JPH0262157A - Led array control circuit - Google Patents

Abstract

PURPOSE:To integrate a light emitting device and a reader by making an analog switch into a current switch at the time of an optical printing operation by means of a control signal, and making it into a photoelectric current input switch at the time of a reading operation. CONSTITUTION:An LED common terminal is grounded so that a voltage in a forward direction is applied to an LED array 7 at the time of the printing operation. Data in synchronization with a clock signal are inputted, when they are shifted by the number of the stages of the shift register, and the printing data are converted into parallel data, the LED emits light, and exposes a photosensitive drum. At the time of the light receiving operation, reverse bias is applied to the LED array 7, and a current/voltage converting circuit and an amplifying circuit are connected to a switch common terminal. When a high level latch signal is inputted to a latch circuit 2, MOS type transistor switches 50-1 to 50-n are successively opened, and the photoelectric currents of LEDs 70-1 to 70-n are outputted to the switch common terminal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an LED array control circuit, and in particular to an LED array control circuit used in a device having a printing function and a reading function, typified by a facsimile machine. The present invention relates to an LED array control circuit that switches a light source to a reading sensor of a reading device.

(Prior art) As a conventional LED array control circuit, Japanese Patent Application No. 62-2
There is one disclosed in the specification No. 16339, and the third
The configuration diagram is shown in the figure.

First, to explain the printing operation using a conventional circuit, first, the cathode side of the LED array is grounded using the switch SW, and a forward voltage is applied to the LED array.Then, by setting the select signal to low level, the switching gate is The - input terminals of the switching gates 101-1 to 101-n are at a high level, and one input terminal of the switching gates 102-1 to 102-n is at a low level. Since a data signal is input to the other input terminal of switching gate 101-1, this data signal is output as is and input to one input terminal of OR gate 103-1. Further, since the other input terminal of the switching gate 102-1 is at a low level, the switching gate 102-1
The output of 2-1 is at a low level and is input to the other input terminal of this output OR gate 103-1. Here, O
It can be seen that the output of R gate 103-1 is the same as the data signal. The output of the OR gate 103-1, ie, the data signal, is input to the D terminal of the D-type flip-flop 104-1. Thereafter, by setting the latch signal to high level, the data signal input from the D terminal is held in the D-type flip-flop 104-1, and by setting the latch signal to low level, the data signal held is output from the 0 terminal. be done. This output data signal is transmitted to the switching gate 10.
It is input to one input terminal of 1-2. Thereafter, the data is shifted in the same manner by the number of stages of the shift register. Each flip-flop that makes up the shift register converts serial data signals into parallel data signals, stores information on whether to turn on each LED connected to it, and lights up the LED array only while the strobe signal is active. A current flows through the drum, emits light, and exposes a photosensitive drum (not shown).

Next, to explain the reading operation by the conventional circuit, first, a reverse voltage is applied to the LED array by the switch SW. Next, in order to obtain optical signals applied to the LEDs 105-1 to 105-n, a select signal is set to a high level, and the switching gates 102-1 to 102-n are activated.

Then, the strength of the optical signal hitting LED 105-1 to 105-n is converted to low level or high level by the Schmitt trigger circuit SH, and the switching gate 102-1
~102-n and D-type flip-flops 104-1 to 104-n via OR gates 103-1 to 103-n.
is input to the D terminal of Thereafter, the strength of the optical signal is held in the D-type flip-flops 104-1 to 104-n by setting the latch signal to a high level. After that, by setting the select signal to low level, the switching gate 10
1-1 to 101-n are selected, and in synchronization with the clock signal, data from the document to be read held in each flip-flop is shifted and output from the data out terminal.

(Problems to be Solved by the Invention) However, in the above conventional LED array control circuit,
When using an LED array as a light-receiving element, the photoelectrically converted signal from the LED array is binarized using a Schmitt trigger circuit, which may cause erroneous recognition of the original, gradation, or colorization due to variations in the characteristics of the LED array. In addition, the control circuit is duplicated for the light emitting part and the light receiving part,
Another problem is that the gate circuit for controlling this is complicated.

The present invention is intended to solve these problems, and it is an object of the present invention to provide an LED array control circuit that can realize a head with integrated light emitting and reading functions at low cost and high performance.

(Means for Solving the Problems) In order to solve the above problems, the present invention uses an LED array formed by arranging a plurality of LEDs as a light source for optical printing and as a reading sensor for optically reading a reading target. The optical printing/optical reading device to be used includes a control unit that outputs a control signal according to the optical printing operation or reading operation, and a switch provided on the cathode side of each LED to switch the direction of applying bias voltage to each LED. , is characterized in that it is provided with an MO8 type transistor switch that is provided on the anode side of each LED and switches the direction of application of bias voltage to each LED in accordance with a control signal from a control section.

(Function) According to the present invention having the above-described configuration, the zero-order clock is connected to the power supply between the switch common terminal and the cathode of the LED array so that a forward voltage is applied to the LED array during light emission operation. When data synchronized with a signal is input to the data input terminal, the data is shifted between shift registers, and after shifting by the number of stages of the shift register, a latch signal is input and the data in the shift register is moved to the latch circuit. As a result, serially input print data is converted into one line of parallel data, and the LED emits light while the strobe signal from the control section is active, exposing the photosensitive drum.

During light receiving operation, a reverse bias is applied to the LED array, and a current-voltage conversion circuit and an amplifier circuit are connected to the switch common terminal. Next, use the shift register to move the MO
By sequentially turning on the 3-type transistor switches, a photocurrent from the LED connected to the MO3-type transistor switch that has been made conductive is output to the switch common terminal. This current is converted to voltage and amplified. This voltage A
By performing /D conversion, a digital signal corresponding to the shading of the original to be read can be obtained.

Therefore, the present invention can solve the above-mentioned problems, and can obtain the photocurrent from the LED as a digital signal corresponding to the density of the original.
Alternatively, it is possible to provide an LED array control circuit that is effective for gradation and that can realize a low-cost, high-performance exposure light source and a reading sensor-embedded head.

(Example) Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a circuit diagram showing one embodiment of the present invention, and FIG.
The figure is a time chart showing the operation of this embodiment.

First, to explain the printing operation, first, the LED common terminal is grounded so that a forward voltage is applied to the LED array 7. Next, a clock signal and a data signal synchronized with this are input from each terminal. Data is transferred to a D-type flip-flop 10 that constitutes a shift register 1.
-1 to 10-n, as shown in Figure 2, when the number of stages of D-type flip-flops 1O-1 to 10-n is reached, the latch signal is changed from low level to high level. Migrate. Furthermore, by shifting the shift register 1 to the low level, the contents of the shift register 1 are changed to D constituting the latch circuit 2.
It is held in type flip-flops 20-1 to 20-n.

Here, the serial data input from the data input terminal is converted to parallel data, and the output of each flip-flop 20-1 to 20-n of the latch circuit 2 is an ANDN-gate group with the strobe signal. The current limiting resistor 60 makes the output transistors 40-1 to 40-n conductive only during the period when the strobe signal inputted to one input terminal of the AND gates 30-1 to 30-n and inputted from the other input terminal is active. -1~60-n via LED7
A current is supplied to 0-1 to 70-n to cause the LEDs to emit light, thereby exposing a photosensitive drum (not shown). Note that the latch circuit 2 is a means for writing the next data while the LED array 7 is emitting light to improve the printing speed, and can be deleted in the case of low-speed operation.

Next, to explain the reading operation, the LED common terminal is connected to a positive power supply so that a reverse voltage is applied to the LED array 7, and the switch common terminal is connected to a current-voltage conversion circuit, an amplifier circuit, Connect A/D conversion circuit, etc. Next, if the data signal is set to high level for a period corresponding to one stage of shift register l synchronized with the clock signal and kept at low level for the other period, one data signal is transferred to the D type of shift register l in synchronization with the clock signal. The output terminals of the D-type flip-flops 20-1 to 20-n are input to the latch circuit 2 by shifting between the flip-flops 1O-1 to 10-n, but they are not input during the period when the latch signal is at a high level. There is a through between the outputs, and the input data becomes the output of the latch circuit 2 as it is, and the AND gate 3
It becomes one input of 1-1 to 31-n. AND gate 3
The other input terminals of 1-1 to 31-n are sense signals, and by keeping this signal at a high level, the shift register 1 is shifted. MO of switch group 5
The S-type transistor switches 50-1 to 50-n are sequentially opened. As a result, LED70
-1 to 70-n photocurrents can be sequentially obtained at the switch common terminal. This situation is shown in the reading operation part of Figure 2. By converting the minute current obtained from the switch common terminal into voltage, further amplifying it, and A/D converting it, it is possible to obtain a digital signal corresponding to the density of the read document. can.

In addition, by shining negative light on the LED array 7 and measuring the output from the switch common terminal, the LED array 70-
You can know the variation in light receiving sensitivity from 1 to 70-n,
By providing an external correction means, a sensor with uniform characteristics can be obtained.

(Effects of the Invention) As described above in detail, according to the present invention, it is possible to extract the gray scale information of the read document received by the LED array to the outside in an analog manner, and an A/D converter is provided outside. As a result, a head incorporating high-performance light emitting and reading functions such as density correction, gradation, and colorization can be realized, and can be used in facsimile machines, image scanners that can also be used as printers, etc.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a time chart showing the operation of this embodiment, and Fig. 3 is a conventional LE
FIG. 3 is a circuit diagram showing a D array control circuit. 1...Shift register, 2...Latch circuit, 3
...AND gate group, 4...Output transistor group, 5...MOS type transistor switch group, 6...
- Current limiting resistor group, 7... LED array.

Claims (1)

[Scope of Claim] An optical printing and optical reading device that uses an LED array formed by arranging a plurality of LEDs as a light source for optical printing and as a reading sensor for optically reading a reading target, comprising: a control unit that outputs a control signal according to the operation; a switch that is provided on the cathode side of each of the LEDs and switches the direction of applying a bias voltage to each of the LEDs; and a switch that is provided on the anode side of each of the LEDs that controls the control. and a MOS type transistor switch that switches the direction of application of a bias voltage to each of the LEDs in response to a control signal from the control unit, and the MOS type transistor switch is configured to switch the direction of applying a bias voltage to each of the LEDs in response to a control signal from the control unit, during an optical printing operation. An LED array control circuit characterized in that the current switch that supplies current is a photocurrent input switch that takes out a photoelectric signal obtained by photoelectrically converting light reflected from the object to be read from the LED array during a reading operation. .