JPH05218546A - Laser power controller - Google Patents

Abstract

PURPOSE:To surely prevent the temperature ripple at record of laser power by providing a temperature compensating circuit at the previous stage of a control circuit, which is provided for a constant current power source for supplying a record current, and compensating the reference voltage, according to temperature. CONSTITUTION:This controller is equipped with a constant current source 4, which supplies a laser diode 1 with a record current, and a reference power source 12, which sets a reference record current. Furthermore, it is equipped with a temperature compensating circuit 13, which varies the voltage of the reference voltage source 12 by the temperature, and a constant current controller 14, which controls the constant current source 4, according to the output of this temperature compensating circuit 13. What is more, the temperature compensating circuit 13 is arranged to perform power control geared to temperature, by installing a heat-sensitive element, wherein the electric properties change by temperature, in a housing of light pickup with a built-in laser diode 1. Hereby, the temperature ripple of the laser diode 1 can be detected accurately, and temperature control being accurate by that amount can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power control device for a recording laser diode.

[0002]

2. Description of the Related Art As a laser diode power control device of this type, a first constant current source 2 for supplying a reproducing current to a laser diode 21 is shown in FIG.
2 and a recording current is superimposed on the reproduction current and supplied to the laser diode 21 when the switch 23 is turned on.
Constant current source 24 is provided, the output voltage of the monitoring photodiode 25 is detected by the detection circuit 26, and the monitor output voltage is compared with the reference voltage provided by the first reference voltage source 27 by the comparator 28. The comparison output is sampled and held by the sample and hold circuit 30 via the switch 29, and the control voltage applied to the first constant current source 22 is controlled according to the sampled and held value so that the reproduction current becomes constant. A circuit 31 is known to be controlled.

In this power control device, the second constant current source 24 is controlled only by one control circuit 33 according to the reference voltage given by the second reference voltage source 32. Therefore, as a result of the change in the current of the second constant current source 24 due to the temperature fluctuation and the like, there is a problem that the power during recording cannot be kept constant. In order to solve this problem, Japanese Patent Laid-Open No. 64-76545 discloses
As shown in FIG. 6, for the second constant current source 24 for recording, the same voltage control system as the first constant current source 22, that is, the switch 35, the sample hold circuit 36, and the control circuit 3 is used.
7 is installed in parallel with the voltage control system of the first constant current source 22, not only the reproduction current but also the recording current is monitored, and APC (auto power control) is performed so that both currents become constant. Such a power control method has been proposed.

In this system, not only the reproducing current but also the recording current can be maintained constant, but the above APC
Since it is necessary to provide the circuits in parallel, the circuit scale becomes large and the cost becomes high. In addition, since the recording current holds the value sampled by the sample hold circuit before and controls the current using the held value, the sampling value disappears due to the leakage immediately after the power is turned on. If
It takes a long time for the recording power to stabilize, and there is a problem that normal recording pits are not formed due to overpower or underpower immediately after the start of recording. Furthermore, if the playback time is long, the sampling value is lost as above. There is also a problem that correct recording cannot be performed in the recording operation immediately after the reproducing operation.

[0005]

As is apparent from the above, in the conventional laser power control circuit, it was difficult to control the recording current constant without increasing the size of the circuit. Therefore, it is a basic object of the present invention to provide a control circuit capable of controlling the recording current to a constant value with respect to temperature fluctuations without increasing the size of the circuit.

[0006]

In order to solve the above problems, the present invention provides a constant current source for supplying a recording current to a laser diode, a reference voltage source for setting a reference recording current, and a voltage of the reference voltage source. A temperature compensation circuit that varies with temperature,
A laser power control device provided with a constant current control circuit for controlling the constant current source according to the output of the temperature compensation circuit.

As the temperature compensating circuit, a temperature sensitive element whose electrical characteristics change with temperature is provided, and this temperature sensitive element is mounted in a housing of an optical pickup in which a laser diode is incorporated, and a power corresponding to the temperature is supplied. You may make it control.

[0008]

In the present invention, since the recording current is controlled by the temperature compensating circuit, the temperature fluctuation of the recording current can be surely prevented without using the APC circuit. Further, by mounting the temperature sensitive element of the temperature compensating circuit in the housing of the optical pickup, it is possible to accurately detect the temperature fluctuation of the laser diode and to perform the temperature compensation as accurately as that.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a laser diode 1 for reproducing / recording with a laser is supplied with a first constant current source 2 for supplying a reproducing current and a recording current through a switch 3. And a second constant current source 4 for supplying the same, and a reproducing current is supplied from the first constant current source 2 to the laser diode 1 at the time of reproduction, and at the time of recording, in addition to the reproducing current, a second constant current is supplied. A recording current is supplied from the source 4 to increase the power of the laser diode 1.

An APC circuit is provided for the first constant current source 2 as in the conventional case. That is, the reference voltage provided by the reference voltage source 5 and the monitor voltage obtained by detecting the current generated in the monitoring photodiode 6 as the voltage by the detection circuit 7 are compared by the comparison circuit 8, and the switch 9
The sample and hold circuit 10 samples and holds the comparison result via the, and the control circuit 11 receives the sampled and held value as an input and applies it to the constant current source 2 so that the reproduction current becomes constant. Control the voltage.

On the other hand, the second constant current source 4 is provided with a temperature compensating circuit 13 for temperature compensating the reference voltage provided by the second reference voltage source 12, and the temperature compensated voltage by the temperature compensating circuit 13 is supplied. The control voltage to the second constant voltage source 4 is controlled according to the temperature so that the recording current is kept constant. The temperature compensation circuit 1
Various circuits can be adopted as 3, and for example, a feedback type differential amplifier circuit as shown in FIG. 2 can be used. That is, while the inverting input of the differential amplifier 15 is grounded, the non-inverting input is connected to the second reference voltage source 12 via the resistor 16 and the output of the differential amplifier 15 is connected to the non-inverting input. A temperature-sensitive resistance element 17 whose electric resistance changes according to temperature is connected to compensate the output voltage according to temperature. It is preferable that the above-mentioned temperature faithfully reflects the operating temperature of the laser diode 1. For this purpose, as shown in FIG. 3, the aluminum housing of the optical pickup 18 incorporating the laser diode 1 is used. It is preferable to mount the temperature sensitive resistance element 17 on the side wall using, for example, silicon grease having good thermal conductivity so that the temperature rise of the laser diode 1 can be accurately detected. Both ends of the temperature-sensitive resistance element 17 are connected by soldering to a flexible tube FT which connects the optical pickup 18 and the board B via a connector C, and the resistance change is measured on the board B side in which the control circuit is incorporated. Tell.

In the temperature compensation circuit shown in FIG. 2, the resistance 16 is 18 KΩ (temperature characteristic is about +100 ppm /
℃), temperature characteristic 2500p as temperature-sensitive resistance element 17
Using a pm / ° C. standard resistance value of 18 KΩ, the temperature characteristic of the gain of the temperature compensation circuit was + 0.25% / ° C. As a result, the recording current exhibits a temperature characteristic of + 0.25% / ° C. FIG. 4 shows the conventional circuit shown in FIG. 6, the temperature-sensitive resistance element 17 of the temperature compensation circuit according to the present invention shown in FIG. 2 mounted on the substrate B, and the temperature-sensitive resistance element 17 mounted on the optical pickup 18. With respect to the case, the measurement result of the temperature characteristic of the recording power is shown. In case of optical disk drive, it is -5
A change in ambient temperature of + 55 ° C can be expected, but in the conventional circuit of Fig. 5 without the temperature compensation circuit, it is about -0.25%.
It exhibits a temperature characteristic of / ° C. and the recording power fluctuates about ± 10% in the worst case, and cannot be put to practical use in terms of reliability. On the other hand, according to the present invention, even when the temperature sensitive resistance element 17 is mounted on the substrate, the fluctuation can be suppressed within ± 3%, and when it is mounted on the optical pickup, it is ± 0.
It was shown that the fluctuation of the recording power could be suppressed within 1 mW, which was extremely effective.

Further, in the above embodiment, a predetermined recording power was obtained from the beginning even when the recording operation was started immediately after the power was turned on or after a long reproduction time. Incidentally, in the conventional example of FIG. 5, when the recording operation is started immediately after the power is turned on or after the reproduction operation is performed for 10 minutes or more, the sampling value of the recording current disappears due to the leak, and therefore, the recording power immediately after the recording is started. Becomes zero and it takes 50 msec or more to obtain a predetermined recording power. In the above embodiment, the temperature sensitive resistance element is used as the temperature compensation element, but a platinum resistance, thermistor, diode or the like may be used instead.

[Brief description of drawings]

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

2 is a circuit diagram showing a specific example of the temperature compensation circuit 13 of FIG.

FIG. 3 is a perspective view of an optical pickup showing a preferred arrangement of the temperature sensitive device of FIG.

FIG. 4 is a graph showing measurement results of temperature fluctuation of recording power in the case of using the laser power control circuit according to the example of the present invention and in the case of the conventional circuit.

FIG. 5 is a block diagram showing an example of a conventional laser power control circuit.

FIG. 6 is a block diagram showing another example of a conventional laser power control circuit.

[Explanation of symbols]

 1 ... Laser diode 2 ... 1st constant current source (constant current source for reproduction) 4 ... 2nd constant current source (constant current source for recording) 6 ... Photodiode 7 ... Detection circuit 10 ... Sample hold circuit 11 ... Control circuit 13 ... Temperature compensation circuit 17 ... Temperature sensitive resistor

Claims (2)

[Claims] 1. A constant current source for supplying a recording current to a laser diode; a reference voltage source for setting a reference recording current;
A laser power control device comprising: a temperature compensation circuit for varying the voltage of a reference voltage source according to temperature; and a constant current control circuit for controlling the constant current source according to the output of the temperature compensation circuit. 2. The laser power control device according to claim 1, wherein the temperature compensating circuit includes a temperature sensitive element whose electrical characteristics change depending on temperature, and the temperature sensitive element is a light incorporating a laser diode. Characterized by being installed in the pickup housing.