JPH08118722A - Driving circuit for led print head - Google Patents

Abstract

PURPOSE: To provide an LED print head in which a white or black stripe of the print result can be eliminated without remounting a chip even when a gap of the width different from a pitch occurs between adjacent LEDs disposed on a different chip. CONSTITUTION: The current flowing to an LED 11a disposed at the end of a chip is regulated by the larger amplitude as compared with an LED 11 disposed at the intermediate part of the chips by using regulating means 22, 23, 24 connected to the chips.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for driving an LED in an LED print head mounted on a printer or a fax machine, and more particularly, a plurality of chips in which a plurality of LEDs are aligned and arranged at a fixed pitch on a substrate. Arrayed LE
The present invention relates to a drive circuit in a D print head.

[0002]

2. Description of the Related Art In an LED print head, generally, a plurality of chips having a plurality of LEDs arranged in an array are aligned along a print row to form one LED row. The drive circuit selectively supplies a current to the LEDs corresponding to the print dots to cause the LEDs to emit light, thereby performing line printing line by line. With this type of printhead,
A uniform print quality without uneven density of each LED is desired.

Conventionally, in order to eliminate print unevenness, the amount of current flowing through each LED and the current supply time to each LED have been adjusted. For example, a main transistor and a sub-transistor are connected to each LED to control whether or not the sub-transistor is turned on during printing. The amount of current passing through the sub-transistor is added to the amount of reference current passing through the main transistor, so that the amount of current can be adjusted and the amount of light emitted from the LED is adjusted. Also,
Each main transistor that passes a preset current amount is set to L
Connected to ED, the on time of this main transistor is changed by turning on / off the additional pulse,
The light emission amount of the ED is adjusted.

As described above, by adjusting the amount of light emission of each LED by adjusting the amount of current and the current supply time in each LED, the amount of light of the LEDs in the entire print head is made uniform and uneven density is eliminated. It

[0005]

Here, in the normal case,
In order to form one print line, a plurality of chips are linearly arranged on the substrate. In such a case, since the gap between the chips is not appropriate, the distance between the LEDs at the ends of different chips (hereinafter referred to as the gap) is different from the interval between the LEDs on the chip (hereinafter referred to as the pitch). It may happen. This is because it is difficult to accurately control the gap between chips when mounting the chips on the substrate. If the adjacent LEDs are too far apart from each other via the gap, a gap is created in the LED irradiation area of the LED, and white streaks are generated in the print result.
If D is too close, overlapping of the LED irradiation areas of the LEDs will occur and black streaks will occur in the printed result.

That is, conventionally, as shown in FIG.
Even if the pitch P between the LEDs 11 on the chips 10a, 10b is made uniform, the chips 10a,
When mounting the 10b, an error occurs in the distance between the chips 10a and 10b, and a gap G having a width different from the pitch P is generated between the adjacent LEDs 11a and 11b arranged on the different chips 10a and 10b. This gap G is
The white streaks and the black streaks are generated depending on the size. Therefore, conventionally, there is a problem in that when an error occurs in the gap G, the chips 10a and 10b must be mounted on the substrate 12 again.

The present invention has been made in view of the above circumstances, and even if an error occurs in the distance between adjacent LEDs which are arranged on different chips, the whiteness of the print result can be obtained without re-mounting the chips. An object of the present invention is to provide an LED print head capable of eliminating streaks and black streaks.

[0008]

According to a first aspect of the present invention, an LED is provided which supplies a drive current to each LED of an LED print head in which a plurality of chips in which a plurality of LEDs are aligned and arranged at a constant pitch are linearly arranged on a substrate. The drive circuit of the print head is characterized in that adjustment means for adjusting the current supplied to the LED at the end of each chip is provided.

The second invention is a plurality of LEDs at a constant pitch.
L which supplies a drive current to each LED of the print head in which a plurality of chips arranged in line are arranged in a line on the substrate.
In the drive circuit of the ED print head, each LED mounted on each of the plurality of chips is connected to each LE.
The main transistor connected to the LED located at the end of the chip includes a plurality of main transistors and a first sub-transistor for turning on and off the drive current flowing through D and setting the amount of drive current when the drive current is on. The current capacity is set smaller than that of the main transistor connected to the other LED, and the second sub-transistor capable of supplying an additional drive current is connected to the LED at this end,
The adjustment range of the drive current amount for the LED at the end is set to other LED
It is characterized by being made larger.

A third aspect of the invention is to provide a plurality of LEDs with a constant pitch.
L which supplies a drive current to each LED of the print head in which a plurality of chips arranged in line are arranged in a line on the substrate.
In the drive circuit of the ED print head, each LED mounted on each of the plurality of chips is connected to each LE.
It includes a plurality of main transistors for turning on and off the driving current flowing to D and setting the amount of driving current when the driving current is turned on. It is set smaller than the main transistor connected to the LED, and the first sub-transistor that can supply an additional drive current is connected to the LED at this end, and the adjustment range of the drive current amount for the LED at the end is adjusted to other LEDs. It is characterized by being made larger.

The fourth invention is a plurality of LEDs with a constant pitch.
L which supplies a drive current to each LED of the print head in which a plurality of chips arranged in line are arranged in a line on the substrate.
In the drive circuit of the ED print head, each LED mounted on each of the plurality of chips is connected to each LE.
A main transistor connected to an LED located at the end of the chip, which includes a plurality of main transistors and a first sub-transistor for turning on and off the drive current flowing in D and setting the amount of drive current when turned on. It is characterized in that a correction circuit for correcting the ON time when turning on the first sub-transistor is provided, and the adjustment range of the light emission time with respect to the LED at the end is made larger than that of the other LEDs.

A fifth aspect of the invention is to provide a plurality of LEDs with a constant pitch.
In a print head in which a plurality of chips arranged in a line are arranged in a straight line on a substrate, in a drive circuit of the LED print head that supplies a drive current to each LED, each is connected to each LED mounted on the plurality of chips. And a correction circuit that includes a plurality of main transistors for turning on and off the drive current flowing through each LED, and that corrects the on-time when turning on the main transistor connected to the LED located at the end of the chip, LED on the edge
It is characterized in that the adjustment range of the light emission time with respect to is larger than that of other LEDs.

[0013]

According to the structure of the first invention, the adjusting means adjusts the drive current of the LED provided at the end portion of the chip.
As a result, the amount of light emitted from the LED at the end of the chip can be increased or decreased particularly. Therefore, when the distance between the LEDs of the adjacent ends arranged on different chips is large and a gap is generated in the drum irradiation area of the LEDs, the light amount of the LEDs is increased by the adjusting means, and the white color generated in the print result is obtained. You can eliminate streaks.
On the contrary, when the distance between the LEDs at the adjacent ends arranged on different chips is small and the overlapping of the LED irradiation areas of the LEDs is too large, the light amount of the LEDs is reduced by the adjusting means, which causes the print result. Black streaks can be eliminated.

Further, according to the structure of the second invention, in the LED located in the middle portion of the chip, the amount of current flowing through the LED is adjusted in two stages by turning on / off the first sub-transistor. Is corrected. on the other hand,
In the LED located at the end of the chip, the amount of current in the main transistor is smaller than that of the other main transistors. Therefore, when a current is applied to the main transistor connected to the LED at the end of the chip, the LED at the end emits light with a smaller amount of light emission than the amount of light emitted from the LED at the other middle part. As a result, when the gap between chips is small and the overlap of the drum irradiation areas of the end LEDs is too large, the light amounts of these LEDs are greatly reduced compared to the light amounts of the other LEDs, and the black streaks that occur in the printed result are eliminated. be able to. On the other hand, the second sub-transistor is connected to the LED at the end of the chip. Therefore, when a current is passed through the main transistor and the first and second sub-transistors, the LED emits a light amount larger than that when the LED in the middle portion emits light due to the passing current amount due to the combination of the main transistor and the first sub-transistor. To do. As a result, when the gap between the chips is large and a gap occurs in the LED irradiation area of the LED,
It is possible to increase the light intensity of the LED at the end portion more than the light intensity of the other LEDs and eliminate the white streak generated in the print result.

Further, according to the configuration of the third invention, in the LED located at the end of the chip, the amount of current of the main transistor connected to this is smaller than that of the other main transistors, while the sub-transistor is provided here. It is connected. Also with this configuration, the amount of adjustment of the light emission amount of the LED at the end portion can be further increased, and the occurrence of black streaks and white streaks can be prevented.

According to the structure of the fourth aspect of the invention, in the LED in the middle part of the chip, the amount of current flowing into the LED is adjusted in two stages by the combination with the main transistor and the first sub-transistor, whereby the light amount of the LED is adjusted. Is corrected. On the other hand, the on-time of the main transistor connected to the end LED can be longer than that of the main transistor connected to the middle LED. As a result, the light amount of the LED at the end can be increased. In this way, the on-time of the main transistor at the end can be adjusted to greatly adjust the amount of light emitted from the LED at the end to prevent the occurrence of white lines and black lines.

Further, according to the structure of the fifth invention, the ON time of the main transistor connected to the LED at the end is
It can be longer than the main transistor connected to the middle LED. As a result, the light amount of the LED at the end can be increased. In this way, it is possible to prevent the occurrence of white lines and black lines by adjusting the on-time of the main transistor at the end and greatly adjusting the light emission amount of the LED at the end.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. The drive circuit of the LED print head according to the present invention is applied to a print head having the same configuration as the LED print head of FIG.

In FIG. 1, this LED print head is provided with a plurality of chips 10a, 10b in which a plurality of LEDs 11 are aligned and arranged at a constant pitch P. Chip 10
a and 10b are arranged on the substrate 12 along the print line.
A gap G is formed between the adjacent LEDs 11a and 11b arranged on different chips 10a and 10b based on the arrangement of the chips 10a and 10b. The width of the gap G is preferably equal to the pitch P, but the chip 1
It may differ depending on the mounting error of 0a and 10b on the substrate 12.

FIG. 2 shows a circuit configuration of an LED print head provided with a drive circuit according to the first embodiment of the present invention. The drive circuit 20 includes LEDs 11 that are not adjacent to the gap G.
Transistor group TR1 for setting the amount of current flowing into the transistor
And a second transistor group TR2 that sets the amount of current flowing into the LED 11a adjacent to the gap G. The first and second transistor groups TR1 and TR2 are on / off controlled based on the data signal supplied from the data latch group LC.

The first transistor group TR1 includes the LED 11
And a first main transistor 21 for supplying a first basic current Ia1 and a first sub-transistor 22 for supplying a first auxiliary current Ib1 added to the first basic current Ia1. The first transistor group TR1 has a first auxiliary current I
LEs that are not adjacent to the gap G depending on the presence or absence of b1
The current flowing into D11 is adjusted in two steps.

The second transistor group TR2 has a second basic current Ia2 having a smaller current value than the first basic current Ia1.
A second main transistor 23 supplied to the ED 11a,
First and second auxiliary currents I added to the second basic current Ia2
First and second sub-transistors 2 for supplying b1 and Ib2
2, 24 are provided. This second transistor group TR2
Serves as an adjusting means for stepwise adjusting the current flowing into the LED 11a adjacent to the gap G depending on the presence or absence of the first and second auxiliary currents Ib1 and Ib2. The sources and drains of the transistors 21 to 24 of the first and second transistor groups TR1 and TR2 are connected to the power supply VDD and the LEDs 11 and 11a, and the current I from the power supply VDD is supplied to the LED 11 according to the voltage applied to the gate. 1
Supply to 1a.

The gates of the transistors 21 to 24 are
The switch element 25 is connected. The switch element 25 is interposed between the gate power supply VG and the gates of the transistors 21 to 24 and controls switching of the voltage applied to the gates of the transistors 21 to 24.

The data latch group LC includes a main transistor latch 26 and a first sub-transistor latch 27.
And a second sub-transistor latch 28. The main transistor latch 26 includes LEDs 11 and 11a.
An ON signal is supplied to the first and second main transistors 21 and 23 when illuminating, and an OFF signal is supplied to the first and second main transistors 21 and 23 when the LEDs 11 and 11a are not emitting light. The first sub-transistor latch 27 supplies an ON signal to the first sub-transistor 22 when using the first sub-transistor 22 to increase the light amount of the LEDs 11 and 11a. The second sub-transistor latch 28 supplies an ON signal to the second sub-transistor 24 when the light amount of the LED 11a is increased by using the second sub-transistor 24 (when the print dot is OFF, the OFF signal remains).

When the ON signal supplied by the main transistor latch 26 and the strobe signal STR are simultaneously input to the main AND gate 29, the strobe signal ST
A high signal is output from the AND gate 29 only while R is high, the switch element 25 is opened, and the voltage from the gate power source VG is the first and second main transistors 21 and 23.
Applied to the gate of. When the ON signal supplied from the first and second sub-transistor latches 27 and 28 and the high signal from the main AND gate 29 are simultaneously input to the sub AND gate 30, the high signal from the AND gate 30 is output. The switch element 25 is output and the voltage from the gate power supply VG is applied to the gates of the first and second sub-transistors 22 and 24.

The data signal is once inputted to the shift register 31 by the clock signal CLK and then taken in by the latches 26 to 28 by the latch signals LA1, LA2, LA3. That is, the print data for causing the LEDs 11 and 11a corresponding to the dots to be printed to emit light is
The latch signal LA1 is taken into the main transistor latch 26, and the LEDs 11 and 11 are read based on the measured values.
The correction data for correcting the light amount of a is the latch signal L
The correction data, which is fetched by the first sub-transistor latch 27 by A2 and is used to correct the light amount of the LEDs 11a at both ends of the chip in order to eliminate the black streaks and the white streaks of the print result, is output in accordance with the input of the latch signal LA3. It is taken into the latch 28 for the two sub-transistors.

In the first embodiment, the ratio of the current capability of the first sub-transistor 22 to the first main transistor 21, that is, the first basic current Ia1 and the first auxiliary current I.
The ratio of the current amount of b1 is 1.0: 0.1 (first basic current Ia
1 is set to 1.0). Therefore, the light amount of the LED 11 which is not adjacent to the gap G can be adjusted with a relative ratio of 1.0 or 1.1. Similarly, the ratio of the current capabilities of the first main transistor 21 and the second main transistor 23 is set to 1.0: 0.9. Therefore, in the second main transistor 23 and the first sub-transistor 22 connected to the LED 11a adjacent to the gap G, the first basic current Ia1 can be adjusted to 0.9 or 1.0 with 1.0 as the first basic current Ia1. In this embodiment, the second sub-transistor is provided, and the current capability ratio of the first main transistor 21 and the second sub-transistor 24 is set to 1.0: 0.2. Therefore,
By turning on the second main transistor 23 and the second sub-transistor 22, the amount of current supplied to the LED 11a adjacent to the gap G is adjusted to 0.9 or 1.1 with respect to the amount of current of the first main transistor. It is possible.

Therefore, due to the combination of the second main transistor and the first and second sub-transistors, the drive current for the LED at the end adjacent to the gap G is 0.
It is possible to adjust in five steps of 9, 1.0, 1.1, 1.2 and 1.3. Thus, the LED adjacent to the gap G
The light amount of 11a is adjusted widely in both the increasing and decreasing directions.

Next, the operation of the drive circuit according to the first embodiment will be described. The serial binary data signal supplied from the main body of the print head is input to the shift register 31 by the clock signal CLK as described above. When the shift register 31 receives the required data signal, the latch signals LA1, LA2, LA3 are sent to the main transistor latch 26, the first sub-transistor latch 27, and the second sub-transistor latch 28, respectively. The latches 26, 27 and 28 take in the data signal.

Each of the latches 26, 27 and 28 outputs an on / off signal based on the fetched data signal. The main AND gate 29 to which the ON signal is supplied from the main transistor latch 26 outputs a high signal at a time corresponding to the pulse width of the strobe signal STR. This high signal is transmitted to the first and second sub-transistor latches 27,
If the ON signal supplied from the sub AND gate 30 from 28 is also high, the switch element 25 is turned on.
As a result, the voltage from the gate power supply VG is supplied to the first and second transistor groups TR1 and TR2. The supplied voltage is applied to the gates of the transistors 21 to 24, and the transistors 21 to 24 supply currents from the power supply VDD to the LEDs 11 and 11a according to the applied voltages. This allows LEs corresponding to the dots you want to print.
D11 and 11a emit light, and the opposing drum (not shown)
Is irradiated.

Here, the LED is used in the entire chip 10a.
Consider adjusting the light amounts of 11 and 11a to the target values. This target value is set to the light amount of the LED 11 which emits light by the first basic current Ia1 passing through the first main transistor 21. Therefore, the LED1 which is emitted by the second basic current Ia2 smaller than the first basic current Ia1
In 1a, a current obtained by adding the first auxiliary current Ib1 passing through the first sub-transistor 22 to the second basic current Ia2 in advance is supplied to the LED 11a. At this point, if the light amounts of the LEDs 11 and 11a of the entire chip 10a are made uniform,
There is no need to correct the light quantity.

When the light amount of the LED 11 not adjacent to the gap G is less than the target value, the first auxiliary current Ib1 passing through the first sub-transistor 22 is changed to the first basic current Ia.
1 to increase the light amount of the LED 11. When the light amount of the LED 11a adjacent to the gap G is less than the target value, instead of the first auxiliary current Ib1 described above,
The second auxiliary current Ib passing through the second sub-transistor 24
2 is added to the second basic current Ia2 to increase the light amount of the LED 11a. Through these light amount corrections, the chip 10a
The LED light amount of the whole is made uniform.

The chip 10a obtained as a result of the light amount adjustment is mounted on the substrate 12. At this time, the pitch P between the LEDs 11 and 11a is constant in the same chip 10a. However, a gap G larger than the width of the pitch P may occur between the LEDs 11a and 11b adjacent to each other while being arranged on different chips 10a and 10b. The large gap G forms a gap in the drum irradiation area of the LEDs 11a and 11b and causes white streaks in the print result. According to the first embodiment, in the LED 11a adjacent to the gap G, the second basic current Ia2 and the first basic current Ia2
When the auxiliary current Ib1 is supplied, if the gate voltage VG is applied to the second sub-transistor 24 instead of the first sub-transistor 22, the LE adjacent to the gap G can be obtained.
The light quantity of D11a increases and the white streaks are eliminated. In addition, the LED 1 adjacent to the gap G is adjusted by adjusting the light amount.
When the light amount of 1a is increased and corrected in advance and the second basic current Ia2 and the second auxiliary current Ib2 are supplied, if the gate voltage VG is further applied to the first sub-transistor 24, the LED 11a adjacent to the gap G is detected. And the white streaks are eliminated.

On the other hand, when mounted on the board 12, the LEDs 10a, 1 which are adjacent to each other while being arranged on different chips are mounted.
A gap G smaller than the width of the pitch P may occur between 0b. This small gap G is the LED 11a,
The drum irradiation areas of 11b overlap each other too much, causing black streaks in the printed result. According to this first embodiment,
When the second basic current Ia2 and the first auxiliary current Ib1 are supplied to the LED 11a adjacent to the gap G, the gate voltage V to the first sub-transistor 22 is increased.
If the application of G is stopped, the LED 1 adjacent to the gap G
The light amount of 1a is reduced and the black streaks are eliminated. Also,
The LED 11a adjacent to the gap G is adjusted by adjusting the light amount.
When the second basic current Ia2 and the second auxiliary current Ib2 are supplied, the first sub-transistor 22 is replaced by the first sub-transistor 22.
When the gate voltage VG is applied to, the light amount of the LED 11a adjacent to the gap G is reduced and the black streaks are eliminated.

FIG. 3 shows a circuit configuration of an LED print head provided with a drive circuit according to the second embodiment of the present invention. The drive circuit 40 is provided for the LED 11 not adjacent to the gap G.
The first main transistor TR1 that sets the amount of current flowing into a and the transistor group TR2 that sets the amount of current flowing into the LED adjacent to the gap G are provided. First main transistor TR1 and transistor group TR2
Is on / off controlled based on the data signal supplied from the control circuit 41.

The first main transistor TR1 causes a preset first basic current Ia1 to flow into the LED 11.
The first main transistor TR1 has power supplies VDD and L.
It is interposed between the EDs 11 and supplies a current from the power supply VDD to the LEDs 11 according to the voltage applied to the gate.

The transistor group TR2 has a first basic current I
LED 2nd basic current Ia2 whose current value is smaller than a1
A second main transistor 42 supplied to
First and second auxiliary currents Ib added to the basic current Ia2
First and second sub-transistors 4 for supplying 1 and Ib2
3, 44. The transistor group TR2 functions as an adjusting unit for stepwise adjusting the current flowing through the LED 11a adjacent to the gap G depending on the presence / absence of the first and second auxiliary currents Ib1 and Ib2. Transistor group TR2
Each of the transistors 42, 43, and 44 is interposed between the power supply VDD and the LED 11a and supplies a current from the power supply VDD to the LED 11a according to the voltage applied to the gate.

A switch element 45 is connected to each of the transistors 42, 43 and 44. This switch element 45 is
Gate power supply VG and transistors TR1, 42, 43,
It is interposed between the gate of the transistor 44 and the transistor TR1, 4
The voltage applied to the gates of 2, 43 and 44 is switching-controlled.

The control circuit 41 outputs a data signal for setting the on-time of the first and second main transistors TR1 and 42. The control circuit 41 includes LEDs 11, 11
When making a emit light, the first and second main transistors TR
An ON signal is supplied to the first and second main transistors TR1 and 42 when the LEDs 11 and 11a are not caused to emit light.
A print data latch 46 for supplying an OFF signal to 42,
A time correction data latch 47 for supplying an ON signal to the first and second main transistors TR1 and 42 connected to the LEDs 11 and 11a to emit light is provided to increase and correct the light amount of the LEDs 11 and 11a. Latches 46, 47
The print data / correction data switching circuit 48 connected in common to the print data output from the print data latch 46 and the time correction data output from the time correction data latch 47 according to the pulse of the strobe signal STR. And are alternately supplied to the switch element 45. The switch element 45 is opened by the ON signal of each data, and the gate power source V
The voltage from G is applied to the gates of the transistors TR1, 42. The pulse width of the strobe signal STR is set to, for example, print data: correction data = 1.0: 0.1.
The emission time of a is changed, and the light amounts of the LEDs 11 and 11a can be adjusted at a relative ratio of 1.0 or 1.1 (see FIG. 4).

The control circuit 41 includes a sub-transistor switching latch which supplies an ON signal to the first and second sub-transistors 43 and 44 when the light quantity of the LED 11a is increased by using the first and second sub-transistors 43 and 44. 49 is provided. The switching data from the sub-transistor switching latch 49 is supplied to the switch element 45 through the AND gate 50 together with the print data or the time correction data. LEs at both ends of the chip are turned on by the ON signal of the switching data.
The light amount of D11a is increased and corrected, and it becomes possible to eliminate black streaks and white streaks in the print result.

In the second embodiment, as in the first embodiment, the current capability ratio of the first main transistor TR1 and the second main transistor 42 is 1.0: 0.9 (the current of the first basic current). (When the amount is set to 1.0). The ratio of the current capabilities of the first main transistor TR1 and the first sub-transistor 43 is set to 1.0: 0.1. Further, the ratio of the current capabilities of the first main transistor TR1 and the second sub-transistor 44 is set to 1.0: 0.2. Therefore, by the second main transistor 42 and the first and second sub-transistors 43 and 44, LE
The light amount of D11a is 0.9, 1.0, 1.1, 1.2,
It becomes possible to adjust in stages within the range of 1.3.

Next, the operation of the drive circuit according to the second embodiment will be described. Similar to the above-described first embodiment, the data signal is input to the shift register 51 by the clock signal CLK, and at the time when each data signal is input, the print data latch 46, the time correction data latch 47, and the sub-data latch 47. Latch signals LA1 and LA are input to the transistor switching latch 49.
2, LA3 are sent, and the latches 46, 47, 49 fetch the data signals, respectively. The print data latch 46 and the time correction data latch 47 supply the fetched data to the print data / correction data switching circuit 48.

The print data / correction data switching circuit 48 is supplied with a strobe signal STR composed of a pulse pair for each dot (see FIG. 4). Switching circuit 48
Outputs the printing data at a time corresponding to the width of the print data pulse, and outputs the time correction data at a time corresponding to the width of the time correction data pulse. The high signal included in the print data or the time correction data opens the switch element 45 when the data signal supplied from the sub-transistor switching latch 49 to the AND gate 50 is high. As a result, the voltage from the gate power supply VG is supplied to the first main transistor TR1 and the transistor group TR2. The supplied voltage is applied to each of the transistors TR1 and 42-4.
4 is applied to the gate of transistor TR1, 42-4
4 supplies a current from the power supply VDD to each LED 11, 11a according to the applied voltage. The LEDs 11 and 11a corresponding to the dots to be printed emit light and illuminate the opposing drum (not shown).

In the second embodiment, the chip 1
For adjusting the light amount of the LEDs 11 and 11a at 0a, whether or not the correction data pulse is added is used. To adjust the light amount of the LED 11a at the end adjacent to the gap,
This is dealt with by turning on / off the sub-transistors 43 and 44 according to the data stored in the sub-transistor switching latch 49. As a result, similarly to the first embodiment, it is possible to prevent the generation of black streaks and white streaks.

Further, in the second embodiment, the pulse width of the time correction data pulse is set to 0.1 with respect to the pulse width of the print data pulse, and the first main transistor TR1 is set.
Second main transistor 4 when the current capacity of the
2, by setting the current capability of the first and second sub-transistors 43 and 44 to 0.9, 0.05 and 0.15, the gap is corrected by the combination of the time correction and the current amount correction using the sub-transistor. LED1 adjacent to G
1a of light intensity in finer increments (in this case 0.0
It becomes possible to adjust in 5 steps.

FIG. 5 shows a circuit configuration of an LED print head provided with a drive circuit according to the third embodiment of the present invention. This drive circuit 60 is provided for the LED 11 not adjacent to the gap G.
Transistor group TR1 for setting the amount of current flowing into the transistor
And a second transistor group TR2 that sets the amount of current flowing into the LED 11a adjacent to the gap G. The first and second transistor groups TR1 and TR2 are on / off controlled based on the data signal supplied from the control circuit CC.

The first transistor group TR1 includes the LED 11
And a first sub-transistor 62 for supplying a first auxiliary current Ib1 added to the first basic current Ia1. The first transistor group TR1 has a first auxiliary current I
LEs that are not adjacent to the gap G depending on the presence or absence of b1
The current flowing into D11 is adjusted in two steps.

The second transistor group TR2 has a second basic current Ia2 having a smaller current value than the first basic current Ia1.
A second main transistor 63 supplied to the ED 11a;
A first sub-transistor 62 for supplying a first auxiliary current Ib1 added to the second basic current Ia2. The second transistor group TR2 adjusts the current flowing into the LED 11a adjacent to the gap G in two stages depending on the presence or absence of the first auxiliary current Ib1. Transistors 61 to 63 of the first and second transistor groups TR1 and TR2
Is interposed between the power supply VDD and the LEDs 11 and 11a,
The current I from the power supply VDD is supplied to the LEDs 11 and 11a according to the voltage applied to the gate.

A switch element 64 is connected to each of the transistors 61 to 63. The switch element 64 is interposed between the gate power supply VG and the gates of the transistors 61 to 63 and controls switching of the voltage applied to the gates of the transistors 61 to 63.

The control circuit CC outputs a data signal for controlling the switch control of the switch element 64 for the LED 11 not adjacent to the gap G, and a print data switching circuit 65.
A print data / correction data switching circuit 66 for outputting a data signal for controlling switching of the switch element 64 connected to the LED 11a adjacent to the gap G.
The print data switching circuit 65 and the print data / correction data switching circuit 66 convert the supplied data to the strobe signal S.
It is selectively output according to the TR pulse (see FIG. 6).

The data supplied to both the switching circuits 65 and 66 is the main transistor latch 67 of the control circuit CC.
It is supplied from the sub-transistor latch 68 and the gap correction data latch 69. The main transistor latch 67 supplies an ON signal to the first and second main transistors 61 and 63 when the LEDs 11 and 11a emit light, and when the LEDs 11 and 11a do not emit light,
An off signal is supplied to the first and second main transistors 61 and 63. The sub-transistor latch 68 has a first
An ON signal is supplied to the first sub-transistor 62 when increasing the light amount of the LEDs 11 and 11a using the sub-transistor 62. The gap correction data latch 69 supplies an ON signal when the light emission time of the LED 11a adjacent to the gap G is increased.

The print data switching circuit 65 continues to output data while the print data pulse (see FIG. 6) of the strobe signal STR is at high level, but the gap correction data pulse (see FIG. 6) is at high level. Even if there is, the data is not output. Further, the print data / correction data switching circuit 66 functions as a correction circuit that outputs a data signal that increases the current passage time of the second main transistor 63 and the first sub-transistor 62. This switching circuit 66 adds the gap correction pulse of the strobe signal STR to the light amount of the LED 11a at a ratio of 1.
It can be increased at 0: 1.1.

The serial data signal is the clock signal CL.
After being input to the shift register 70 in synchronization with K,
The latch signals LA1, LA2, LA3 are taken into the respective latches 67 to 69 in response to the input. The data signal is based on the print data and the measured value for causing the LEDs 11 and 11a corresponding to the dots to be printed to emit light.
It includes correction data for correcting the light amount of 1a, and correction data for correcting the light amount of the LEDs 11a at both ends of the chip to eliminate black streaks and white streaks in the print result.

In the third embodiment, the ratio of the current capabilities of the first main transistor 61 and the first sub-transistor 62 is 1.0: 0.1 (the current amount of the first basic current Ia1 is 1.0). Case). Therefore, the gap G
The light amount of the LED 11 not adjacent to the
Alternatively, it can be adjusted by 1.1. Similarly, the ratio of the current capabilities of the first main transistor 61 and the second main transistor 63 is set to 1.0: 0.9. Therefore, in the second main transistor 63 and the first sub-transistor 62 connected to the LED 11a adjacent to the gap G,
First main transistor 6 connected to another LED 11
The passing current amount is set to be smaller than that of the first and first sub-transistors 62 at a ratio of 0.1, whereby the light amount of the LED 11a adjacent to the gap G can be relatively adjusted to 0.9 or 1.0. . L adjacent to the gap G
If the light emission by the two gap correction pulses set only for the ED 11a is turned on / off, the light amount of the LED 11a adjacent to the gap G has a relative ratio of 0.9-.
It becomes possible to adjust in 1.2 (in steps of 0.1).

FIG. 7 shows a circuit configuration of an LED print head provided with a drive circuit according to the fourth embodiment of the present invention. The drive circuit 80 is provided for the LED 11 not adjacent to the gap G.
Transistor TR1 for setting the amount of current flowing into the transistor
And a second transistor TR2 for setting the amount of current flowing into the LED 11a adjacent to the gap G. First
The second transistors TR1 and TR2 are connected to the control circuit C.
On / off control is performed based on the data signal supplied from C.

The first transistor TR1 supplies the LED 11 with the first basic current Ia1. Second transistor TR2
Supplies the second basic current Ia2 having a smaller current value than the first basic current Ia1 to the LED 11a. First and second
The transistors TR1 and TR2 have power supplies VDD and LE.
The current I from the power supply VDD is sent to the LEDs 11 and 11a in accordance with the voltage applied to the gate, which is interposed between D11 and 11a.

A switch element 81 is connected to each of the transistors TR1 and TR2. The switch element 81 is interposed between the gate power supply VG and the gates of the transistors TR1 and TR2, and controls switching of the voltage applied to the gates of the transistors TR1 and TR2.

The control circuit CC outputs the data signal for controlling the switch control of the switch element 81 for the LED 11 not adjacent to the gap G, and the switch element 81 for the LED 11a adjacent to the gap G. And a second print data / correction data switching circuit 83 for outputting a data signal for controlling ON / OFF of the switch. The first and second print data / correction data switching circuits 82 and 83 selectively output the supplied data according to the pulse (see FIG. 8) of the strobe signal STR.

The data supplied to both switching circuits 82 and 83 are supplied from the print data latch 84, the first time correction data latch 85 and the second time correction data latch 86 of the control circuit CC. The print data latch 84 is
When the LEDs 11 and 11a are caused to emit light, an ON signal is supplied to the first and second transistors TR1 and TR2,
When 11 and 11a are not made to emit light, an OFF signal is supplied to the first and second transistors TR1 and TR2. First
The time correction data latch 85 supplies an ON signal when the light amount of each of the LEDs 11 and 11a is corrected by increasing the current passage time. Second time correction data latch 86
Supplies an ON signal when the light amount of the LED 11a adjacent to the gap G is corrected by increasing the current passage time.

First print data / correction data switching circuit 82
Is a print data pulse of the strobe signal STR (see FIG. 8).
While the reference) is at the high level, the print data output from the print data latch 84 continues to be output. In addition, the switching circuit 82 operates while the first time correction pulse is at the high level.
The first time correction data output from the first time correction data latch 85 is continuously output. However, the switching circuit 82
Does not output any data even if the second and third time correction pulses (see FIG. 8) are at high level. Therefore,
In the LED 11 which is not adjacent to the gap G, the light amount thereof is adjusted at a relative ratio of 1.0: 1.1 by the increase of the current passage time corresponding to the first time correction pulse.

Second print data / correction data switching circuit 83
Serves as a correction circuit that outputs a data signal that increases the current passage time of the second transistor TR2. The switching circuit 83 adds the second and third time correction pulses of the strobe signal STR to change the light amount of the LED 11a to another L level.
The ratio can be increased by 0.1 compared to the ED11.

A serial data signal composed of a combination of an ON signal and an OFF signal is once input to the shift register 87 in synchronization with the clock signal CLK, and then each latch 84 is input according to the input of the latch signals LA1, LA2, LA3. ~
It is taken in by 86. The data signal includes print data for causing the LEDs 11 and 11a corresponding to the dots to be printed to emit light, correction data for correcting the light amount of the LEDs 11 and 11a based on the measured value, and black and white lines of the print result. It includes correction data for correcting the light amount of the LEDs 11a at both ends of the chip to eliminate the problem.

In the fourth embodiment, the first transistor T
The ratio of the current capability of the second transistor TR2 to R1,
That is, the second basic current I with respect to the first basic current Ia1
The current amount of a2 is set to 0.9: 1.0 (when the current amount of the first basic current Ia1 is 1.0). Therefore, in the first transistor TR1 connected to the LED 11a adjacent to the gap G, the second transistor connected to another LED 11 is connected to the second transistor TR1.
The passing current amount is set to be smaller than that of the transistor TR2 at the ratio of 0.1. The light amount of the LED 11 which is not adjacent to the gap G can be adjusted at a relative ratio of 1.0 or 1.1 in consideration of the first time correction pulse. Similarly, the light amount of the LED adjacent to the gap G is the first, the second, and the third.
Considering the time correction pulse, 0.9 to 1.2 (0.
Adjustment is possible in 1 steps.

[0064]

As described above, according to the first invention, when the chips are mounted on the substrate, a pitch different from the normal LED pitch occurs between the adjacent chips based on the error of the gap between the chips. Also, by adjusting the current of the adjusting means, it is possible to eliminate black streaks and white streaks occurring in the print result without remounting.

Further, according to the second aspect of the invention, since the passing current amount of the main transistor connected to the LED located at the end portion of the chip is set to be small, when the chip is mounted on the substrate, it is based on the arrangement of the chips. Even if a pitch smaller than the normal pitch between LEDs occurs between adjacent chips, the LED
By reducing the light amount of, it is possible to eliminate the black streaks occurring in the printed result without remounting.
On the other hand, since the second sub-transistor is connected to the LED at the end of the chip and the passing current amount which is larger than the passing current amount due to the combination of the main transistor and the first sub-transistor connected to another LED is defined, the chip is mounted on the substrate. Even if a pitch larger than the normal pitch between LEDs occurs between adjacent chips based on the arrangement of chips when mounting on,
By increasing the light amount of the LED, it is possible to eliminate the white streak generated in the print result without remounting.

Furthermore, according to the third invention, the first sub-transistor is connected to the LED adjacent to the gap, and the other L
Since the amount of passing current that is larger than the amount of passing current by the main transistor connected to the ED is specified, when mounting the chips on the substrate, a pitch larger than the normal pitch between LEDs based on the arrangement of the chips is provided between adjacent chips. Even if it occurs, by increasing the light amount of the LED, it is possible to eliminate the white streak generated in the print result without remounting.

Furthermore, according to the fourth aspect of the invention, the current passing time of the main transistor and the first sub-transistor connected to the LED located at the end of the chip is different from that of other L
Since it is specified to be longer than the current passage time due to the combination of the main transistor and the first sub-transistor connected to the ED, when mounting the chip on the substrate, a pitch larger than the normal pitch between LEDs is set based on the arrangement of the chips. Even if it occurs between the adjacent chips, by increasing the light amount of the LED, it is possible to eliminate the white streaks that occur in the printed result without remounting.

Furthermore, according to the fifth invention, the current passage time of the main transistor connected to the LED located at the end of the chip is longer than the current passage time of the main transistor connected to another LED. Therefore, even when a pitch larger than the normal pitch between LEDs is generated between adjacent chips based on the arrangement of the chips when mounting the chips on the substrate, re-mounting is performed by increasing the light amount of the LEDs. It is possible to eliminate white streaks that occur in the printed result.

[Brief description of drawings]

FIG. 1 is a schematic enlarged view showing a configuration of a print head.

FIG. 2 is a circuit configuration diagram of a drive circuit according to a first embodiment of the present invention.

FIG. 3 is a circuit configuration diagram of a drive circuit according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a strobe signal.

FIG. 5 is a circuit configuration diagram of a drive circuit according to a third embodiment of the present invention.

FIG. 6 is a diagram showing a strobe signal.

FIG. 7 is a circuit configuration diagram of a drive circuit according to a fourth embodiment of the present invention.

FIG. 8 is a diagram showing a strobe signal.

[Explanation of symbols]

10a, 10b Chip 11 LED 11a, 11b Adjacent to the gap LED 12 substrate 22-24, 42-44 Transistor 66,83 as adjusting means Data switching circuit as adjusting means G Gap P Pitch

Claims (5)

[Claims] 1. A drive circuit of an LED print head, which supplies a drive current to each LED of an LED print head in which a plurality of chips in which a plurality of LEDs are aligned at a fixed pitch are linearly arranged on a substrate. A drive circuit for an LED print head, which is provided with an adjusting means for adjusting a current supplied to an LED at an end of the LED print head. 2. A drive circuit for an LED printhead, which supplies a drive current to each LED of a printhead in which a plurality of chips in which a plurality of LEDs are arranged in a row at a fixed pitch are linearly arranged on a substrate, Connected to each LED mounted on the chip to turn on / off the drive current flowing to each LED,
A plurality of main transistors for setting the amount of drive current at the time of turning on and a first sub-transistor, and the current capacity of the main transistor connected to the LED located at the end of the chip is connected to another LED. The size is set smaller than the main transistor, the second sub-transistor that can supply additional drive current is connected to the LED at this end, and the adjustment range of the amount of drive current for the LED at the end is made larger than other LEDs. Characterized by L
ED print head drive circuit. 3. A drive circuit for an LED printhead, which supplies a drive current to each LED of a printhead in which a plurality of chips in which a plurality of LEDs are arranged in a row at a fixed pitch are linearly arranged on a substrate, Connected to each LED mounted on the chip to turn on / off the drive current flowing to each LED,
The main transistor including a plurality of main transistors for setting the amount of drive current at the time of turning on is smaller than the main transistor connected to the other LED in the current capacity of the main transistor connected to the LED located at the end of the chip. The LE is characterized in that the first sub-transistor capable of supplying an additional drive current is connected to the LED at the end while being set, and the adjustment range of the drive current amount with respect to the LED at the end is made larger than that of the other LEDs.
D print head drive circuit. 4. A drive circuit for an LED print head, which supplies a drive current to each LED of a print head in which a plurality of chips in which a plurality of LEDs are arranged in a row at a fixed pitch are linearly arranged on a substrate. Connected to each LED mounted on the chip to turn on / off the drive current flowing to each LED,
On when turning on the main transistor and the first sub-transistor, which includes a plurality of main transistors and a first sub-transistor for setting a driving current amount at the time of turning on, and is connected to an LED located at an end of the chip A drive circuit for an LED print head, characterized in that a correction circuit for correcting the time is provided, and the adjustment range of the light emission time for the LED at the end is made larger than that of the other LEDs. 5. In a print head in which a plurality of chips in which a plurality of LEDs are aligned and arranged at a constant pitch are linearly arranged on a substrate, LE which supplies a drive current to each LED is provided.
In the drive circuit of the D print head, each LED mounted on each of a plurality of chips includes a plurality of main transistors for turning on / off a drive current flowing through each LED, and the LED located at the end of the chip. A drive circuit for an LED print head, characterized in that a correction circuit for correcting the ON time when turning on the main transistor connected to is provided, and the adjustment range of the light emission time with respect to the LED at the end is made larger than that of the other LEDs.