JP5152714B2 - Light emitting device and lamp - Google Patents

Description

  The present invention relates to a light-emitting device and a lamp, and more particularly, to a multi-chip type light-emitting device that compensates for temperature characteristics of a semiconductor light-emitting element such as a light-emitting diode (LED) as a component, and a lamp equipped with the same. .

  A typical example of a semiconductor light emitting element is a light emitting diode (LED). An LED die has a light emitting layer (active layer) sandwiched between a p-type cladding layer and an n-type cladding layer and having a smaller band gap than both the cladding layers. With this three-layer structure as a basic structure, electrodes are provided above and below the cladding layer and a forward current is passed through the basic layer structure of the LED chip, whereby the active layer emits light. Since LED chips are difficult to use as they are, they are mounted on a package (envelope) and energized. LED packages include a shell type and a SMD (Surface Mount Device) type.

  In an LED using a single chip, the light emission efficiency (output efficiency with respect to current) decreases as the temperature around the LED increases due to the heat generation of the LED itself or the change in environmental temperature. For this reason, the light emission output decreases as the temperature rises. Further, since the emission peak wavelength shifts to the longer wavelength side as the temperature rises, the chromaticity changes. For example, yellow at room temperature and orange at high temperatures (red-shift).

  FIG. 25 is a diagram illustrating an example of a temperature change in the emission spectrum of the LED. The emission intensity is shown as a relative intensity normalized so that the peak value is 1. The spectral peak at 25 ° C. (yellow at 592 nm) shifts to about 8 nm longer wavelength side at 85 ° C. (spectral peak is 600 nm), and the intensity of the peak also decreases.

  In the case of an AlInGaP-based LED, the peak wavelength of the emission spectrum can be selected in the range from red to yellow-green depending on the composition of the mixed crystal. The temperature change of the peak wavelength is approximately around 0.14 nm / ° C. However, chromaticity is related to the visibility of the human eye. In the red band, the longer the wavelength, the lower the human visibility. Usually, discussions are made in terms of dominant wavelengths that take into account the stimulation of the human eye for the three primary colors. On the longer wavelength side than green (555 nm), the longer the actual wavelength, the shorter the dominant wavelength.

  Even if the spectral peak moves to the longer wavelength side due to temperature rise, it seems that the red band does not shift so much in terms of dominant wavelength. That is, the red shift is effectively compensated by the visibility. However, as the wavelength approaches 555 nm, the actual peak wavelength change due to temperature change is reflected. In the yellow example of FIG. 25, the dominant wavelength moves from 589 nm to 594 nm with a change from 25 ° C. to 85 ° C.

  FIG. 26 is a diagram illustrating an example of a temperature change of the dominant wavelength of the LED, in which the room temperature value is normalized to be 0 and plotted. In the temperature change of the dominant wavelength, the yellow-green, yellow and amber wavelength bands (586 nm in the example of FIG. 26) change from 582 nm to 593 nm with the temperature change of −20 ° C. to 100 ° C., and the red wavelength band (FIG. 26). In this example, it is about twice as large as the change from 628 nm to 633 nm in the temperature change from −20 ° C. to 100 ° C. at 630 nm).

  FIG. 27 is a diagram illustrating an example of the temperature change of the luminous intensity of the LED, in which the room temperature value is normalized to be 1 and plotted. The change in luminous intensity / light flux temperature is also affected by human visual sensitivity. The physical light output (light power) generally decreases with increasing temperature.

  The red band (630 nm in the example of FIG. 27) of the dominant wavelength 610 nm to 640 nm is shifted to the longer wavelength side, and therefore, the luminous intensity / light flux is more significantly reduced due to the decrease in the visibility. In this case, the light intensity decreases by 35% with a change from 25 ° C. to 85 ° C. However, since the red-band AlInGaP-based LED has a high efficiency of the active layer in terms of material / structure characteristics, the optical power can be reduced by about 10%.

  On the other hand, in the yellow band of 586 nm at the dominant wavelength, although the decrease in the visibility is small, the optical power decreases due to the poor characteristics of the active layer, and the optical power exceeds 40% with a change from 25 ° C. to 85 ° C. Indicates a decrease in As a result, the luminous intensity is lower by 55% than the red band.

  When the LED is used outdoors, the above temperature characteristics become a problem. For example, a red LED having a small temperature change is used for a lamp such as a rear lamp (rear combination) of an automobile, and the range of applications is widened. However, the amber (yellow) LED, which is the color of the turn signal, has not spread more than expected due to its large temperature change, and a short-life bulb is still used. Since mounting both the LED and the light bulb as the lamp causes an increase in the total cost, it is desirable that the exterior lighting of the automobile be unified with the LED. Even in other application ranges, the poor temperature characteristics often obstruct the spread.

  Further, in the case of a mixed color or white (pseudo white) LED instead of the single color LED as described above, it is combined with a wavelength conversion material such as a plurality of LEDs and phosphors (for example, see Patent Document 1). In this case, the color mixture, the excitation efficiency of the phosphor, and the like change in a complicated manner with temperature.

  For example, in the case of a pseudo white LED using a YAG phosphor and a blue LED, the wavelength of the blue LED is red-shifted or the output is lowered due to a temperature rise. That is, the chromaticity and luminous flux change in a complicated manner as the YAG excitation efficiency and the ratio of blue light absorption and transmission change. Even in a white LED that mixes the light emission of three primary color (RGB) LEDs, the chromaticity and luminous flux of the synthesized white light change in a complicated manner because the temperature characteristics of each LED are different. Such a change becomes a big problem for the application to the backlight of LCD.

  In order to solve these problems, it is only necessary to control the temperature of a semiconductor light emitting element such as an LED or a lamp equipped with them to be constant. However, it is not realistic from the viewpoint of cost and energy saving. Even in the case of white LEDs, the method of adjusting each LED by monitoring the chromaticity and wavelength is complicated and expensive.

As described above, the above-described temperature characteristics of semiconductor light emitting devices such as LEDs are a problem in promoting the practical application and spread of semiconductor light emitting devices.
JP 2005-235847 A

  The present invention provides a light emitting device that compensates for temperature changes in light output and wavelength and exhibits stable characteristics with respect to temperature changes.

  According to one aspect of the present invention, a first semiconductor light emitting element and a second semiconductor light emitting element connected in parallel are provided, wherein the first semiconductor light emitting element is higher than the second semiconductor light emitting element. The temperature coefficient of the series resistance of the first semiconductor light emitting element is negative, and the absolute value of the temperature coefficient of the series resistance of the first semiconductor light emitting element is the second semiconductor light emitting There is provided a light emitting device characterized in that the absolute value of the temperature coefficient of the series resistance of the element is larger.

  The present invention provides a light-emitting device that compensates for temperature changes in optical output and wavelength and exhibits stable characteristics with respect to temperature changes.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In the first embodiment of the present invention, the first LED and the second LED are arranged close to each other and connected in parallel, and the luminous efficiency (light output efficiency with respect to the current) of the first LED and negative By making the absolute value of the temperature coefficient of the second LED larger than that of the second LED, temperature compensation of the light output is realized.

Specifically, the light emission efficiency and the temperature coefficient are set to different values in the first LED and the second LED by differentiating the density of the surface electrode network from which light is extracted.
Furthermore, temperature compensation of the wavelength is realized by setting the emission peak wavelength of the first LED to be slightly shorter than that of the second LED.
As described above, a light-emitting device having a plurality of LEDs having different temperature characteristics and wavelengths and outputting a combined spectrum of output light from each LED, and having characteristics stable with respect to temperature changes is provided.

  FIG. 1 is a circuit configuration diagram of a light emitting device according to a first embodiment of the present invention. This light emitting device has a circuit configuration in which a light emitting diode (LED) D1 and a light emitting diode (LED) D2 are connected in parallel. The symbols D1 and D2 attached to the light emitting diodes can also mean LED chips, and can also mean LED packages mounted with LED chips. 1 and the subsequent drawings, the same elements as those described with reference to the previous drawings are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 2 is a diagram showing the temperature characteristics of the forward voltage (rising voltage of forward current) Vf of the light emitting diodes D1 and D2 according to the first embodiment of the present invention. As shown in FIG. 2, the light-emitting diode D1 has a higher forward voltage value at 25 ° C., whereas the light-emitting diode D2 has a higher forward voltage value at 85 ° C.

  FIG. 3 is a diagram illustrating a specific example of the LED chip according to the first embodiment of the present invention, in which (a) is an LED chip 1a corresponding to the light emitting diode D1, and (b) is an LED corresponding to the light emitting diode D2. Chip 1b. In this specific example, the series resistance of the LED chip (the series resistance component of the LED chip itself) is different. The series resistance of the LED chip can have different series resistance values by making the density of the electrode network on the surface from which light is extracted different.

  As shown in FIG. 3A, an electrode pad 2a is provided on the surface (upper surface) from which light is extracted from the LED chip 1a, and the electrode network 4a extends from the electrode pad 2a. 2a and the electrode network 4a constitute an upper electrode of the LED chip 1a.

  Similarly, as shown in FIG. 3B, an electrode pad 2b is provided on the surface (upper surface) from which the LED chip 1b extracts light, and the electrode network 4b extends from the electrode pad 2b. These electrode pads 2b and the electrode network 4b constitute the upper electrode of the LED chip 1b.

  The density of the electrode network 4a of the LED chip 1a (D1) is lower (rougher) than the density of the electrode network 4b of the LED chip 1b (D2). By reducing the density of the electrode network, the spreading resistance to the region of the active layer away from the electrodes is increased, so that the series resistance value of the LED chip 1a is higher than that of the LED chip 1b. Moreover, since the LED chip 1a has a rougher electrode network 4a that hinders light extraction of light emission than the LED chip 1b, the light extraction efficiency (light emission efficiency) is larger than that of the LED chip 1b. Furthermore, the absolute value of the negative temperature coefficient of the series resistance of the LED chip 1a is larger than that of the LED chip 1b.

  Further, the emission spectrum of the light emitting diode D1 is set slightly shorter than the emission spectrum of the light emitting diode D2. Thereby, since the band gap of the light emitting layer of the light emitting diode D1 becomes slightly larger than that of the light emitting diode D2, the forward voltage Vf (see FIG. 2) of the light emitting diode D1 can be set to a higher value.

  FIG. 4 is a diagram showing the emission spectra of the light-emitting diodes D1 and D2 and the combined spectrum thereof according to the first embodiment of the present invention. In FIG. 4, (a) is a spectrum from the light emitting diodes D1 and D2 at 25 ° C. and a combined spectrum thereof, and (b) is a spectrum from the light emitting diodes D1 and D2 at 85 ° C. and these spectra. It is a synthetic spectrum.

  At 25 ° C. shown in FIG. 4A, the light emitting diode D1 has a peak on the short wavelength side and the light emission efficiency is high. However, since the forward voltage due to the series resistance is high, the current I1 flowing through the branch of the light emitting diode D1 is Get smaller. On the contrary, the current I2 flowing through the branch of the light emitting diode D2 is increased, and the light output of the light emitting diode D2 on the long wavelength side is larger than that of the light emitting diode D1. As a result, the peak of the combined spectrum (wavelength λp (25)) is strongly influenced by the light emitting diode D2 on the long wavelength side.

  At 85 ° C. shown in FIG. 4B, since the absolute value of the negative temperature coefficient of the series resistance of the light emitting diode D1 is larger than that of the light emitting diode D2, the light emitting efficiency is higher than the light emitting diode D2 and the light emitting wavelength is short. The current I1 flowing through the light emitting diode D1 increases more than that at 25 ° C. Therefore, it is possible to compensate for a decrease in light output under high temperature conditions. Further, in the synthetic spectrum, the peak of the light emitting diode D1 on the short wavelength side becomes dominant, so the peak of the synthetic spectrum (wavelength λp (85)) is the peak at 25 ° C. (wavelength λp (25)). The wavelength shift can be compensated without much change.

  5 to 7 are schematic perspective views illustrating a first specific example of the light emitting device according to the first embodiment of the invention. 5 shows the LED chip as an SMD (Surface Mount Device) type package (LED package), FIG. 6 shows the structure of the lead frame made easy by removing the upper half of the package of FIG. 5, and FIG. 5 is mounted on a substrate to form an optical module.

  On the cathode side lead frame 11, the LED chips 1a (D1) and 1b (D2) are mounted with a conductive material such as silver paste. The LED chips 1a (D1) and 1b (D2) are mounted close to each other. Next, the upper electrode pads 2a and 2b of the LED chips 1a (D1) and 1b (D2) are connected to the anode-side lead 12 by gold wires 3a and 3b, respectively.

Outside the lead frames 11 and 12 and the LED chips 1a and 1b, an envelope 20 made of white PPA (polyphthalamide) resin that reflects under conditions close to perfect diffuse reflection is disposed. The concave portion in which the LED chips 1a and 1b are mounted from the upper surface opening 21 of the envelope 20 is filled with a transparent resin material 30 made of epoxy resin or the like, and the LED chips 1a and 1b are sealed, so that the SMD type The LED package 40 is used.
The LED package 40 is mounted on a substrate 100 made of PCB (polychlorinated biphenyl) or the like. The cathode side solder pattern 110 on the substrate 100 and the cathode side lead frame 11 of the LED package 40 are connected by solder 111, and the anode side solder pattern 120 and the anode side lead frame 12 are connected by solder 121.

  In the first specific example, a compact configuration can be achieved by providing two LED chips in one package (envelope). Further, since the LED chips are close to each other, the colors are easily mixed and a uniform emission color is easily obtained.

  8 to 10 are schematic perspective views illustrating an example of the structure of the light emitting device according to the first embodiment of the invention. 8 shows the LED chip as an SMD type LED package, FIG. 9 shows that the upper half of the package of FIG. 8 is removed to make the structure of the lead frame easier to understand, and FIG. 10 shows that the package of FIG. This is an optical module.

  In the first specific example, two LED chips 1a and 1b corresponding to the light emitting diodes D1 and D2, respectively, are mounted on a lead frame of one SMD type package. On the other hand, in the second specific example, the LED chip 1a is mounted on the SMD type package (LED package) 40a, and the LED chip 1b is mounted on the SMD type package (LED package) 40b. The SMD type packages 40a and 40b are mounted on the PCB substrate 100 so as to be connected in parallel as in the first specific example. Since the manufacturing method of the SMD type packages 40a and 40b is the same as the manufacturing method of the SMD type LED package 40 described in the first specific example, the description is omitted here.

In the PCB substrate 100, the cathode side solder pattern 110 on the PCB substrate 100 and the cathode side lead frame 11a of the SMD type package 40a are connected by the solder 111a, and the anode side solder pattern 120 and the anode side lead frame 12a are connected by the solder 121a. Is done. Similarly, the cathode side solder pattern 110 and the cathode side lead frame 11b of the SMD type package 40b are connected by the solder 111b, and the anode side solder pattern 120 and the anode side lead frame 12a are connected by the solder 121a.
In the second specific example, the package configuration can be simplified by using two LED chips as separate packages.

  FIG. 11 is a schematic perspective view showing a third specific example of the light emitting device according to the first embodiment of the invention. FIG. 12 is a circuit configuration diagram illustrating a third specific example of the light emitting device according to the first embodiment of the invention.

This third specific example is an auxiliary resistance element (external resistance element) for emphasizing the temperature coefficient difference between the series resistances of the LED chips 1a and 1b in the second specific example (see FIGS. 8 to 10). ) 130 is provided in series with the SMD type package 40a on which the LED chip 1a is mounted.
As shown in FIG. 11, in the PCB substrate 100, the cathode-side solder pattern 110a connected to the cathode-side lead frame 11a of the SMD type package 40a and one electrode of the resistance element 130 are connected by solder 121a. Further, the cathode-side solder pattern 110b connected to the cathode-side lead frame 11b of the SMD type package 40b and the other electrode of the resistance element 130 are connected by the solder 112b.

As shown in FIG. 12, the third specific example has a circuit configuration in which a series circuit of a light emitting diode D1 and a resistance element 130 and a light emitting diode D2 are connected in parallel. It is also possible to provide an auxiliary resistance element for emphasizing the difference in temperature coefficient of the series resistance between the LED chips 1a and 1b and the light emitting diode D2.
In the third specific example, by providing a resistance element for emphasizing the difference between the temperature coefficients of the two LEDs, highly accurate temperature compensation can be performed.

As described above, according to the first embodiment of the present invention, it is possible to obtain a light emitting device that compensates for temperature changes in light output and wavelength and exhibits stable characteristics with respect to temperature changes. Furthermore, since a special external circuit for temperature compensation can be omitted, the cost of the entire light emitting module can be greatly reduced.
The present invention is not limited to the first embodiment, and includes a configuration in which a plurality of LED chips or LED packages are connected in series to the parallel branch circuit of the light emitting diodes D1 and D2. Further, the parallel branch circuit is not limited to two of the light emitting diodes D1 and D2, and includes one in which three or more are connected in parallel. Furthermore, various combinations of wavelengths are also applicable.

Next, a second embodiment of the present invention will be described.
In the second embodiment of the present invention, in the compensation temperature range, the first LED whose emission peak wavelength is close to the first wavelength at a higher temperature than at a low temperature, and the emission peak wavelength at a lower temperature than at a high temperature. The second LED close to the first wavelength, a temperature monitor (temperature sensor) that directly or indirectly detects the temperature of the LED, and the first LED and the second LED based on the detected temperature of the LED A drive control circuit for independently controlling a current flowing through the LED; For example, the emission peak wavelength of the first LED is set slightly shorter than that of the second LED, the first LED on the short wavelength side emits light strongly at high temperatures, and the second LED on the long wavelength side emits strongly at low temperatures. Then, by outputting the combined spectrum of the first LED and the second LED, light output and temperature compensation of the wavelength are realized with an inexpensive configuration.

  In particular, the LED emits visible light, the wavelength of which is a dominant wavelength considering human visual sensitivity, and the light output controlled by the drive control circuit is a luminous intensity or luminous flux considering human visual sensitivity. When it is expressed by, etc., an extremely large effect is produced.

Specifically, a remarkable temperature compensation effect is produced when the active layer of the LED is made of an AlInGaP-based material and the desired emission peak wavelength is in a wavelength band of 560 nm to 610 nm in terms of a dominant wavelength.
The temperature compensation effect is also great in the case of a mixed color or white (pseudo-white) LED having a wavelength of the wavelength conversion material that is excited by the LED, and the emission peak wavelength of the LED itself is shorter than 555 nm.

FIG. 13: is a circuit block diagram showing the light-emitting device concerning the 2nd Embodiment of this invention. The light emitting device includes a light emitting diode (LED) D3 and a light emitting diode (LED) D4. The light emitting diodes D3 and D4 are connected in parallel between the drive control circuit 500 and the ground.
Further, the light emitting diodes D3 and D4 are arranged close to each other, and if necessary, the optical system is devised to output a combined spectrum of both LEDs. The symbols D3 and D4 attached to the light emitting diodes can mean LED chips, and can also mean LED packages on which the LED chips are mounted.

  The emission spectrum of the light emitting diode D3 is set slightly shorter than that of the light emitting diode D4. For example, a yellow AlInGaP LED having a large temperature change is used, the spectral peak wavelength of the light-emitting diode D3 is 584 nm at 25 ° C. (582 nm at the dominant wavelength), and the spectral peak wavelength of the light-emitting diode D4 is 594 nm at 25 ° C. (591 nm at the dominant wavelength). ).

Furthermore, this light-emitting device includes a temperature monitor 600 that detects the temperature of the LED itself or its surroundings, and values and currents of currents I3 and I4 that flow through the two LEDs in parallel according to the detection output from the temperature monitor 600. And a drive control circuit 500 for controlling the ratio. For the temperature monitor 600, a thermistor or the like is used.
In the light emitting device according to the second embodiment, according to the temperature detection output from the temperature monitor 600, the drive control circuit 500 controls and compensates the chromaticity and light flux in the combined spectrum of the plurality of LEDs connected in parallel. .

  FIG. 14 is a diagram showing the emission spectra of the light-emitting diodes D3 and D4 according to the second embodiment of the present invention and their combined spectrum. FIG. 14A shows the light-emitting diode D3 (emission peak wavelength at 25 ° C.). 584 nm) and D4 (emission peak wavelength 594 nm) and a synthetic spectrum of these emissions, (b) is an emission spectrum of light emitting diodes D3 (emission peak wavelength 592 nm) and D4 (emission peak wavelength 602 nm) at 85 ° C. And a synthetic spectrum of these emissions.

  In the case of 25 ° C. shown in FIG. 14A, the drive control circuit 500 follows the total current I and the branch according to the output of the temperature monitor 600 so that the power ratio of the spectrum becomes D3: D4 = 1: 2. Currents I3 and I4 are controlled. In the case of 25 ° C., the chromaticity of the composite spectrum is strongly influenced by the light emitting diode D4 having a long emission wavelength, and (Cx, Cy) = (0.563, 0.436), and the peak wavelength of the composite spectrum is The dominant wavelength is 588 nm.

  In the case of 85 ° C. shown in FIG. 14B, the temperature rises, so that the peak wavelength of each LED is shifted to the longer wavelength side by about 8 nm. Further, if the current is not controlled, the light output (light flux) is also reduced to about half or more. At 85 ° C., the drive control circuit 500 controls the total current I and the branch currents I3 and I4 according to the output of the temperature monitor 600 so that the power ratio of the spectrum becomes D3: D4 = 5: 1. In the case of 85 ° C., the chromaticity of the composite spectrum is strongly influenced by the LED 1d (D4) having a long emission wavelength, and (Cx, Cy) = (0.560, 0.431), and the peak wavelength of the composite spectrum Is 589 nm at the dominant wavelength.

  The dominant wavelength is only 1 nm at 25 ° C. and 85 ° C., and the chromaticity does not change much. Compared with the case where a single-chip yellow LED is red-shifted by 5 nm or more at a dominant wavelength, the color change is sufficiently suppressed, and there is no practical problem. This is because, in the synthetic spectrum, the light-emitting diode D3 on the short wavelength side is controlled to be dominant at a high temperature.

The decrease in the luminous flux can be compensated by increasing the current flowing through the light emitting diode D3. Considering the output ratios of 1: 2 (25 ° C.) and 5: 1 (85 ° C.), the luminous flux is halved by temperature rise without changing the current I3 flowing through the light-emitting diode D4, so that it flows through the light-emitting diode D3. If the current I3 is 10 times that at 25 ° C., the total light flux can be made substantially the same as at 25 ° C. by compensating for the natural decrease in the output of the light emitting diode D3 due to temperature rise.
Thus, higher performance is required for the light emitting diode D3 having a shorter wavelength. For this reason, for example, it is possible to suppress an increase in the total cost by arranging a light emitting diode D3 having a high emission efficiency and a slightly expensive LED, and arranging the light emitting diode D4 as an inexpensive LED.

FIG. 15 is a schematic perspective view showing a first specific example of the light emitting device according to the second embodiment of the present invention. FIG. 16 is a circuit configuration diagram showing a first specific example of the light emitting device according to the second embodiment of the present invention.
As shown in FIG. 15, the first specific example is a light-emitting device according to the second embodiment embodied by an SMD type package. Two LED chips, an LED chip 1c corresponding to the light-emitting diode D3 and an LED chip 1d corresponding to the light-emitting diode D4, are mounted in parallel on the lead frames 11c and 11d, respectively, and are mounted on the lead frame 12 with gold wires 3c and 3d. The SMD type LED package 40 is configured by connection. An NTC (Negative Temperature Coefficient) thermistor 601 is connected to the lead frame 11c which is a terminal of the LED chip 1c (D3).

  As shown in FIG. 16, in the first specific example, a series connection circuit of a light emitting diode D3 (LED chip 1c) and an NTC thermistor 601 and a light emitting diode D4 (LED chip 1d) are connected in parallel. . In FIG. 16, Rs is a series resistance of each LED chip, and R0 and R2 are resistances inserted for assisting the characteristics of the NTC thermistor 601 and adjusting the currents I, I3 and I4.

The NTC thermistor 601 has a characteristic that the resistance value is high at a low temperature and the resistance value is low at a high temperature, and is a resistance element having a negative temperature coefficient. The NTC thermistor 601 functions as the drive control circuit 500 and the temperature monitor 600 shown in FIG. 13, and controls the current I3 flowing through the LED chip 1c (D3) according to the temperature to compensate for the temperature change of the combined spectrum. To do.
The circuit configuration of the first specific example is extremely simple and low in cost. Moreover, since two LED chips are mounted in one package, a compact configuration can be achieved.

  The NTC thermistor 601 is provided on the cathode side of the LED chip 1c in FIG. 15 and is provided on the anode side of the LED chip 1c in FIG. 16, but may be provided on either side.

  In contrast to the first specific example, it is also possible to connect a PTC (Positive Temperature Coefficient) thermistor to the lead frame 11d which is a terminal of the LED chip 1d. This PTC thermistor exhibits a characteristic that a resistance value is small at a low temperature and a resistance value is large at a high temperature, and is a resistance element having a positive temperature coefficient. Furthermore, it is possible to provide both an NTC thermistor and a PTC thermistor. Further, these thermistors can be housed in the envelope 20 of the SMD type package 40 shown in FIG.

FIG. 17 is a schematic perspective view showing a second specific example of the light emitting device according to the second embodiment of the present invention. The second specific example is a modification of the first specific example (see FIG. 15).
In the first specific example, two LED chips are mounted in parallel in one SMD type package. However, in the second specific example, the SMD in which the LED chip 1c is mounted on the upper surface opening of the envelope 20c. The LED package 40c and the SMD LED package 40d in which the LED chip 1d is mounted on the upper surface opening of the envelope 20d are mounted on the substrate 100. However, in this case, it is desirable to provide an optical system for mixing output light from two LED packages that are slightly separated from each other.
In the second specific example, a commercially available product can be used as the two LED packages having different emission wavelengths, so that the cost is low in this respect.

FIG. 18 is a schematic perspective view illustrating a third specific example of the light emitting device according to the second embodiment of the present invention. The third specific example is a modification of the second specific example (see FIG. 17).
In the third specific example, a plurality of piranha type LED packages 45c corresponding to the light emitting diode D3 and a plurality of piranha type LED packages 45d corresponding to the light emitting diode D4 are mounted on the substrate 100. That is, two groups of a plurality of piranha type LED packages having different emission wavelengths are mounted close to each other on one substrate. However, also in this case, it is desirable to provide an optical system for mixing the output light from the two groups of LED packages that are slightly separated from each other.
In the third specific example, the NTC thermistor 601 is commonly used in a plurality of LED packages, which is economical.

FIG. 19 is a circuit configuration diagram illustrating a fourth specific example of the light-emitting device according to the second embodiment of the present invention. The fourth specific example is obtained by connecting two light emitting diodes D3 (LED chips 1c) in series in the first specific example (see FIG. 16).
In the second embodiment of the present invention, higher performance is required for the LED chip 1c having a shorter wavelength. For this reason, for example, a highly efficient LED is disposed as the light emitting diode D3, and the light emitting diode D4 can suppress an increase in the total cost by disposing an inexpensive LED.

However, there are limits to maximizing overall efficiency. Therefore, in the fourth specific example, high-efficiency LED chips are used on both the light emitting diode D3 side and the D4 side, and two light emitting diodes D3 are provided in series. As a result, the branch voltage on the light emitting diode D3 side and the D4 side rises, but at the same current value, the light emission output can be increased as compared with the case where there is one light emitting diode D3. The branch voltage can be adjusted by appropriately selecting the characteristics of the thermistor 601 on the light emitting diode D3 side and the resistance value of the resistor R2 on the light emitting diode D4 side.
As in the fourth specific example, it is possible to arrange various electronic elements such as a plurality of LEDs and resistance elements in each of the branch on the light emitting diode D3 side and the branch on the D4 side.

FIG. 20 is a circuit configuration diagram illustrating a fifth specific example of the light emitting device according to the second embodiment of the present invention. In the fifth specific example, a photodiode (PD: Photo Diode) 650 is used as the temperature monitor 600 (see FIG. 13).
In each of the above specific examples (see FIGS. 15 to 19), an element that directly senses temperature, such as a thermistor, is used as the temperature monitor 600, but a sensor that can indirectly reflect temperature characteristics, such as a photodiode. It is also possible to use.

Since the light output of the light emitting diodes D3 and D4 itself decreases with the temperature rise, the photodiode 650 that detects the light output can be used as the temperature monitor 600, and the temperature can be indirectly monitored by the output current of the photodiode 650. .
The drive control circuit 500 controls the currents I3 and I4 flowing through the branch circuit based on the output current of the photodiode 650 and the temperature coefficient of the light output of the light emitting diodes D3 and D4 obtained in advance.

  In this fifth specific example, the temperature is detected from the light output of the light emitting diodes D3 and D4. However, since the characteristics (light output characteristics) of the LED itself reflect the junction temperature, more realistic and accurate control is possible. There is also an effect that can be done. Other indirect temperature monitoring methods can also be used.

  FIG. 21 is a schematic perspective view showing a sixth specific example of the light emitting device according to the second embodiment of the present invention. In the sixth specific example, an InGaN blue LED chip 1e is used as an LED chip corresponding to the light emitting diode D3, and an InGaN blue LED chip 1g is used as an LED chip corresponding to the light emitting diode D4. The spectrum peak wavelength of the blue LED chip 1e (D3) is 460 nm at 25 ° C., and the spectrum peak wavelength of the blue LED chip 1f (D4) is slightly shifted from this.

  In each of the specific examples so far (see FIGS. 15 to 20), the example in which the second embodiment of the present invention is applied to a single wavelength LED has been described. However, the second embodiment of the present invention can also be applied to a white (pseudo white) LED using a phosphor. In this sixth specific example, a specific example applied to the white LED will be described.

In the visible light band, a short light source having a wavelength of 555 nm or less excites a wavelength conversion material such as a phosphor, and obtains white light (pseudo white) by mixing the excitation light and the wavelength-converted light. Is possible.
As shown in FIG. 21, InGaN blue LED chips 1 e and 1 f whose emission wavelengths are slightly shifted from each other are mounted on lead frames 11 c and 11 d, respectively, and a YAG phosphor 80 is mixed in the transparent resin material 30. The YAG phosphor is excited by the light emission of the InGaN-based blue LED, and the blue LED and the yellow light whose wavelength is converted from YAG are mixed to obtain a pseudo white color.

  FIG. 22 is a schematic perspective view showing a comparative example with the sixth specific example of the light emitting device according to the second embodiment of the present invention. Moreover, FIG. 23 is a figure showing the emission spectrum of the comparative example with the 6th specific example of the light-emitting device concerning the 2nd Embodiment of this invention. This comparative example is constituted by a single chip having only the blue LED chip 1e. The spectrum of the output light of this comparative example becomes a pseudo white spectrum as shown in FIG. 23, and a spectrum shift due to temperature change occurs. Due to this spectral shift, the excitation efficiency of the YGA phosphor 80 varies. Also, the blue light output itself is reduced. Therefore, chromaticity and luminous flux change in a complicated manner.

However, in the sixth specific example shown in FIG. 21, by using the combined light of the blue LED chips 1e and 1f as the excitation light source, the peak wavelength of the excitation light source and the temperature change of the output can be compensated. As a result, the excitation efficiency of the YAG phosphor 80 and the temperature characteristics of blue light transmission can be stabilized, so that the white (pseudo-white) / color mixture chromaticity and luminous flux are stabilized as a whole.
In the same manner, even in the case of using three LEDs that respectively emit the three primary colors of RGB, the second embodiment of the present invention is applied to each of the two colors, and the two emission wavelengths slightly deviated from each other. By arranging the LEDs and controlling them, the white / mixed chromaticity and luminous flux can be stabilized against temperature changes.

  FIG. 24 is a drive waveform diagram showing a specific example of the drive control circuit according to the second embodiment of the present invention. The drive control circuit 500 (see FIG. 13 and the like) is based on the DC drive method. However, the light output of the LED can be controlled not only by simply controlling the DC value of the branch currents I3 and I4 (see FIG. 13 and the like) but also by a PWM (Pulse Width Modulation) drive system.

  As shown in FIG. 24, the PWM drive method controls the brightness with the pulse width in pulse drive faster than the eye response. The wider the pulse width, the brighter. Accordingly, the case of driving with the driving pulse having the pulse width Pw2 (> Pw1) shown in FIG. 24B is brighter than the case of driving with the driving pulse having the pulse width Pw1 shown in FIG.

Such a PWM drive method can be realized by making the drive control circuit 500 a digital circuit capable of PWM. That is, the drive control circuit 500 modulates the light emitting diode D3 side and the D4 side independently with different pulse widths. Each pulse width is controlled based on the output from the temperature monitor 600 (see FIG. 13 and the like). In such a PWM drive system, loss of resistance for adjustment and the like is reduced, and energy saving can be realized.
As described above, according to the second embodiment of the present invention, it is possible to obtain a light-emitting device that compensates for temperature changes in optical output and wavelength and exhibits stable characteristics against temperature changes.

  In addition, this invention is not limited to the said 2nd Embodiment, The structure which connected the some LED chip or LED package in series to the parallel branch circuit of light emitting diode D3, D4 is also included. Further, the parallel branch circuit is not limited to two of the light emitting diodes D3 and D4, and includes those in which three or more are connected in parallel. Furthermore, various combinations of wavelengths are also applicable.

Moreover, in the said embodiment of this invention, although the temperature range was 25 to 85 degreeC, it can be extended also to a wider temperature range. In addition, current control can be flexibly performed according to the temperature characteristics of LEDs having various wavelengths.
The light emitting device having excellent temperature characteristics according to the embodiment of the present invention can improve the performance of a lamp equipped with the same. The lamp and the visible light emitting device function only when integrated, and are difficult to separate. By mounting the light emitting device having the temperature compensation function of the present invention on a lamp, it is possible to realize a lamp having a stable characteristic compensated for a temperature change at low cost.

It is a circuit block diagram of the light-emitting device concerning the 1st Embodiment of this invention. It is a figure showing the temperature characteristic of the forward voltage of the light emitting diode concerning the 1st Embodiment of this invention. It is a figure showing the specific example of the LED chip concerning the 1st Embodiment of this invention. It is a figure showing the temperature change of the spectrum at the time of mounting the light emitting diode concerning the 1st Embodiment of this invention close. It is a model perspective view showing the 1st specific example of the light-emitting device concerning the 1st Embodiment of this invention. It is a model perspective view showing the 1st specific example of the light-emitting device concerning the 1st Embodiment of this invention. It is a model perspective view showing the 1st specific example of the light-emitting device concerning the 1st Embodiment of this invention. It is a model perspective view showing an example of the structure of the light-emitting device concerning the 2nd Embodiment of this invention. It is a model perspective view showing an example of the structure of the light-emitting device concerning the 2nd Embodiment of this invention. It is a model perspective view showing an example of the structure of the light-emitting device concerning the 2nd Embodiment of this invention. It is a model perspective view showing the 3rd specific example of the light-emitting device concerning the 1st Embodiment of this invention. It is a circuit block diagram showing the 3rd specific example of the light-emitting device concerning the 1st Embodiment of this invention. It is a circuit block diagram showing the light-emitting device concerning the 2nd Embodiment of this invention. It is a figure showing the emission spectrum of the light emitting diode concerning the 2nd Embodiment of this invention, and these synthetic spectra. It is a model perspective view showing the 1st specific example of the light-emitting device concerning the 2nd Embodiment of this invention. It is a circuit block diagram showing the 1st specific example of the light-emitting device concerning the 2nd Embodiment of this invention. It is a model perspective view showing the 2nd specific example of the light-emitting device concerning the 2nd Embodiment of this invention. It is a model perspective view showing the 3rd specific example of the light-emitting device concerning the 2nd Embodiment of this invention. It is a circuit block diagram showing the 4th specific example of the light-emitting device concerning the 2nd Embodiment of this invention. It is a circuit block diagram showing the 5th specific example of the light-emitting device concerning the 2nd Embodiment of this invention. It is a model perspective view showing the 6th specific example of the light-emitting device concerning the 2nd Embodiment of this invention. It is a model perspective view showing the comparative example with the 6th specific example of the light-emitting device concerning the 2nd Embodiment of this invention. It is a figure showing the emission spectrum of the comparative example with the 6th specific example of the light-emitting device concerning the 2nd Embodiment of this invention. It is a drive waveform diagram showing the specific example of the drive control circuit concerning the 2nd Embodiment of this invention. It is a figure showing an example of the temperature change of the emission spectrum of LED. It is a figure showing an example of the temperature change of the dominant wavelength of LED. It is a figure showing an example of the temperature change of the luminous intensity of LED.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 LED chip, 2 Electrode pad, 3 Gold wire, 4 Electrode network, 11 Cathode side lead frame, 12 Anode side lead frame, 20 Envelope, 21 Upper surface opening part, 30 Transparent resin material, 40 SMD type LED package, 45 Piranha type LED package, 80 YAG phosphor, 100 substrate, 110 cathode side solder pattern, 111,112 solder, 120 anode side solder pattern, 121 solder, 130 resistance element, 500 drive control circuit, 600 temperature monitor, 601 NTC thermistor, 650 Photodiode, D1, D2, D3, D4 Light emitting diode (LED)

Claims (6)

A first semiconductor light emitting element and a second semiconductor light emitting element connected in parallel;
The first semiconductor light emitting device has higher luminous efficiency than the second semiconductor light emitting device,
The temperature coefficient of the series resistance of the first semiconductor light emitting element is negative,
The absolute value of the temperature coefficient of the series resistance of the first semiconductor light emitting element is larger than the absolute value of the temperature coefficient of the series resistance of the second semiconductor light emitting element.   The light emitting device according to claim 1, wherein the first semiconductor light emitting element has an emission peak wavelength shorter than an emission peak wavelength of the second semiconductor light emitting element. The first and second semiconductor light emitting elements have an electrode network formed on a surface from which light is extracted,
3. The light emitting device according to claim 1, wherein a density of the electrode network of the first semiconductor light emitting element is lower than a density of the electrode network of the second semiconductor light emitting element. A first package containing the first semiconductor light emitting element;
A second package containing the second semiconductor light emitting element;
A substrate on which the first and second packages are mounted;
The light-emitting device according to claim 1, further comprising: A resistance element that increases a difference between the temperature coefficient of the series resistance of the first semiconductor light emitting element and the temperature coefficient of the series resistance of the second semiconductor light emitting element;
The light emitting device according to claim 4, wherein the resistance element is mounted on the substrate and connected in series to the first semiconductor light emitting element or the second semiconductor light emitting element. A lamp comprising the light emitting device according to any one of claims 1 to 5 .

Images