JPH04132275A - Light emitting diode light source - Google Patents

Abstract

PURPOSE:To adjust the quantity of light with high accuracy by a small number of procedures by connecting serially-connected LED chips, one end of each of which is connected to an electrode, a plurality of resistors of different resistance values, and a plurality of fuses one end of each of which is connected to an electrode. CONSTITUTION:LED chips D1-D4 are tie-bonded on LED patterns 15 and one end of each of them is connected to the wiring patterns 15 in series by wire bonding. A probe is applied in this state to determine adjusting resistance to obtain the most suitable light output value and one or more resistors are selected from resistors R1-R6 to obtain combined resistance the closest to the adjusting resistance. An over-current is passed between a cathode electrode 3 and trim pads 8 connected to the resistors not selected and trim fuses 7 are blown to open the circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an LED light source, and particularly to an LED light source for an image sensor used for reading a document in a facsimile terminal.

[Prior Art] LEDs (light emitting diodes) have been used as light sources for image sensors and the like, but these EDs have characteristics in which individual outputs vary due to variations during manufacturing, especially during epitaxial growth. is common. Therefore, as shown in FIG.
A method of adjusting the light amount is used in which DDI to D4 and a resistor R for adjusting the light amount are connected in series. That is, by applying a probe to the LED chip, a current is actually applied to the LED chip to cause it to emit light, and a resistance value RO that optimizes the amount of light emitted from the LED chip is determined. Then, a chip resistor R having a resistance value closest to this optimum resistance value RO is selected and connected in series with the four LED chips.

However, since the types of resistance values of chip resistors are limited, it is extremely difficult to adjust the optical output of the LES chip with high precision. Therefore, the applicant of the present application has previously proposed an LED light source as shown in FIG.

In this LED light source, a plurality of resistors R1 to R6 having different resistance values are formed in advance, and a probe is applied to apply a current to LEDDI to p4 to determine the value RO of the adjustment resistor that optimizes the light output. . Then, one or more resistors are selected from the plurality of resistors R1 to R6 so as to obtain a value closest to this adjusted resistance value RO,
It is bonded to the LED DI-D4 connected in series using a wire.

In this LED light source, multiple resistors are formed in advance, so the number of combinations of resistors increases, and therefore a very wide variety of combined resistance values can be obtained, compared to when using chip resistors. This makes it possible to adjust the light output with extremely high precision.

[Problems to be Solved by the Invention] However, when using an LED light source as shown in FIG. 3, although highly accurate light output adjustment can be obtained, multiple resistor R1
- a process of selecting one or more from Re;
It is necessary to go through a process of wire bonding one or more resistors selected in this way to a wiring pattern such as a cathode electrode, which poses a problem in that the process becomes complicated.

The present invention was made in view of the above-mentioned conventional problems, and its purpose is to provide an LE that allows highly accurate light M adjustment with a small number of steps.
D. To provide a light source.

[Means for Solving the Problems] In order to achieve the above object, an LED light source according to the present invention includes a plurality of series-connected VCLED chips, one end of which is connected to an electrode, and a plurality of series-connected VCLED chips that are connected to the series-connected LED chips. , a plurality of resistors having mutually different resistance values, and a plurality of fuses having one end connected to each of the plurality of resistors and the other end connected to an electrode.

[Function] The LED light source of the present invention has such a configuration, in which a plurality of resistors having different resistance values are formed in advance, and these resistors are connected between the LED chip and the electrode via a fuse. When adjusting the light intensity of the LED chip,
By energizing and blowing out fuses connected to resistors other than the desired resistor, an optimum resistance value can be obtained without going through a wire bonding process.

C Embodiment] Hereinafter, preferred embodiments of the LED light source according to the present invention will be described with reference to the drawings.

FIG. 1 shows a part of the wiring pattern of the printed circuit board of the LED light source of this embodiment. This printed circuit board is in the form of a strip, and glass epoxy, which is inexpensive and has excellent workability, is used as the material for the printed circuit board itself, but ceramic, glass, etc. may also be used.

The wiring pattern formed on the printed circuit board includes an anode electrode 3, a cathode electrode 4, an LED pattern 15, a wire bonding pattern 16, and a plurality of resistors R1-Re formed in parallel and having different resistance values in stages. and a plurality of fuses 7 connected in series to each of the plurality of resistors R1-Re. LED pattern 1
5. The wire bonding pattern 16 and the resistor 5 are provided for each block, and a part of the LED pattern 15 is integrated with the anode electrode 3.

Furthermore, LED chips DJ, D2, D3, and D4 are die-bonded onto the LED pattern 15, respectively.

On the other hand, the resistors R1 to R6 are formed by diffusing impurities onto a silicon chip, and each of the resistors R1 to Re is formed to have a resistance value that is successively different in a stepwise manner by adjusting the impurity concentration. Furthermore, a trim pad 8 is formed in parallel with the fuse 7 described above for each resistor R1-Re.

The LED light source of this example has such a configuration,
- The LED chips Di SD2, D3, and D4 are connected in series by wire bonding to the wiring pattern 15, respectively. In this state, a probe (not shown) is applied to actually cause the LED chips DISD2, D3, and D4 to emit light, and the light output thereof is measured. Then, an adjustment resistor RO is determined so that the optical output becomes the optimum value, and one or more resistors are selected from among the resistors R1 to R6 so as to obtain a combined resistance closest to this adjustment resistor RO. . At this time, resistor R
Since there are many combinations of 1 to R6, fine adjustment of the resistance value is possible.

For the resistors not selected, an overcurrent is passed between the trim pad connected to the resistor and the cathode electrode, and the trim fuse 7 connected in series to the resistor is passed through.
burn out and open the circuit.

In this way, when adjusting the light amount, it is possible to select the resistor and electrically connect only the selected resistor, thereby making it possible to eliminate the wire bonding process.

After burning out the fuse to obtain the desired resistance value, the LED chip Dl-D4, the resistor, and the fuse are covered with resin, and a cover is attached to this printed circuit board to construct the LED light source of this example. and each LED chip D
A desired amount of light from l-D4 is irradiated onto the surface of the document to perform reading.

In this example, one or more resistors are selected from among the six resistors and connected in parallel, but the resistors of the present invention are of course not limited to this.
Alternatively, selected resistors may be connected in series.

Further, the number of LEDs in each block is not limited to four, and the design can be changed as appropriate.

[Effects of the Invention] As explained above, according to the LED light source according to the present invention, the wire bonding process after adjusting the light amount is not required, making it possible to finely adjust the light amount with high accuracy, and reducing costs. effective.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of an LED light source according to the present invention, and FIGS. 2 and 3 are explanatory diagrams of a conventional LED light source. 3... Cathode electrode 4... Anode electrode R1-R6... Resistor 7... Fuse 8... Trim pad

Claims (1)

[Scope of Claims] A plurality of series-connected LED chips having one end connected to an electrode; a plurality of resistors having mutually different resistance values connected to the series-connected LED chips; and one end connected to the plurality of resistors. A plurality of fuses connected to each of the resistors and having the other end connected to an electrode.