JPS62208965A - Led array head for led printer - Google Patents

Abstract

PURPOSE:To reduce a variation in a luminance of an LED to obtain a good printing quality, by a method wherein a current limit resistor is provided at the side of a drive circuit in a matrix wiring and the sum of values of resistance with respect to respective lead-out wires of the LED side and the current limit resistor is made constant by varying the difference in the electric resistance between the lead-out wires of the LED side and the value of resistance of the current limit resistor. CONSTITUTION:In a production of an LED array head, a current limit resistor 6 is trimmed with being controlled to have the value of resistance which makes a constant sum with values of resistance of lead-out wires 3 of the LED wide in a matrix wiring at the completion of the trimming. In this manner, variation in the values of resistance of the lead-out wires 3 of the LED side is corrected, whereby the LED is prevented from variation in the set current and the quantity of emission. In this case, the dynamic drive type LED array head having little variation in the quantity of light can be obtained with a simple construction using a constant-voltage output type drive circuit 7 together with the current limit resistor 6, rather than employing a current limit drive circuit.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is a type of page printer using an electrophotographic method, and an LED array light source that uses an LED array light source for exposure of one line.
The present invention relates to an LED array head for a printer, and in particular to an LED array head that uses a dynamic drive method in which the LEDs are lit separately for each LED chip to keep the emitted light 1 of the LED constant and perform good printing. .

[Prior Art] There are two types of driving methods for an LED array head: a static method and a dynamic method. An example of the static drive method is shown in FIG. LED in static drive
The light emitting portions 12 of the LEDs on the array chip 1 and the output terminals 13 of the drive circuit correspond to one pair, and the common side terminals of the LED array chips are all connected in parallel. In this case L
The ED drive circuit uses a constant current output type, and there is no need for the same number of current limiting resistors as the number of light emitting parts, which is required in the case of a constant voltage output type circuit. However, the drive circuit requires a large number of ICs.
For example, 300DPI for A4 size
(Approximately 12 dots/MM>The light emitting part of the LED head is 2
There are 560 pieces, and when they are driven by an IC with 32 outputs,
The number of ICs is 8 ([]. Therefore, in the static drive type, the drive IC and the cost of mounting the IC chip cannot be ignored, making the LED array head very expensive. .

On the other hand, an example of a dynamic driving method, which is the other driving method for the LED array head, is shown in FIG. In this case, the ratio of the number of LED array chips and driving IC 7 is:
If the drive duty ratio is N, it becomes N:1, which allows the number of ICs to be reduced, but on the other hand, the common side drive circuit 9
and matrix wiring section 8 are required.

Generally, when a matrix wiring 8 is formed to dynamically drive an LED array head, the density of the lead lines 3 on the LED side of the matrix wiring is high, so the width thereof becomes very narrow and the resistance value becomes large. In comparison, the lateral connection lines 4 of the matrix and the lead lines 5 on the drive circuit side have a low density, so their resistance is low and does not pose much of a problem. FIG. 5 shows an example of the LED side lead lines 3 of the matrix wiring. In this example, 64 bonding wires 14 are drawn out in parallel from one side of the LED array chip 1 at a dot density of 300 DPI, and the pitch of the bonding pads 2 is 85 μm between the LEs of the wiring in one matrix.
The straight part of the D side lead wire 3 has a wiring pitch of 60 to 70 μm.
, the conductor width is 30-40 μm, and the horizontal connection lines 4 of the matrix have a pitch of 200-400 μm 1 conductor width is 10
It is 0 to 200 μm. Here, L of matrix wiring
The length of the ED side lead line 3 is 17 to 27 at the longest.
#, the shortest one is 2m, sheet resistance is 10-20mΩ
Since it is a mouth, its resistance value is 4 to 11Ω at its longest length.
, the shortest one is 0.4 to 1Ω, and the difference is 3.5
~10Ω.

Further, when this type of LED array head is driven in combination with a constant voltage output type drive circuit with a power supply voltage of 5V and a current limiting resistor, the value of the resistance is approximately 40 to 80Ω. Therefore, if all N flow limiting resistors 6 are set to the same resistance value, L
Variations in the resistance value of the lead wire 3 on the ED side are added up as variations in the overall resistance value. The resistance value varies by 5 to 20%, and the current flowing through the LED also varies within the same range.

Therefore, although the circuit shown in Fig. 4 has the disadvantage of increased cost due to an increase in the area of the LED driving IC chip, it is possible to use a driving IC with a constant current output circuit.
14 was used to eliminate the current limiting resistor and to avoid being affected by variations in resistance values in the matrix wiring.

[Problems to be solved by the invention] In the above-mentioned LED printer, the GaA
s P/GaAs LED array chip 1 is a cathode common type, so the driving IC has a current output (
Source) type must be used.

However, it is difficult to produce a highly accurate driving IC of this current output type, resulting in a considerable increase in cost.

Furthermore, since the power that should normally be absorbed by the current limiting resistor is consumed within the IC chip, the amount of heat generated cannot be ignored, and the area of the IC chip must be increased. The cost was significantly higher than that of a constant voltage output type IC, making the price of the LED array head extremely high.

For this reason, the cost advantage of the dynamic drive method, which reduces the number of drive ICs by several meters, over the static drive method is reduced, or, on the contrary, it creates a cost disadvantage.

The present invention was made in view of the above problems, and
A constant voltage output type dynamic drive circuit uses a current limiting resistor. Although it is a simple and inexpensive circuit that uses a current limiting resistor, it eliminates the influence of variations in the resistance value of the lead wire on the LED side, and Reduce variations in brightness,
The purpose is to obtain good printing quality.

Means for solving the problem
An LED array chip is provided on a mounting board, a matrix wiring for dynamic driving of the LED array, and a current limiting resistor is provided on the drive circuit side of this matrix wiring, and the difference in electrical resistance between the lead wires on the ED side of the matrix wiring is suppressed. By changing the resistance value of the current limiting resistor, the sum of the resistance values of each lead line on the LED side and the current limiting resistor is made constant.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows that the trimming setting value of the resistor 6 in one embodiment of the present invention is changed according to the expected value of the resistance value difference of the LED side lead line 3, and the resistance value is detected at both ends of the current limiting resistor 6. Measurements are made by bringing a blowing needle into contact with the blowing pad 10 and the terminal 11.

Another method is to detect the resistance value between the terminal 11 and the wire bonding pad 2. In this case, EDD
Since trimming is performed while monitoring the sum of the resistance values of the side wire 3 and the current limiting resistor 6, there is no need to change the resistance value setting, and the resistance value of the LED side lead wire changes due to changes in sheet resistance. Even in this case, the sum of the resistance values can be kept constant.

Furthermore, as Haku's method, although the figure is omitted, the vertical current limiting resistor 6,
By changing the ratio of the horizontal dimensions and changing the resistance value without trimming the resistor, it is possible to correct the difference in the resistance value of the lead wire on the LED side.

[Effects of the Invention] By adopting the configuration as described above, 1. In the present invention, a circuit diagram of an expensive constant current output type, and FIG. 2 shows its pattern configuration.

In the figure, 1 is an LED array chip, 2 is a wire bonding pad, 3 is a lead line on the LED side of the matrix wiring, 4 is a horizontal wiring of the matrix wiring, 5 is a lead line on the drive circuit side of the matrix wiring, 6 is a matrix wiring A current limiting resistor provided between the wiring and the drive circuit, 7 is a constant voltage output type individual side drive ICl 3 is a matrix wiring, 9
is determined by the common drive circuit of the LED array chip. Reference numeral 10 denotes a probing pad provided for measuring the resistance value when trimming the resistance value of the current limiting resistor 6, and 11 is a terminal for connecting the substrate and the drive circuit 7. When manufacturing such an LED array head, when trimming the current limiting resistor 6, so that the sum of the resistance value of the lead wire 3 on the LED side of the matrix wiring and the resistance value of the current limiting resistor 6 is kept constant. Controls the resistance value at the end of trimming. In this way, the LED
By correcting variations in the resistance values of the side lead wires 3, variations in the set current of the LEDs are prevented, and variations in the amount of light emitted are prevented. In this case, a dynamically driven LED can be driven by a simple configuration consisting of a constant voltage output type drive circuit 7 and a current limiting resistor 6 without using a current limiting drive circuit.
It is possible to obtain an array head with little variation in light m.

In addition, in a constant voltage output type drive circuit, the IC chip generates heat.
can be lower than that of a constant current output type drive circuit, so I
The area of the C chip can be reduced, and the cost of the IC can be reduced. Therefore, the adoption of the dynamic drive system has a significant cost reduction effect.
The cost of the entire LED head can be kept low.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an ED array head according to an embodiment of the present invention, FIG. 2 is a substrate pattern diagram of an LED array head according to the present invention, and FIG. 3 is a schematic diagram of a conventional static drive type LED array head. 4 is a circuit diagram of a conventional dynamic drive type LED array head, and FIG. 5 is a detailed diagram of the LED side lead line portion of the matrix wiring of the dynamic drive type LED array head. 1...LED array chip 2...Wire bonding pad 3...LED side lead line of matrix wiring 4...Matrix lateral connection line 5...Drive circuit side lead line 6...Current Limiting resistor 7... Constant voltage output type individual side drive IC 8... Matrix wiring section 9... Common side drive circuit 10... Blobbing pad 11... Terminal W-1 Figure 2 Collection of Figures 3 diagram

Claims (1)

[Claims] In an LED array head for an LED printer that uses an electrophotographic method and prints by exposing a photoreceptor to an LED array light source, an LED array chip is mounted on an LED mounting board, a matrix wiring for dynamic driving of the LED array, and this matrix wiring. A current limiting resistor is provided on the drive circuit side of the LED, and by changing the resistance value of the current limiting resistor, the sum of the resistance values of each lead line on the LED side and the current limiting resistor is made constant. LED array head for LED printers.