JPH03239384A - Semiconductor laser protection circuit - Google Patents

Abstract

PURPOSE:To eliminate the need for manual protection operation by either applying voltage below pinchoff voltage to a gate of a field-effect transistor or keeping said gate in an open state when a semiconductor laser is not in operation and applying voltage above the pinchoff voltage when the semiconductor laser is acting. CONSTITUTION:When a semiconductor laser 1 is separated from a drive circuit under the condition where a drain D and source S of a field-effect transistor are connected in parallel or connected in reverse order between an anode 11 and a cathode 12 of the semiconductor laser 1, an attempt must be made to keep each electrode D and S, including a gate electrode G under an open state or apply voltage below pinchoff voltage as a gate voltage. This maintains the impedance between the drain D and the source S of the field-effect transistor 15 at several hundreds ohms. It is, therefore, possible to obtain the same protection effect that can be available when the span between the anode 11 and the cathode of the semiconductor laser 1 is automatically reduced, thereby eliminating the need for manual protection operation.

Description

[Detailed Description of the Invention] [Summary] Regarding a protection circuit for a semiconductor laser used as a light source for optical disks, etc., the purpose of the present invention is to provide a protection circuit for a semiconductor laser that does not require manual protection operation, and to protect the drain and source of a field effect transistor. one is connected to the anode of the semiconductor laser, and the other is connected to the cathode of the semiconductor laser, and when the semiconductor laser is not operating, a voltage lower than the pinch-off voltage is applied to the gate of the field effect transistor, or the gate is left open. The configuration is such that a voltage higher than the pinch-off voltage is applied to the gate during operation.

[Industrial application field]

The present invention relates to a protection circuit for a semiconductor laser used as a light source for optical discs and the like.

Semiconductor lasers have light emission characteristics of a single wavelength and a single phase, and have properties that are completely different from conventional light sources, such as directivity and energy, and are used in a wide range of applications from optical communication to optical disks and even measurement. There is. In particular, semiconductor lasers for optical disks are already on par with consumer products in terms of production numbers and shipping costs. Semiconductor lasers are used in a wide variety of ways, but the one with the highest track record of use is undoubtedly the optical disk market, including CDs (compact discs).

Optical disk devices record and reproduce information on a recording medium using a minute spot focused on the wavelength, so they are capable of higher density recording than conventional recording devices. Furthermore, since it is non-contact recording in which the objective lens that focuses the laser beam and the surface of the recording medium are separated by about 1 mm, it is currently the mainstream external storage device for large computers to small machines. In addition, in order to maximize the storage density, the head-to-medium spacing has been narrowed down to the submicron range, making it possible to ensure higher reliability than magnetic disks, which suffer from problems such as 7-D cracks.

It also has the same interchangeability as floppy disks and magnetic tapes, which are the main reason for the spread of current WS (workstations)/PCs (personal computers).

Therefore, it is expected to have a wide range of applications, from large general-purpose computers to WS/PCs.

Furthermore, with the advancement of optical disk technology, the traditional write-once type optical disk, on which the user can write data only once, has changed.
There has been progress toward rewritable disks, such as magnetic disks and floppy disks, where data can be recorded and erased as many times as desired.

Along with this, the field of application is also becoming much broader.

[Conventional technology]

FIG. 4 shows a block diagram of main parts of a conventional optical disk device. In the figure, diverging light from a semiconductor laser 1 serving as a light source is converted into parallel light 7 by a collimating lens 2, transmitted through a beam splitter 3, and then incident on an objective lens 5 via a reflection plane -4. The objective lens 5 irradiates a laser beam as a minute spot on a predetermined track by following the surface deflection and eccentricity of the recording medium 6 which is being rotated at a constant speed by a spindle (not shown). (The driving/moving mechanism is not shown).

The reflected light from the recording medium 6 travels backward along the same optical path as when it was incident, is reflected by the beam splitter 3, is focused on the photodetector 9 by the condensing lens 8, and is directed to the reproduction signal and the objective lens 5 along the optical axis. Focus for driving in direction and trunk direction
A track error signal is detected.

In FIG. 4, only a so-called optical head, which records and reproduces information, of the optical disk device is shown. This optical head portion is installed at a predetermined position in the device after the optical system and the like are adjusted independently with the semiconductor laser 1 still attached and usually separated from the device. At this time of disconnection, the semiconductor laser 1 is disconnected from the semiconductor laser drive circuit (not shown) on the device side, resulting in an open circuit state. By the way, the semiconductor laser 1 has the disadvantage that it is very sensitive to static electricity in the human body or in the storage environment, surges when power is turned on in the drive circuit, etc., and is easily broken, so some kind of countermeasure must be taken.

FIG. 5 is a diagram for explaining a conventional protection circuit. In the figure, ■ is a semiconductor laser mounted in the optical head 16, and is composed of an anode 11 and a cathode 12. It has a circuit configuration that supplies current. Further, a switch 14 having a function such as a short bar or a slide switch is used to short-circuit between the anode and cathode 12 of the semiconductor laser. This switch 14 protects the semiconductor laser by turning it on before opening it, and has a structure that is built into, for example, a multicore flexible lead wire connected to the semiconductor laser. .

[Problem to be solved by the invention]

Since the above-mentioned switch 14 mechanically shorts the cathode and anode, it is natural that the operator forgets to operate it.

There was a possibility that poor contact or short circuits could occur.

Furthermore, since the switch 14 must be operated each time the optical head is attached or removed, there is a problem in that the process becomes complicated.

The present invention has been made in view of the above-mentioned conventional drawbacks, and an object of the present invention is to provide a semiconductor laser protection circuit that does not require manual protection operations.

[Means to solve the problem]

FIG. 1 shows a protection circuit of the invention. One of the drain and source of the field effect transistor 15 is connected to the semiconductor laser 1.
and the other to the cathode of the semiconductor laser, and when the semiconductor laser is not in operation, a voltage below the pinch-off voltage is applied as the gate voltage of the field effect transistor, or the gate is in an open state, and when it is in operation, a voltage below the pinch-off voltage is applied. A voltage higher than a pinch-off voltage is applied as the gate voltage.

[For production]

When the semiconductor laser 1 is separated from its drive circuit (optical head) with the drain and source of the field effect transistor 15 connected in parallel between the anode and cathode of the semiconductor laser 1, or vice versa, each part including the gate electrode By opening the electrodes or applying a voltage lower than the pinch-off voltage as the gate voltage, the impedance between the drain and source of the field effect transistor 15 is maintained at about several hundred ohms, which makes the semiconductor The same protection effect as automatically shorting the anode and cathode of the laser 1 can be obtained.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

Note that, in order to make the explanation of the configuration and operation easier to understand, the same parts are given the same reference numerals throughout all the figures, and repeated explanation thereof will be omitted.

FIG. 1 shows the protection circuit of the invention. In the figure, one of the drain and source of the field effect transistor 15 is connected to the anode of the semiconductor laser 1, and the other is connected to the cathode of the semiconductor laser, and when the semiconductor laser 1 is not in operation, the gate is connected to the gate of the field effect transistor 15. The configuration is such that a voltage equal to or lower than the pinch-off voltage is applied as a voltage, or the gate is left in an open state, and a voltage equal to or higher than the pinch-off voltage is applied to the gate as the gate voltage during operation. In this figure, the power source for applying the voltage is not shown.

To protect a semiconductor laser, it is sufficient to connect the cathode and anode with a finite resistance when not in operation (even when no external power is supplied).

Therefore, as an element (normally-on) whose resistance can be controlled externally and whose resistance is small when the power is turned off, a field effect transistor (Field Effect Transistor) is used.
(hereinafter referred to as FET).

FIG. 2 is a characteristic diagram of the FET used in the present invention,
Figure 2 (al is a static characteristic diagram, Figure 2 (bl is an electrode).

FIG. 3 is a diagram showing the relationship between voltages. In both figures, FET is
It consists of a semiconductor region called a P-type channel into which genuine cards are injected as majority carriers or an N-type channel into which electrons are injected as majority carriers, and a gate G having the opposite polarity. The operation of the FET is performed by controlling the channel resistance with a reverse biased gate voltage (voltage between the gate and the source) Vg.

The first quadrant of this static characteristic shows the change in drain current when the drain-source voltage Vds is changed with the gate voltage sig constant, and the second quadrant shows the drain-source voltage Vcls. It shows the drain current when the gate F i voltage Vg is changed while being fixed. Here gate voltage ν
When g is zero, that is, it is open, there is a certain finite resistance between the drain and source, which generally maintains a resistance of around 100Ω. On the other hand, when the gate voltage Vg is above a certain level, the drain current becomes almost zero. The gate voltage at which this drain current becomes zero is called the pinch-off voltage. At this time, the resistance between the drain and source is several MΩ or more, and it can be considered as an open state.

FIG. 3 is a diagram showing an embodiment of the present invention. Here, only the portion of the semiconductor laser 1 mounted on the optical head 16 is extracted and shown. The part surrounded by the broken line shows the extraction part when the optical head 16 is separated from the semiconductor laser drive circuit, and has a structure in which it can be extracted integrally with the optical head 16. Therefore, when the optical head 16 is disconnected from the semiconductor laser drive circuit or when power is not supplied to the semiconductor laser 1, the semiconductor laser 1
=9=0 The gate voltage of the FET 15 connected between the sword and the anode is zero. In other words, both terminals of the semiconductor laser 1 are connected with low resistance. In addition, when actually making the semiconductor laser l emit light, if the gate voltage of the FET 15 is set to be higher than the pinch-off voltage using an external control voltage, etc., the resistance between the drain and source of the FET 15 is
Since the resistance value is maintained at an almost infinite value, both terminals of the FET 15 are equivalent to being disconnected, and normal semiconductor laser driving becomes possible.

[Brief explanation of drawings]

FIG. 1 is a protection circuit of the present invention, FIG. 2 is a characteristic diagram of F E 'r used in the present invention, FIG. 3 is a diagram showing an embodiment of the present invention, and FIG. 4 is a diagram of a conventional optical disk device. A main part configuration diagram, FIG. 5, is a diagram for explaining a conventional protection circuit. In FIG. 1, ▪ indicates a semiconductor laser, and 15 indicates a field effect transistor (FET). [Effects of the Invention] As is clear from the following explanation, according to the present invention, the protection of the semiconductor laser can be controlled by a circuit, so manual mechanical operations are not required in each adjustment process, and reliability is improved. Connect. It also has the effect of being able to save cost and space compared to short berth inches.

Claims (1)

[Claims] One of the drain and source of the field effect transistor (15) is connected to the anode of the semiconductor laser (1), and the other is connected to the cathode of the semiconductor laser, and when the semiconductor laser is not in operation, the gate of the field effect transistor is pinched off. 1. A semiconductor laser protection circuit, characterized in that a voltage lower than a pinch-off voltage is applied or a gate is left in an open state, and a voltage higher than a pinch-off voltage is applied to the gate during operation.