JPH0397276A - Light-emitting diode array device - Google Patents

Abstract

PURPOSE:To prevent an unbalance from generating in currents, which are made to flow through blocks, by a change in the applying voltage by a method wherein diodes of a non-radiative emission property are connected with light-emitting diodes in series and resistors are selectively added in parallel to the diodes of a non-light emission property. CONSTITUTION:Diodes 11 of a non-light emission property are series-connected to light-emitting diodes 10 and the forward voltages of blocks are made uniform. Whereby rising voltages between terminals Ta and Tb are made equal. Since the amount of adjustment of the forward voltages through the diodes 11 is as large as 0.6V or higher, parallel resistors(r) are selectively provided so that the rising voltage can be regulated with small relating step amount. Thereby, the current characteristics of the blocks can be completely uniformized and even if an applying voltage is changed, the currents of the blocks can be equalized.

Description

[Detailed description of the invention] [Table of contents] Overview Industrial field of application Prior art (Figures 5 and 6) Problems to be solved by the invention Means for solving the problems (Figure 1) Working examples (a) Description of one embodiment (Figures 2 and 3) (bl
Description of another embodiment (Fig. 4) Effect of the invention [Summary] In an optical reading device, etc., regarding a light emitting diode array device that illuminates the surface to be read, even if the applied voltage changes, the current flowing through each block remains unchanged. For the purpose of preventing imbalance, in a light emitting diode array device, multiple sets of blocks each having a plurality of light emitting diodes connected in series are connected in parallel, and an adjustment resistor is connected in series to the plurality of light emitting diodes in each block. A non-light-emitting diode was connected in series with the light-emitting diode, and a resistor was selectively added in parallel with the non-light-emitting diode.

[Industrial application field]

The present invention relates to a light emitting diode array device that illuminates a surface to be read in an optical reading device or the like.

Facsimile machines, optical character readers, mark readers, etc. that optically scan paper to read and process characters and graphics.
Optical reading devices such as image scanners use light-emitting diodes as light sources to achieve miniaturization and high reliability.
The number of products using LEDs is increasing.

Usually, a single LED can only illuminate a small area, so elements are used in which a large number of LEDs are arranged in a line and further provided with lenses to increase the intensity of light, arranged in an array.

In such a seven-layer array of light emitting diodes, it is required that the brightness of each light emitting diode be uniform.

[Conventional technology]

FIGS. 5 and 6 are explanatory diagrams of the prior art.

The forward voltage of an LED varies depending on the emission wavelength, material, etc., but is about 161 volts to 2.5 volts, and when driven alone, the voltage stsv, 1
(2V, 15V, etc.) becomes less efficient.

For this reason, as shown in Figure 5 (A>), if several to several dozen LEDIOs are connected in series and the number of LEDs is insufficient to illuminate the entire width of the page, the LEDs in this series
Multiple blocks are connected in parallel.

In FIG. 5(A), five LEDIOs are connected in series to form a series block, and five series blocks 1a to 1e are connected in series.
are connected in parallel and covered with a lens (glass rod) LNS provided on the substrate BS and supported by the lens holder LSH, as shown in FIGS. 5(B) and 5(C).

By the way, when the series blocks 1a to 1e are connected in parallel and a constant voltage is applied between the terminals Ta and Tb, due to the difference in the forward voltages Vdl to Vds of the series blocks 1a to 1e,
The flowing current characteristics are different as shown in FIG. 6(A).

FIG. 6A shows, for example, voltage-current characteristics a, b, and c of three series blocks, each having a different rising voltage and slope.

Therefore, even if the same voltage is applied, each series block la-
The current flowing through 1e is different, and each series block 13 to 1e
The brightness (amount of light emitted) will differ.

In order to correct this, conventionally, as shown in FIG.
Rs, and as shown in FIG. 6(B), each series bronch 1
By changing the slopes of a to 1e as a', b, and c', the current flowing through each block 1a to 1e at a specified voltage V1 is made to be approximately constant I1.

[Problem to be solved by the invention]

In this way, if the voltage between the terminals is constant, each block 1
Adjustment resistors R1 to Rs are provided in a to 1e, and each block 1
By making the current flowing through a to 1e uniform, a uniform amount of light emission can be obtained. Incidentally, in an optical reading device, it is necessary to keep the amount of light incident on the sensor constant, but the amount of incident light changes depending on the background color of the paper and the aging of the elements.

For this reason, the voltage or current of the light emitting diode array is automatically controlled so that the amount of light incident on the sensor is constant.

In the adjustment using the adjustment resistor R s −R s of the prior art,
At a certain terminal voltage, all blocks 1a to 1e
However, if the voltage between the terminals changes, the current flowing through each series block 1a to 1e depends on the forward voltage Vdj of that block, so the voltage v in FIG. 6(B)
Current 12+, ti2, ■ at 2! 3, an imbalance of currents in each block occurs.

For this reason, the conventional technology has a problem in that the distribution of illumination light is distorted.

Therefore, in the present invention, by changing the applied voltage,
It is an object of the present invention to provide a light emitting diode array device that can prevent imbalance in current flowing through each block.

[Means to solve the problem]

FIG. 1 is a diagram showing the principle of the present invention.

As shown in FIG. 1, the present invention connects a plurality of blocks 1a to 1In in parallel in which a plurality of light emitting diodes 10 are connected in series.
In a light emitting diode array device in which adjustment resistors Rl to Rn are connected in series with the light emitting diode 10, a non-light emitting diode 11 is connected in series with the light emitting diode 10, and a resistor r is selectively connected in parallel with the non-light emitting diode 11. is added.

[Effect]

In the present invention, the non-light emitting diode 11 is a light emitting diode.
10 in series to equalize the forward voltage of each block, thereby making the rising voltages in FIG. 6CB) equal.

However, since the amount of forward voltage adjustment by the non-light-emitting diode 11 is as large as 0.6 volts or more, the parallel resistance r
is provided, allowing the rise voltage to be adjusted in small adjustment steps.

As a result, the current characteristics of each block can be made completely uniform, and even if the applied voltage changes, the current of each block can be made uniform.

〔Example〕

(a) Description of one embodiment FIG. 2 is an explanatory diagram of an embodiment of the present invention.

As shown in FIG. 2(A), five light emitting diodes 10 are connected in series to form a series block 1a, and a non-light emitting diode (hereinafter referred to as a rectifier diode) is connected in series to this.
11a, llb are connected, and furthermore, an adjustment resistor R is connected in series, and a resistor rL. ．． rt is connected. Here, the applied voltage is V, the flowing current is I, the forward voltage of the series block la is Vd, and the two rectifier diodes Il
Let the forward voltages of a and llb be Vdx and Vd2.

The series block la is equivalently connected to a resistor Rd and a voltage source Vd, and each rectifier diode lla, Ilb is equivalently connected to a resistor rdl, rd2 and a voltage source Vdt, Vd. Let it be expressed as .

In a range where the applied voltage V is larger than the sum of the forward voltages of the diodes, the circuit of FIG. 2(A) is equivalent to the circuit of FIG.
) can be approximated by the resistance RE on the right side and the potential source VE.

Here, the relationship between the applied voltage V and the current I is expressed by equation (1).

R.E. ? be.

(From Equation 11, it can be seen that the slope of the voltage-current characteristic is determined by 1/RE, and the rising point is determined by ①A.

Therefore, if it is possible to adjust so that ■, and R are constant, even if the applied voltage V is slightly changed to adjust the light amount,
The current value of each block will change equally.

Now, r1≠r2, and r1=I/3rgmrd(rdl,
rd■). In addition, the rectifier diode Ila, l
The forward voltages Vd1 and Vd2 of lb are almost equal (=
Vdo).

When doing this, if the parallel circuit in Figure 2 (A) is not cut, if 01 in the parallel circuit in Figure 2 (B) is cut, C! in the parallel circuit in Figure 2 (C)! The relationship between current and voltage will be explained in the case where c1 and c02 of the parallel circuit in FIG. 2(D) are cut.

■If there is no Kasoto r 1 +rd+ tx+rdx・-・1・1(
3) Since r1=rdx=rdi=rd and r2-3rd, Rt=R+Rd+54rd...--(4).

Also, in equation (3), r1=rd1=rd2=rd,
Since r2=3rdSVd1=Vd2=Vdo, Vt 5 4 vao+'yd. - (5) It becomes.

■This is the case when c1 (rl side) is cut, and since r2=3rd and rdt=rd2=rd, 7 RE =R+Rd+ 4. Next, VE is rd・1・− (6) and r! =3rd, rd2=rd, Vd*=Vdo
Therefore, 7 V1=Vdo+Vd 4 -----171. ■If cz (rz side) is cut, it becomes Vd 1 and r1=rd1=rd2=rd, so 2 3 r d −−−−−−−(8) =R+Rd+ RE. Next, V, is, r1=rdl=rd, Vcll-Vdz=Vd
o, so V, = − V d o + V d −−
-----(9)2.

■C1, cxcr+, r! Since r1=rdI=rd2=rd, rx=3rd, 4 RE =R+Rd+ 3 is obtained.

Next, V0 is d・1-1-1・0Φ, and r1=rdi=rd41=rdSr2=3rd
, Vd1=Vd2=Vdo, so 4 V, = V do 10 V d
Qυ3 From (1) to (2) above, first, with r1 and r2 connected together, Vf is measured with the adjustment resistor R short-circuited.

5 From equation (5), this value is (-V d a + V d
).

4. Since Vd varies depending on the LED chip, cutting is performed so that Vd is approximately constant for all blocks 1a to 1n.

In Kaft's method, Va is calculated as (■d+
1.25Vd o), from the QD formula (V d +1.3
3V d o ), from formula (9) (V d +1.5
From the formula (?), (Vd+1.75V
d o ) can be taken.

In this way, after vE is made approximately constant in each block, an adjustment resistor R is determined and mounted for each block, and a predetermined voltage V
o, the current in each block can be set to IO.

The current-voltage relationship of each block is as follows from Equation 11.

Since V,,R, are approximately equal in each block, it is possible to eliminate the inconvenience that a large current flows only in one block when Vo is changed.

FIG. 3 is an implementation diagram of one embodiment of the present invention.

The manufacturing procedure will be explained using FIG.

(2) Mount the LED chip 10, rectifier diodes lla and llb, and resistors rl and r2 on the printed board BS by die bonding.

■ Next, the LED chip 10, the rectifier diode 11a,
llb is connected by wire bonding.

■ Attach the lens LNS and lens boulder LSt{. This covers the bonding portion (inside the dotted line).

(2) Probe the measurement pad sp to measure the forward voltage of the diodes 10, lla, and Ilb for each block.

■ Cut the cutting pattern locations C1 and C1 according to the forward voltage measured above ■ ■ Based on the measured voltage in step ■ and the cutting pattern in step ■, determine the adjustment resistor R so that the current in the block becomes constant. Attach.

■ Supply voltage between the terminals, make each block emit light, measure the light distribution, and confirm that the measured value is within the specified value.

(b) Description of other embodiments FIG. 4 is an explanatory diagram of another embodiment of the present invention.

In the above embodiment, two rectifier diodes lla, 1lb
However, in FIG. 4(A), three rectifier diodes lla, llb, llc and their parallel resistance r1,
r! , r3, it is possible to make seven adjustments, as shown in Figure 4 (
In B), the four rectifier diodes lla, llb, llc
, lid and their parallel resistances rlsr2, r3, and r4, it is possible to adjust in 11 ways, and the number of rectifier diodes and parallel resistances may be any number.

In addition, in the above-mentioned embodiment, one parallel resistance is provided for one rectifier diode, but as shown in FIG.
Two parallel resistances rl or r2 may be provided, and as shown in FIG. 4(D), one parallel resistance rl is connected to the rectifier diode lla, and two parallel resistances rl and
One parallel resistor r2 to C, three rectifier diodes 1l
One parallel resistor r9 may be provided for d, lie, and Ilf, and in this way, the adjustment range can be varied.

Furthermore, as shown in FIG. 4(E), a parallel resistor r3 may be provided in addition to the resistor r2 to expand the trimming range by pattern cutting.

Although the present invention has been described above using examples, the present invention can be modified in various ways according to the gist of the present invention, and these are not excluded from the present invention.

〔Effect of the invention〕

As explained above, according to the present invention, (1) the voltage-current characteristics of each series block of light emitting diodes connected in parallel can be matched, so that the applied voltage can be varied to adjust the light intensity;

(2) In other words, even if the intensity is adjusted by varying the applied voltage, the current value of each block is the same, so the distortion of the amount of light on the line is reduced, and the reading performance can be improved.

[Brief explanation of drawings]

Figure 1 is a diagram of the principle of the present invention. FIG. 2 is an explanatory diagram of an embodiment of the present invention; FIG. 3 is an implementation diagram of one embodiment of the present invention. FIG. 4 is an explanatory diagram of another embodiment of the present invention, FIGS. 5 and 6 are explanatory diagrams of the prior art. In the figure, 1a to In one series block, 10-light emitting diode, 11 - non-emissive diode, R1 Adjustment resistance, r・-・Additional resistance.

Claims (1)

[Claims] A plurality of blocks (1a to 1n) in which a plurality of light emitting diodes (10) are connected in series are connected in parallel, and each block (1a
~1n) In a light emitting diode array device in which adjustment resistors (R_1 to Rn) are connected in series to a plurality of light emitting diodes (10), a non-light emitting diode (11) is connected in series with the light emitting diodes (10). A light emitting diode array device characterized in that a resistor (r) is selectively added in parallel with the non-light emitting diode (11).