JPH09246602A - Light emitting diode array light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a high luminous intensity per unit length by preventing the temp. rise of a light emitting diode array light source to increase the operating current. SOLUTION: Current limiting resistors 10 connected in series to a number of series connected light emitting diode chips are removed from a printed board of this light source. Instead of them, one or more current limiting resistors 10 are connected to a set 21 which mounts this light source, so as to be in series to all the chips 12.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode array light source suitable for a light source used in an image scanner for image reading of a facsimile, a word processor or a copying machine.

[0002]

2. Description of the Related Art In recent years, light emitting diode aligned light sources for image reading have been used as parts for illuminating a document whose image information is read by an image sensor in a facsimile, a word processor or an image scanner section of a copying machine. There is. Hereinafter, an example of a conventional light emitting diode array light source for image reading will be described with reference to FIGS.

FIG. 4 is a sectional view of a main part of a contact type image scanner section using this light emitting diode array light source.
The contact-type image scanner unit includes a light emitting diode alignment light source 1, a document 2, a SELFOC lens (trade name of Nippon Sheet Glass Co., Ltd.) array 4, and an image sensor 5. Position 3 is on the optical axis of the Selfoc lens array 4. An optical fiber array may be used instead of the SELFOC lens array 4. In this contact-type image scanner unit, light is emitted from the light emitting diode alignment light source 1 along a reading line in a direction perpendicular to the paper surface of FIG. 4 on the original 2, and reflected light from the original 2 is reflected by the SELFOC lens array 4. It is focused and guided to the image sensor 5 arranged on the same straight line. The reflected light is received by the image sensor 5, and the image information decomposed into minute pixels is taken out as an electric signal corresponding to each pixel density.

5 and 6 are a perspective view and a cross-sectional view taken along line VI-VI of FIG. 5, respectively, of a light emitting diode alignment light source used in this contact type image scanner unit. As shown in FIG. 5, the light emitting diode array light source includes a printed wiring board 6 on which a predetermined conductive circuit (not shown) is formed, a light emitting diode chip 7, thin metal wires 8, a transparent resin sealing body 9,
And a current limiting resistor 10.

Printed wiring board 6 on which a conductive circuit is formed
A plurality of light emitting diode chips 7 are linearly attached to each of the predetermined locations with a conductive adhesive, and one electrode of the light emitting diode chips 7 is electrically connected. The other electrode of the light emitting diode chip 7 is connected to a predetermined conductor of the printed wiring board 6 by a thin metal wire 8. The current limiting resistor 10 is for limiting the supply current to the light emitting diode chips 7 connected in series to a predetermined value. As shown in the circuit diagram of FIG. 7, for each group of a certain number (four in FIG. 7) of light emitting diode chips 7 connected in series, the number of the light emitting diode chips 7 connected in series corresponds to the number of diode chips. A current limiting resistor 10 having a predetermined resistance value is mounted on the printed wiring board 6 and electrically connected to the conductor. The current limiting resistor 10 also reduces the variation in the operating current between the groups of the light emitting diode chips 7 connected in parallel due to the variation in the forward voltage of the individual light emitting diode chips 7. According to such a conventional contact type image scanner unit, as shown in FIG. 4, the light emitted from the light emitting diode chip 7 is transmitted to the outside through the transparent resin encapsulant 9, and the position of the document 2 is reduced. Illuminate 3.

[0006]

In the conventional LED array light source, it is necessary to increase the luminous intensity of the LED chip 7 in order to achieve the higher luminous intensity required by the market. However, in recent semiconductor technology, the increase in luminous intensity has leveled off, and further improvement in luminous intensity cannot be expected. Therefore, in order to improve the luminous intensity, it is necessary to increase the operating current per chip of the light emitting diode chip 7. When the operating current is increased, the temperature of the current limiting resistor 10 is further increased due to heat generation, so that the temperature thereof rises, which may exceed the allowable temperature of the junction portion of the light emitting diode chip 7. Therefore, a problem occurs in the reliability of the light emitting diode chip 7, and it is difficult to increase the luminous intensity by increasing the current more than the current one. Further, due to the heat generation of the current limiting resistor 10, the temperature of the light emitting diode chip 7 in the vicinity of the current limiting resistor 10 becomes higher than that of the other light emitting diode chips 7, and the wavelength of the emitted light changes to that of the other light emitting diode 7. To change. As a result, the emission wavelength of the light emitting diode aligned light source as a whole varies. It is difficult to eliminate the wavelength variation due to the heat generation of the current limiting resistor 10 only by devising the arrangement of the current limiting resistor 10 on the printed wiring board 6. Further, since the light emitting diode chips 7 have variations in forward voltage, current variations between groups of the light emitting diode chips 7 connected in parallel are large when the current limiting resistor 10 is not provided. There is a problem that the light intensity variation in the entire light emitting diode aligned light source becomes large. Therefore, the current limiting resistor 1 having a function of reducing the variation in the operating current between the groups of the light emitting diode chips 7 connected in parallel
It is difficult to remove 0.

Further, in an apparatus incorporating such a light emitting diode array light source, there is a demand for downsizing and weight reduction of the apparatus itself. Therefore, it is also required for each component of the apparatus to be light, thin and short. . However, in the structure of the conventional light emitting diode aligned light source, it is very difficult to miniaturize because it is necessary to secure a space for mounting the current limiting resistor 10 and a space for heat dissipation, and it is necessary to meet the market needs. There was a problem that I could not.

Further, the heat generation of the current limiting resistor 10 on the printed wiring board 6 restricts the arrangement of the light emitting diode chip 7 in a position close to the current limiting resistor 10, depending on the intended use and application. Therefore, it was not possible to arrange an arbitrary number of light emitting diode chips 7 at an arbitrary pitch, and it was not possible to form an arbitrary illuminance distribution.

The present invention solves the above-mentioned problems of the prior art by avoiding heat generation from the current limiting resistor 10 to increase the luminous intensity by increasing the operating current and to improve the variation of the emission wavelength of the light emitting diode chip 7. An object of the present invention is to provide a light source for aligning light emitting diodes for image reading, which can cope with downsizing of a light source and can form an arbitrary illuminance distribution.

[0010]

In order to achieve the above object, a light emitting diode array light source of the present invention is arranged linearly at a predetermined position of a conductive circuit on a printed wiring board having a conductive circuit formed thereon. A plurality of light emitting diode groups, which are attached and attached and in which a fixed number of light emitting diodes are connected in series, are electrically connected in parallel. Further, instead of providing the current limiting resistor on the printed wiring board of the light emitting diode aligned light source, on the side of the device to which the light emitting diode aligned light source is mounted instead, there is a series connection between the power source of the light emitting diode aligned light source and the light source aligned with the light emitting diode. In some cases, one or more current limiting resistors are provided.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A light emitting diode array light source of the present invention comprises a printed wiring board on which a conductive circuit is formed and a plurality of light emitting diodes linearly arranged at predetermined locations of the conductive circuit of the printed wiring board. The plurality of light emitting diodes are connected in parallel by a plurality of light emitting diode groups in which a fixed number of light emitting diodes are connected in series by the conductive circuit.

There is also an invention in which a current limiting resistor for a light emitting diode is provided between the printed wiring board and a power source and provided in an apparatus incorporating the light emitting diode alignment light source.

Since the current limiting resistor is removed from the printed wiring board and mounted on the device side instead, the influence of heat generated from the current limiting resistor is eliminated, and the operating current of the light emitting diode can be increased, which is It is possible to achieve the desired high luminous intensity. Further, it is possible to improve the variation in the emission wavelength of the light emitting diode due to the heat generated from the current limiting resistor.

Further, since the current limiting resistor is not provided on the printed wiring board, it is possible to reduce the number of parts, the number of assembling steps, and the width of the printed wiring board. Further, not only the cost can be reduced by reducing the material cost due to the increase in the number of the printed-circuit boards taken from the standard size material, but also the miniaturization of the light source is facilitated and the degree of freedom in design is increased. On the other hand, as for the entire device, a plurality of current limiting resistors, which were conventionally equipped for a fixed number of light emitting diode groups connected in series, were removed from the printed wiring board of the light emitting diode array light source, and instead the light emitting diodes were replaced. On the side of the device to which the aligned light source is attached, one or more current limiting resistors are provided between the light emitting diode aligned light source and the power source. Therefore, the number of resistor parts is reduced, and the cost is reduced.

Further, by removing the current limiting resistor from the printed wiring board, there is no restriction on the arrangement of the light emitting diodes, the conductor pattern of the printed wiring board is formed in an arbitrary shape, and an arbitrary number of light emission is performed. The diodes are arranged linearly at an arbitrary pitch. Therefore, it is possible to realize the illuminance according to the intended purpose and application. Further, the pitch of the arrangement of the light emitting diodes is equal pitch, and the illuminance distribution of the same magnification system for obtaining a uniform illuminance distribution, or by arbitrarily changing the pitch of the light emitting diodes, an arbitrary illuminance distribution, for example, with respect to the central part As a result, it becomes easy to obtain a reduced illuminance distribution that draws a 1 / cos 4θ curve in which the illuminance at both ends is high, and it is possible to easily design products according to market demands.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of an embodiment of the light emitting diode aligned light source of the present invention will be described below with reference to FIGS. 1 is a perspective view of this embodiment, and FIG. 2 is FIG.
11 is a sectional view taken along line II-II of FIG. In FIG. 1 and FIG. 2, first, the printed wiring board 11 is formed by cutting a fixed-sized material into processed substrates (not shown) of a size including a plurality of printed wiring boards 11, and taking a plurality of printed wiring boards 11 for cost reduction. And A plurality of conductive circuits 15 having a predetermined wiring circuit pattern are simultaneously formed on this processed substrate. After forming the conductive circuit 15, the processed substrate is cut into a predetermined size and divided into individual printed wiring boards 11. As shown in FIGS. 1A and 1B, each light emitting diode chip 12 has a conductive circuit 15
One of the electrodes is linearly attached to a predetermined position of the conductive adhesive to electrically connect the electrodes. The other electrode of the light emitting diode chip 12 is connected to a predetermined portion of the other conductive circuit 15 by a thin metal wire 13. The pitch of the arrangement of the light emitting diode chips 12 is, for example, 2 to 10 mm.
It is.

The light emitting diode chips 12 arranged linearly, a part of the conductive circuit 15 to which the light emitting diode chips 12 are electrically connected, and the thin metal wires 13 are placed on the surface of the printed wiring board 11. It is sealed with resin. The resin encapsulation protects the parts by encapsulating the parts on the printed wiring board 11 with the transparent resin encapsulant 14 such as a silicone resin. A resist layer 16 is formed on the surface of the printed wiring board 11 by applying a resist agent in order to prevent the adhesion of solder, except for the conductor portion connecting the light emitting diode chip 12 and the thin metal wire 13. Resist layer 16
Is preferably a color having a high light reflectance, for example, white in order to reflect the emitted light of the light emitting diode chip 12 and extract it efficiently.

With the recent development of semiconductor manufacturing technology, variations in the forward voltage of the light emitting diode chip 12 can be suppressed to a small level. In addition to this, since a technique for selecting a forward voltage has been developed, by using the light emitting diode chip 12 thus selected, the forward voltage of a series connection body of a certain number of light emitting diodes connected in series can be improved. The variation is reduced. Therefore, it has become possible to reduce variations in operating current between the series-connected bodies 18, 19 ... Therefore, as shown in FIG. 7 of the conventional example, the light emitting diode chips 7 are divided into several groups, the light emitting diode chips 7 in each group are connected in series, and the current limiting resistor 10 is provided for each group. No longer needed. Therefore, a large number of light emitting diode chips 12
It is sufficient to connect one current limiting resistor 10 in series to the series-parallel connection body 22 in which a plurality of series connection bodies are connected in parallel. Two or more current limiting resistors 10 may be connected. As a result, the current limiting resistor 10 is applied from above the printed wiring board 11.
It is possible to adopt a method in which one or more current limiting resistors 10 are mounted on the side of the device 21 in which the printed wiring board 11 is incorporated by removing the above. FIG. 3 is a circuit diagram showing a connection example of the light emitting diode chip 12 of the light emitting diode aligned light source of this embodiment. In the figure, the light emitting diode chips 12 are divided into a first group 18 and a second group 19, and all the groups 18 and 19 are connected in series. The first group 18 and the second group 19 are connected in parallel with each other. The current limiting resistor 10 includes a series-parallel connection body 22 including a first group and a second group, which are connected in parallel with each other, and a power supply 2.
It is connected in series with 0. The method of connecting the light emitting diode chips 12 is not limited to the circuit diagram shown in FIG. 3, and any method may be used. A printed wiring board for a large number of mounting components is generally used on the side of the device 21 in which the light emitting diode array light source is incorporated, so that there is room in terms of space. Therefore, even if the size is large, 1
Incorporating one or more current limiting resistors 10 into the device side poses no problem. For example, the resistor 10 may be mounted simultaneously with other mounted components on a printed wiring board shared with other mounted components.

According to the embodiment of the present invention, the current limiting resistor 1 is provided on the printed wiring board of the light emitting diode array light source.
Since 0 is not provided, it is not affected by heat generated from the current limiting resistor 10. Therefore, the operating current of the light emitting diode chip 12 can be increased, and the luminous intensity of the light emitting diode can be increased, which is a market demand. Further, since the current limiting resistor 10 is not provided on the printed circuit board 11, the temperature imbalance between the light emitting diode chips 12 is eliminated, and the variation in the light emission wavelength between the light emitting diode chips 12 due to the temperature imbalance occurs. Can be improved. Regarding the light emitting diode array light source itself, the cost can be reduced by not providing the current limiting resistor and shortening the assembly process accordingly. Further, since the current limiting resistor is not provided, the width of the printed wiring board 11 can be narrowed and the light emitting diode aligned light source can be miniaturized. Further, the material cost is reduced due to an increase in the number of substrates that can be taken from the standard length sheet material, resulting in cost reduction.

Further, since the light emitting diode array light source of this embodiment does not have a current limiting resistor, there is no restriction on the arrangement of the light emitting diode chip 12, and the pattern of the conductive circuit 15 can be changed according to the application or purpose of use. Any number of the light emitting diode chips 12 can be arranged at any pitch. Therefore, it is possible to obtain an arbitrary illuminance according to the purpose or purpose of use. In the case of being used by being incorporated in an image scanner or the like, it is possible to obtain a light emitting diode aligned light source having an equal magnification illuminance distribution in which the pitch of the light emitting diode chips 12 is equal. Also, if the illuminance of the original surface illuminated by the light emitting diode alignment light source is directly incorporated into a device that needs to have higher illuminance at both ends of the original, the pitch of the light emitting diode chips can be changed arbitrarily. Allows any illuminance distribution, for example 1
It is possible to realize a light emitting diode aligned light source that forms a reduced system illuminance distribution that conforms to the / cos 4θ curve. In this way, product design according to market demands becomes easy. In this embodiment, the light emitting diode chip 12 is directly arranged on the printed wiring board 11 and fixed by a conductive adhesive. However, the light emitting diode chip 12 is adhered and fixed by a lead frame or the like and is fixed by an epoxy resin or the like. The same effect can be obtained by using a sealed single type light emitting diode.

[0021]

Since the light emitting diode array light source of the present invention does not have a current limiting resistor on the printed wiring board,
There is no temperature rise due to heat generated from the current limiting resistor.
Therefore, the operating current of the light emitting diode chip is increased by that amount, and high luminous intensity can be realized. Further, it is possible to eliminate the variation in the emission wavelength of the light emitting diode due to the heat generated from the current limiting resistor and to reduce the variation in the luminous intensity due to the temperature imbalance.

Moreover, since the current limiting resistor is not provided on the printed circuit board forming the light emitting diode aligned light source, the number of parts is reduced and the assembly process is shortened, resulting in cost reduction. Further, since there is no current limiting resistor, the width of the wiring board can be narrowed, which allows the LED light source to be further miniaturized, and as a result, the device for mounting the LED light source to be miniaturized. You can In addition, the increase in the number of printed wiring boards obtained from the regular-sized sheet material reduces the material cost and enables cost reduction.

Furthermore, by changing the conductor pattern of the printed wiring board according to the application or purpose of use, it is possible to arrange an arbitrary number of light emitting diode chips in a straight line at an arbitrary pitch. As a result, it is possible to realize the illuminance level according to the purpose and purpose of use. Further, by reducing the illuminance distribution of equal magnification system in which the pitch of the light emitting diode chips is equal, or by arbitrarily changing the pitch of the light emitting diode chips, a reduced system illuminance distribution of an arbitrary illuminance distribution, for example, a 1 / cos 4θ curve is formed. This makes it easier to design products according to market demands.

[Brief description of drawings]

FIG. 1A is a perspective view of a light emitting diode array light source according to an embodiment of the present invention. FIG. 1B is a partially enlarged view of the perspective view of FIG.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is a circuit diagram of a connection example of light emitting diode chips of a light emitting diode aligned light source that is an embodiment of the present invention.

FIG. 4 is a sectional view of a main part of an image scanner using a conventional light emitting diode aligned light source.

5 is a perspective view of a conventional light emitting diode alignment light source used in the image scanner of FIG.

6 is a sectional view taken along line VI-VI of FIG.

FIG. 7 is an example of a circuit diagram showing connection of light emitting diode chips of a conventional light emitting diode array light source.

[Explanation of symbols]

 10 Current Limiting Resistor 11 Printed Wiring Board 12 Light Emitting Diode Chip 15 Conductive Circuit 20 Power Supply 21 Device

Claims (2)

[Claims] 1. A printed wiring board having a conductive circuit formed thereon, and a light emitting diode group in which a fixed number of light emitting diodes are linearly arranged at predetermined locations of the conductive circuit of the printed wiring board and connected in series by the conductive circuit. And a plurality of light emitting diode aligned arrays electrically connected in parallel to each other. 2. The at least one current limiting resistor for limiting the current of the light emitting diode is provided between the printed wiring board and the power source and in a device incorporating the light emitting diode aligned light source. 1. The light emitting diode aligned light source according to 1. [0001]