JP2005303175A - LED light source - Google Patents

Abstract

To provide an LED light source having a simple structure and reliably increasing resistance to static electricity.
The present invention provides an LED light source that has a simple configuration and reliably increases resistance to static electricity by a configuration in which capacitors are connected in parallel with both ends of three or more GaN-based LEDs connected in series. Can do.
[Selection] Figure 1

Description

  The present invention relates to an LED light source with increased resistance to static electricity.

  A GaN-based LED has a low withstand voltage against static electricity, and many studies have been made on improvement of withstand voltage. For example, a conventional LED light source (chip-type light emitting element) has a terminal of an LED in order to increase the withstand voltage against static electricity. An example is shown in which a Zener diode is connected in parallel as a protective element (for example, Patent Document 1). 5 and 6 show a conventional LED light source (chip-type light emitting element) described in Patent Document 1. FIG.

In FIG. 6, the Zener diode chip 5 is connected to the LED chip 3 in parallel. FIG. 5 shows a circuit diagram.
Japanese Patent Laid-Open No. 11-54804 (see FIGS. 1 and 4)

  However, the amount of light per LED is small, and it is necessary to use a large number of LEDs for use in applications such as lighting. Therefore, in the configuration of FIG. 8, it is necessary to connect a Zener diode for each LED chip, and in the configuration using a large number of LEDs, the configuration is complicated and the number of parts increases. There is a problem that it is not realistic in terms of cost.

  Therefore, in order to reduce the number of Zener diodes when a large number of LEDs are used, consider a case where only one Zener diode is connected to both ends of 32 series-connected LEDs, for example. When a voltage is applied so that a current flows in a direction in which the LED is lit, a voltage generated at both ends of the Zener diode is applied to the LED. However, if the rated voltage per LED is 3.6 V, 3.6 × 32 = 115V. Thus, since a Zener diode capable of handling a high voltage is not commercially available, it cannot be realized.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an LED light source having a simple structure and a small number of parts, which reliably increases resistance to static electricity.

  In order to solve the above conventional problems, in the LED light source according to the present invention, capacitors are connected in parallel to both ends of GaN-based LEDs connected in series of three or more.

  In a preferred embodiment, the capacitor is 100 pF or greater.

  As described above, according to the present invention, a capacitor is connected in parallel to both ends of three or more GaN-based LEDs connected in series, so that it is simple and reliable with respect to static electricity with a small number of parts. It is possible to provide an LED light source with an improved height.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 shows a circuit diagram of an LED light source according to the first embodiment of the present invention.

  In FIG. 1, an LED 101 is a GaN-based LED having an emission center wavelength of 350 to 550 nm. The size of the LED chip is about 0.3 to 2 mm square. Rated light output at about 3-4V. The rated current of the LED is proportional to the area of the light emitting layer, and a current of 10 to 60 mA per 0.3 mm square is appropriate. The LED 101 according to the present embodiment has an emission center wavelength of 470 nm, a chip size of 0.3 mm square, and a rating of 3.6 V and 20 mA.

  32 LEDs of the same type are connected in series, and a capacitor 102 is mounted in parallel with both ends of the LED light source. The capacitor 102 is a ceramic capacitor and has a capacity of 100 p to 10,000 μF. A capacitor of 470 pF was used in this embodiment.

  Between the terminals of this LED light source, when a direct current of about 100 to 120 V is applied, it is designed so that it is almost lit.

FIG. 2 shows an overview of the LED light source. The LED 101 is directly mounted by flip chip on a substrate 201 whose main component is a material having high thermal conductivity such as aluminum, ceramic, or copper. Here, the direct mounting indicates a state in which the wiring pattern and the LED on the substrate are mounted only through the metal for connection. On the substrate, two LED light sources shown in FIG. 1 are configured in parallel, and are configured by a total of 64 LEDs 101 and two chip capacitors 102. The range in which the LED is mounted is 20 mm square. Further, the mounting density per substrate area of this portion is 16 pieces / cm ² . The power per substrate area of the light emitting part is about 1.2 W / cm ² . The mounting density is about 1 to 100 / cm ² . Moreover, about 0.1-10 W / cm < ² > is used for the electric power per said board | substrate area.

  In the present embodiment, a substrate having a structure in which the LED 101 is flip-chip mounted on a composite substrate mainly composed of aluminum via bumps and a chip capacitor is mounted on the substrate is used.

  The substrate 201 has a size of about 24 × about 29 mm and a thickness of about 1 mm. Most of the thickness is made of Al. The power supply terminal 202 is on the same surface as the LED mounting surface on the substrate, and the LED is lit by applying a voltage to the terminal. There are 4 terminals for 2 parallel terminals. The capacitor 102 is mounted on the same surface as the substrate surface on which the LEDs are mounted.

  Although not shown in the drawing, the wiring pattern on the substrate 201 is covered with an insulating layer on the surface other than the portion connected to the LED and the portion of the terminal 202, and external static electricity is generated on the substrate pattern. Is not applied to.

  The contents of the electrostatic breakdown test of this LED light source will be described below. This test was performed based on the method of the human body model (HBM: human body charging model) determined by the standard of the electrostatic breakdown test. This experimental method will be described below. FIG. 3 shows a circuit diagram of the test apparatus. The voltage of the DC power supply 301 in the figure is changed, the switch 302 is operated, and the two terminals are reciprocated three times every second. When the switch is set to the charge side, the charge of the power source 301 is charged to the capacitor. When the switch 302 is set to the discharge side, the charge stored in the capacitor passes through the resistor and the charge is applied to the LED light source connected between the connection terminals 303. Is done.

  The terminal 202 of the LED light source in FIG. 2 and the terminal 303 in FIG. 3 were connected, and an electrostatic breakdown test was performed. As a method of checking, when a current of 1 mA was applied to 32 LEDs connected in series with respect to a rated current of 20 mA and there was an LED element that did not light, it was determined that the LED element was damaged. The above experiment was repeated by gradually increasing the voltage of the DC power supply 301, and the maximum voltage (voltage of the power supply 301) at which no LED element was damaged was defined as the electrostatic withstand voltage of the LED light source.

  As a result, when the voltage application direction was the forward direction, the withstand voltage was 5 kV and the reverse direction was 5 kV. Here, considering that the LED light source according to the present embodiment is used for various purposes such as general lighting, the necessary breakdown voltage is about 1 kV, and the examination was advanced. From this result, it can be seen that it has a sufficient breakdown voltage.

  On the other hand, as shown in FIG. 4, when the capacitor 102 was removed from the LED lighting circuit of the present embodiment shown in FIG. 1, the electrostatic breakdown test was similarly performed, and the forward direction was 4 kV and the reverse direction was 600 V. Does not meet the requirements of electrostatic withstand voltage. In addition, the withstand voltage in the case of only one LED 101 is 200 V in the reverse direction. Since the LED light source of this embodiment has 32 LEDs connected in series, it should theoretically exhibit a breakdown voltage of 6.4 kV, which is 32 times the breakdown voltage per LED. It has only about double the pressure resistance.

  When the numbers D1, D2,..., D31, D32 are assigned in order from the current input side, the LEDs that are damaged when a reverse voltage is applied are D1, D2, D3 and D30, D31, D32. There is a tendency that the LED is damaged and both ends of the series connection are damaged. In general, when LEDs having the same rated voltage are connected in series, the voltage is equally applied to all the LEDs, so that there should be no such regularity that the LEDs are damaged. However, as described above, the fact that both end portions of LEDs connected in series are intensively damaged is considered to be caused by the following phenomenon. In the electrostatic breakdown test, a large voltage and current are instantaneously applied in order to instantaneously input the electric charge of the capacitor to the LED element. In such a transitional change, the minute conductance or inductance of the LED has an effect, and it is considered that a load is concentrated on the ends of the LEDs in series.

  Therefore, as in this embodiment, an LED light source with high electrostatic withstand voltage can be obtained by simply connecting a capacitor in parallel to both ends of a plurality of LEDs connected in series.

  Note that even if the LED 101 does not have the same emission color, a similar effect can be obtained because it is an element having a low electrostatic withstand voltage if it is a GaN-based one.

  In the configuration of the present embodiment, a great effect can be obtained for both forward and reverse voltages. However, since the electrostatic withstand voltage can be increased with one capacitor, the number of countermeasure parts for the number of LEDs can be reduced as the number of series increases. The case of 3 or more is particularly preferable.

  In order to obtain a high luminous flux, it is necessary to arrange the LEDs at as high a density as possible. However, by directly mounting on a substrate with high heat dissipation as in this embodiment, the heat from the LEDs efficiently passes through the substrate. Since the heat is exhausted, the mounting density of the LEDs can be increased. Further, when mounted at a high density, a Zener diode is not required for each LED as in the prior art, so that a simple configuration and a low cost configuration can be achieved, and the mounting density can be increased. Further, as shown in the present embodiment, by flip-chip mounting, a wire connecting the LED and the substrate becomes unnecessary, and a higher density LED mounting density can be realized.

  Here, FIG. 7 shows the result of the withstand voltage test performed by changing the capacitance of the capacitor 701. From this result, the electrostatic withstand voltage depends on the capacitance, and when it exceeds 100 pF, the withstand voltage becomes 1 kV or more.

  Thus, by inserting a capacitor of 100 pF or more in parallel at both ends of the LED light source, the electrostatic withstand voltage is dramatically improved and becomes 1 kV or more. Particularly preferred is 470 pF or more, and the electrostatic withstand voltage is 5 kV or more.

  In all of the above-described embodiments, the LED has an emission center wavelength of 350 to 550 nm. However, an LED using a wavelength conversion means such as a phosphor around the LED can achieve the same effect.

  In all the above embodiments, the capacitor added to the LED is preferably mounted on the same surface as the surface on which the LED of the substrate is mounted as shown in the embodiment. In addition, these elements are also mounted through bumps, so that heat dissipation is improved.

  In all of the above-described embodiments, examples of LED lighting circuits in which LEDs are densely mounted on a small substrate have been described. With such a configuration, a small light source can be obtained. Of course, it is not limited to this embodiment.

  In all the embodiments described above, the LED is simply mounted on the substrate. However, a device in which an optical system such as a phosphor, a reflecting mirror, or a lens is formed around the LED has the same effect. In particular, by using a blue LED and a yellow phosphor, a white light source can be obtained by forming a reflecting mirror and a lens around the phosphor, so that it is possible to obtain a light source suitable for applications such as illumination. I can do it. An example of this is shown in FIG. FIG. 8 is a partial cross-sectional view of an LED light source. With such a configuration, a white focused light source with high luminance can be obtained.

  The present invention is particularly useful for illumination and light sources using LEDs because the resistance to static electricity of GaN LEDs connected in series of three or more in series can be reliably increased with a simple configuration.

The circuit diagram of the LED light source in Embodiment 1 of this invention Schematic of the LED light source in Embodiment 1 of this invention Circuit diagram of electrostatic breakdown device The figure which changed the position of the rectifier diode of the lighting circuit of this Embodiment 1. Schematic diagram of a conventional LED light source (chip-type light emitting device) Circuit diagram of conventional LED light source (chip-type light emitting device) The figure showing the relationship between the capacitor capacity and withstand voltage in the first embodiment of the present invention The fragmentary sectional view of the LED light source in Embodiment 1 of this invention

Explanation of symbols

101 LED
102 Capacitor 201 Board 202 Terminal 301 DC Power Supply 302 Switch 303 Terminal

Claims (2)

An LED light source in which three or more light emission center wavelengths connected in series are connected in parallel to both ends of a GaN LED in parallel. The LED light source according to claim 1, wherein the capacitor is 100 pF or more.

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