JPH05259547A - Protection of semiconductor laser and protective circuit - Google Patents

Abstract

PURPOSE:To stop reliably a current supply to a semiconductor laser even in the case where an abnormal state, such as a trouble in a first-stage amplifier, is generated in a luminescent power detecting part and to make it possible to prevent the laser from being broken down. CONSTITUTION:Before a semiconductor laser is lighted, an output voltage of a current-voltage conversion circuit 3 is detected by a voltage detecting circuit and the detected result is held by a holding circuit 10, whereby when the output voltage of the circuit 3 is abnormal, a current supply stopping means 7 is actuated and the laser 1 is not lighted. Thereby, the normal state or abnormal state of the output voltage of the circuit 3 can be confirmed and in the case where the output voltage is abnormal, a current supply to the laser 1 is stopped. Accordingly, the more reliable protection of the laser 1 becomes possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser protection method and a protection circuit in an electronic device having a semiconductor laser as a light source such as an optical disk device, a laser printer, an optical card drive device, and the like. The present invention relates to a semiconductor laser protection method and a protection circuit which can prevent the semiconductor laser from being broken by surely stopping the current supply to the semiconductor laser even when an abnormality occurs in the emission power detection unit.

[0002]

2. Description of the Related Art Since semiconductor lasers are easily destroyed by overcurrent, various protection methods and protection circuits have been proposed. For example, there is known a drive device that stops driving of a semiconductor laser when the power supply voltage is abnormal by detecting and monitoring the voltage of various power supplies supplied to the drive circuit part of the semiconductor laser (Japanese Patent Laid-Open No. 61-61). Two
79188 publication). By detecting and monitoring the power supply voltage in this manner, it is possible to prevent an uncontrolled current from flowing to the semiconductor laser and protect the semiconductor laser.

By the way, in general, the emission characteristics of a semiconductor laser greatly vary with temperature, so the emission power of the semiconductor laser is detected and controlled so that the emission power reaches a predetermined value. Therefore, for example, when an abnormality occurs in the light emission power detection unit such as a failure of the first stage amplifier,
A state occurs in which an abnormally large current flows through the semiconductor laser.

However, the conventional semiconductor laser driving device (Japanese Patent Laid-Open No. 61-279188) is effective only for the abnormality of the power supply voltage, and a part of the light emission power detecting portion, especially the first stage amplifier is broken. If it occurs, there is a disadvantage that the semiconductor laser cannot be protected.

[0005]

SUMMARY OF THE INVENTION The present invention solves these disadvantages in the conventional semiconductor laser protection method, and ensures that not only when the power supply voltage is abnormal, but also when the light emission power detection unit is abnormal. An object of the present invention is to provide a semiconductor laser protection method and a protection circuit capable of protecting the semiconductor laser.

[0006]

The present invention is, firstly, a protection circuit for a semiconductor laser, and a light receiving element for receiving a part of light emitted from the semiconductor laser and an output of the light receiving element. A current-voltage conversion circuit that performs current-voltage conversion with reference to a certain predetermined voltage, a control circuit that controls the emission power of the semiconductor laser by the output of the current-voltage conversion circuit, and a current supply of current to the semiconductor laser. A cutoff unit, a voltage detection circuit that detects the output voltage of the current-voltage conversion circuit, and a holding circuit that holds the output of the voltage detection circuit are provided, and before the semiconductor laser is turned on, the voltage detection circuit is used. When the output voltage of the current-voltage conversion circuit is detected and the detection result is held by the holding circuit, the current supply is performed when the output voltage of the current-voltage conversion circuit is abnormal. And the cross-sectional section is operated, a semiconductor laser protection method that does not perform the lighting of the semiconductor laser.

Secondly, a semiconductor laser protection circuit,
Further, a light receiving element that receives a part of the light emitted from the semiconductor laser, a current-voltage conversion circuit that converts the output of the light receiving element into a current-voltage based on a predetermined voltage, and the current-voltage conversion circuit. A control circuit for controlling the emission power of the semiconductor laser by the output of the semiconductor laser, a means for interrupting current supply to the semiconductor laser, a voltage detection circuit for detecting the output voltage of the current-voltage conversion circuit, and the voltage detection circuit. A holding circuit for holding the output of the current supply cutoff means, the current supply cutoff means has a switch circuit, and detects the output voltage of the current-voltage conversion circuit by the voltage detection circuit before lighting of the semiconductor laser. And, by holding the detection result by the holding circuit, when the output voltage of the current-voltage conversion circuit is abnormal, the current supply cutoff means,
The switch circuit disconnects the control circuit or stops the operation of the control circuit.

Thirdly, in the above-mentioned second semiconductor laser protection circuit, the current supply cutoff means has a power-off circuit, and the power supply to the semiconductor laser is stopped by the power-off circuit. I am configuring.

[0009]

According to the present invention, not only the ON / OFF signal of the semiconductor laser but also the current supply (or voltage) to the semiconductor laser is detected by the normal abnormality of the output voltage of the current-voltage conversion circuit for detecting the emission power of the semiconductor laser. Supply). Therefore, when an abnormality is detected in the output voltage of the current-voltage conversion circuit, the drive current is not supplied to the semiconductor laser, so that more reliable protection becomes possible.

[0010]

First Embodiment A semiconductor laser protection method and a protection circuit according to the present invention will be described in detail with reference to the drawings. This embodiment corresponds to the inventions of claims 1 and 2.

FIG. 1 is a functional block diagram showing an embodiment of the main configuration of a semiconductor laser protection circuit according to the present invention. In the figure, 1 is a semiconductor laser (LD),
2 is a light receiving element, 3 is a current-voltage conversion circuit, 4 is a reference voltage generation circuit, 5 is a buffer amplifier, 6 is a comparison circuit, 7 is a switch circuit, 8 is a constant current circuit, 9 is a window comparator, 10 is a holding circuit. , 11 are AND gate circuits,
Further, 5Vref indicates a reference voltage.

A part of the light emitted from the semiconductor laser 1 enters the light receiving element 2 and is converted into a current according to the amount of light. The output current is converted into a voltage by the current-voltage conversion circuit 3, and is supplied to the + input side of the comparison circuit 6 and the input side of the window comparator 9.

The window comparator 9 outputs an "H" signal to the holding circuit 10 when the output of the current-voltage conversion circuit 3 is within a predetermined range, and outputs an "L" signal when the output is out of the predetermined range. Output the detection signal. The holding circuit 10 holds the previous detection signal according to a control signal supplied from a control circuit (not shown) and outputs it to the AND gate circuit 11 as a gate control signal.

The AND gate circuit 11 controls the switching of the switch circuit 7 according to an AND condition between the gate control signal (detection signal) and an ON / OFF signal similarly supplied from a control circuit (not shown). Therefore, the switch circuit 7 is turned on only when the output of the current-voltage conversion circuit 3 is normal and the on / off signal is on (H).

When the switch circuit 7 is turned on, the reference voltage 5Vref created by the reference voltage generation circuit 4 and the buffer amplifier 5 and the output of the current-voltage conversion circuit 3 are compared by the comparison circuit 6. The constant current circuit 8 is controlled according to the light emission amount, the current flowing through the semiconductor laser 1 is controlled, and the light emission power is controlled.

On the other hand, if an abnormality occurs in the output of the current-voltage conversion circuit 3 before the semiconductor laser 1 is turned on (the reference voltage 5Vref is not input or the amplifier used is defective). If the ON / OFF signal for controlling the switch circuit 7 is turned ON, the AND gate circuit 11 does not satisfy the AND condition, and therefore the switch circuit 7 is not turned ON. Therefore, even if such an abnormality occurs, no current flows through the semiconductor laser 1 and there is no risk of damage.

[0017]

Second Embodiment Next, another embodiment of the semiconductor laser protection circuit of the present invention will be described. This embodiment corresponds to the invention of claim 2.

FIG. 2 is a functional block diagram showing another embodiment of the main structure of the semiconductor laser protection circuit of the present invention. Reference numerals in the figure are the same as those in FIG. 1, 21 is a comparator, 22 is an up / down counter, 23 is a clock generator, 24 is a D / A converter, and 25 is a NOR gate circuit.

The semiconductor laser protection circuit shown in FIG. 2 is a semiconductor laser control circuit using a digital circuit. Compared to the previous embodiment of FIG. 1, the comparison circuit 6
Instead of the switch circuit 7, a comparator 21, an up / down counter 22, and a clock generator 23.
And a D / A converter 24, and a NOR gate circuit 25 is provided instead of the AND gate circuit 11.

Also in the embodiment shown in FIG. 2, the structure from the semiconductor laser 1 to the current-voltage conversion circuit 3 is the same as that of the protection circuit shown in FIG. Similarly, in the window comparator 9, the output of the current-voltage conversion circuit 3 is
When it is within the predetermined range, it outputs a "H" signal to the holding circuit 10, and when it is outside the predetermined range, it outputs a "L" detection signal.

Further, the detection signal is held by the holding circuit 10 and input to the NOR gate circuit 25. Therefore, when the output of the current-voltage conversion circuit 3 is abnormal, or when the on / off signal is "L" (representing off), the up / down counter 22 is in a clear state.

On the contrary, when the output of the current-voltage conversion circuit 3 is normal and the ON / OFF signal is "H" (indicating ON), the clear state of the up / down counter 22 is released and the up / down counter 22 is up. The down counter 22 becomes active.
The operation of the up / down counter 22 is such that the output of the current-voltage conversion circuit 3 and the reference voltage 5Vref created by the reference voltage generation circuit 4 and the buffer amplifier 5 are compared by the comparator 21, and the up / down counter 22 is operated by the comparison result. It can be counted or down counted.

In this case, the counting is performed by the clock supplied from the clock generator 23. By such an operation, when the emission power of the semiconductor laser 1 is smaller than the target value, the counting is up, and conversely, when it is larger, the counting is down.

The count result from the up / down counter 22 is output to the D / A converter 24, the count value is D / A converted, and a voltage corresponding to the analog count value is obtained. This voltage is applied to the constant current circuit 8 to control the current flowing through the semiconductor laser 1 and control the emission power.

As described above, according to the protection circuit of FIG. 2, the detection result of the output of the current-voltage conversion circuit 3 before lighting of the semiconductor laser 1 is held in the holding circuit 10 and an abnormality occurs. If it is detected, the semiconductor laser 1
It is possible to stop the current supply to the. That is, similar to the analog control circuit of FIG. 1, the control circuit of the semiconductor laser 1 using the digital control circuit can be similarly implemented.

[0026]

[Third Embodiment] A third embodiment of the semiconductor laser protection circuit of the present invention will be described. This embodiment provides claim 3
It corresponds to the invention of.

FIG. 3 is a functional block diagram showing a third embodiment of the main structure of the protection circuit for a semiconductor laser according to the present invention. Reference numerals in the figure are the same as those in FIG. 1, reference numeral 31 is a slow start circuit, and reference numeral 32 is a power supply off circuit.

In the semiconductor laser protection circuit of the present invention shown in FIG. 3, a slow start circuit 31 and a power supply off circuit 32 are added to the protection circuit of FIG. The basic operation is the same as that shown in FIG.

That is, also in the embodiment shown in FIG. 3, after the power is turned on, the window comparator 9 detects whether the output of the current-voltage conversion circuit 3 is in a normal range or not before the semiconductor laser 1 is turned on. To do. Then, if an abnormality occurs, the output of the slow start circuit 31 is forcibly turned off by the power supply off circuit 32.

Therefore, in the case of such an abnormality occurrence, it is surely prevented that the power supply unit of the semiconductor laser 1 is not turned on and an abnormal current flows in the semiconductor laser 1 to destroy it. To be done. In the third embodiment described above, the case of applying to the light emission power control circuit using the analog control has been described, but the same can be applied to the light emission power control circuit using the digital control. ..

Further, in the above-mentioned first to third embodiments, the case where the semiconductor laser 1 is applied to the light emission power control circuit for performing only DC lighting has been described. However, the light emission power control circuit of the semiconductor laser 1 in the optical disk device for recording / reproducing or erasing information to which the modulation circuit is added can be similarly implemented.

Further, it is obvious that not only the optical disk device but also a light emission power control circuit in a laser printer, a digital copying machine, etc. can be implemented in the same manner. Therefore, the semiconductor laser protection method and protection circuit of the present invention include all of these cases.

[0033]

According to the first aspect of the invention, the output voltage of the current-voltage conversion circuit 3 can be confirmed to be normal or abnormal, and the reference voltage input to the current-voltage conversion circuit 3 and the used voltage can be used. It is possible to confirm whether the DC operation of the amplifier is normal or abnormal at the same time, and at that time, before the semiconductor laser 1 is turned on. In the case of abnormality, the current supply to the semiconductor laser 1 is stopped,
The semiconductor laser can be protected more reliably.

According to the second aspect of the present invention, the connection of the control circuit of the semiconductor laser is turned off by the switch element or the operation of the circuit is stopped. Therefore, the same effect as that of the first aspect of the invention can be obtained without controlling a large current.

According to the third aspect of the present invention, the current supply is stopped by stopping the power supply to the semiconductor laser. Therefore, even if a malfunction or failure of the control circuit occurs, the invention of claim 1 and claim 2 can be reliably performed.
The same effect as that of the invention can be obtained.

[Brief description of drawings]

FIG. 1 shows a semiconductor laser protection circuit according to the present invention.
It is a functional block diagram which shows one Example of the principal part structure.

FIG. 2 shows a protection circuit for a semiconductor laser according to the present invention,
It is a functional block diagram showing other examples of the composition of the important section.

FIG. 3 is a functional block diagram showing a third embodiment of the main configuration of a semiconductor laser protection circuit according to the present invention.

[Explanation of symbols]

 1 semiconductor laser 2 light receiving element 3 current-voltage conversion circuit 4 reference voltage generation circuit 5 buffer amplifier 6 comparison circuit 7 switch circuit 8 constant current circuit 9 window comparator 10 holding circuit 21 comparator 22 up / down counter 23 clock generator 24 D / A conversion Unit 31 Slow start circuit 32 Power-off circuit

Claims (3)

[Claims] 1. A light receiving element which is a protection circuit for a semiconductor laser and which receives a part of light emitted from the semiconductor laser, and an output of the light receiving element which is a current-current based on a predetermined voltage.
A current-voltage conversion circuit for voltage conversion, a control circuit for controlling the light emission power of the semiconductor laser by the output of the current-voltage conversion circuit, a current supply cutoff unit for the current to the semiconductor laser, the current-voltage conversion A voltage detection circuit for detecting the output voltage of the circuit; and a holding circuit for holding the output of the voltage detection circuit. Before the semiconductor laser is turned on, the output voltage of the current-voltage conversion circuit is changed by the voltage detection circuit. By detecting and holding the detection result by the holding circuit, when the output voltage of the current-voltage conversion circuit is abnormal, the current supply cutoff means is operated and the semiconductor laser is not turned on. And a method for protecting a semiconductor laser. 2. A light receiving element which is a protection circuit for a semiconductor laser, and which receives a part of light emitted from the semiconductor laser, and an output of the light receiving element with a current-current based on a predetermined voltage.
A current-voltage conversion circuit for voltage conversion, a control circuit for controlling the emission power of the semiconductor laser by the output of the current-voltage conversion circuit, a current supply cutoff unit for the current to the semiconductor laser, the current-voltage conversion A voltage detection circuit for detecting the output voltage of the circuit; and a holding circuit for holding the output of the voltage detection circuit, wherein the current supply / interruption means has a switch circuit. When the output voltage of the current-voltage conversion circuit is detected by the voltage detection circuit and the detection result is held by the holding circuit, the current supply is performed when the output voltage of the current-voltage conversion circuit is abnormal. The cutoff means cuts off the connection of the control circuit or stops the operation of the control circuit by the switch circuit. Road. 3. The semiconductor laser protection circuit according to claim 2, wherein the current supply cutoff means has a power-off circuit, and power supply to the semiconductor laser is stopped by the power-off circuit. Semiconductor laser protection circuit.