JPS62284747A - Semiconductor laser protection circuit - Google Patents

Abstract

PURPOSE:To prevent the destruction of laser by inhibiting lighting of a semiconductor laser when an output voltage of a luminous energy monitoring circuit has exceeded beyond a fixed value. CONSTITUTION:A forced lighting device Sc forces a laser 31 to light for a fixed period of time since a time in which a computer 52 runs in disorderly manner. An inhibit lighting signal Sf detects a level before the destruction of a laser 31 from a resultant laser luminous energy due to driving by the forced lighting signal Sc. Then the enforced inhibition of lighting of a laser 31 occurs. When the computer runs wild, a lighting signal is supplied to the laser 31 and synchronized to this, the level of a current control signal Sa on a current generation circuit 48 is raised gradually using a low pass filter 55. Thus even during the disorderly operation of the computer, the laser 31 is forced to light and a drive current does not flow abruptly in the laser 31. An inhibit lighting means 100 detects this disorderly runaway status halfway through the process of a gradual increase in the drive current, stopping drive of the laser 31.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] This invention is suitable for application to a semiconductor laser drive circuit used in electrophotographic color copying machines, laser printers, etc. This invention relates to a semiconductor laser protection circuit.

[Background of the Invention] Some electrophotographic color copying machines use a semiconductor laser as a means for forming an electrostatic latent image on a photosensitive image forming member 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 an easy-to-read color copying machine. This copying machine attempts to record a color image by separating the color information of a color original into approximately three types of color information. In this example, the color information to be separated is black BK, red R, and blue B.
Illustrate colors.

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 fully 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 units can be arranged in number t=number corresponding to the color separated images.

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

The developing devices 15 to 17 are sequentially selected i1 in synchronization with the rotation of the image forming body 11. For example, by selecting the developing device 17,
A black color separation image (normal black and white image) is developed.

A pre-transfer charger 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 f9 developed on the image forming body 11 is transferred to the transfer device 21.
As a result, the recording material P that has been transferred onto the recording material P 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 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.

In the case of using a laser beam scanning device, in addition to the fact that a small and inexpensive semiconductor laser can be used as the light source of the image recording device, 1. This is because clear color images can 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).

A laser beam emitted from a laser 31 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 imaging.

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 No. 18 indicating the start of laser beam scanning is obtained, and one line of image data is written based on this index signal. will be carried out.

When using the laser printer 30, it is possible to form electrostatic images while shifting them for each color separation image, so that a clear color image can be recorded.

FIG. 8 is a system diagram of essential parts showing an example of a laser drive circuit 40 suitable for use in the above-mentioned color copying machine.

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

The reason for providing this light intensity stabilization circuit is that the temperature characteristics of lasers are very poor, and considering that the laser is used in an environment where the ambient temperature changes, a light intensity stabilization circuit that stabilizes the laser light intensity is required. This is because it becomes necessary.

Note that this example is a case where the appropriate light amount value is controlled by a microcomputer.

Then, the laser 31 is excited by the drive current (excitation current) output from the current generation circuit 48, and emits light with an amount of light corresponding to the drive current. The laser beam emitted from the laser 31 is sent to a photosensor (photodiode, etc.) 4
1 detects the amount of light, and a current corresponding to the amount of light can be supplied to the current/voltage conversion means 42, thereby converting it into a voltage signal corresponding to the amount of light. Therefore, the photosensor 41 and the current/voltage conversion means 42 function as a light amount monitor circuit 60.

The voltage signal is converted into a digital signal by the A/D converter 51 and then supplied to the microcomputer 52, whereby a predetermined output signal for current side i output corresponding to the value of the digital signal is output. .

This control ill signal is latched by the latch circuit 53, and then supplied to the D/A converter 47, where it is converted into an analog control signal (current control signal) according to its output signal. By supplying this TL current control signal to the current generation circuit 48, the laser 3
The excited state of 1 is no longer controlled, and the amount of light changes.

Incidentally, as shown in FIG. 9, the relationship between the drive lri current supplied to the laser 31 and the amount of emitted light increases only extremely slightly until a predetermined drive current value Ith is reached. However, when the driving current Ith is exceeded, the amount of light increases rapidly.

Therefore, until the drive current reaches this inflection point Ith from zero, the range of change in the current value supplied to the current generating circuit 48 is large, and thereafter the control is controlled in small steps. This is because the time it takes for the light amount to converge to an appropriate value can be significantly shortened if the light amount is sold separately.

Taking this into consideration, the microcomputer 52
Now, depending on the value of input digital No. 13 that can be supplied to this, the following signal can be output. In other words, as shown in Figure 10, the maximum value of the amount of laser light required for data writing is Pmax, and the minimum value is Pm1n. In this case, the amount of light smaller than this minimum value Pm1n by a predetermined value is set as Pl. The light amount between Pmin and Pmax becomes the appropriate light amount value.

When the detected light amount is less than P1, the D/A converter 47
Let A be the increase in digital value Δ■ given to . and,
When it is 81 or more and Pm1n or less, the increase Δ
V is set to 8, and in other cases, ΔV is set to -B (therefore, in this case, the amount of decrease). However, A, B
It is assumed that the relationship is selected as A>B>0.

Then, V+Δ■ is calculated from the digital value V outputted to the D/A converter 47 last time, and control 1 is performed so that it can be outputted to the D/A converter 47 as a new V.

It is assumed that ■ can be set to the initial value O in the initialization routine when the power is turned on.

For this reason, when the control 1all routine for stabilizing the light amount starts, the laser 31 is excited by E'& I1 corresponding to the initial value ΔV, and in the next step, 2ΔV is set as the new output signal. The voltage is outputted to the D/A converter 47 side, and the laser 31 is excited by the current 2 corresponding to 2ΔV.

Thereafter, similar control operations are repeated, and when the detected light amount becomes equal to or less than P1 and equal to or less than min, B is used as ΔV instead of A this time.

As a result, the amount of current change is smaller than before, but as the control routine is repeated, the detected light amount gradually increases, and when it exceeds the maximum light amount value P max, -B
Therefore, the excitation current can be controlled.

In this way, the amount of detected light settles down to a value around Pm1n to Pmax.

A and B can be set as follows.

That is, first, A is set to a value that slightly exceeds Pm1n when the weight-based fit step is repeated n times, and B is set so that it exceeds Pmax when the current-based 1all step is repeated once or several times. set to a value.

This is because if A and B are too large, it will not be possible to converge to Pm1r+-Pmax, and if A and B are too small, it will take time to converge.

Next, an example of the control program for stabilizing the amount of light described above will be explained with reference to FIG.

First, when the control routine for stabilizing the light amount is called, the presence or absence of a light amount control request can be checked. Light amount side il
The presence or absence of a l request can be determined by the presence or absence of a flag obtained from a control routine that controls the main body of the apparatus. If there is no request, exit from this control routine (
Step pro 1゜62). When the light intensity control mode is selected, the on state of the laser 31 is determined, and when it is off, the laser 31 is controlled to turn on, and then,
Exit from this control routine (steps 3 to 65)
).

When the laser 31 is in the on state, after all A/D conversion data corresponding to the detected light amount has been input, it is determined whether the detected light amount is within the appropriate range (steps 66 and 67). In this case, the amount of detected light falls within the appropriate range (P min to P max
), the laser 31 is turned off and the light amount control request flag is reset, and then the control routine returns to the main processing control routine (step 68.).
69).

When the detected light amount is not within the appropriate range, the level of the detected light amount is compared with the set light amount P1, and if it is less than P1, the increase A is set as ΔV, and then V + Δ
V is output to the D/A converter 47 as V (step 7
1-73).

Here, in the first control routine, it is initialized to ■20.

When it is detected that the detected light amount is 81 or more, it is determined whether it is within the appropriate range (P win - P max) or not. When Pm1n or less, the increase B is
Set it as V, and then set ■+ΔV as V and set it as D.
/A converter 47 (steps 74 and 75).

As a result of such control, when the detected light amount exceeds Pmax, the process moves to step 76, where the decrease -B is set as ΔV, and then V-ΔV is output to the D/A converter 47. Therefore, when this control routine 74 is called, the light intensity of the laser 31 varies from Pm1n to Pma.
It will be controlled between x.

Therefore, the light intensity of the laser 31 is always from Pm1n to Pma
It will be excited with any light amount value (appropriate light amount value) between x.

The control routine is performed by timer interrupt.

In this case, either the light amount control program described above is placed in this timer interrupt routine, or a flag is set at the timer interrupt, the flag is checked in the main routine, and only when the flag is set, the control program Execute.

Here, since the output of the D/A converter 47 is prone to glitches (whisker-like noise), a low-pass filter is often used at the output stage of the D/A converter. Therefore, the response of the circuit is slow and the conversion time of the A/D converter is required, so it is convenient to perform the light amount control process by interrupting the timer.

Although the light amount control is started from zero, the control routine can also be configured to start from a predetermined value lower than the light ff1P1.

In other words, instead of setting the initial value to ■=0, V =
It can also be set to VO (0<VO<Vl).

Here, Vl is the D/A corresponding to the light intensity P1 at a certain temperature.
This is the data that should be given to the converter.

In this case, as shown in FIG. 11, the control time required to stabilize the light amount to an appropriate value can be roughly shortened.

[Problem to be Solved by the Invention 1] By the way, as mentioned above, when the microcomputer 52 is used to execute the stabilization process to obtain the appropriate value of the light amount, if noise enters the microcomputer 52 from the outside, , this microcomputer 52 may run out of control.

If the microcomputer 52 goes out of control, its output value will not be able to maintain the light amount level when the light amount is stabilized.

In this case, if the output value of the microcomputer 52 becomes abnormally high due to runaway, the current generation circuit 48 will control the laser drive current so that the amount of electricity is larger than that during normal operation.

Therefore, if this drive current is an excessive current for the laser 31, this excessive current may cause the laser 3
1 may be destroyed.

The drive circuit 40 shown in FIG. 8 has no means for protecting the laser against such runaway, and therefore cannot effectively protect the laser 31 when the microcomputer 52 goes out of control.

Therefore, the present invention solves these problems, and even if the microcomputer 52 goes out of control, the laser 31 can be reliably protected, and the laser protection means is configured. This invention proposes a semiconductor laser protection circuit in which a laser protection means can be constructed at low cost by using elements with a slow response speed as circuit elements.

[Technical means for solving the problem] In order to solve the above-mentioned problem, the present invention provides a light amount monitor circuit that monitors the amount of light emitted from a semiconductor laser, and converts the output voltage of this light amount monitor circuit into a digital amount. A/D conversion means for converting a digital quantity into an analog signal;
A current generating means for passing a predetermined drive current through the semiconductor laser according to this analog signal, and a microcomputer for controlling the digital amount given to the D/A converting means so that the A/D converted output is within a certain range. have

In summary, the present invention includes a low-pass filter that filters the current control signal obtained from the D/A conversion means and supplies it to the current generation circuit, and when detecting that the D/A conversion output has changed in one direction, The invention is characterized in that it includes a forced lighting means for lighting the semiconductor laser for a certain period of time, and a lighting prohibition means for prohibiting lighting of the semiconductor laser when it is detected that the output voltage of the light amount monitor circuit has exceeded a certain value. It is something.

[Function] If the microcomputer goes out of control, the level of the current control signal supplied to the current generating circuit will change rapidly, so the forced lighting means detects the point of this change and modulates it. The laser is forcibly turned on regardless of the presence or absence of the signal.

Further, by this forced lighting, the lighting prohibiting means can detect that the amount of laser light has exceeded a predetermined value. When a level equal to or higher than a predetermined value is detected, the lighting state of the laser is forcibly prohibited, thereby making it possible to prevent damage to the laser due to excessive current.

Since the excessive current is filtered by the low-pass filter, the excessive current will not rise suddenly. Therefore, circuit elements with a slow response speed can be used as the circuit elements of the forced lighting means 80 and the lighting inhibiting means 100, which are laser protection means.

[Embodiment 1] Next, an example of the semiconductor laser protection circuit according to the present invention will be described in detail with reference to FIG.

Since the embodiment shown in FIG. 1 is applied to the semiconductor laser driving circuit shown in FIG. 8, the explanation of the same parts as the structure shown in FIG. 8 will be omitted.

FIG. 1 shows two sides of a laser drive circuit 40 that includes laser protection circuitry.

In FIG. 1, the current side 1illll signal Sa obtained from the D/A converter 49 is completely supplied to the current generation circuit 48 via the low-pass filter 55.

An input control means 9o for controlling the lighting signal of the laser 31 is provided at the input stage of the current generating circuit 48.

On this input side (distribution means 9o), in addition to a modulation signal corresponding to image quality data and a lighting control signal used for stabilizing the light amount, forced lighting from a forced lighting means 80 that operates when the microcomputer 52 runs out of control is supplied. The signal Sc and the lighting prohibition signal Sf from the lighting prohibition means 100 are respectively supplied.

The forced lighting signal Sc is used to force the laser 31 to turn on for a certain period of time after the runaway occurs, and the lighting prohibition signal Sf is used to prevent the laser 31 from being destroyed based on the amount of laser light as a result of being driven by the forced lighting signal Sc. It is used to detect the level before the laser 31 is turned on and forcibly prohibit the laser 31 from turning on. The lighting prohibition signal Sf is also supplied to the microcomputer 52 as a signal for determining a runaway state.

FIG. 2 shows a specific example of the forced lighting means 80 and the input control means 90.

The forced lighting means 80 is composed of an edge detection circuit 81 and a pulse generation section 82.A current control signal Sa is supplied to the edge detection circuit 81, and a time point at which the signal level of the microcomputer 52 changes at a certain time is detected. Ru.

In normal use, the current control signal Sa is at a constant level. However, when the microcomputer 52 goes out of control, the level of the current side 1311 signal Sa changes rapidly (FIG. 5A). This level change point is detected and
The pulse generator 82 is driven by the edge detection signal sb obtained at that time, and the forced lighting signal Sc with a constant pulse width can be generated (B and C in the same figure).

The input control means 90 includes an OR gate 91 and an AND gate 9.
2, in addition to the modulation signal, the OR gate 91 is supplied with the lighting control signal sent from the microcomputer 52 side and the above-mentioned forced lighting signal Sc, and when any of these signals is supplied, OR output is obtained.

The OR output and the lighting prohibition signal Sf are supplied to the AND gate 92, and when the lighting prohibition signal Sr shown in FIG. will be supplied to

On the other hand, when a runaway state of the microcomputer 52 is detected, the lighting prohibition signal Sr is inverted to a low level, so that the AND gate 92 is closed and the driving of the laser 31 is forcibly prohibited.

FIG. 3 shows an example of the low-pass filter 55. In this example, an RC time constant circuit including a resistor 56 and a capacitor 57 is used, and the time constant is set to be equal to or less than the pulse width T of the forced lighting signal Sc.

By the way, in addition to the forced lighting means 80 as described above,
The reason for providing the low-pass filter 55 is as follows.

That is, when the modulation signal is in the O state, that is, when the laser 3
When microcomputer 1 is in a stopped state, microcomputer 5
2 goes out of control, when the current control signal Sa is at a much higher level than normal as shown in FIG. 5A, a considerably large drive current is output from the current generating circuit 48. This means that the control I is in a state of failure.

In this state, if the modulation signal becomes 1, an excessive current will instantly flow through the laser 31.

If such a state can be detected immediately by the lighting inhibiting means 100, the lighting signal to the current generating circuit 48 will become zero.
There are no particular problems.

However, if the circuit response speed of the lighting inhibiting means 100 system is slow, there is a high possibility that the laser 31 will be destroyed by excessive current.

Furthermore, even when the modulation signal becomes 1 while the output Sl (FIG. 5A) of the low-pass filter 55 has reached the maximum level of the current control signal Sa, the current generation circuit 48 generates an excessive current. Since the portion is split in such a way that the laser is supplied to the laser 31, there is a strong possibility that the laser 31 will be destroyed in the same manner as described above.

Therefore, in the event of runaway, the laser 31
A predetermined lighting signal is supplied to the current control signal Sa, and in synchronization with this, the level of the current control signal Sa is gradually raised using a low-pass filter 55.

In this way, the laser 31 is forcibly turned on even in the event of runaway, and the driving current does not suddenly flow through the laser 31. While the drive current is gradually increasing, the lighting prohibition means 100 detects this runaway state and stops the laser 3.
This is because the driving of the laser 31 can be stopped by the lighting prohibition signal Sf before an excessive current sufficient to destroy the laser 31 flows.

In this way, by using the low-pass filter 55 to slow the rise of the current control signal Sa, even if a circuit with a slow response speed is used as the lighting prohibition means 100 system and the forced lighting means 8o, it is possible to put it into practical use.

Therefore, circuit elements with slow response speed can be used as the entire laser protection means. This allows the entire circuit to be constructed at low cost.

Roughly, by providing the low-pass filter 55,
Surge current becomes difficult to flow through the laser 31, and the laser 31
can prevent early deterioration.

FIG. 4 shows an example of the point n prohibition means 100.

The voltage No. 13 Sd proportional to the amount of light is compared with the base 4 voltage REF of the base 4 voltage source 110 in the comparison circuit 101 (No. 5
Figure D). In the illustrated example, the comparison output Se is inverted to a high level only when the voltage signal Sd rises above the reference voltage REF (E in the figure).

The base 4 voltage REF is set to be higher than Pmax and lower than a level sufficient to destroy the laser 31.

The comparison output Se is supplied to the clock terminal of the D-type flip-flop 102. Since this flip-flop 102 is cleared when the device power is turned on, when a high-level comparison output Se is obtained, a low-level lighting prohibition signal Sf is output from its inverted output terminal Q (FIG. F).

As a result, when the runaway state of the microcomputer 52 is detected in this way, the level of the lighting prohibition signal S' is reversed and the lighting state of the laser 31 is forcibly turned off. As such, the voltage signal Sd becomes zero.

In the embodiments described above, the microcomputer 52 may be provided as a dedicated microcomputer for stabilizing the amount of light, or may be a microcomputer that controls opening and opening of the apparatus body.

Furthermore, if the microcomputer 52 itself has an A/D conversion function, the A/D converter 51 for A/D converting the appropriate light amount value can be omitted.

Similarly, if the microcomputer 52 itself has a latch function or the D/A converter 47 has a latch function, the latch circuit 53 can of course be omitted. .

[Effects of the Invention] As explained above, according to the present invention, since the forced lighting means 8o and the lighting inhibiting means 100 are provided, excessive current is not applied to the laser 31 as a result of the microcomputer 52 going out of control due to noise or the like. Even if it flows, it can be detected immediately and the driving state of the laser 31 can be forcibly prohibited.

As a result, it is possible to prevent damage to the laser 31 due to runaway of the microcomputer 52.

Also, the current generation circuit 48 is controlled by the low-pass filter 55.
Since the current control signal Sa itself, which has a sharp level change, is not supplied to the control circuit 10, circuit elements with slow response speeds can be used as the lighting inhibiting means 100 and the forced lighting means 80 system. This has the feature that the entire laser protection means can be constructed at low cost.

Furthermore, by connecting the low-pass filter 55 to the output stage of the D/A converter 49, it becomes difficult for a surge Ti flow to flow into the laser 31, thereby preventing deterioration of the laser 31.

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

[Brief explanation of drawings]

FIG. 1 is a system diagram of essential parts showing an example of a semiconductor laser drive circuit including a laser protection circuit according to the present invention, FIG. 2 is a system diagram showing an example of forced lighting means and input control means, and FIG.
The figure is a connection diagram showing an example of a low-pass filter, FIG. 4 is a system diagram showing an example of a lighting prohibition means, FIG. FIG. 7 is a block diagram showing an example of a laser beam scanning device used to explain the present invention, and FIG. 8 is a diagram showing a system of a semiconductor laser drive circuit. 9 is a characteristic diagram showing the relationship between the excitation current of the laser and the amount of emitted light, FIGS.
The figure is a control flowchart showing an example of a stabilization control operation for the amount of laser light. 10...Color copying machine 11...Drum 30 as an image forming body...Laser beam scanning device 31...Semiconductor laser 40...Drive circuit 41...Photo sensor 42...Current/voltage conversion Means 49...D/A converter 51...Δ/D converter 52...Microcomputer 53...Latch circuit 60...Light amount monitor circuit 80...Forced lighting means 90...Input Control means 100...Lighting prohibition means 55...Low pass filter Patent applicant Konishi Roku Photo Industry Co., Ltd. Figure 2 Figure 5 Figure 5 ------
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Figure 12 Figure 10 Figure 11

Claims (5)

[Claims] (1) A semiconductor laser, a light amount monitor circuit that monitors the amount of light emitted from this semiconductor laser, an A/D conversion means that converts the output voltage of this light amount monitor circuit into a digital amount, and a D that converts the digital amount into an analog signal. /A converting means; current generating means for causing a predetermined drive current to flow through the semiconductor laser according to the analog signal;
a microcomputer that controls the digital amount given to the D/A conversion means, and a low-pass filter that filters a current control signal obtained from the D/A conversion means and supplies it to the current generation circuit; forced lighting means for turning on the semiconductor laser for a certain period of time when it is detected that the conversion output has changed in one direction; 1. A protection circuit for a semiconductor laser, comprising lighting prohibition means for prohibiting lighting of the laser. (2) The forced lighting means is characterized by comprising an edge detection means for detecting a rising edge of the D/A conversion output, and a pulse generating section that generates a forced lighting signal for a certain period of time from the edge detection signal. A protection circuit for a semiconductor laser according to claim 1. (3) The lighting prohibition means is composed of a comparison circuit that compares the output voltage of the light amount monitor circuit with a reference voltage, and a pulse generation means section that generates a predetermined pulse when the comparison output changes. A protection circuit for a semiconductor laser according to claim 1, characterized in that: (4) A patent characterized in that the input stage of the current generating circuit is provided with input control means to which at least the forced lighting signal, the lighting prohibition signal, and the laser modulation signal corresponding to the image signal are supplied. A protection circuit for a semiconductor laser according to claims 1 to 3. (5) Claims 1 to 4, characterized in that the low-pass filter is constituted by an RC time constant circuit.
Protection circuit for the semiconductor laser described in Section 1.