JPH0262156A - 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 supplying switch at the time of an optical printing operation, and making it into a photoelectric current input switch at the time of a reading operation. CONSTITUTION:At the time of the light emitting operation, a power source is connected so that the current in a forward direction may be applied to an LED, when a gate signal is made into a high level, the current is supplied through two MOSFETs and a current regulating resistance to the LED, and the LED emits light. At the time of the light receiving operation, the power source is connected so that the current in the reverse direction is applied to the LED, when the gate signal is made into the high level, the current corresponding to the intensity of the light made incident on the LED is applied through the two MOSFETs, and detected by a current detecting terminal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an LED array control circuit. The present invention relates to a LIED array control circuit that switches a light source for printing 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 fourth
The configuration diagram is shown in the figure.

First, to explain the printing operation using the conventional circuit, first, the cathode side of the LED array is grounded by the switch SW, and a forward voltage is applied to the LED array. Next, by setting the select signal to a low level, one input terminal of the switching gates foil to 1oin becomes a high level, and one input terminal of the switching gates +02-1 to +102-n becomes a low level. Since a data signal is input to the other input terminal of the switching gate 101-1, this data signal is output as is and inputted to one input terminal of the OR gate +03-1.

Further, since the other input terminal of the switching gate 102-1 is at a low level, the output of the switching gate 102-1 is at a low level, and this output is input to the other input terminal of the OR gate 103-1. Here, OR gate +03-1
It can be seen that the output of is the same as the data signal. The output of the OR gate 10:1-1, ie, the data signal, is input to the D terminal of the D-type flip-flop 104-1. after that,
By setting the latch signal to high level, the data signal input from the D terminal is transferred to the D-type flip-flop 104-1.
By setting the latch signal to low level, the data signal held is output from the O terminal. This output data signal is input to one input terminal of switching gate 101-2. Thereafter, the data is shifted by the number of stages of the shift register in the same manner. 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 an optical signal hitting the LED 105-I N105-n, the select signal is set to a high level, and the switching gates +02-1 to 102-n are activated.

Then, the strength of the optical signal hitting the LEDs 105-1 to 105-n is converted to low level or high level by the Schmitt trigger circuit Sl+, and the switching gates +02-1 to
D of D type flip-flops +04-1 to +04-n via +02-n and OR gates 103-1 to 103-n.
Manual power is applied to the terminal. After that, by setting the latch signal to high level, the strength of the optical signal can be changed to the D-type flip-flop 1.
04-1-104-n. After that, by setting the select signal to low level, the switching gate +011
= 101-n, synchronized with the clock signal,
The 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, so it is necessary to deal with misrecognition, gradation, and colorization of documents due to variations in the characteristics of the LED array. I can't get it.

Another problem is that the control circuit is duplicated for the light emitting section and the light receiving section, and 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 used includes a control unit that outputs a control signal according to the optical printing operation or reading operation, and a control unit that is provided on the cathode side of each LED and that switches the direction of applying bias voltage to each LED. The device is characterized in that it includes a switch and an analog switch that is provided on the anode side of each LED and switches the direction of applying bias voltage to each LED using a control signal from a control unit depending on the switch.

(Function) According to the present invention having the above-described configuration, all the elements constituting the circuit are shared during the light emitting operation and the light receiving operation.

During light emitting operation, a power source is connected between the switch common terminal and the cathode of the LED array so that a forward voltage is applied to the LED array. Next, when data synchronized with the clock signal is manually input to the data input terminal, the data is shifted between shift registers, and when the data has been shifted by the number of stages of the shift register, a latch signal is input and the data in the shift register is input to the latch circuit. By moving the print data serially manually, it is converted into one line of parallel data.
LED while the strobe signal from the control unit is active
emits light and exposes 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, by sequentially turning on the analog switches using a shift register, the photocurrent from the LED connected to the turned on analog switch is output to the switch common terminal. This current is converted to voltage and amplified. By A/D converting this voltage, a digital signal corresponding to the shading of the original to be read can be obtained.

Therefore, the present invention can solve the above problems, and includes a light receiving section,
It is effective for correcting variations in LED characteristics or for gradation, as it avoids duplication of the circuit of the light emitting part and can obtain the photocurrent from the LED as a digital signal corresponding to the density of the original. A high-performance exposure light source and reading sensor integrated head can be realized at a low price (a 4EO control circuit can be provided).

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

FIG. 1 is a circuit diagram showing an embodiment of the present invention. FIG. 3 is a circuit diagram showing the operating principle of the present invention. In addition, the same figure (
Figure a) illustrates the light emitting operation, and Figure (b) illustrates the light receiving operation. P for analog switch
C- type MO5FET and N type MOSFET connected in parallel
There are MOS types and series types in which the source terminals of the same type (7) MOSFETs are connected, but in both cases, two MOSFETs are turned on at the same time by a gate signal.

OFF L, serves as a switch. In FIG. 3, a G-MOS type analog switch is shown as an example. During the light emitting operation shown in FIG. 3(a), a power supply is connected so that a forward current flows through the LED, and when the gate signal is set to high level, the current flows through two MOSFETs and a current limiting resistor. EO is supplied, and 1 and ED emit light. In the light receiving operation shown in Fig. 3(b), when the power supply connection is changed so that the current flows in the opposite direction to the LED and the gate signal is set to high level, the current corresponding to the strength of the light incident on the LED is divided into two. The current flows through the MOSFET and is detected at the current detection terminal.

Next, referring to FIG. 1 and FIG. 2 which is a time chart showing the operation of this embodiment, the operation of this embodiment based on the operating principle of the present invention shown in FIG. 3 described above will be explained.

First, to explain the printing operation, first, the LED common terminal is grounded so that a forward voltage is applied to the LED array 6, and the switch common terminal of the analog switch group 4 is set to the power supply side. Next, data is shifted between the D-type flip-flops 10-1 to 10-n constituting the shift register 1 by inputting a data signal closely synchronized with the clock signal from each terminal. As shown in FIG. 2, D-type flip-flops l0-1 to 10-n
When the number of stages is reached, the latch signal is shifted from low level to high level. Further, by shifting to the low level, the contents of the shift register 1 are held in the D-type flip-flops 20-1 to 20-n constituting the latch circuit 2. Here, the serial data input from the data input terminal is converted to parallel data, and each of the flip-flops 20-1 to 20-o of the latch circuit 2
The output of is ANDN with the strobe signal - gate group AND
Gates 30-1 to: 1O-n (7) are manually input to one input terminal. The analog switches 40-1 to 40 operate only during the active period when the strobe signal input to the other input terminal is active.
- is made conductive, current is supplied to the LEDs 60-1 to 60-n via the current limiting resistors 50-1 to 50-n, the LEDs emit light, and a photosensitive drum (not shown) is exposed. Note that the latch circuit 2 is 1. This is a means for writing the next data while the εD array 6 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 array 6
The LED common terminal is connected to a positive power source so that a voltage in the opposite direction is applied to the switch common terminal, and a current-voltage conversion circuit, an amplifier circuit, an A/D conversion circuit, etc., although not shown, are connected to the switch common terminal. Then, by setting the data signal to high level for a period corresponding to one stage of shift register 1 synchronized with the clock signal and keeping it low level for the other period, one piece of data is sent to the D-type flip-flop of shift register 1 in synchronization with the clock signal. The data is shifted between 10-1-10-n. D
The output terminals of the type flip-flops 20-1 to 20-n are manually input to the latch circuit 2, but during the period when the latch signal is at a high level, there is a throughput between the input and output, and the input data is directly input to the latch circuit 2. (AND game)
It becomes one input of 30-1 to 30-n.

A strobe signal is input to the other input terminals of the AND gates 30-1 to 30-n, and by keeping this signal at a high level, one high-level data that shifts the shift register 1 is used to shift the analog switch group. 4 will be opened sequentially. As a result, the LED
Photocurrents of 60-1 to 60-n can be sequentially obtained at the switch common terminal. This situation is shown in the reading operation section of FIG. 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 shading of the read document. In addition, by shining negative light on the LED array 6 and measuring the output from the switch common terminal, the LED
It is possible to know the variation in light receiving sensitivity between 60-1 and 60-b, and by providing an external correction means, it is possible to obtain a sensor with uniform characteristics.

(Effects of the Invention) As described above in detail, according to the present invention, the LED has a high degree of integration in which the light emission control section and the light reception control section are duplicated, and only binary data can be obtained as the sensor output. A low-cost, high-performance head with integrated light emitting and reading functions can be realized without using an array control circuit, making it ideal for facsimile,
Can be used for printer-cum-image scanner devices, 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, Fig. 3(a),
(b) is a circuit diagram showing the operating principle of the present invention, and FIG. 4 is a circuit diagram showing a conventional LED array control circuit. 1...Shift register, 2...Latch circuit, 3-A
NDN-gate group 4...Analog switch group, 5.
...Current limiting resistor group, 6-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. an analog switch that switches the direction of applying a bias voltage to each of the LEDs in response to a control signal from the controller; and a control signal from the controller that causes the analog switch to supply current to the LED array during optical printing operation. As a current supply switch, the LED
An LED array control circuit characterized in that the LED array control circuit is a photocurrent input switch that takes out a photoelectric signal obtained by photoelectrically converting reflected light from a reading target from the array.