JPH0410677A - Driving circuit for semiconductor laser - Google Patents

Abstract

PURPOSE:To effectively recognize an abnormality caused by a detection resistance by a method wherein a first monitoring signal and a second monitoring signal are formed individually by using two mutually connected detection resistance and, when the relative resistance ratio of the two detection resistance is changed by a deterioration with the passage of time or the like, the second monitoring signal for abnormality detection use is changed with reference to the first monitoring signal for automatic light-quantity control use. CONSTITUTION:When a photodiode 1b gets out of order or is disconnected, the voltage level of a second monitoring signal Vdet2 is dropped suddenly or gradually. When this stopped portion exceeds the controllable range of an automatic light-quantity control mechanism, the automatic light-quantity control mechanism does not function any more. The voltage level of the second monitoring signal Vdet2 becomes apart from a reference voltage level Vref and is dropped to be much lower than a lower-limit reference voltage level V11t. When the voltage level of the second monitoring signal becomes lower than the lower-limit reference voltage level, a status signal as the inverse of LDREADY is reversed again to a high level from a low level by the action of a comparator 25. As a result, the signal as the inverse of LDREADY indicates that a semiconductor-laser drive circuit is not in a normal state. As a result, the output signal appearing at an output terminal Q of an RS flip-flop 31 is changed form the low level to the high level and is output as an abnormal signal LDNG.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser drive circuit, and particularly to an abnormality detection technique thereof.

[Conventional technology]

In recent years, high-performance semiconductor lasers have become available at low cost. Semiconductor lasers are widely used as heads of various information devices.

For example, information read head of compact disc player, information read/write head of optical disc memory, PO8
It is widely used as a laser light source for read heads of terminal barcode readers or print heads of laser beam printers. - Generally, when a semiconductor laser is used as a light source for a head of an information device, the semiconductor laser drive circuit has an automatic light amount control mechanism built in to keep the laser beam light amount constant in a steady state.

[Problem that the invention seeks to solve]

However, if a failure occurs in the automatic light amount control mechanism, the light amount control of the laser beam will no longer work, and there is a risk that the semiconductor laser will emit abnormal light.

For example, in an optical disk memory, if abnormal excessive light emission occurs, there is a risk that information written on the optical disk may be destroyed. Furthermore, if excessive light emission occurs in a barcode reader used in a PO8 terminal or a so-called pointer that utilizes the excellent directivity of a laser beam, there is a risk that the light may accidentally enter the eyes of people nearby and cause blindness. On the other hand, if abnormally low light emission occurs, the normal operation of the main device will be hindered.

In conventional semiconductor laser drive circuits, no measures have been taken against failures of the automatic light amount control mechanism, and there have been problems with safety and stability.

[Means for solving problems]

In view of the above-mentioned problems of the conventional technology, a general object of the present invention is to improve the safety and stability of a semiconductor laser drive circuit and to prevent abnormal light emission from a semiconductor laser.

Generally, an automatic light amount control mechanism includes a light receiving element that receives a laser beam, and a detection resistor that detects an electrical signal output from the light receiving element and outputs a monitor signal for automatic light amount control.

The resistance value of this detection resistor may change over time due to deterioration or the like. Therefore, a characteristic object of the present invention is to effectively detect abnormalities in the automatic light amount control mechanism due to such deterioration of the detection resistor and to prevent abnormal light emission.

In order to achieve the above object, a semiconductor laser drive circuit according to the present invention has a basic configuration shown in FIG. That is,
As shown in the figure, the semiconductor laser drive circuit has a laser package 1, and the package 1 houses a semiconductor laser such as a laser diode 1a and a light receiving element such as a photodiode 1b. Photodiode 1b
receives the laser beam emitted from the laser diode 1a, photoelectrically converts it, and outputs a corresponding electric signal. A monitor circuit 101 is connected to the photodiode 1b, which monitors the electrical signal and outputs a monitor signal according to fluctuations in the amount of laser beam light.

The monitor circuit 101 has a first detection resistor for detecting an electrical signal, and outputs a first monitor signal based on the detection result. Furthermore, it has a second detection resistor connected to the first detection resistor to separately detect the electric signal, and outputs a second monitor signal correlated to the first monitor signal based on the detection result. A control circuit 102 is connected to the monitor circuit +01, which compares the first monitor signal with a predetermined reference signal and outputs a control signal according to the difference. A power circuit 103 is connected to the control circuit 102, and supplies driving power to the laser diode 1a so as to cancel out the difference according to the control signal. In this way, the laser diode la, the photodiode lb, and the monitor circuit 101.

A servo loop is formed by a control circuit 102 and a power circuit 103 to automatically control the amount of laser beam light. An abnormality detection circuit 104 is connected to the monitor circuit 101, which detects an abnormality by comparing a reference signal different from the reference signal and the second monitor signal, and outputs an abnormality signal LDNG.

Preferably, the control circuit 102 includes a forced extinguishing circuit for forcibly extinguishing the laser diode 1a in response to the abnormality signal LDNG.

More preferably, the abnormality detection circuit 104 detects when the second monitor signal is lower than the lower limit reference signal, which is set to be smaller than the magnitude of the reference signal, or when the second monitor signal is lower than the upper limit reference signal, which is set to be larger than the magnitude of the reference signal. When the second monitor signal exceeds the second monitor signal, an abnormality signal is output to warn of an abnormality in the semiconductor laser drive circuit.

In addition, the monitor circuit has first and second detection resistors connected in series to detect the electrical signal, and the first monitor circuit detects the electrical signal depending on the potential difference generated across the first detection resistor. It includes a circuit that forms a signal, and a circuit that forms a second monitor signal in response to the potential difference generated across the second detection resistor.

[For production]

According to the present invention, when an abnormality occurs in the laser diode, photodiode, or overflow light amount control servo loop and the second monitor signal fluctuates significantly compared to the reference signal, an abnormal signal is immediately output. There is. This abnormality signal is output when the amount of laser beam light decreases or disappears due to failure or deterioration of the laser diode. Alternatively, it is output when the first monitor signal fluctuates due to a failure of the photodiode and there is a risk that the laser diode will emit excessive light via the servo loop. In particular, in the present invention, two detection resistors connected to each other are used to individually form the first and second monitor signals. Therefore, if the relative resistance ratio of the two detection resistors fluctuates due to deterioration over time, the second monitor signal for abnormality detection will fluctuate in correlation with the first monitor signal for automatic light amount control, so the detection resistor Abnormalities caused by can be effectively recognized.

〔Example〕

Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 2 is a detailed circuit diagram showing a first embodiment of the semiconductor laser drive circuit according to the present invention. As shown,
The semiconductor laser drive circuit has a laser package 1. A laser diode 1a is housed in this package, and its anode terminal is connected to a power supply line V1. Furthermore, a photodiode 1b is housed, and its cathode terminal is connected to the power supply line VC.

It is connected to the.

The semiconductor laser drive circuit further includes a monitor circuit, a control circuit, a power circuit, and an abnormality detection circuit. The monitor circuit has a variable first detection resistor 2 connected between the anode terminal of the photodiode 1b and the ground line. This resistor 2- converts the photocurrent output from the photodiode 1b into a corresponding voltage. One end of the resistor 2 is connected to the positive input terminal of the differential amplifier 3.

Further, the negative input terminal and output terminal of the differential amplifier 3 are connected. Therefore, the differential amplifier 3 acts as a buffer, converts the impedance, and then outputs the first monitor signal Vdell to its output terminal. This first monitor tie No. 5 Vd
The voltage level of ell is proportional to the amount of light received by the photodiode 1b.

The monitor circuit further includes a variable second detection resistor 63 connected in series between the photodiode 1b and the first detection resistor 2. One end of this resistor 63 is connected to a positive input terminal of a differential amplifier 64, and its negative input terminal and output terminal are connected to each other. Therefore, the amplifier 64 acts as a buffer, and a voltage equal to the potential difference appearing across the first and second series detection resistors 2 and 63 is outputted to its output terminal. The output terminal of the amplifier 64 is connected to the positive input terminal of the differential amplifier 65 via voltage dividing resistors 68 and 69.
The output terminal of is connected to the negative input terminal of a differential amplifier 65 via a voltage dividing resistor 66. Further, the negative input terminal and output terminal of this amplifier 65 are connected to each other via a voltage dividing resistor 67. Therefore, the output terminal of the differential amplifier 65 has exactly the node 2.
If the ratio is set equal to the potential difference generated across the detection resistor 63, and the resistance values of the two variable detection resistors 2 and 63 are adjusted to be equal, the magnitude of the first monitor signal V and the second monitor signal Vd8t2 will be It becomes equal to el1.

The control circuit includes an integrating resistor 4, a differential amplifier 5, an integrating capacitor 6, and an analog switch 7. Integrating resistor 4 is connected between the output terminal of differential amplifier 3 and the negative input terminal of differential amplifier 5, and integrating capacitor 6 is connected between the negative input terminal and output terminal of differential amplifier 5. . Furthermore, a reference signal Vref having a preset voltage is input to the positive input terminal of the differential amplifier 5. The resistor 4, the differential amplifier 5, and the integrating capacitor 6 constitute an integrating circuit, and the first monitor signal Vd8t1 and the reference signal vr
A control signal corresponding to the difference in ef is output. Furthermore, the analog switch 7 is inserted between the negative input terminal and the output terminal of the differential amplifier 5. In addition, this control circuit includes a forced extinguishing circuit consisting of an AND gate 24 having two input terminals.

A lighting signal LDON instructing the laser diode 1a to turn on is input to one inverting input terminal of the AND gate 24, and an abnormality signal LDNG is input to the other inverting input terminal. There is. The inverting output terminal is connected to an analog switch 7 to control this conduction state.

The power circuit is composed of a pair of voltage dividing resistors 8 and 9, a driving transistor IO, and a voltage-current converting resistor 11.

The base terminal of the transistor 10 is connected to the output terminal of the differential amplifier 5 via one voltage dividing resistor 8, the collector terminal is connected to the cathode terminal of the laser diode 1a, and the emitter terminal is connected via a resistor 11. and grounded.

The abnormality detection circuit has a pair of window comparators 25 and 33. The second monitor signal vd8t2 is input to the negative input terminal of one comparator 25, and the lower limit reference signal v11t is input to the positive input terminal. The voltage level of the lower limit reference signal v11□ is set to the reference signal vre by the voltage dividing resistors 70, 71, 72 and 73 connected in series.
It is set to a predetermined value lower than the voltage level of f'. In this embodiment, the magnitude of the lower limit reference signal V is set to be +11 5% lower than the reference signal Vref. The output terminal of the comparator 25 receives the second monitor signal v, 81° and the lower limit reference signal V1.
A state signal LDREADY is output whose voltage level is inverted depending on the magnitude of 1t.

The abnormality detection circuit further includes a two-man gate 30. The output terminal of the comparator 25 is connected to the first input terminal of the AND gate 30, the lighting signal LDON is inputted to the second input terminal via the inverter 58, and the third input terminal is connected to the output terminal of the comparator 25. A lighting signal LDON is manually input to the input terminal via an inverter 58 and a delay circuit 29.

And an OR gate 74 is connected to the output terminal of the AND gate 30.
A set terminal S of the RS flip-flop 31 is connected through the RS flip-flop 31. Further, a clear circuit 32 is connected to the reset terminal R of the RS flip-flop 31. This clear circuit 32 clears the flip-flop 3 when the power is turned on.
This is for resetting 1. flip flop 3
An abnormality signal LDNG is output to the output terminal Q of No. 1. In the embodiment described above, AND gates 24 and 30,
Although the delay circuit 29, the inverter 58, the OR gate 74, and the flip-flop 31 are composed of individual circuit elements, they can also be constructed by software using a microcomputer built into the semiconductor laser control mechanism.

The second monitor signal is input to the positive input terminal of the other comparator 33, and the upper limit reference signal vU is input to the negative input terminal.
1t has been input. This upper limit reference signal Vu1 is obtained from the upper end of the second resistor 71 among the series voltage dividing resistors 70 to 73, and is set to be 5% to 10% higher than the reference signal Vr8f obtained from the lower end. Under normal conditions, this is a value that the second monitor signal vd8□2 never exceeds. An inverted signal LDOVER is output to the output terminal of the comparator 33 when the second monitor signal Vdet2 exceeds the upper limit reference signal Vu1□. RS flip flop 31
The set terminal S of is connected to the output terminal of the comparator 33 via an OR gate 74. flip flop 3
1 stores the inverted signal LDOVER and outputs the abnormal signal LDON.
is output to output terminal Q.

Next, the operation of the semiconductor laser drive circuit shown in FIG. 2 will be explained. First, automatic light amount control operation will be explained. When the lighting signal LDON becomes a low level, the analog switch 7 becomes non-conductive via the AND gate 24, the control circuit and the power circuit start operating, the laser diode 1a emits light, and a photocurrent proportional to the amount of laser beam is generated. occurs in diode 1b. This photocurrent is converted into a corresponding voltage by the first detection resistor 2, and the differential amplifier 3
After impedance conversion is performed, the first monitor signal vdeL1 appears at the output terminal of the differential amplifier 3. Therefore, this first monitor signal is a signal having a voltage proportional to the amount of light received by the photodiode 1b. Note that by manually adjusting the resistance value of the variable detection resistor 2, it is possible to adjust the level of steady drive power obtained by the automatic light amount control operation. That is, the power of the laser diode 1a can be adjusted. An integrator is formed by an integrating resistor 4, a differential amplifier 5, and an integrating capacitor 6, and a reference signal V is applied to the positive input terminal of the differential amplifier 5. , and the first monitor signal Vdet□ applied to the negative input terminal, the integrating capacitor 6 is charged and discharged. As a result, a control signal having an output voltage corresponding to the difference is output to the output terminal of the differential amplifier 5. This output voltage is divided by voltage dividing resistors 8 and 9, and current is converted by drive transistor IO to drive laser diode 1a. This drive current is supplied to the laser diode 1a so as to cancel the voltage difference between the monitor signal and the reference signal, so that in a steady state, the voltage of the first monitor signal vdell and the reference signal v, 8.
The voltages become the same, and the amount of laser beam light is controlled to be constant regardless of changes in ambient temperature or slight deterioration of the laser diode. Furthermore, when the lighting signal LDON is inverted from a low level to a high level, the analog switch 7 becomes conductive via the AND gate 24, and the charge accumulated in the integrating capacitor 6 is discharged. As a result, the output voltage of the control signal becomes equal to the reference signal Vref. The resistance ratio of the resistors 8 and 9 is set so that when the output voltage equal to this reference voltage is divided by the voltage dividing resistors 8 and 9, the drive transistor 10 becomes non-conductive, so the laser diode 1a turns off. be done.

Next, the abnormality detection operation will be explained in detail with reference to timing charts shown in FIGS. 3 and 4. As shown in FIG. 3, first, the lighting signal LDON changes from high level to low level to instruct the laser diode 1a to light up. This lighting signal LDON is applied to one input terminal of the AND gate 30. Furthermore, this lighting signal LDON is passed through a delay circuit 29 for a predetermined period of time, for example, 1. The signal is delayed by ms and is applied to the other input terminal of the AND gate 30 as a delayed signal. This delay time is set to be longer than the time required for the automatic light amount control to function normally and for the laser beam light amount to become steady. For example, the time constant of the integrating circuit is 500 μs.
Therefore, the delay time is set to 1 ms. As a result, the AND gate 30 is opened 1 ms after the instruction to turn on the laser diode is given. Now, when a driving current is supplied and the laser diode starts emitting light in accordance with the opposite axis of the lighting signal LDON, the second monitor signal V,8
At 1□, its voltage level begins to rise. Note that the second variable detection resistor 63 is adjusted in advance so that the magnitude of the second monitor signal vdot2 becomes equal to the reference signal Vref in the steady state of automatic light amount control. That is, it is abnormality detection level adjustment. Then, the second monitor signal Vd
When the voltage level of ot2 exceeds the lower limit reference voltage level V111, the state signal LDREADY, which is the output signal of the comparator 25, changes from high level to low level.

This change indicates that the light emission of the laser diode 1a is transitioning from a transient state to a steady state. Therefore, when the status signal goes low, the solid device or peripheral device enters a normal operating state. As mentioned above, this inversion of the state signal LDREADY usually occurs within a preset delay time, so this inversion change does not pass through the AND gate 30, and the output level of the SR flip-flop 31 does not change. do not have. second monitor signal V,
. After the voltage of 1° exceeds the lower limit reference voltage level Vlit, it continues to rise by automatic light amount control and reaches the reference voltage level VrOf, which is set about 5% higher than the lower limit reference voltage level VIlt, thereby realizing a steady state. At this point, since the delay time has elapsed, the AND gate 30 is opened and the abnormality detection circuit is also activated.

As time passes, an abnormality may occur in the laser diode LAS photodiode 1b or the automatic light amount control mechanism. If this abnormality is due to a failure or significant deterioration of the laser diode 1a, a failure of the automatic light amount control mechanism, or a failure or disconnection of the photodiode 1b, the voltage level of the second monitor signal Vde□2 decreases rapidly or gradually. If this decrease exceeds the controllable range of the automatic light amount control mechanism, the automatic light amount control mechanism no longer functions, and the voltage level of the second monitor signal VdeL2 departs from the reference voltage level V, and reaches the lower limit reference voltage level Vllt. further decreases below tel'. When the voltage level of the second monitor signal falls below the lower limit reference voltage level, the status signal LDRE
ADY is again inverted from low level to high level by the action of comparator 25. As a result, the status signal LDREA
DY indicates that the semiconductor laser drive circuit is no longer in a normal state.

At the same time, the inverse change of the state signal is passed through the open AND gate 30 to the set terminal S of the RS flip-flop 31.
can be conveyed to. As a result, the output signal appearing at the output terminal Q of the RS flip-flop 31 changes from a low level to a high level and is output as an abnormal signal LDNG. This abnormality signal LDNG is a signal that informs the operator, a host system such as a CPU, or a peripheral device that an abnormality has occurred. Furthermore, the abnormality signal LDNG is applied to the inverting input terminal of the AND gate 24 constituting the forced extinguishing circuit, the analog switch 7 becomes conductive, the operation of the control circuit and the power circuit is stopped, and the laser diode 1a is forcibly extinguished. Ru. As a result, it is possible to prevent the laser diode from emitting excessive light due to the inability to automatically control the amount of light.

Next, the operation related to the other comparator 33 of the abnormality detection circuit will be explained with reference to FIG. As mentioned above,
When the automatic light amount control mechanism is operating normally, the voltage level of the second monitor signal is equal to the reference voltage level Vr8r.

The second monitor signal Vd8L□ is input to the positive input terminal of the comparator 33, and the upper limit reference voltage vu1□ is applied to the negative input terminal. This upper limit reference voltage vulL is set higher than the reference voltage Vrer to such an extent that it does not exceed it under normal conditions. Therefore,
The inverted signal LDO appearing at the output terminal of the comparator 33
VER is maintained at a low level under normal conditions.

However, if excessive light emission of the laser diode occurs due to an abnormality in the automatic light amount control mechanism, or if a short-circuit abnormality occurs in the photodiode for monitoring the amount of laser beam light, the second monitor signal V,. The voltage level at t2 rises above the upper limit reference voltage level Vul□, and the inverted signal LDOVOR appearing at the output terminal of comparator 33 is inverted to a high level. - When the inversion signal becomes high level even momentarily, the flip-flop 31 is inverted via the OR gate 74, and the abnormal signal LDNG changes from low level to high level. As a result, the abnormal state that occurs in the automatic light amount control mechanism is transmitted to the outside as a change in the level of the abnormal signal. In addition, when the abnormality signal LDON changes from a low level to a high level, the AND gate 24 is forcibly closed and the lighting signal LDO
Regardless of N, the analog switch 7 is placed in a conductive state. As a result, the automatic light amount control mechanism stops operating and the laser diode 1a is forcibly turned off. That is, in the above-described embodiment, if an abnormal situation occurs even in time, the inverted signal changes, and by latching the change, the abnormal signal is continuously output. Therefore, abnormalities can be detected and effective countermeasures can be taken before a serious accident occurs.

By the way, in the present invention, the first and second detection resistors are used to generate the first monitor signal and the second monitor signal, respectively. The first monitor signal is used for automatic light intensity control, and the second
The monitor signal is used for abnormality detection. The first and second detection resistors are connected to each other, and if one of them becomes disconnected, short-circuited, or has a resistance value fluctuation failure due to deterioration over time, the relative resistance ratio of the pair of detection resistors changes, and the first In addition to the monitor signal, a second monitor signal changes up and down.

When this change exceeds the lower limit or upper limit reference voltage, an abnormality signal is output. Therefore, failures in the detection resistor can also be effectively detected. Since the probability that both detection resistors fail at the same time is extremely low, the safety of the semiconductor laser drive circuit can be further improved by determining failure by looking at the relative change in resistance between the two. Note that in the steady state, the first monitor signal vdot1
is equal to the reference voltage V, and the second monitor signal vd
8t2 is also ref' adjusted in advance to be equal to the reference voltage Vref'. Therefore, it is possible to perform automatic light amount control and abnormality detection using a common monitor signal instead of using separate monitor signals. However, in this case, even if the value of the detection resistor changes, the level of the monitor signal is kept constant by the automatic light amount control function, so there is a drawback that abnormality cannot be detected.

FIG. 5 is a circuit diagram showing a second embodiment of the semiconductor laser drive circuit according to the present invention. Hereinafter, parts that are the same as those in the first embodiment shown in FIG. 2 are given the same reference numerals. Therefore, the explanation of the common points will be omitted and only the differences will be explained. In this example, the second detection resistor 63 is a fixed resistor, and a variable resistor 75 is connected to the output terminal of the differential amplifier 65.

The variable resistor 75 is adjusted to match the level of the second monitor signal vd8t2 to the reference voltage Vr8r.

In this example, fluctuations in the resistance value of the first main variable detection resistor 2 are monitored based on the more stable fixed resistance value of the second sub-detection resistor 63.

FIG. 6 is a circuit diagram showing a third embodiment of the semiconductor laser drive circuit according to the present invention. In this embodiment, a differential amplifier is configured by a pair of non-inverting amplifiers 3 and 64, and each outputs a first monitor signal vdetl and a second monitor signal Vd8t.
2 is output. Therefore, the differential amplifier 65 can be omitted compared to the first and second embodiments. In this case, it is desirable that the voltage dividing resistors ee, e'y, as, and 69 have the same resistance value. However, if it is desired to have a relative gain between both monitor signals, the resistance values of resistors 67 and 68 are set to be equal, and the resistance values of resistors 66 and 69 are set to be equal. In addition, in this embodiment, in order to further stabilize the monitor circuit, the pair of detection resistors 2 and 63 are both fixed resistors, and instead, a variable resistor 7 is connected to the output terminal of one amplifier 3.
6 to adjust the first monitor signal Vdell and adjust the power of the laser diode, and the other amplifier 64
A variable resistor 75 is connected to the output terminal of the second monitor signal V.
,. Adjustment for t2 is being made.

FIG. 7 is a circuit diagram showing a fourth embodiment of the semiconductor laser drive circuit according to the present invention. Although the first to third embodiments were circuits that operated with a single power supply, this embodiment has a circuit configuration that is applicable when using positive and negative power supplies. One amplifier 3 outputs a first monitor voltage Vdetl having a voltage equal to the voltage drop that occurs when the photocurrent output from the photodiode 1b flows through the first detection resistor 2. The photocurrent is connected to the second detection resistor 6
A second monitor signal Vdet2 having a voltage equal to the voltage drop that occurs when flowing through the second monitor signal Vdet2 is output. Therefore, like the third embodiment, no additional differential amplifier 65 is required.

FIG. 8 is a schematic cross-sectional view showing a barcode reader using a laser light source incorporating a semiconductor laser drive circuit according to the present invention, and represents one application example of the present invention. As shown in the figure, the barcode reader has a laser light source 42 housed in a casing 41. This laser light source 42 has a circuit configuration as shown in FIG. 1, and includes a laser diode, an automatic light amount control mechanism, and an abnormality detection circuit.

A laser beam emitted from a laser light source 42 is transmitted to a polygon mirror 44 which is rotated by a scan motor 43.
After being reflected in a scanning manner by a mirror 45, the light is irradiated onto a barcode 46 attached to the surface of the article via a reflecting mirror 45. After scanning the barcode 46, the reflected light travels backward, is focused by a condenser lens 47, and is then received by a light receiving sensor 49 via a reflecting mirror 48. The barcode 46 is read by analyzing the fluctuation components contained in the received light. In such a barcode reader, a laser light source 4
When an abnormal state occurs due to failure or deterioration of the automatic light amount control mechanism including the laser diode or photodiode built in the optical sensor 2, an abnormality signal is output. In response to this abnormal signal, the barcode reader stops reading operations. This prevents the risk of erroneous detection if the barcode league continues reading even though the laser diode has deteriorated significantly and normal reading is no longer possible. Alternatively, in the event of a disconnection failure in the photodiode, it is possible to prevent an accident in which an excessive laser beam emitted from the laser diode accidentally irradiates the operator's or customer's eyes.

〔Effect of the invention〕

As explained above, according to the present invention, in a semiconductor laser drive circuit having an automatic light amount control mechanism, when the automatic light amount control mechanism including the laser diode and the photodiode for monitoring the laser beam light amount deteriorates or breaks down, an abnormality signal is immediately generated. By having a configuration that outputs , it is possible to prevent malfunctions of devices using laser diodes and to prevent accidents caused by excessive light emission of laser diodes. In particular, by using a plurality of detection resistors, it is possible to detect abnormalities caused by failures of the detection resistors themselves.

[Brief explanation of drawings]

Figure 1 is a block diagram of the semiconductor laser drive circuit;
The figure is a detailed circuit diagram showing the first embodiment of the semiconductor laser drive circuit, Figures 3 and 4 are timing charts of the semiconductor laser drive circuit, and Figures 5 to 7 are the second to seventh embodiments of the semiconductor laser drive circuit. A detailed circuit diagram showing the fourth embodiment and FIG. 8 are a schematic cross-sectional view of a barcode reader incorporating a semiconductor laser drive circuit. 1...Laser package 1a...Laser diode 1b...Photodiode 2...First detection resistor 3...Amplifier 4...
Integrating resistor 5... Amplifier 6... Integrating capacitor 7... Analog switch 10... Drive transistor 24... AND gate 25... Comparator 29... Delay circuit 30... AND gate 31. RS flip-flop 33... Comparator 64... Amplifier 101... Monitor circuit 103... Power circuit 63... Second detection resistor 65... Differential amplifier 102... Control circuit 104... ...Abnormality detection circuit applicant Copal Co., Ltd. (1 other person)

Claims (1)

[Claims] 1. A semiconductor laser that emits a laser beam, a light receiving element that photoelectrically converts the laser beam and outputs a corresponding electric signal, and a first detection resistor that detects the electric signal. Based on the detection results, the first
A second detection resistor is connected to the first detection resistor for outputting a monitor signal and separately detecting the electrical signal, and a second detection resistor that correlates to the first monitor signal based on the detection result.
a monitor circuit that outputs a monitor signal, a control circuit that compares the first monitor signal and a reference signal and outputs a control signal according to the difference, and supplies drive power to the semiconductor laser so as to cancel the difference according to the control signal. and an abnormality detection circuit that detects an abnormality and outputs an abnormal signal by comparing a reference signal different from a reference signal and a second monitor signal. 2. The semiconductor laser drive circuit according to claim 1, further comprising a forced extinguishing circuit for forcibly extinguishing the semiconductor laser in response to an abnormal signal. 3. The abnormality detection circuit detects when the second monitor signal is lower than the lower limit reference signal, which is set smaller than the magnitude of the reference signal, or when the second monitor signal is lower than the upper limit reference signal, which is set larger than the magnitude of the reference signal. 2. The semiconductor laser drive circuit according to claim 1, further comprising a circuit for outputting an abnormal signal when the second monitor signal exceeds the second monitor signal. 4. The monitor circuit has first and second detection resistors connected in series to detect the electric signal, and detects the first monitor signal according to the potential difference generated across the first detection resistor. 2. The semiconductor laser drive circuit according to claim 1, comprising: a circuit for forming a second monitor signal; and a circuit for forming a second monitor signal in response to a potential difference generated across the second detection resistor. 5. The circuit forming the first monitor signal has a first adjusting means for adjusting the magnitude of the first monitor signal in order to adjust the driving power, and the circuit forming the second monitor signal is adjusted. 5. The semiconductor laser drive circuit according to claim 4, further comprising second adjustment means for adjusting the magnitude of the second monitor signal in accordance with the reference signal.