIG. 6, the selection means 2 in the present embodiment is composed of a switch element S that collectively short-circuits the five light emitting diodes LD1 to LD5. The switch element S is composed of a field effect transistor and is controlled to be turned on / off by the control means 4 (microcomputer MC).

When the detection voltage of the detection means 3 falls below a predetermined threshold due to the fluctuation (decrease) in the power supply voltage Vs, the microcomputer MC turns on the switch element S of the selection means 2 and ends the five light emitting diodes LD1 to LD5. Short circuit. At this time, the drive current I _LD gradually increases due to the action of the inductor L inserted between the external power source Vs and the light source 1. On the other hand, when the fluctuation of the power supply voltage Vs is settled and the detection voltage of the detection means 3 falls below a predetermined threshold value, the microcomputer MC turns on the switch element S of the selection means 2 and turns on the five light emitting diodes LD1 to LD5. A drive current I _{LD is} passed. At this time, the drive current I _LD gradually decreases due to the action of the inductor L inserted between the external power source Vs and the light source 1.

By connecting the inductor L in series with the light source 1 as described above, when the switch element S of the selection means 2 is switched from on to off and from off to on, the drive current I _LD is gradually changed to The change in the amount of luminescence can be made inconspicuous. However, as shown in FIG. 7, all six light emitting diodes LD1 to LD18 constituting the light source 1 are divided into three groups of six, and three switch elements S1, S2, S3 that are collectively short-circuited for each group are provided. It may be provided. Further, as shown in FIG. 7, the control means 4 may perform on / off control of these three switch elements S1, S2, and S3 with an optical signal.

  Here, the number n of the light emitting diodes LD constituting the light source 1 is desirably set to a number that makes the sum of the forward voltages (forward voltages) of the light emitting diodes LD larger than the maximum value of the input voltage (power supply voltage Vs). . In addition, the number of light emitting diodes LD that are short-circuited together by one switch element S is the sum of the forward voltages of these light-emitting diodes LD that are short-circuited together, and the fluctuation value (rated value) of the input voltage (power supply voltage Vs). It is desirable that the number be larger than the difference between the minimum value and the minimum value.

  Incidentally, as shown in FIG. 7, when the selection means 2 has a plurality (three in the illustrated example) of switch elements S1 to S3, one control means 4 or one control means 4 according to the detection voltage of the detection means 3 or When the two switch elements S1 to S3 are turned on, the switch elements S1 to S3 that are turned on every predetermined time (for example, several seconds) may be changed. Alternatively, instead of sequentially turning on the switch elements S1 to S3, the switch elements S1 to S3 to be turned on may be switched randomly according to a random number generated by the microcomputer MC. However, instead of switching the switch elements S1 to S3 that are turned on every predetermined time, the switch elements S1 to S3 that are turned on at an arbitrary time are replaced and the switch elements S1 to S3 are turned on per unit time. The control means 4 may perform on / off control of the selection means 2 so that the sum is substantially constant.

  In the present embodiment, one inductor L is connected between the light source 1 and the external power source PS. However, in the configuration shown in FIG. 7, inductance elements (inductors) are connected between the light emitting diodes LDi constituting the light source 1, respectively. It doesn't matter. In this case, it is desirable that the inductance value of each inductance element be a value that makes the combined impedance equal to one inductor L. As a result, the shape of each inductance element can be reduced, and a thinner circuit implementation can be realized.

  Meanwhile, the light source 1 is configured by mounting a plurality of light emitting diodes LD1 to LDn on a mounting substrate (not shown). In this case, a group of light emitting diodes LD (hereinafter referred to as a first group) in which the switch element S of the selection means 2 is connected in parallel and a light emitting diode in which the switch element S of the selection means 2 is not connected in parallel. It is desirable that the LD groups (hereinafter referred to as “second group”) are substantially evenly arranged on the mounting surface of the mounting board. For example, when all the light emitting diodes LD are arranged side by side on the mounting surface, the second group of light emitting diodes LD is arranged on both sides of the first group of light emitting diodes LD, and the light emission of the same group is arranged on both sides obliquely. A diode LD may be disposed. In this way, when the first group of light emitting diodes LD is short-circuited by the switch element S, the light emission luminance on the mounting surface of the mounting substrate can be equalized.

In the first and second embodiments described above, the detection unit 3 detects the magnitude of the drive current I _LD as the state of the light source 1, but the magnitude of the input voltage applied to the light source 1 and the light source 1 are input. The magnitude of input power or the light output (luminance or illuminance) of the light source 1 may be detected.

(Embodiment 3)
As shown in FIG. 8, the light emitting device of this embodiment is characterized in that it includes voltage conversion means 5 that converts (boosts or steps down) the power supply voltage Vs of the external power supply PS to obtain the input voltage of the light source 1. However, since the light source 1, the selection unit 2, the detection unit 3, and the control unit 4 are the same as those in the first or second embodiment, the same components are denoted by the same reference numerals, and illustration and description thereof are omitted as appropriate. .

  The voltage conversion means 5 in this embodiment includes a pair of switching elements SW1 and SW2 connected in series between the positive and negative electrodes of the external power source PS, and a diode having an anode connected to the connection point between the positive electrode of the external power source PS and the switching element SW1. A step-up (double voltage) type switched capacitor circuit (hereinafter abbreviated as SC circuit) comprising D1 and a capacitor (capacitor) C1 inserted between the connection point of the cathode of diode D1 and switching elements SW1 and SW2. Consists of. The open / close elements SW1 and SW2 are composed of semiconductor switching elements such as transistors, and are individually controlled to open and close by the open / close control means. However, since the opening / closing control means can be shared by the microcomputer MC constituting the control means 4, the illustration thereof is omitted.

  Next, the operation of the voltage conversion means 5 will be described. First, when the open / close control means closes (turns on) the low-side open / close element SW2 with the high-side open / close element SW1 open, the positive electrode of the external power supply PS → diode D1 → capacitor C1 → open / close element SW2 → external power supply PS A closed circuit (charging path) of the negative electrode is formed. The capacitor C1 is charged by the current (direct current) flowing through the closed circuit. Subsequently, when the switching control means closes (turns on) the high-side switching element SW1 and opens (turns off) the low-side switching element SW2, the capacitor C1 → light source 1 → external power source PS → switching element SW1 → capacitor C1. A closed circuit (discharge path) is formed. At this time, since the charging voltage of the capacitor C1 is equal to the power supply voltage Vs of the external power supply PS, a voltage obtained by superimposing the charging voltage of the capacitor C1 on the power supply voltage Vs of the external power supply PS at both ends of the light source 1, that is, the power supply voltage Vs. Twice the voltage (input voltage). Thereafter, the open / close control means alternately opens and closes the pair of open / close elements SW1 and SW2, so that an input voltage twice the power supply voltage Vs can be stably supplied to the light source 1.

  As described above, according to the present embodiment, the voltage conversion means 5 doubles the power supply voltage Vs and applies it to the light source 1, so that the number of light emitting diodes LD constituting the light source 1 is determined by the light emitting diode LD. Can be increased until the total sum of the forward voltages becomes higher than the power supply voltage Vs of the external power supply PS (a maximum of 2 times). Note that an inductor L may be inserted between the voltage conversion means 5 and the light source 1 as shown in FIG. Further, the configuration of the selection unit 2 is not limited to the illustrated one, and any configuration of the selection unit 2 described in the first and second embodiments can be applied.

(Embodiment 4)
The voltage conversion means 5 in this embodiment includes a pair of diodes D2 and D3 connected in series between the positive and negative electrodes of the external power supply PS with the cathode as the positive electrode side, and between the negative electrode of the external power supply PS and the anode of the low-side diode D3. A step-down SC circuit comprising a pair of switch elements SW3 and SW4 connected in series, and a capacitor (capacitor) C2 inserted between a connection point of the diodes D2 and D3 and a connection point of the switch elements SW3 and SW4. Become. The open / close elements SW3 and SW4 are composed of semiconductor switching elements such as transistors, and are individually controlled to open and close by the open / close control means. However, since the opening / closing control means can be shared by the microcomputer MC constituting the control means 4, the illustration thereof is omitted.

Next, the operation of the voltage conversion means 5 will be described. First, when the switching control means closes (turns on) the switching element SW3 with the switching element SW4 opened, the positive polarity of the external power supply PS → light source 1 → diode D3 → capacitor C2 → switching element SW3 → negative polarity of the external power supply PS A closed circuit (charging path) is formed. The capacitor C2 is charged by the current flowing through the closed circuit (drive current I _LD ). At this time, the capacitor C2 is charged to a voltage obtained by subtracting the sum of forward voltages of the light emitting diodes LD1 to LD18 constituting the light source 1 from the power supply voltage Vs. Subsequently, when the switching control means closes (turns on) the switching element SW4 and opens (turns off) the switching element SW3, the closed circuit (discharge path) of the capacitor C2, the diode D2, the light source 1, the switching element SW4, and the capacitor C2. And the charging voltage of the capacitor C2 is applied to the light source 1 as an input voltage. At this time, in order for the driving current I _LD to flow from the capacitor C2 to the light source 1, the charging voltage of the capacitor C2 needs to be higher than the sum of the forward voltages of the light emitting diodes LD1 to LD18. Therefore, the power supply voltage Vs of the external power supply PS needs to be at least twice the sum of the forward voltages of the light emitting diodes LD1 to LD18. Thereafter, the open / close control means alternately opens and closes the pair of open / close elements SW3 and SW4, whereby an input voltage substantially half the power supply voltage Vs can be stably supplied to the light source 1.

  Note that an inductor L may be inserted between the voltage conversion means 5 and the light source 1 as shown in FIG. Further, the configuration of the selection unit 2 is not limited to the illustrated one, and any configuration of the selection unit 2 described in the first and second embodiments can be applied.

(Embodiment 5)
The voltage conversion means 5 in this embodiment includes a series circuit of a capacitor C3 and a diode D3, a series circuit of a diode D4 and a capacitor C4, a diode D5 inserted between the midpoints of these two series circuits, and an external power source PS. And a switching element SW5 inserted between one end of the capacitor C3 and the cathode of the diode D4, and a switching element SW6 inserted between one end of the light source 1, one end of the capacitor C3 and the cathode of the diode D4. The step-down SC circuit is configured such that the anode of the diode D3 and one end of the capacitor C4 are connected to the negative electrode of the external power source PS and the other end of the light source 1. The open / close elements SW5 and SW6 are composed of semiconductor switching elements such as transistors, and are individually controlled to open and close by the open / close control means. However, since the opening / closing control means can be shared by the microcomputer MC constituting the control means 4, the illustration thereof is omitted.

Next, the operation of the voltage conversion means 5 will be described. First, when the switching control means closes (turns on) the switching element SW5 with the switching element SW6 opened, the positive polarity of the external power supply PS → the switching element SW5 → the capacitor C3 → the diode D5 → the capacitor C4 → the negative polarity of the external power supply PS A closed circuit (charging path) is formed. The capacitors C3 and C4 are charged by the current flowing through the closed circuit. At this time, since the capacitors C3 and C4 have the same capacitance value, they are charged to voltages obtained by dividing the power supply voltage Vs into two equal parts. Subsequently, when the switching control means closes (turns on) the switching element SW6 and opens (turns off) the switching element SW5, the closed circuit (discharge path) of the capacitor C3 → the switching element SW6 → the light source 1 → the diode D3 → the capacitor C3. Then, a closed circuit (discharge path) of capacitor C4 → diode D4 → switching element SW6 → light source 1 → capacitor C4 is formed, and charging voltages of capacitors C3 and C4 are applied to light source 1 as input voltages, respectively. At this time, in order for the driving current I _LD to flow from the capacitors C3 and C4 to the light source 1, the charging voltage of the capacitors C3 and C4 needs to be higher than the sum of the forward voltages of the light emitting diodes LD1 to LD18. Therefore, the power supply voltage Vs of the external power supply PS needs to be at least twice the sum of the forward voltages of the light emitting diodes LD1 to LD18. Thereafter, the open / close control means alternately opens and closes the pair of open / close elements SW5 and SW6, whereby an input voltage that is half the power supply voltage Vs can be stably supplied to the light source 1.

  Note that an inductor L may be inserted between the voltage conversion means 5 and the light source 1 as shown in FIG. Further, the configuration of the selection unit 2 is not limited to the illustrated one, and any configuration of the selection unit 2 described in the first and second embodiments can be applied.

DESCRIPTION OF SYMBOLS 1 Light source 2 Selection means 3 Detection means 4 Control means
LD light emitting diode (solid state light emitting device)
PS External power supply

Claims (25)

  A light source composed of a plurality of solid state light emitting elements connected in series, a solid state light emitting element that passes a driving current in the light source, a selection means that selects a solid state light emitting element that does not pass the driving current, and a detection that detects the state of the light source And a solid-state light emitting element that controls the selection means so as to suppress the fluctuation of the detection result when a fluctuation occurs in the detection result of the detection means and a solid-state light emission that does not pass the driving current A light-emitting device comprising: control means for selecting an element.   The light emission according to claim 1, wherein the detection unit detects the drive current, and the control unit controls the selection unit so as to suppress fluctuations in the drive current detected by the detection unit. apparatus.   The said detection means detects the light output of the said light source, The said control means controls the said selection means so that the fluctuation | variation of the said light output which the said detection means detects is controlled. Light-emitting device.   The detection means detects an input voltage input to the light source, and the control means controls the selection means so as to suppress fluctuations in the input voltage detected by the detection means. Item 2. The light emitting device according to Item 1.   The detection means detects input power input to the light source, and the control means controls the selection means so as to suppress fluctuations in the input power detected by the detection means. Item 2. The light emitting device according to Item 1.   The selection means includes one or more switch elements that individually short-circuit both ends of the solid-state light-emitting element, and the control means includes a solid-state light-emitting element that controls on / off of the switch element and allows a drive current to flow. The light-emitting device according to claim 1, wherein a solid-state light-emitting element that does not pass a driving current is selected.   The light emitting device according to claim 6, wherein the switch element is provided for every solid state light emitting element.   The selection means includes one or more switch elements that are connected to one end of the light source and one end of the solid light emitting element to short-circuit both ends of the solid light emitting element, and the control means turns on the switch element. The light-emitting device according to claim 1, wherein a solid-state light-emitting element that conducts a drive current by being turned off and a solid-state light-emitting element that does not allow the drive current to flow are selected.   An inductor connected in series with the light source; and the selection means includes one or more switch elements that collectively short-circuit the plurality of solid-state light emitting elements connected in series, and the control means includes the switch 6. The light emitting device according to claim 1, wherein a solid light emitting element that causes a driving current to flow by controlling on / off of the element and a solid light emitting element that does not flow the driving current are selected.   10. The light emitting device according to claim 9, wherein the number of the solid state light emitting elements constituting the light source is a number such that a sum of forward voltages of the solid state light emitting elements is larger than a maximum value of the input voltage.   The number of the solid-state light emitting elements collectively short-circuited by the switch element is a number that makes a total sum of forward voltages of the solid-state light emitting elements larger than a fluctuation value of an input voltage. The light-emitting device of description.   A mounting surface of the mounting substrate, comprising: a mounting substrate on which the solid light emitting element is mounted, the solid light emitting element collectively short-circuited by the switch element, and the solid light emitting element not collectively short-circuited by the switch element The light emitting device according to any one of claims 9 to 11, wherein the light emitting device is arranged substantially evenly.   The light-emitting device according to claim 9, wherein the inductor includes a plurality of inductance elements connected in series with the solid-state light-emitting element.   The light-emitting device according to claim 9, wherein the control unit performs on / off control of the plurality of switch elements in a time-sharing manner.   15. The light emitting device according to claim 14, wherein the control means performs on / off control so that a sum of ON periods of the plurality of switch elements is substantially constant.   The light emitting device according to claim 1, wherein the switch element is turned on / off by an optical signal output from the control unit.   The light-emitting device according to claim 1, wherein the control unit controls an on-duty ratio of the switch element.   The light-emitting device according to claim 1, wherein the control unit sequentially switches the switch elements that are on / off controlled.   The light emitting device according to any one of claims 1 to 16, wherein the control means switches the switch elements to be turned on / off at random.   20. The light emitting device according to claim 18 or 19, wherein the control means performs on / off control so that a sum of on periods of the plurality of switch elements is substantially constant.   21. The light-emitting device according to claim 1, wherein the control unit obtains an operating power source from both ends of the one or more solid-state light-emitting elements via rectifier elements.   The light-emitting device according to any one of claims 1 to 21, further comprising voltage conversion means for converting a power supply voltage of an external power supply into an input voltage of the light source.   The voltage conversion means includes one or more capacitors charged by the external power source, an opening / closing element for opening / closing a charging path to the capacitor and a discharging path from the capacitor, and an opening / closing control for opening / closing the opening / closing element. 23. The light-emitting device according to claim 22, wherein a discharge voltage of the capacitor is used as an input voltage of the light source.   The voltage conversion means includes one or more capacitors charged by the external power source, an opening / closing element for opening / closing a charging path to the capacitor and a discharging path from the capacitor, and an opening / closing control for opening / closing the opening / closing element. 23. The light emitting device according to claim 22, wherein a voltage obtained by superimposing a discharge voltage of the capacitor on a power supply voltage of the external power supply is used as an input voltage of the light source.   24. The light emitting device according to claim 23, wherein the capacitor is connected in series with the light source with respect to the external power source during charging.

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