JPS62285482A - Drive circuit for semiconductor laser - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a laser, and to protect the laser positively by forcibly setting an optical modulation signal to the laser at zero when the amount of light detected reaches set quantity or more and controlling a driving-current path for the laser. CONSTITUTION:When a voltage signal corresponding to the amount of light emitted from a laser 31 is elevated abnormally and made higher than a reference voltage value REF, an output from a comparison circuit 61 reaches an H level, and a latch circuit 63 latches the H level. When an output from the latch 63 is inverted to the H level, a light-emission preventive signal from a means 60 is kept to '1' at all times regardless of the level of a modulation signal by an NAND circuit 6, a transistor 42 holds an ON state continuously, and the state of the control of the lighting of the laser 31 is inhibited forcibly.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a semiconductor laser drive circuit suitable for application to electrophotographic color copying machines, laser printers, and the like.

[Background of the Invention] Some electrophotographic color copying machines use a semiconductor laser as means for forming an electrostatic latent image on a photosensitive image forming body using an image signal corresponding to a document.

FIG. 6 is a block diagram showing an example of such a color copying machine 10.

The figure shows an example of a simple color copying machine. This copying machine attempts to record a color image by separating the colors and information of a color document into approximately three types of color information. In this example, three colors, black BK, red R, and blue B, are illustrated as color information to be separated.

In the figure, 11 indicates a drum-shaped image forming body,
A photoconductive photoreceptor surface layer made of selenium or the like is formed on its surface, so that an electrostatic image (electrostatic latent image) corresponding to an optical image can be formed.

The following members are sequentially arranged on the circumferential surface of the image forming body 11 in the direction of rotation thereof.

The surface of the image forming body 11 is uniformly charged by a charger 12. The surface of the charged image forming body 11 is subjected to image exposure (the light is indicated by 14) based on each color separation image.

After image exposure, the image is developed by a predetermined developing device.

The developing devices are arranged in a number corresponding to the color separation images.

In this example, developing device 1 filled with red toner developer
5, a developing device 16 completely filled with blue toner developer,
The developing devices 17 filled with a black toner developer are sequentially disposed facing the surface of the image forming body 11 in this order toward the rotation direction of the image forming body 11.

The developing devices 15 to 17 are sequentially selected in synchronization with the rotation of the image forming body 11. For example, by selecting the developing device 17, a black color separation image is developed.

A pre-transfer charger 19 and a pre-transfer exposure lamp 20 are provided on the developing device 17 side, and these make it easy to transfer the color image onto the recording medium P. However, the pre-transfer charger 1
9 and a pre-transfer exposure lamp are provided as necessary.

The color image developed on the image forming body 11 is transferred onto the recording medium P by the transfer device 21.

The recording material P that has been completely transferred is subjected to a fixing process by the fixing device 22 at the subsequent stage, and then the recording material P is discharged.

Note that the static eliminator 23 includes one or a combination of a static eliminator I3 lamp and a corona discharger for static elimination.

The cleaning device 24 includes a cleaning blade and a fur brush, and is used to remove residual toner adhering to the drum surface after the color image of the image forming member 11 has been transferred.

As the charger 12 described above, a scorotron corona discharger or the like can be used. This is because stable charging can be applied to the image forming body 11 with less influence from previous charging.

As the image exposure, image exposure obtained by a laser beam scanning device is used.

This is because when a laser beam scanning device is used, a small and inexpensive semiconductor laser can be used as the light source of the image recording device, and a clear color image can also be recorded.

The image exposure means shown in FIG. 7 is an example of this laser beam scanning device 30.

The laser beam scanning device 30 includes a semiconductor laser 31, and the laser 31 is optically modulated based on a color separation image (for example, binary data).

The laser beam emitted from the laser beam +f31 enters a mirror scanner 34 made of a rotating polygon mirror via a collimator lens 32 and a cylindrical lens 33.

A laser beam is deflected by the mirror scanner 34 and irradiated onto the surface of the image forming body 11 through an f-θ lens 35 and a cylindrical lens 36 for image formation.

The laser beam is directed to the image forming body 1 by the mirror scanner 34.
1 is scanned at a constant speed in a predetermined direction a, image exposure corresponding to a color separation image is performed by such scanning.

Note that 39 indicates a photosensor, and by receiving the laser beam reflected by the mirror 38, an index signal indicating the start of scanning of the rape beam is obtained, and one line of image data is written based on this index signal. It will be.

1. When using the laser beam scanning device 30, it is possible to easily form electrostatic images while shifting them for each color separation image. Clear color images can be formed.

FIG. 8 is a system diagram showing an example of the laser drive circuit 40.

The laser drive circuit 40 is provided with a light amount stabilizing circuit for stabilizing the laser light amount in addition to a circuit that drives the laser using a modulation signal.

In the figure, a current bypass transistor 42 is connected in parallel to the laser 31, and a modulation signal based on image data supplied to a terminal 43 is supplied to this transistor 42 via a driver 44. As a result, the transistor 42 is turned on and off by the modulation signal, so that the state of energization of the laser 31 can be fully controlled.

A variable constant current circuit 45 is connected within the current path of the laser 31, and the amount of current is controlled according to the amount of light emitted by the laser 31.

Therefore, the amount of light emitted from the laser 31 is detected by the photosensor 50, and this detected current is transmitted to the current/voltage converter 51.
The detected current is converted into a voltage signal proportional to the amount of emitted light. For this reason, the photo sensor 50 and the current/voltage converter 51 constitute the light amount monitor circuit 52.

The voltage signal is supplied to a control circuit 53, which generates a control signal according to the level of the voltage signal. The variable constant current circuit 45 is controlled by the output of the control circuit 53. This constant current circuit 45 is composed of a differential amplifier 46 and a transistor 47.

Therefore, when the amount of light emitted by the laser 31 becomes larger than that during normal operation, the control obtained from the control circuit 53 (qI times the signal becomes smaller, so the drive current flowing through the laser 31 becomes smaller, and the amount of light emitted from the laser 31 is suppressed. It turns out.

[Problem to be Solved by the Invention 1] By the way, although the drive current supplied to the laser 31 is controlled by the output of the control circuit 53 so as to be constant, since the laser 31 has temperature characteristics, such Even in the controlled state, there is a drawback that the amount of emitted light fluctuates due to fluctuations in ambient temperature.

Further, although not shown, when performing light amount feedback control on the laser 31, the amount of emitted light may become too large, leading to deterioration of the laser 31.

In addition, there is a method of monitoring the driving current of the laser 31 and stopping the driving of the laser when the current value exceeds a certain value, but with this method, the characteristics of the driving current of the laser 31 and the amount of emitted light vary. If there is, it is not necessarily possible to protect the laser 31 sufficiently.

Of course, even if the driving current of the laser is stopped when the driving current exceeds a certain value due to a change in the ambient temperature, the laser 31 cannot be sufficiently protected.

Therefore, the present invention proposes a semiconductor laser drive circuit that solves these problems with a simple structure and that ensures prevention of laser deterioration and protection of the laser.

[Technical means for solving the problem] In order to solve the above-mentioned problem, the present invention provides a sight monitor circuit that monitors the amount of light emitted from the semiconductor laser, and a comparison circuit that compares the monitor output with a reference value. , and a light emission blocking means for blocking light emission of the semiconductor laser according to the comparison output.

The emission blocking means blocks an optical modulation signal to the semiconductor laser, and the emission blocking means may be configured to reduce the output of a current source that drives the semiconductor laser, or may be configured to reduce the output of a current source that drives the semiconductor laser. It can also be configured to reduce the output.

[Function] When the detected light amount is equal to or greater than the set light amount, the light emission blocking means operates, and the light modulation signal to the laser is forcibly set to zero, and the laser drive current path is restricted.

As a result, an excessive current will not flow through the laser compared to during normal operation, so the laser will not deteriorate or be destroyed.

[Example] Next, an example of a semiconductor laser drive circuit according to the present invention will be described in detail with reference to FIG. 1 and subsequent figures.

FIG. 1 shows an example of a semiconductor laser drive circuit 40 according to the present invention, and description of the same parts as shown in FIG. 8 will be omitted.

In this invention, when the amount of light from the laser f31 exceeds a predetermined value, the light emission blocking means prohibits the laser from emitting light.

In the embodiment shown in FIG. 1, a negative-input NAND circuit 65 is provided upstream of the driver 44, and the modulation signal and the light emission blocking signal formed by the light emission blocking means 60 are supplied to this NAND circuit 65.

The light emission blocking means 60 has a comparison circuit 61 and a latch circuit 63, and the comparison circuit 61 compares the voltage signal obtained from the current/voltage converter 51 with the reference voltage of the reference voltage source 62, and the reference voltage When the voltage signal becomes higher than this, the comparison output is inverted to high level (FIGS. 2A and 2B).

This comparison output is latched by a latch circuit 63, which is reset to a low level by a reset signal obtained when the power of the device is turned on. 64 indicates a reset circuit.

The latch output is supplied to the above-mentioned NAND circuit 65 as a light emission blocking means, and is also supplied as a light quantity abnormality signal to a macrocomputer (particularly not shown) that controls the main body of the apparatus. 66 indicates its output terminal.

In this configuration, when the laser 31 is normally excited and emitting light at a normal level, the level of the voltage signal at that time is lower than the reference voltage REF, so the comparison output remains at a low level. Therefore, since the latch output is also held at a low level, the transistor 42 is turned on and off by the modulation signal itself.

On the other hand, when the voltage signal corresponding to the amount of light emitted by the laser 31 increases abnormally and becomes higher than the reference voltage value REF, the comparison output is inverted to a high level. As a result, the latch output will also latch at a high level (Figure 2C)
.

When the latch output is inverted to high level, the NAND circuit 65
Due to the existence of
Since the current is always 1° and the transistor 42 is always kept on, the laser 31 is forcibly prohibited from being turned on.

For this reason, a driving current that exceeds a predetermined amount of light does not flow through the laser 31. This control condition does not change even if the ambient temperature in which the laser 31 is placed changes or the current/light emission characteristics of the laser 31 change.

FIG. 3 shows another example of the present invention, in which a variable constant current circuit is used as in FIG. This is a case where the laser 31 is controlled by supplying .

Therefore, in this example, the modulation signal supplied to the terminal 43 is supplied directly to the driver 44, and the latch output is supplied to the control circuit 53. When the latch output is supplied,
The variable constant current circuit 45 controls i! so that the drive current flowing through the laser 31 becomes minimum or zero. II will be done. As a result, even if the amount of laser light becomes abnormally high due to the above-mentioned causes, such a state can be detected immediately, and early deterioration or destruction of the laser 31 can be prevented.

The example shown in FIG. 4 is a case where a variable constant voltage circuit 70 is used as a rape drive system, and this is an embodiment corresponding to FIG. 1.

That is, the variable constant voltage circuit 70 includes a differential amplifier 71 for voltage adjustment and a variable impedance element (transistor) 72 that functions for voltage adjustment. A current bypass transistor 42 is connected in series to the emitter side of this transistor 72, and the current of this transistor 42 is
A laser 31 is connected in series within the flow path.

The output of the current/voltage converter 51 is supplied to the control circuit 53, and normally the transistor 4
2 is controlled so that a predetermined electric source voltage is applied to it. However, when the drive current flowing through the laser 31 becomes abnormally large, the level of the voltage signal also becomes large. Ru. As a result, an excessive drive current no longer flows through the laser 31, resulting in an operation similar to that shown in FIG.

The example shown in FIG. 5 is an embodiment corresponding to FIG.
A variable constant voltage circuit 70 is used as in FIG. 4. In this embodiment, the latch output is supplied to the control circuit 53, and the modulation signal is supplied directly to the driver 44.

Even in this configuration, if the drive current flowing through the laser 31 becomes abnormally large, the control circuit 53 operates to reduce the voltage applied to the transistor 42.

Note that in each of the embodiments described above, a flip-flop may be used instead of the latch circuit 63.

[Effect of the invention 1] As explained above, in this invention, a light emission blocking means is provided for the laser 31, and the light emission of the laser 31 is prohibited when the drive current flowing through the laser 31 becomes abnormally large. With this configuration, it is possible to prevent early deterioration of the laser caused by the flow of a large drive current, and it is also possible to prevent damage to the laser due to excessive current.

Therefore, as described above, the present invention is extremely suitable for application to simple color copying machines, laser printers, and the like.

Further, the present invention is particularly effective as a countermeasure against CPU runaway when performing light quantity control i1T in 5PUs.

[Brief explanation of drawings]

FIG. 1 is a system diagram of essential parts showing an example of a drive circuit for a semiconductor leopard according to the present invention, FIG. 2 is a waveform diagram for explaining its operation, and FIGS. 3 to 5 are other examples of the present invention, respectively. Fig. 6 is a system diagram similar to Fig. 1 showing the system, Fig. 6 is a configuration diagram of the main part showing an example of simple color copying (a stirring example), and Fig. 7 is a diagram showing a laser beam used to explain the invention. A configuration diagram showing an example of an optical scanning device, and FIG. 8 is a system diagram of a semiconductor laser drive circuit. 10...Color copying machine 11...Drum 30 as an image forming body...Lepe optical scanning device 31 ... Semiconductor laser 40 ... Drive circuit 45 ... Variable constant current circuit 50 ... Photo sensor 51 ... Current/voltage converter 53 ... Control circuit 60 ... Light emission inhibiting means 61 ... Comparison circuit 63 ... Latch circuit (flip-flop) 70 ...
Variable constant voltage circuit patent applicant Konishi Roku Photo Industry Co., Ltd. Figure 7 Dan Q; Ray f Kusho J To Eel 2

Claims (3)

[Claims] (1) A semiconductor laser, a light amount monitoring circuit that monitors the amount of light emitted by this semiconductor laser, a comparison circuit that compares the output voltage of this light amount monitoring circuit with a reference voltage, and a light emission amount of the semiconductor laser according to the comparison output. What is claimed is: 1. A semiconductor laser drive circuit comprising a light emission blocking means for blocking light emission. (2) The semiconductor laser drive circuit according to claim 1, wherein the light emission blocking means blocks an optical modulation signal to the semiconductor laser. (3) The semiconductor laser drive circuit according to claim 2, wherein a current source for driving the semiconductor is used as the light emission blocking means, and the current source is throttled when blocking light emission. . (3) The semiconductor according to claim 2, wherein a voltage source for driving the semiconductor is used as the emission blocking means, and the output of the voltage source is reduced when blocking the emission. Laser drive circuit.