JP3387803B2 - LED array drive - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-scanning LED array (SL) used as a light emitting element for recording for forming a permanent visible image on a recording medium by an electrophotographic recording method.
The present invention relates to an LED array driving device that drives an ED).

[0002]

2. Description of the Related Art Conventionally, an SLED (self-scanning LED array: hereinafter referred to as SLED) has been disclosed in Japanese Patent Laid-Open No. 1-28896.
No. 2, JP-A-2-208067, JP-A-2-
No. 212170, No. 3-20457, No. 3-194978, No. 4-5872, No. 4-23367, No. 4-2965.
79, JP-A-5-84971, and Japan Hardcopy '91 (A-17) "Proposal of light emitting element array for optical printer integrated with drive circuit", IEICE ('90 .3.5. ) "Proposal of self-scanning light emitting device (SLED) using PNPN thyristor structure" and the like, and it is attracting attention as a light emitting device for recording.

FIG. 3 shows an example of a general SLED that can be controlled by the present invention. Figure 4 shows this SLED
An example of a conventional control signal and timing for controlling is shown. Here, the case where all the elements are turned on is illustrated.

The VGA of FIG. 3 corresponds to the power supply voltage of the SLED, and is connected to the diode connected in cascade to the start pulse ΦS via the resistor of 50 KΩ to 100 KΩ. As shown in FIG. 3, the SLED is composed of transfer thyristors 1'-5 'arranged in an array and light-emitting thyristors 1-5 arranged in an array.
The gate signals of the respective thyristors are connected, and the gates of the first thyristors 1'and 1 are connected to the signal input portion of the start pulse ΦS. Second thyristor 2 ', 2
Is connected to the cathode of the diode connected to the terminal of the start pulse ΦS, and the third thyristor is connected to the cathode of the next diode in the same manner.

The transfer and light emission operations of the SLED of FIG. 3 will be described with reference to the timing chart of FIG. The transfer is started by changing the start pulse ΦS from 0V to 5V. When ΦS becomes 5V, Va = 5V, Vb = 3.7V (the forward voltage drop of the diode is 1.3V), Vc = 2.4V, Vd =
After 1.1V, Ve becomes 0V, and the gate signals of the transfer thyristors 1'and 2'are changed from 0V to 5V, and 3.
It changes to 7V.

In this state, by shifting the shift pulse Φ1 from 5V to 0V, the respective potentials of the transfer thyristor 1'become anode: 5V, cathode: 0V, gate: 3.7V, which turns on the thyristor. As a condition, the transfer thyristor 1'is turned on. Even if the start pulse ΦS is changed to 0V in this state, Va≈5V because the thyristor 1'is turned on. The reason is that a pulse is applied to ΦS via a resistor. This is because when the thyristor is turned on, the potential between the anode and the gate becomes almost equal.

Therefore, even if .PHI.S is set to 0V, the ON condition of the first thyristor is maintained and the first shift operation is completed. In this state, set the ΦI signal for the light emitting thyristor to 5
When the voltage is changed from V to 0 V, the condition is the same as when the transfer thyristor is turned on. Therefore, the light emitting thyristor 1 is turned on and
The second LED will light up.

When the light emitting thyristor driving clock ΦI of the first LED is returned to 5V, the potential difference between the anode and the cathode of the light emitting thyristor disappears and the minimum holding current of the thyristor cannot flow, so the light emitting thyristor 1 is turned off.

Next, the transfer under the ON condition of the thyristor from the transfer thyristors 1'to 2'will be explained. Even if the light emitting thyristor 1 is turned off, the shift pulse Φ1 remains 0V, so that the transfer thyristor 1'is Since it remains ON, the gate voltage Va of the transfer thyristor 1'is approximately 5V, and Vb = 3.7V.

In this state, the shift pulse Φ2 is changed from 5V to 0.
By changing to V, the potential of the transfer thyristor 2 ′ is anode: 5V, cathode: 0V, gate: 3.7.
Since it becomes V, the transfer thyristor 2'is turned on.

After the transfer thyristor 2'is turned on, the shift pulse Φ1 is changed from 0V to 5V, so that the transfer thyristor 1'is turned off in the same manner as the light emitting thyristor 1 is turned off. In this way, the transfer thyristor is turned on.
Moves from 1'to 2 '. Then, when the light emitting thyristor driving clock ΦI is changed from 5V to 0V, the light emitting thyristor 2 is turned on to emit light.

The reason why only the light emitting thyristor in which the transfer thyristor is ON can emit light is that the gate voltage is 0V except when the transfer thyristor is in the ON state, except for the thyristor adjacent to the thyristor in the ON state. , Because the thyristor does not turn on. By turning on the light emitting thyristor for the adjacent thyristor,
Since the potential of the light emitting thyristor drive clock ΦI is 3.4 V (the amount of forward voltage drop of the light emitting thyristor), the adjacent thyristor cannot be turned on because there is no potential difference between the gate and the cathode.

As described above, in the prior art, the drive pulses (shift pulses) Φ1 and Φ2 of the transfer thyristor are used.
Always turned on the transfer thyristor of the pixel regardless of whether the light emitting thyristor corresponding to the transfer thyristor of a certain pixel is turned on or off.

[0014]

However, in the conventional SLED described above, the gate voltage of the transfer thyristor, which is a characteristic of the SLED, is sequentially transferred depending on the manufacturing conditions of the semiconductor wafer forming the SLED. When the speed changes and the transfer and light emitting operations are performed at high speed, the transfer of the gate voltage of the transfer thyristor is delayed,
The light-emitting thyristor you are trying to emit does not light up,
A phenomenon occurs in which the light emitting thyristor on the B-side, which has the highest gate voltage of the other light emitting thyristors, lights up, and as a result, the transfer of the light emitting operation becomes unstable.

In order to solve this problem, the transfer thyristor 1'and the transfer thyristor 2'have been conventionally used.
Are turned on at the same time and the time for transferring the gate voltage is made sufficiently long to stabilize the operation of the SLEDs for sequentially transferring. However, in such a conventional method,
There is a problem to be solved in that the light emission time of the light emitting thyristor (DUTY of lighting ON) becomes shorter as the transfer time becomes longer, and the light amount of the light emitting thyristor becomes insufficient for forming an image.

Further, in the conventional SLED driving method, when the light emitting thyristor is ON, the transfer thyristor is also ON.
Therefore, the current consumption of both the light emitting thyristor and the transfer thyristor is required, and therefore the current consumption varies depending on the number of light emitting thyristors to emit light.

Particularly, a recording L for arranging several SLED chips in an array to form a permanent visible image on a recording medium.
When the ED head is made to drive several SLED chips at the same time, the current consumption depends on the number of chips in which the light emitting thyristors of the same pixels of all of the SLEDs are on. It increases in proportion to the number of chips.

Fluctuations in current consumption depend on SLED and SLED
This causes a change in the voltage drop due to the wiring from the power supply that supplies the drive circuit.Therefore, the more light emitting thyristors that emit light, the more voltage drops, resulting in a change in the light amount of the light emitting thyristors. However, the image density had changed.

The present invention has been made in view of the above points, and a first object thereof is to reduce current consumption and to lengthen a lighting time (light emission DUTY) of a light emitting thyristor. It is to provide an LED array driving device.

A second object of the present invention is, in addition to the above-mentioned first object, irrespective of the number of lit light emitting thyristors.
It is an object of the present invention to provide an LED array driving device which can always make the current consumption almost constant, eliminate the fluctuation of the light amount due to the fluctuation of the current consumption, and always form an image of uniform density.

[0021]

In order to achieve the first object, the invention of claim 1 is such that at least one transfer thyristor is arranged in an array, and transfer between adjacent transfer thyristors is performed. A control signal can be externally applied, and at least one light emitting thyristor is arranged in parallel in parallel with the transfer thyristor, and the gates between the transfer thyristor and the light emitting thyristor are connected to each other. The self-scanning LED array
In an LED array drive device that sequentially generates light emission states of the transfer thyristors by an external control signal and generates a drive signal that also sequentially emits light emission thyristors, the drive signals are input to the drive device. The transfer thyristor of the pixel that has caused the light emitting thyristor to emit light according to the image data is turned on when the light emitting thyristor is turned on.
With respect to the pixel which is turned on and the light emitting thyristor is not made to emit light, the transfer thyristor corresponding to the pixel is continuously turned on.

In order to achieve the second object, the second aspect
According to another aspect of the invention, at least one transfer thyristor is arranged in an array, and a control signal for transfer between adjacent transfer thyristors can be externally applied, and the light emitting thyristor is parallel to the transfer thyristor. Similarly, at least one or more are arranged in an array, and the gate between the transfer thyristor and the light emitting thyristor is connected to each self-scanning LED array, and the transfer thyristor is controlled by an external control signal. In an LED array driving device that generates a drive signal that sequentially emits light and the light emitting thyristor also sequentially emits light accordingly, the drive signal is used to cause the light emitting thyristor to emit light in accordance with image data input to the drive device. The pixel transfer thyristor is turned off when the light emitting thyristor is turned on, and the light emitting thyristor is turned on. For a pixel that does not exist, the current consumption when the transfer thyristor corresponding to the pixel is continuously turned on and only the transfer thyristor is turned on and the current consumption when the light emitting thyristor is turned on and the transfer thyristor is turned off are substantially constant. It is characterized by driving so that

According to a third aspect of the invention, an image data output section for outputting image data for forming a permanent visible image on a recording medium by an electrophotographic recording method, and the image data is read out to the image data output section. A READ clock for outputting the image data from the image data output unit, and based on the input image data, a start pulse ΦS as an SLED drive signal, and an image data signal Φ of nbit
D, an SLED control circuit for generating transfer clocks Φ1, Φ2, and a plurality of SLs to which the SLED drive signal from the SLED control circuit is input and which are arranged in an array.
An LED array having a plurality of SLED drive circuits for driving an SLED head array including EDs, and sequentially driving the SLED transfer thyristor and the light emitting thyristor of the SLED head array by driving the SLDE drive circuit. In the drive device, the transfer clocks Φ1 and Φ2 for the transfer thyristors output from the SLED control circuit to the SLED drive circuit turn on all transfer thyristors sequentially regardless of lighting of the light emitting thyristors. And a signal waveform for driving so as to sequentially transfer the gate voltage of the thyristor.

According to the present invention, the transfer thyristor of the pixel in which the light emitting thyristor has emitted light according to the image data input to the driving device is turned off when the light emitting thyristor is turned on to emit light. Since the transfer thyristor corresponding to the pixel is kept ON for the pixel which does not emit light from the thyristor, the current consumption can be reduced and the lighting time (light emission DUTY) of the light emitting thyristor can be lengthened.

According to the present invention, the transfer thyristor of the pixel in which the light emitting thyristor emits light according to the image data input to the driving device is turned off when the light emitting thyristor is turned on, and the light emitting thyristor is turned on. For a pixel that does not emit light, the transfer thyristor corresponding to that pixel is continuously turned on to reduce the current consumption, and the current consumption when only the transfer thyristor is turned on, and when the light emitting thyristor is turned on and the transfer thyristor is turned off. Since it is designed to drive so that the current consumption is almost constant,
Regardless of the number of light-emitting thyristors that emit light, the current consumption can be kept substantially constant, and the light-emitting thyristor lighting time (light emission DUTY) can be lengthened.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the configuration of an SLED driving device for driving an SLED according to an embodiment of the present invention. This SLED driving device has an image data output unit 301 that outputs image data for forming a permanent visible image on a recording medium by an electrophotographic recording method, and an SLED control unit 303. SL
The ED control unit 303 outputs a READ clock (reading clock) for reading the image data to the image data output unit 301, inputs the image data from the image data output unit 301, and then based on the input image data. SL
S for generating ED drive signal (LED array drive signal)
An LED control circuit 302 is provided. Further, it has a plurality of SLED drive circuits 305 for receiving SLED drive signals from the SLED control circuit 302 and driving a plurality of SLED chips arranged in an array. This SLDE
The SLED head array 3 is driven by the driving circuit 305.
The 04 SLED transfer thyristor and the light emitting thyristor are sequentially turned on. The SLED head array 304 to be controlled may have, for example, the general configuration of FIG. 3 described above.

FIG. 2 is a timing chart showing the control signals and timings for SLED control, which best represents the operation of the embodiment of the present invention. The SLED control circuits 302 to S of the SLED control unit 303 of FIG.
The waveforms of the transfer clocks Φ1 and Φ2, the start pulse ΦS, the light emitting thyristor drive clock ΦI, and the image data signal ΦD having an n-bit (n-bit) width, which are SLED drive signals output to the LEDs, are shown.

In the present invention, first, the SLED control circuit 302 has the start pulse ΦS and the image data signal Φ of nbit Φ as in the drive waveform of the prior art (see FIG. 4).
D and the transfer clocks Φ1 and Φ2 are set to the SLED drive circuit 30.
Output to 5.

At this time, from the SLED control circuit 302 to SL
The transfer clocks Φ1 and Φ2 of the transfer thyristors output to the ED driving circuit 305 are driven so that all the transfer thyristors are sequentially turned on regardless of lighting of the light emitting thyristors, and the gate voltages of the thyristors are sequentially transferred. It has a signal waveform to drive.

At the same time, the light emitting thyristor is turned on again.
Regarding the light emitting thyristor drive clock ΦI that controls the time, unlike the prior art, the SLED control of the light emitting thyristor drive clock ΦI that lengthens the ON time of the light emitting thyristor until the OFF time of the bit transfer thyristor corresponding to the light emitting thyristor that emits light Output from the circuit 302 to the SLED drive circuit 305.

Each signal input from the SLED control circuit 302 to the SLED drive circuit 305 will be described.
In the LED drive circuit 305, first, the light emitting thyristor drive clock ΦI and the parallel image data ΦD of nbit width
Is converted to 1-bit serial data (serial image data) ΦD 'and an AND gate is taken, and the signal ΦI input from the SLED control circuit 302 is directly input to the SLED 304 to the light emitting thyristor to be illuminated.
In the case of a light emitting thyristor that outputs to and does not emit light, set it to an OFF signal so that the light emitting thyristor does not turn on and SLE
Output to D304.

In the SLED drive circuit 305, the signal of the transfer thyristor corresponding to the light emitting thyristor to be illuminated is controlled so as to be turned off when the light emitting thyristor is turned on. If the light emitting thyristor is not turned on, the transfer clock from the SLED control circuit 302 is transmitted. The signals of Φ1 and Φ2 are directly output to the SLED 304.

The time until the light emitting thyristor turns on and the transfer thyristor corresponding to the bit turns off is SL.
The setting value is written in advance in R0M (not shown) in the ED drive circuit 305 so that adjustment can be performed.

Next, transfer of the gate voltage from the bit in which the transfer thyristor is OFF and only the light emitting thyristor is ON to the next bit is performed while the transfer thyristor of the next bit is ON while the light emitting thyristor is ON. By doing so, to the same potential as the gate voltage of the light emitting thyristor that is lighting now,
The gate voltage of the next thyristor becomes, and by turning off the thyristor emitting light at that time, the gate voltage moves to the next transfer thyristor, and the next light emitting thyristor is turned on.
It becomes a state that can be made N.

When the light emitting thyristor is turned on by driving the LED 304 as described above, the transfer thyristor corresponding to the light emitting thyristor is turned off.
As a result, in the present embodiment, the current consumption can be reduced and the lighting time (light emission DUTY) of the light emitting thyristor can be lengthened as compared with the conventional driving method.

In the above driving method according to the present invention, the ON current of the transfer thyristor and the ON of the light emitting thyristor are turned on.
By making the currents equal, the amount of current consumed becomes substantially constant regardless of the number of light-emitting thyristors turned on. Also, S
By keeping the voltage drop due to the wiring from the power supply supplying to the LED and SLED drive circuits constant,
The light quantity of the light emitting thyristor becomes stable, and as a result, the image density can be stabilized.

[0038]

As described above, according to the present invention,
The transfer thyristor of the pixel that causes the light emitting thyristor to emit light according to the image data input to the drive device is turned off when the light emitting thyristor turns on, and the transfer thyristor corresponding to that pixel turns on for the pixel that does not emit light. Since this is continued, the current consumption can be reduced and the lighting time (light emission DUTY) of the light emitting thyristor can be lengthened.

Further, according to the present invention, in the above driving device, current consumption when only the transfer thyristor is turned on,
The current consumption when the light emitting thyristor is turned on and the transfer thyristor is turned off is controlled so that the current consumption becomes almost constant. Therefore, the current consumption should always be almost constant regardless of the number of light emitting thyristors that emit light. Therefore, it is possible to always form an image of uniform density by eliminating the fluctuation of the light amount due to the fluctuation of the current consumption.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a basic configuration of an SLED drive device that is an embodiment of the present invention.

FIG. 2 is a timing chart showing control signals and timing for SLED control according to an embodiment of the present invention.

FIG. 3 is a circuit diagram showing an example of a basic configuration of a general SLED that can be a control target of the present invention.

FIG. 4 is a timing chart showing control signals and timings of the related art for controlling the SLED of FIG.

[Explanation of symbols]

1-5 Light emitting thyristor 1'-5 'Transfer thyristor 301 Image data output unit 302 SLED control circuit 303 SLED control unit 304 SLED head array 305 SLED drive circuit Φ1, Φ2 Transfer clock (shift pulse) ΦS Start pulse ΦI Light emitting thyristor Drive clock ΦD nbit width parallel image data ΦD ′ Signal converted to serial data (serial image data)

Continuation of the front page (56) Reference JP-A-8-264838 (JP, A) JP-A-9-141929 (JP, A) JP-A-61-248483 (JP, A) JP-A-8-187892 (JP , A) JP-A-5-84972 (JP, A) JP-A-10-297017 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B41J 2/44 B41J 2/45 B41J 2/455

Claims (6)

(57) [Claims] 1. At least one transfer thyristor is arranged in an array, and a control signal for transfer between adjacent transfer thyristors can be externally applied to the transfer thyristor to emit light in parallel with the transfer thyristor. Similarly, at least one or more thyristors are arranged in an array, and the gate between the transfer thyristor and the light emitting thyristor is connected to the self-scanning LED array. The transfer thyristor is controlled by an external control signal. In the LED array driving device that generates a drive signal that sequentially causes the light emitting thyristors to sequentially emit light, the light emitting thyristor is caused to emit light in accordance with image data input to the drive device using the drive signal. The pixel transfer thyristor turns off when the light emitting thyristor turns on, and the light emitting thyristor emits light. For the pixels not to LED array drive apparatus characterized by continuing to turn ON the transfer thyristor corresponding to the pixel. 2. At least one transfer thyristor is arranged in an array, a control signal for transfer between adjacent transfer thyristors can be externally applied, and light is emitted in parallel with the transfer thyristor. Similarly, at least one or more thyristors are arranged in an array, and the gate between the transfer thyristor and the light emitting thyristor is connected to the self-scanning LED array. The transfer thyristor is controlled by an external control signal. In the LED array driving device that generates a drive signal that sequentially causes the light emitting thyristors to sequentially emit light, the light emitting thyristor is caused to emit light in accordance with image data input to the drive device using the drive signal. The pixel transfer thyristor turns off when the light emitting thyristor turns on, and the light emitting thyristor emits light. And current consumption in the case of ON the transfer thyristors corresponding to the pixel continues to turned ON, and only the transfer thyristor for the pixels not to, O transfer thyristor the light-emitting thyristor is turned ON
An LED array driving device characterized by driving so that current consumption when FF is performed is substantially constant. 3. An image data output section for outputting image data for forming a permanent visible image on a recording medium by an electrophotographic recording method, and a RE for reading the image data to the image data output section.
The AD clock is output, the image data from the image data output unit is input, and SL is input based on the input image data.
The start pulse ΦS and the image data signal ΦD of nbit as the ED drive signal, the SLED control circuit that generates the transfer clocks Φ1 and Φ2, and the SLED drive signal from the SLED control circuit are input and arranged in an array. Multiple SLEDs for driving an SLED head array consisting of multiple SLEDs
An LED array driving device which has a driving circuit and sequentially turns on the SLED transfer thyristor and the light emitting thyristor of the SLED head array by driving the SLDE driving circuit, wherein the SLED driving circuit drives the SLED driving circuit. Transfer clocks Φ1, Φ2 for the transfer thyristor output to the circuit
The LED has a signal waveform that drives all the transfer thyristors to be sequentially turned on and to sequentially transfer the gate voltage of the thyristors, regardless of lighting of the light emitting thyristors. Array drive. 4. The light emitting thyristor drive clock ΦI for controlling the ON time of the light emitting thyristor, wherein the ON time of the light emitting thyristor is extended until the OFF time of the transfer thyristor of the bit corresponding to the light emitting thyristor that emits light. A thyristor drive clock ΦI is output from the SLED control circuit to the SLED drive circuit, and the light emitting thyristor drive clock ΦI and the nbit are output.
An AND gate is formed with the signal ΦD ′ obtained by converting the parallel image data ΦD of the width into 1-bit serial data, and the signal ΦI input from the SLED control circuit is directly output to the SLED to the light emitting thyristor to be illuminated,
4. The LED array driving device according to claim 3, wherein in the case of a light emitting thyristor that does not emit light, an OFF signal is output to the SLED so that the light emitting thyristor does not turn on. 5. In the SLED drive circuit, the signal of the transfer thyristor corresponding to the light emitting thyristor to be illuminated is controlled so as to be turned off when the light emitting thyristor is turned on. If the light emitting thyristor is not turned on, the transfer clock from the SLED control circuit is transmitted. The signals of Φ1 and Φ2 are directly used for SL
The time until the light emitting thyristor is turned on and the transfer thyristor corresponding to the bit is turned off is outputted to the ED
The LED array drive device according to claim 4, wherein the setting value is written in advance in a ROM in the drive circuit so that the setting value can be adjusted. 6. An ON current of the transfer thyristor and an ON current of the light emitting thyristor are made equal to keep a constant voltage drop due to a wiring from a power supply supplying to the SLED and the SLED drive circuit. The LED array driving device according to claim 5.