JPH0727657B2 - Optical disk drive light source drive - Google Patents

Description

The present invention relates to a semiconductor laser drive circuit, and more particularly to an improvement of a circuit for protecting a semiconductor laser used as a light source in an optical disc device from surge.

FIG. 1 shows a semiconductor laser drive circuit in a readable / writable optical disk device.

The semiconductor laser 10 is incorporated in a part of the optical head 1, and drive circuits for a current source 3 for supplying a read current and a current source 4 for supplying a write current are connected to the semiconductor laser 10. The read current is a constant current, but the write current is a pulse current corresponding to the write information. In order to supply a high-speed pulse current, a high-speed switch element 43 is used in a series circuit of a voltage source 41 and a resistor 42 instead of the current source, and the switch 43 is turned on / off according to the write information, as shown in FIG. The method is also often used in practice. In FIG. 1, reference numeral 11 is a detector for monitoring the output of the semiconductor laser 10, and controls the read and write power sources 3 and 4 so that the monitor output 50 provides a predetermined read and write power. 53 and 54 are control signals for this purpose.

Semiconductor lasers generate laser light by passing a current in the forward direction as a diode. However, if a voltage exceeding a certain value is applied in the reverse direction for some reason, the element is destroyed. Although a normal diode or the like also has a reverse breakdown, a semiconductor laser has a very low withstand voltage against the reverse voltage. That is, the number of normal diodes
A reverse breakdown voltage of 10 to several hundreds of volts can be easily obtained, but this is several volts in a semiconductor laser. Therefore, Fig. 1 and 2
In the drive circuit shown in the figure, the read circuit 30, the write circuit
A brass voltage (surge voltage) is generated at the 0 terminal, and if this value exceeds the reverse withstand voltage, there is a problem that the semiconductor laser is destroyed. If a power supply of 10 and a few volts is used as the power supply such as the read power supply 3 and the write power supply 4, a surge or noise voltage of a few volts can easily occur when the power supply is turned on and off. Furthermore, if there is a mechanical contact near the drive circuit to turn on / off the current, several hundreds
Alternatively, a surge voltage exceeding 1000 V is generated, and the above breakdown voltage can sufficiently occur even through stray capacitance of the circuit. In particular, the semiconductor laser is an extremely high-speed response element, so it responds (breaks) sufficiently to high-speed surge voltage, and if a normal surge absorption element is connected in parallel with the semiconductor laser, it is faster than the protection element because of its high speed. It may be destroyed. Further, there is a problem that the forward write current waveform, which is the original function, is deteriorated due to the capacity of the protection element. Incidentally, a technique for preventing element destruction at the time of applying a reverse voltage by connecting a protection diode and a semiconductor laser in parallel in reverse polarity has been proposed, for example, in JP-A-54-105990.

An object of the present invention is to provide a semiconductor rage drive circuit which prevents a semiconductor laser from being destroyed by a reverse voltage applied to it by a surge generated when the power is turned on or off from the drive circuit or a nearby device.

The present invention is described in detail below with reference to examples. FIG. 3 is a drive circuit diagram showing an embodiment corresponding to FIG. The lead current source 3 is a transistor 33, a resistor 32, a control current source 34, a power source 3
Composed of 1. There are no restrictions on the configuration of the read current source, and other methods or configurations may be used. The write current source 4 includes a voltage source 41,
It consists of a resistor 42 and a switch transistor 43. The transistor 43 is driven from a write signal source 45 through a driver (amplifier) 44, and controls the switch 43 according to write information. The write signal source 45 generates a signal obtained by modulating the write data according to the recording format. The power supplies 31 and 41 generate outputs in which the voltages supplied from the input terminals 36 and 46 are stabilized. Inputs 36, 46, etc. are supplied from a power source as shown in FIG. In FIG. 4, an input 7 is an AC power supply, 70 is a power switch, 6 is a power supply circuit including a transformer and a rectifying circuit, and outputs 60, 61, 62 and the like are output. The power supply circuit 6 and the voltage sources 31 and 41 may be the same power supply circuit. The laser output is converted into a current by the monitor detector 11, and is input to the control current source 34 and the write voltage source 41 as a monitor output by the resistor 51 and the amplifier 5 so that the read power and the write parameter are controlled to predetermined values. It

In such a semiconductor laser drive circuit, the read current path
Diodes 300 and 400 each having a high reverse breakdown voltage are respectively inserted in the forward direction in the 30 and the write current path 40, and the semiconductor laser 1
It is a feature of the present invention that the resistor 100 is connected in parallel with 0.

In the drive circuit according to the present invention as described above, when the power source of the device is turned on and off, and the power source switch 70 of FIG. 4 is turned on and off, the power source 31, 41 and the electrodes of the transistors 33, 34 are controlled. Even if a surge or noise voltage that is not generated occurs and the potentials of the current paths 30 and 40 become reverse voltages with respect to the semiconductor laser 10, this voltage is
Since it is divided by the very large reverse resistance of 300,400 and the resistance 100, the laser 10 is not subjected to a surge that causes destruction. A current that bypasses the current flowing through the laser 10 flows through the resistor 100, but since it can be set to a sufficiently small value (about 0.1%) with respect to the normal laser current, there is no effect on the read and write currents. On the other hand, the diodes 300 and 400 have 100 to several
A device having a reverse breakdown voltage of 100 V and a high-speed response can be easily obtained, and does not adversely affect the normal operation.

As described above, according to the present invention, it is possible to prevent the reverse voltage from being applied to the semiconductor laser due to the on / off of the power supply or the uncontrollable surge voltage or noise voltage from other devices, and to eliminate the damage due to these surges. it can. In particular, various power supplies used in the device, conditions for the on / off sequence, on / off speed, etc. are unnecessary.
In addition to surges and noises, the effect of sufficient protection is obtained against uncontrollable causes such as momentary power failure and power failure, which is extremely useful in practice.

[Brief description of drawings]

1 and 2 are diagrams showing a semiconductor laser drive circuit in an optical disk, FIG. 3 is a diagram showing an embodiment of a semiconductor laser drive circuit according to the present invention, and FIG. 4 is a diagram showing the power supply in FIG. It is a figure which shows an example.

Claims (1)

[Claims] 1. A semiconductor laser, a recording power source and a reproducing power source which drive the semiconductor laser and have internal resistance, a resistor connected in parallel with the semiconductor laser, and a current from the recording power source. In a semiconductor laser driving device having a mechanical contact, a forward direction arranged between a connection point between the semiconductor laser and the resistor and the recording power supply, and between the connection point and the reproduction power supply. When the potential of the recording power source or the reproducing power source has a reverse voltage with respect to the semiconductor laser,
A light source drive device for an optical disk device, wherein the reverse voltage is divided by the reverse resistance of the diode, the resistance, and the internal resistance.