JP2014179451A - Light emission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology for allowing a light emission device in which a plurality of circuit blocks each having a different number of serially connected LEDs are connected in parallel to uniformly emit light with a small number of components.SOLUTION: A light emission device includes: a transistor 100; a first circuit part having a plurality of serially connected light emission elements 11, 12, 13, 21, 22 and 23 with one ends connected to a high potential end +V of a power source and with the other ends connected to a reference potential end GND of the power source; and a second circuit part having a smaller number of serially connected light emission elements 32, 33, 42 and 43 than the first circuit part with one ends connected to the emitter of the transistor and with the other ends connected to a reference potential end. The first circuit part has a node A between the light emission elements at the reference potential end side equal in number to the second circuit part and the other light emission elements at a high potential end side. The transistor is configured such that the base is connected to the node A of the first circuit part, and that the collector is connected to a high potential end.

Description

  The present invention relates to a light emitting device having a plurality of light emitting elements.

  In recent years, a vehicular lamp configured using a light-emitting device including a plurality of light-emitting elements (LEDs) has become widespread. When used as a vehicular lamp, in order to satisfy predetermined light distribution requirements, it is necessary to supply a uniform current to each LED to cause these LEDs to emit light uniformly. For this reason, when manufacturing a light emitting device, LEDs having substantially the same characteristics are selected and used. The characteristics here are mainly luminous intensity characteristics and IF (forward current) -VF (forward voltage) characteristics.

  As a method of supplying a uniform current to a plurality of LEDs, for example, it is conceivable to connect all the LEDs in series and apply a voltage to both ends thereof. However, in this case, if the number of LEDs is large to some extent, it is necessary to use an expensive booster circuit in order to apply a high voltage to the series circuit of those LEDs, which is disadvantageous in terms of cost. On the other hand, it is also conceivable to connect the LEDs in parallel. For example, when several circuit blocks in which three LEDs are connected in series are connected in parallel, it is only necessary to apply a voltage corresponding to the circuit block composed of these three LEDs, so that an expensive booster circuit is not used. can do. In the case of such parallel driving, if the number of LEDs in each circuit block is the same, the same current flows through each LED. However, if the number of LEDs in each circuit block is different, the brightness becomes uneven. Compared with a circuit block with a large number of LEDs, an LED of a circuit block with a small number of LEDs has a large load voltage and therefore a large current. For this reason, at present, in order to make the brightness uniform, a voltage load is created by inserting a resistance element or a rectifier diode instead of the insufficient LED, and the current is adjusted. However, even when the applied voltage is the design voltage, current flows evenly. However, if the voltage fluctuates, the current varies due to the difference in voltage load characteristics of the LED, resistance element, and rectifier diode, resulting in uneven brightness. End up.

  As a prior example that can eliminate such inconvenience, for example, in Japanese Patent Application Laid-Open No. 2007-096287 (Patent Document 1), in an LED light emitting unit in which a plurality of modules in which different numbers of LEDs are connected in series are connected in parallel, A circuit configuration in which a resistance element and a transistor are connected in series to each module is disclosed (see FIGS. 12 and 13 of Patent Document 1). And according to this structure, it is demonstrated that the electric current which flows into each module (series circuit) which is a branch can be controlled accurately and uniformly. However, in the configuration of this preceding example, since it is necessary to incorporate a current control transistor and a resistance element in each module, the number of parts increases as the number of modules increases, resulting in higher costs and larger circuits. There is room for improvement in terms of inviting.

JP 2007-096287 A

  A specific aspect of the present invention is to provide a technique capable of uniformly emitting light with a small number of components in a light emitting device in which a plurality of circuit blocks in which different numbers of LEDs are connected in series are connected in parallel. One.

  A light-emitting device of one embodiment according to the present invention includes (a) a transistor and (b) a plurality of light-emitting elements connected in series, one end of which is connected to the high potential end of the power source and the other end of the power source. A first circuit portion connected to the reference potential end; and (c) a smaller number of light emitting elements than the first circuit portion, and when there are a plurality of light emitting elements, the light emitting elements are connected in series. A second circuit portion having one end connected to the emitter of the transistor and the other end connected to the reference potential end; and (d) the first circuit portion emits light of the same number of reference potential ends as the second circuit portion. (E) the transistor has a base connected to the node of the first circuit unit and a collector connected to the high potential end. It is a light emitting device.

  According to the above configuration, substantially the same voltage can be applied to the node of the first circuit unit and one end of the second circuit unit via the transistor. Since the transistor itself is autonomously turned on when the voltage at the node of the first circuit section is applied to the base, it is not necessary to provide a means such as a microcomputer for controlling on / off of the transistor. Therefore, the light emitting device in which a plurality of circuit blocks in which different numbers of LEDs are connected in series is connected in parallel can be made to emit light uniformly with a small number of components.

  In the above light-emitting device, the first circuit section preferably further includes a rectifier diode connected in series on the reference potential end side.

  Strictly speaking, the voltage at the node of the first circuit section and the voltage at one end of the second circuit section are shifted by the base-emitter voltage of the transistor, but this shift can be offset by the forward voltage of the rectifier diode. Become. Accordingly, it is possible to make the luminous intensity when each light emitting element is turned on more uniform.

  The light emitting device preferably further includes a current limiting resistance element connected between the first circuit portion and the high potential end.

  Even when the current limiting resistance element is provided in this way, in principle, only the element corresponding to the first circuit part needs to be provided, and the element corresponding to the second circuit part is unnecessary. high.

FIG. 1 is a circuit diagram illustrating a configuration of a light emitting device according to an embodiment. FIG. 2 is a graph showing an example of the relationship between the current if and the current ie when the power supply voltage is changed in the light emitting device shown in FIG. FIG. 3 is a circuit diagram illustrating a configuration of a light emitting device according to another embodiment. FIG. 4 is a graph illustrating an example of the current ie when the power supply voltage is changed in the light emitting device illustrated in FIG. 3. FIG. 5 is a circuit diagram illustrating a configuration of a light emitting device according to another embodiment. FIG. 6 is a circuit diagram illustrating a configuration of a light emitting device according to another embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the meaning of “connection” in the present specification includes the case where other circuit elements are interposed between circuit elements such as circuit elements in a form that does not hinder the operation necessary for obtaining the intended technical effect. Shall also be included.

  FIG. 1 is a circuit diagram illustrating a configuration of a light emitting device according to an embodiment. 1 includes an NPN bipolar transistor 100, a current limiting resistor element 101, and a plurality of light emitting elements (LEDs) 11, 12, 13, 21, 22, 23, 32, 33, 42, 43. It is comprised including. This light emitting device is connected to a power source having a high potential end + V and a reference potential end GND, and receives power supply from the power source to light each light emitting element. In the present embodiment, each light emitting element has substantially the same characteristics. The characteristics here are mainly luminous intensity characteristics and IF (forward current) -VF (forward voltage) characteristics.

  The light emitting elements 11, 12, and 13 are connected in series with each other, the anode side of the light emitting element 11 is connected to the high potential end + V through the current limiting resistance element 101, and the cathode side of the light emitting element 13 is the reference potential end GND. Connected with.

  The light emitting elements 21, 22, and 23 are connected in series with each other, the anode side of the light emitting element 21 is connected to the high potential terminal + V through the current limiting resistor element 101, and the cathode side of the light emitting element 23 is the reference potential terminal GND. Connected with. The series circuit portion (circuit block) made up of the light emitting elements 21, 22, and 23 corresponds to the “first circuit portion”.

  The light emitting elements 32 and 33 are connected in series with each other, the anode side of the light emitting element 32 is connected to the emitter of the NPN bipolar transistor 100, and the cathode side of the light emitting element 33 is connected to the reference potential terminal GND. Similarly, the light emitting elements 42 and 43 are connected in series with each other, the anode side of the light emitting element 42 is connected to the emitter of the NPN bipolar transistor 100, and the cathode side of the light emitting element 43 is connected to the reference potential terminal GND. Yes. The series circuit unit composed of the light emitting elements 32 or the like or the series circuit unit composed of the light emitting elements 42 or the like has a smaller number of light emitting elements than the series circuit unit composed of the above light emitting elements 21 or the like. Part. The emitter of the NPN bipolar transistor 100 and each second circuit portion are connected at a node B.

  The first circuit portion including the light emitting element 21 and the like has the same number of light emitting elements 22 and 23 on the reference potential end GND side as the second circuit portion including the light emitting element 32 and the like (or the light emitting element 42 and the like), and other high potentials. A node A is provided between the light emitting element 21 on the end side + V.

  The NPN bipolar transistor 100 has a base connected to the node A of the first circuit portion, a collector connected to the high potential end + V, and an emitter connected to one end of each second circuit portion.

  The light emitting device of the present embodiment has the above-described configuration, and the operation will be described in detail next.

  If the characteristics of each light emitting element are the same, it is necessary to apply the same voltage to each light emitting element in order to light them with uniform brightness. For this reason, first, in the parallel circuit block such as the light emitting element 11 and the light emitting element 21 which are series circuit portions having a large number of light emitting elements, the resistance constant is applied so that the forward voltage VF having the luminous intensity required by each light emitting element is applied. To decide. In addition, in order to make each light emitting element of the parallel circuit block such as the light emitting element 32 and the like, which is a series circuit portion having a small number of light emitting elements, have the same luminous intensity, the forward voltage VF equivalent to the above is set. Give it. That is, if the node A and the node B shown in FIG. 1 have the same potential, the same forward voltage VF is applied to each light emitting element, and each light emitting element is lit with brightness.

  In order to make the node A and the node B have the same potential, the NPN bipolar transistor 100 may be turned on. In the light emitting device shown in FIG. 1, a voltage sufficient to bring the NPN bipolar transistor 100 into a conducting state is supplied to the base by the voltage at the node A, so that the NPN bipolar transistor 100 is autonomously brought into a conducting state. be able to. As a result, the node A and the node B have substantially the same potential, and a current is supplied to the second circuit portion from the high potential end side + V of the power source to the node B through the collector-emitter of the NPN bipolar transistor 100. . Strictly speaking, a minute current flows between the base and emitter of the NPN bipolar transistor 100, but it is negligible and can be ignored. Thereby, since the equivalent forward voltage VF is applied to each light emitting element, it becomes possible to light each light emitting element uniformly.

  FIG. 2 is a graph showing an example of the relationship between the current if and the current ie when the power supply voltage is changed in the light emitting device shown in FIG. FIG. 2 shows that the current if and the current ie change similarly even if the power supply voltage fluctuates. That is, even if the power supply voltage fluctuates, each light emitting element can be lit with the same brightness. Here, there is a slight deviation between the current if and the current ie because the base-emitter voltage (0.7 V as an example) of the NPN bipolar transistor 100 exists. If the current difference due to the voltage deviation is acceptable, a light emitting device capable of uniformly emitting light with a circuit having a very small number of parts can be realized. Conventionally, the current limiting resistor element is also required on the block side where the number of light emitting elements is small. However, in this embodiment, only the current limiting resistor element 101 on the block side where the number of light emitting elements is large is sufficient. Therefore, the number of parts can be reduced.

  If the deviation between the current if and the current ie due to the base-emitter voltage of the NPN bipolar transistor 100 cannot be tolerated, this deviation can be easily corrected by adopting a circuit configuration as shown in FIG. can do.

  The light-emitting device shown in FIG. 3 basically has the same configuration as that of the light-emitting device shown in FIG. 1, and is connected in series to the reference potential terminal GND side of each series circuit unit including the light-emitting elements 11 and 21 and the like. The difference is that it further includes a connected rectifier diode 102. In addition, about the common structure, after attaching the same code | symbol, those description is abbreviate | omitted. By adding such a rectifier diode 102, the base-emitter voltage of the NPN bipolar transistor 100 can be canceled by the forward voltage of the rectifier diode 102.

  FIG. 4 is a graph illustrating an example of the current ie when the power supply voltage is changed in the light emitting device illustrated in FIG. 3. As shown in the drawing, since the currents ie flowing through the respective light emitting elements can all be the same, it is possible to make the luminous intensity at the time of lighting of each light emitting element more uniform.

  FIG. 5 is a circuit diagram illustrating a configuration of a light emitting device according to another embodiment. The light-emitting device shown in FIG. 5 has the same configuration as that of the light-emitting device shown in FIG. 3 described above, and is different in that more series circuit units including two light-emitting elements are connected in parallel. In addition, about the common structure, after attaching the same code | symbol, those description is abbreviate | omitted.

  The light-emitting device shown in FIG. 5 includes a series circuit unit composed of light-emitting elements 52 and 53, a series circuit unit composed of light-emitting elements 52 and 53, a series circuit unit composed of light-emitting elements 52 and 53, and a series circuit composed of light-emitting elements 62 and 63. Unit, a series circuit unit composed of light emitting elements 72 and 73, and a series circuit unit composed of light emitting elements 82 and 83, all of which are connected in parallel. Each series circuit unit corresponds to a “second circuit unit”, and one end of each series circuit unit is connected to the emitter of the NPN bipolar transistor 100, and the other end of each series circuit unit is a reference. It is connected to the potential terminal GND.

  As described above, even if the number of series circuit units having a relatively small number of light emitting elements is increased, the currents other than the parallel circuit blocks such as the light emitting element 11 and the light emitting element 21 which are series circuit units having a large number of light emitting elements are used. Since it is not necessary to provide the limiting resistance element 101, a reduction in size and cost can be realized.

  FIG. 6 is a circuit diagram illustrating a configuration of a light emitting device according to another embodiment. The light-emitting device shown in FIG. 6 is based on the principle common to the above-described embodiments, and includes NPN-type bipolar transistors 100a and 100b, a current limiting resistor element 101, a rectifier diode 102, and a plurality of light-emitting elements. (LED) 11, 12, 13, 21, 22, 23, 32, 33, 42, 43, 52, 53, 63b, 73b, 83b are comprised.

  The series circuit unit composed of the light emitting element 11 and the like and the series circuit unit composed of the light emitting element 21 and the like are connected in parallel, one end side thereof is connected to the high potential end + V, and the other end side is connected to the reference potential via the rectifier diode 102. It is connected to the end GND. The base of the NPN bipolar transistor 100a is connected to the node A1 of the series circuit portion including the light emitting element 21 and the like, and the base of the NPN bipolar transistor 100b is connected to the node A2.

  The series circuit portion composed of the light emitting elements 32 and the like, the series circuit portion composed of the light emitting elements 42 and the like, and the series circuit portion composed of the light emitting elements 52 and the like are connected in parallel to each other, and one end side thereof is connected to the emitter of the NPN bipolar transistor 100a. The other end side is connected to the reference potential terminal GND. The collector of the NPN bipolar transistor 100a is connected to the high potential end + V.

  The light emitting elements 63b, 73b, and 83b are connected in parallel to each other, and one end side thereof is connected to the emitter of the NPN bipolar transistor 100b, and the other end side is connected to the reference potential terminal GND. The collector of the NPN bipolar transistor 100b is connected to the high potential end + V.

  In the light emitting device shown in FIG. 6, the series circuit unit including the light emitting element 21 and the like corresponds to the “first circuit unit”, and the series circuit unit including the light emitting element 32 and the like, the series circuit unit including the light emitting element 42 and the like, Each of the series circuit portions including the elements 52 corresponds to the “second circuit portion”. On the other hand, the series circuit portion composed of the light emitting elements 21 and the like corresponds to the “first circuit portion”, and each of the light emitting elements 63b, 73b, and 83b corresponds to the “second circuit portion”.

  As described above, even if the number of circuit units having different numbers of light emitting elements is increased, the current limiting resistor element is used in addition to the parallel circuit blocks such as the light emitting element 11 and the light emitting element 21 which are series circuit units having a large number of light emitting elements. Since there is no need to provide 101, it is possible to achieve downsizing and cost reduction. Further, the number of light emitting elements can be designed freely.

  In addition, this invention is not limited to the content of embodiment mentioned above, In the range of the summary of this invention, it can change and implement variously.

11, 12, 13, 21, 22, 23, 32, 33, 42, 43: Light-emitting element 100: NPN-type bipolar transistor 101: Current-limiting resistor element 102: Rectifier diode A, B: Node + V: High potential end GND: Reference potential terminal

Claims (3)

A transistor,
A first circuit unit having a plurality of light emitting elements connected in series, having one end connected to a high potential end of a power source and the other end connected to a reference potential end of the power source;
When the number of the light emitting elements is smaller than that of the first circuit portion and the number of the light emitting elements is plural, the light emitting elements are connected in series, one end is connected to the emitter of the transistor, and the other end is A second circuit unit connected to the reference potential terminal;
Including
The first circuit section has a node between the same number of light emitting elements on the reference potential end side as the second circuit section and the other light emitting elements on the high potential end side,
The transistor has a base connected to the node of the first circuit unit and a collector connected to the high potential end.
Light emitting device. The first circuit unit further includes a rectifier diode connected in series to the reference potential end side.
The light emitting device according to claim 1. A current limiting resistor connected between the first circuit portion and the high potential end;
The light emitting device according to claim 1.

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