JPH05243655A - Semiconductor laser controller - Google Patents

Abstract

PURPOSE:To prevent damage to a recording medium by outputting reproduced power of a predetermined or layer value even if temperature dependency of a semiconductor laser is varied due to a temperature change. CONSTITUTION:The semiconductor laser controller comprises a semiconductor laser 4, a photodiode 5 for monitoring it, circuits 6, 7, 8, 9 and 10 for controlling to feed back reproduced power, and error processors 15, 16 and 17 for stopping reproduced power driving current when a voltage applied across a heat sensitive resistor 14 exceeds a predetermined value by using the resistor 14 to monitor the reproduced power driving current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to control of a semiconductor laser of an optical recording / reproducing apparatus for recording / reproducing information on / from a recording medium by using the semiconductor laser as a light source.

[0002]

2. Description of the Related Art FIG. 3 shows, for example, a utility model application publication No. 3-2.
3819 is a conventional semiconductor laser control device shown in FIG. 38, in which 1 is a recording medium, 2 is a motor for rotating the recording medium, 3 is an optical pickup for irradiating the recording medium 1 with a laser beam, and 4 is the optical system. A semiconductor laser installed inside the pickup 3, 5 is a photodiode for monitoring the light intensity of the light guide laser, 6 is an IV conversion circuit for converting the current output from the photodiode 5 into a voltage, and 7 is an IV A sample and hold circuit that samples and holds the output of the conversion circuit 6, 8 is an error detection circuit that compares the output of the sample and hold circuit 7 with a desired reproduction power output value, and 9
Is a V-I conversion circuit for converting a voltage into a current according to the output value of the error detection circuit 8, 10 is a circuit for adding the reproduction power drive current and the recording power drive current, and 11 is the timing of sampling and holding to the sample hold circuit 7. An SH pulse generation circuit for instructing the recording power, and a recording power setting circuit 12 for generating a recording power drive current.

Next, the operation will be described. The laser light output from the semiconductor laser 4 is detected by the photodiode 5 and converted into a current proportional to the optical power. The current output from the photodiode 5 is converted into a voltage by the IV conversion circuit 6 in the next stage, and is compared with the reference voltage by the error detection circuit 8 through the sample hold circuit 7.
The voltage of the difference is compared and output from the error detection circuit 8 and becomes the reproduction power drive current in the next VI conversion circuit 9, which is supplied to the LD through the current addition circuit 10. With the above circuit, feedback control is applied to the reproduction power, and a constant reproduction power output light is always obtained. At the time of recording, the sample-hold circuit 7 outputs a high output power from the semiconductor laser 4. Therefore, the sample-hold circuit 7 is set to the sampling state when the reproducing power is being output, and is set to the hold state when the recording power is being output. Only the power output is controlled by footback control. Switching between sampling and holding is passed to the sample and hold circuit 7 through the sample and hold pulse generation circuit according to the control signal 13. Further, the recording power setting circuit 12 produces a pulsed recording power drive current according to the control signal 13, is combined with the reproduction power drive current in the current adding circuit 10 and is flown to the semiconductor laser 4 to record the reproduction power in pulse form. A laser output in the form of superimposed power is obtained.

[0004]

Since the conventional semiconductor laser control circuit is constructed as described above, the reproduction power may be output higher than the target value and the recording medium may be destroyed due to some accident. there were.

The present invention has been made in order to solve the above problems, and provides a semiconductor laser control device which prevents an excessive reproduction power from being output from a semiconductor laser and does not destroy a recording medium. With the goal.

[0006]

A semiconductor laser control device according to the present invention is, for example, provided with an element having a temperature dependence capable of correcting a current value according to temperature at a place where a reproduction power drive current flows. It has the elements of. (A) a semiconductor laser that outputs a laser beam, (b) a laser drive current generating unit that generates a laser drive current for driving the semiconductor laser, and (c) so that the laser light output of the semiconductor laser becomes constant. , In response to temperature changes,
Current correction means for correcting the laser drive current generated by the laser drive current generation means.

[0007]

In the semiconductor laser control device according to the present invention, the temperature dependence of the semiconductor laser is offset by an element (for example, a heat sensitive resistor) having a temperature dependence having a predetermined relationship with the temperature characteristic of the semiconductor laser to drive the reproduction power. The current is corrected and the reproduction power drive current is controlled so that the reproduction power output has an output that does not depend on temperature. Also, by monitoring this element, it is possible to know the abnormality of the reproduction power output, and in the case of abnormality, it is possible to prevent the recording medium from being destroyed by turning off the reproduction power drive current.

[0008]

EXAMPLES Example 1. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 14 is a heat-sensitive resistor whose resistance value becomes smaller as the temperature becomes higher (an example of current correction means in the present invention), 15 is a differential circuit for detecting a voltage difference between both ends of the heat-sensitive resistor 14, and 16 is a differential circuit. The comparator circuit for comparing the output of the circuit with the reference set value, 17 is an error processing circuit for stopping the reproduction power drive current according to the output of the comparator circuit 16, and others are the same as the configuration of FIG. However, the thermal resistor 15 needs to be installed near the semiconductor laser 4.

FIG. 2 is a diagram showing the characteristics of a general semiconductor laser. As the temperature of the semiconductor laser rises, the threshold current for outputting laser light increases, and the efficiency (increase in laser light power relative to the increase in current) also decreases, and a large current is required to obtain the same reproduction power light. .. For example, if temperature a <temperature b in the figure, the threshold current I _thb at temperature b becomes larger than the threshold current I _{tha at} temperature a. Further, when the same reproduction power X is obtained, I _LDa <I _LDb , and a higher current requires a larger current to obtain the same light output level.
Therefore, a heat-sensitive resistor 14 having a smaller resistance value as the temperature rises is provided at a portion where the reproduction power drive current flows, and the temperature coefficient thereof uses a value that cancels the temperature coefficient of the current required to output a constant reproduction power. Thus, in the state where a constant reproduction power is output, the same voltage is applied to both ends of the thermal resistor 14 even if the temperature changes. Next, the voltage between both ends thereof is input to the differential circuit 15 and taken out as a voltage difference, and the comparator 16 compares the voltage difference with the reference voltage. If the voltage difference is larger than the reference voltage, an excessive reproducing power is output. Therefore, the error processing circuit 17 sends a signal to the error processing circuit 17, and the error processing circuit 17 works on the VI converting circuit 9 to stop the output of current. However, the reference voltage input to the comparator 16 needs to be set to a value that does not damage the recording medium. As described above, in this embodiment, in the semiconductor laser control device of the optical recording / reproducing apparatus for recording / reproducing information on / from the recording medium using the semiconductor laser as the light source, the optical output detection for monitoring the optical output of the semiconductor laser is performed. Means, means for detecting the laser light intensity at the time of reproduction and sampling this, means for holding the sample value of the laser light intensity at the time of recording, comparing the sample hold value with a desired value, and reproducing Means for controlling the laser drive current during playback, means for detecting the laser drive current during playback with a temperature-dependent sensor, and playback when the magnitude of the detected laser drive current during playback exceeds a certain value. The semiconductor laser control device has been described, which comprises a means for stopping the laser drive current at the time.

Embodiment 2. Although the thermal resistance 14 is used to cancel the temperature dependence of the driving current of the semiconductor laser 4 in the above embodiment, the temperature dependence of the driving current of the semiconductor laser 4 is used in the element having another temperature dependence. Sex may be offset.

[0011]

As described above, according to the present invention, the temperature dependence of the reproduction power drive current of the semiconductor laser is canceled, so that the semiconductor laser control device for maintaining the reproduction power constant even if the temperature changes. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram showing a semiconductor laser control circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing input / output characteristics of a general semiconductor laser.

FIG. 3 is a block diagram showing a conventional semiconductor laser control circuit.

[Explanation of symbols]

 1 recording medium 2 motor 3 optical pickup 4 semiconductor laser 5 photodiode 6 IV conversion circuit 7 sample hold circuit 8 error detection circuit 9 VI conversion circuit 10 current addition circuit 11 sample hold pulse generation circuit 12 recording power setting circuit 13 Control signal 14 Thermal resistance 15 Differential circuit 16 Comparator 17 Error processing circuit

Claims (1)

[Claims] 1. A semiconductor laser control device having the following elements: (a) a semiconductor laser for outputting a laser beam; (b) a laser drive current generating means for generating a laser drive current for driving the semiconductor laser; ) Current correction means for correcting the laser drive current generated by the laser drive current generation means in response to temperature changes so that the laser light output of the semiconductor laser becomes constant.