JPS6374367A - Light emitting element drive device - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a light emitting element driving device, and more particularly to a light emitting device driving device that stabilizes the operation of a light emitting element.

(Prior Art) Recently, optical technology using optical semiconductor elements has been developed and is widely used in optical communications, laser facsimiles, laser printers, etc.

Optical semiconductor elements include light-emitting elements, light-receiving elements, etc. Examples of light-emitting elements include laser diodes and light-emitting diodes, and examples of light-receiving elements include photodiodes.

A light-emitting element is used as a light source by biasing the element to generate light, and a light-receiving element receives light and converts it into an electrical signal, which is used in optical communication receivers, laser diodes, and light-emitting devices. It is used as a motion detection element such as a diode.

For example, in a laser printer, a laser diode is used as a light source for a recording head section, and a latent image is formed on the photosensitive drum by projecting laser light from the laser diode onto the photosensitive drum.

The driving of this laser diode was controlled by a driving device shown in FIG.

In FIG. 4, 1 is a recording head section of a laser printer, and the recording section 1 includes a drive circuit 2, a laser diode 3,
It is equipped with a polygon motor 4, etc. The drive circuit 2 is D/
A current pulse corresponding to the voltage set by the A converter 5 is supplied to the laser diode 3 to drive the laser diode 3, and the laser diode 3 projects a laser beam with an amount of light corresponding to the supplied current onto a polygon mirror (not shown). . The laser light projected from the laser diode 3 is pulsed light that is turned on/off for each pixel based on an image signal, and after being reflected by a polygon mirror, it is irradiated onto a photosensitive drum (not shown). The polygon mirror is a polygon mirror, and is rotated at a constant high speed by a polygon motor 4.

The laser light projected from the laser diode 3 is also irradiated onto the photodiode 6, and the amount of light from the laser diode 3 is detected by the photodiode 6. The output of the photodiode 6 is converted into a digital signal by an A/D converter 7 and input to a control section 8. The control unit 8 controls the output of the laser diode 3 based on the detection result of the photodiode 6 so that the recording density set by the operator at the operation unit of the laser printer is obtained. That is,
The control unit 8 outputs a digital signal (8-bit parallel signal) corresponding to the concentration (light intensity of the laser diode 3) to the D/A converter 5 at regular intervals, for example, every 6 seconds, and
The A converter 5 converts this digital signal into a D/A (digital/analog) signal and sends it to the drive circuit 2 as a voltage signal.
Output to. The drive circuit 2 is mainly composed of transistors, and the output from the D/A converter 5 is added to the base terminal of the drive circuit 2 to supply the laser diode 3 with a current corresponding to the potential difference between the base and emitter. The control unit 8 also
Based on the detection result of the photodiode 6, the digital signal output to the D/A converter 5 is controlled so that the target light amount is achieved. Therefore, the light amount of the laser diode 3 is feedback-controlled to a predetermined light amount based on the detection result of the photodiode 6.

However, in the conventional light-emitting element driving device, since a digital signal for concentration setting is outputted from the control unit 8 to the D/A converter 5 at regular intervals, it is possible that disturbances such as temperature rise within the regular interval Even if the current value changes and the light intensity of the laser diode 3 changes, it cannot be corrected until the next digital signal is output, which will not only deteriorate the print quality (but also cause the laser diode 3 to be damaged). Ta.

(Object of the Invention) Accordingly, the present invention provides a driving means for supplying a current value corresponding to a set voltage to a light emitting element, and a current limiting means for limiting the current value to a predetermined limit current value. To provide a light emitting element driving device capable of precisely controlling the current value supplied to a target luminous intensity in accordance with a target luminous intensity, preventing overcurrent, and preventing damage to the light emitting element while accurately controlling the current value to the target luminous intensity. The purpose is to

(Structure of the Invention) In order to achieve the above object, the present invention includes a voltage setting means for setting a voltage value corresponding to a target luminous intensity of a light emitting element, and a current that corresponds to the set voltage value of the voltage setting means to the light emitting element. a driving means for supplying current to drive the light emitting element and detecting the driving state of the light emitting element to control the supplied current to a target value corresponding to the set voltage; and a driving means for controlling the supplied current to a target value corresponding to the set voltage; current limiting means for limiting the current to a limiting current value of;
It is characterized by having the following.

Hereinafter, the present invention will be specifically explained based on examples.

FIG. 1.2 is a diagram showing an embodiment of the present invention, which is applied to a laser printer.

FIG. 1 is a diagram showing the optical system of a laser printer, and 11
is a laser diode. A current pulse is supplied to the laser diode 11 from a drive circuit which will be described later, and the laser diode 11 is driven by this current pulse and emits a laser beam. A laser beam sent out from a laser diode 11 is converted into a parallel beam by a collimator lens 12 and is incident on a polygon mirror 13 . The polygon mirror 13 is rotated at high speed by a polygon motor 14, and the laser beam projected onto the polygon mirror 13 is swung at a constant angular velocity in the direction indicated by the arrow in the figure as the polygon mirror 13 rotates. The laser beam reflected by the polygon mirror 13 passes through the f.theta. lens 15 and scans the surface of the photoreceptor 16 with uniform linear movement, thereby forming an electrostatic latent image on the surface of the photoreceptor 16. That is, the laser beam sent out from the laser diode 11 is turned on/off based on image information, and the photoreceptor 16 has areas that are irradiated with the laser beam and areas that are not irradiated, corresponding to this on/off. . Before the photoreceptor 16 is irradiated with the laser beam, it is uniformly charged by a charger (not shown), and when the photoreceptor 16 is irradiated with the laser beam, the charge on the irradiated area disappears and an electrostatic latent image is formed. be done. The photoreceptor 16 rotates in the direction of the arrow in FIG. 1, and electrostatic latent images are formed line by line one after another, and toner having opposite polarity charges is attached to the surface of the photoreceptor 160 and developed. When the photoconductor 16 to which the toner is attached faces the recording paper 17, a corona discharge is applied from the back side of the recording paper 17 to transfer the toner to the recording paper 17 by applying an electric charge of the opposite polarity to the toner, and the recording paper 17 is transferred to the recording paper 17 as shown in the figure. The toner on the photoreceptor 16 is successively transferred onto the recording paper 17 by moving in the direction of the arrow. Thereafter, the toner is fixed on the recording paper 17 by heating and applying pressure by a fixing means (not shown).

The laser beam reflected by the polygon mirror 13 is also projected onto a reflecting mirror 18 installed near the photoreceptor 16, and the laser beam reflected by the reflecting mirror 18 is incident on a light detector 19. The output of this optical detector 19 is used for main scanning synchronization.

The laser diode 11 is driven by a driving device 2 shown in FIG.
The drive is controlled by 1. The driving device 21 includes a voltage setting means 22, a driving means 23, a current limiting means 24, etc., and drives the laser diode 11 based on a control signal from a control section 25 of the laser printer.

The voltage setting means 22 includes a control section 25 and a D/A converter 26, and the control section 25 outputs voltage information corresponding to the target current value to be supplied to the laser diode 11.
It is output to the D/A converter 26 as bit data.

The D/A converter 26 receives the 8 data sent from the control unit 25.
The bit data is D/A converted (digital/analog conversion) and a voltage value Vs corresponding to the voltage information is output to the driving means 23.

The driving means 23 is an operational amplifier (hereinafter referred to as OP amplifier) OPI.
, OF2, diodes D1, D2, D3, resistors R1, R
2 and a photodiode PD, and supplies a target value of current to the laser diode 11. O
The output voltage Vs of the D/A converter 26 is input to the positive terminal of the P amplifier OP1, and the diode D1 is connected between the negative terminal and the P amplifier OP1. The negative terminal of OP amplifier OP1 is grounded via resistor R1, and the output of OP amplifier OP1 is fed back to the negative terminal of OP amplifier OPI via diode D2 and photodiode PD. The photodiode PD is irradiated with a laser beam from the laser diode 11, and when the photodiode PD is irradiated with the laser beam while a reverse voltage is applied, a current corresponding to the light intensity of the laser beam flows through the photodiode PD. . The voltage at the negative terminal of the OP amplifier OPI is input to the positive terminal of the OP amplifier OP2, and the laser diode 11 is connected to a feedback circuit for the output of the OP amplifier OP2 to the negative terminal. Further, the laser diode 11 is grounded via a resistor R2.

In the driving means 23, the OP amplifier OP2 operates as a non-inverting amplifier, and a current 2 corresponds to the voltage value Va input to the positive terminal of the OP amplifier OP2.

do. The voltage Va input to the OP amplifier OP2 is connected to the resistor R.
1, and this voltage Va is controlled to be equal to the output voltage Vs from the D/A converter 26, as will be described later. Therefore, the driving means 23 generates a current corresponding to the set voltage Vs of the voltage setting means 22! , is supplied to the laser diode 11.

The current limiting means 24 includes an OP amplifier OP3 and a diode D4.
, a variable resistor VR, and an alarm means 27, which includes a resistor R3 and a transistor Tri.
and a warning lamp 28. OP amplifier O
The voltage vb of the resistor R2 is input to the negative terminal of P3, and the reference voltage VC set by the variable resistor VR is input to the positive terminal. oP amplifier OP3
outputs a high-level signal (H signal) when the voltage vb is lower than the reference voltage Vc, and outputs a low-level signal, for example, a signal at potential O (L signal) when the voltage vb becomes higher than the reference voltage VC. do. This voltage vb is a voltage drop caused by the current 1t passing through the laser diode 11 flowing through the resistor R2, and corresponds to the current value IL supplied to the laser diode 11. On the other hand, the reference voltage Vc
The current value IL is appropriately set by the variable resistor VR to a value (limit current value) that does not cause an overcurrent to the laser diode 11. When the output of the OP amplifier OP3 is an H signal, the diode D4 is reverse biased and becomes a reverse blocking state, and the transistor Tri is also in an OFF state. When the output of the OP amplifier OP3 becomes the L signal state, the diode D4
is forward biased and turned ON, and the voltage Va input to the positive terminal of the OP amplifier OP2 decreases. At this time, the transistor Tri is also turned on and the alarm lamp 28
lights up.

That is, the OP amplifier OP3 detects the current Ic flowing through the laser diode 11, and when it exceeds the limit current, lowers the voltage Va, which is the reference voltage of the OP amplifier OP2, to reduce the current IL.
decrease.

Next, the action will be explained.

During printing, when print data is input, this laser printer stores the print data for one page or several pages in the RAM of the control unit 25, and prints the print data based on the preset print density and print data. Voltage information is output to the D/A converter 26 as 8-bit data for each pixel line by line. A voltage Vs corresponding to this voltage information is output from the D/A converter 26. Now, if the voltage Vs rises to a voltage value at which a current IL sufficient for the laser diode 11 to emit light flows, current flows through the diode D1 to the resistor R1 due to the voltage Vs, and the OP amplifier OP
2 is applied with voltage Va. This voltage Va supplies the laser diode 11 with a current {circle around (2)}, causing the laser diode 11 to emit light. On the other hand, the output of the OP amplifier OPI becomes a positive potential due to the rise in the voltage v5, and a reverse voltage is applied to the photodiode PD. Therefore, the photodiode PD receives the laser beam from the laser diode 11 and generates a current (2) corresponding to the amount of light. flows through the resistor R1, and the potential Va at the negative terminal of the OP amplifier OPI rises. When the voltage Va becomes higher than the voltage Vs, the output of the OP amplifier OPI becomes O potential, and the photodiode PD enters the cut-off state. Therefore, the current due to photodiode PD is ■. becomes O, and the voltage V
a descends. However, when the voltage Va becomes lower than the voltage Vs, the output of the OP amplifier OPI becomes positive again, and currents 2 and D flow from the photodiode PD to the resistor R1. That is, the negative terminal voltage Va of the OP amplifier OPI (also the positive terminal input voltage of the OP amplifier OP2) is determined by detecting the amount of light that is the driving state of the laser diode 11 with the photodiode PD, and adjusting the current flowing through the resistor R1. By doing so, Vs and Vs -0,6V
(0.6V is the voltage drop across the diode D1). That is, the driving means 23 drives the laser diode 11
The amount of light that is the driving state of the laser diode 11 is detected by the photodiode PD, and the positive terminal voltage Va of the OP amplifier OP2 is controlled to a voltage value Vs corresponding to the target amount of light.
The current value IL supplied to the current value IL is controlled to a target value corresponding to the set voltage value Vs. Therefore, the laser diode 11
The current IL supplied to the voltage setting means 22 is quickly and accurately controlled to a value corresponding to the voltage Vs set by the voltage setting means 22. In addition, since the photodiode PD and the laser diode 11 are inserted into the feedback circuits of the OP amplifier OPI and the OP amplifier OP2, the nonlinearity of the photodiode PD and the laser diode 11 is corrected. Variations in the elements of No. 11 are absorbed by the OP amplifier OPI and OP amplifier OP2, and the accuracy is further improved.

The current value IL supplied to the laser diode 11 is determined by the resistance R.
2 is detected as a voltage drop vb due to OP amplifier OP
3, the 0 normal voltage vb is compared with the reference voltage Vc.
is lower than the reference voltage Vc. At this time, OP amplifier OP3
The output of D4 is at a high level, and diode D4 is in a reverse blocking state. However, if the current IL of the laser diode 11 increases and the voltage vb becomes higher than the reference voltage Vc due to some abnormality such as a setting error in the voltage setting means 22 or a rise in temperature, the output of the OP amplifier OP3 becomes a low level, and the diode D4 is turned on. do. As a result, the OP amplifier OP
The voltage V a 73 at the positive terminal of No. 2 decreases, and the current IL supplied to the laser diode 11 decreases. Therefore, an overcurrent exceeding the limit current set by the variable resistor VR does not flow through the laser diode 11, and damage to the laser diode 11 is prevented.

Further, when the output of the OP amplifier OP3 becomes low level, the transistor Tri is turned on, and the alarm lamp 28
lights up to notify the operator of an abnormality.

In this way, the current IL set for each pixel can be applied to the laser diode 11 while preventing damage to the laser diode 11.
The laser diode 11 can be supplied with light to cause the laser diode 11 to emit light, and the printing quality of the laser printer can be improved.

Note that the frequency of the current flowing through the laser diode 11 is varied for each pixel based on print data by a circuit not shown.

FIG. 3 is a diagram showing another embodiment of the present invention, and this embodiment is intended to reduce costs. In the description of this embodiment, the same components as in the above embodiment are given the same reference numerals, and the explanation thereof will be omitted.

In the driving device 31 of this embodiment, as shown in FIG. 3, the driving means 32 includes an OP amplifier OPI, a diode D
3. Consists of resistor R2 and resistor R11, OP
The output voltage Vs of the D/A converter 26 is input as Va to the positive terminal of the amplifier OPI via the resistor R12.

Therefore, also in this embodiment, the laser diode 1
1 has a current I corresponding to the input voltage Va of the OP amplifier OPI.
L is supplied, and the laser diode 11 is connected to the OP amplifier OP.
Since it is inserted into the feedback circuit of I, the nonlinearity of the laser diode 11 is corrected and a stable current IL is supplied to the laser diode 11.

Further, in this embodiment as well, it is possible to prevent overcurrent to the laser diode 11 and damage to the laser diode 11 as in the above embodiments.

(Effects) According to the present invention, it is possible to accurately control the current supplied to the light emitting element in accordance with the target luminous intensity, and also to prevent overcurrent, and while preventing damage to the light emitting element, The luminous intensity of the light emitting element can be precisely controlled to the target luminous intensity.

[Brief explanation of the drawing]

Fig. 1.2 is a diagram showing an embodiment of the light emitting element driving device of the present invention, Fig. 1 is a conceptual diagram of a recording section of a laser printer to which the light emitting element driving device is applied, and Fig. 2 is a diagram showing the light emitting device. FIG. 2 is a circuit diagram of an element driving device. FIG. 3 is a circuit diagram of another embodiment of the light emitting device driving device of the present invention. FIG. 4 is a block diagram of a conventional light emitting element driving device. 11... Laser diode, 21.31... Drive device, 22... Voltage setting means, 23.32... Drive means, 24... ... Current limiting means, 25 ... Control section, 26 ... D/A converter, 27 ... Alarm means, 28 ... Warning lamp, D1 ~ D5...Diode, R1-R3, R11, R12...Resistance, VR.
...Variable resistor, OPI~OP3...OP amplifier, Tr...
...Transistor, PD...Photodiode.

Claims (2)

[Claims] (1) Voltage setting means for setting a voltage value corresponding to the target luminous intensity of the light emitting element; supplying a current corresponding to the set voltage value of the voltage setting means to the light emitting element to drive the light emitting element; a driving means for detecting the driving state of the light emitting element and controlling the supplied current to a target value corresponding to the set voltage; and a current limiting means for limiting the current value supplied from the driving means to the light emitting element to a predetermined limit current value. A light emitting element driving device comprising: (2) The driving means has a light receiving element that receives light from the light emitting element and converts it into electricity, and compares the detection result of the light receiving element with the set voltage value of the voltage setting means to determine a current value. Claim 1 characterized in that the control is performed to a target value.
The light-emitting element driving device described in 1.