JPH064601Y2 - Optical output control circuit - Google Patents

Description

The present invention relates to a light output control circuit, and more particularly to a light output control circuit suitable for an optical information recording / reproducing apparatus.

(Prior Art) FIG. 3 is a configuration diagram showing a configuration example of a main part of a light output control circuit for controlling a light output of a semiconductor laser. In this figure, 1 is a current control transistor as a drive current control means for driving the semiconductor laser, 2 is a semiconductor laser whose optical output is controlled by the current control transistor 1, and 3 is on / off control of the semiconductor laser 2. A switching element 4 composed of a transistor for performing the operation is a time constant circuit as a slow starter circuit.

FIG. 4 is a block diagram showing the overall configuration of the light output control circuit. In this figure, 5 is an optical output control unit for controlling the optical output of the semiconductor laser 2, 6 is a photodetector such as a photodiode for receiving the optical output of the semiconductor laser 2, 7
Is a monitor circuit that gives a control signal to the optical output control section 5 based on the detection result of the photodetector 6.

In such a light output control circuit, the time constant circuit 4 is
This circuit protects the semiconductor laser 2 by making the drive current of the semiconductor laser 2 rise gently (slow start) when the power is turned on or when the semiconductor laser 2 is switched from ON to OFF.

Further, FIG. 5 is a circuit diagram showing a specific circuit configuration of a conventional light output control circuit. The optical output of the semiconductor laser 2 is detected by the pin photodiode 9 built in the semiconductor laser 2. Then, a voltage corresponding to the light output detected by the pin photodiode 9 is generated in the resistors 10 and 11. The voltage generated in the resistors 10 and 11 and the reference voltage of the Zener diode (reference voltage source) 12 are compared in the transistor 13, and the difference between them is calculated in the transistor 13
It becomes the collector current of. Therefore, this transistor 13
By controlling the base voltage of the current control transistor 1 with the collector current of, the optical output of the semiconductor laser 2 becomes constant. In this circuit diagram, the capacitor 8 constitutes the time constant circuit 4.

(Problems to be Solved by the Invention) In the above-mentioned conventional light output control circuit, since the time constant circuit 4 is directly arranged at the input of the current control transistor 1 as the drive current control means, the light output control section 5 is provided. There is a drawback that the response speed to the control input from is slow.

The present invention has been made in view of the above problems, and an object thereof is to protect a semiconductor laser when the semiconductor laser is turned on without sacrificing high-speed response to an optical output control signal. To realize a light output control circuit capable of

(Means for Solving the Problems) The present invention for solving the above problems is a drive current control means capable of increasing or decreasing a drive current supplied to a semiconductor laser according to a control signal supplied to an input section, and the semiconductor device. And a light output detection means for outputting a signal according to the light output of the laser, so that the output signal of the light output detection means is a constant value, by giving a control signal to the input part of the drive current control means, In a light output control circuit for stabilizing a light output when driving a semiconductor laser, a time constant circuit for receiving a drive signal for turning on / off the semiconductor laser, an input section of the drive current control means, and the semiconductor laser in the input section. Connected to a point that can supply a voltage such that the drive current to
The resistance value changes according to the value of the drive signal input via the time constant circuit, and the change in the resistance value is caused by the drive signal input via the time constant circuit turning on the semiconductor laser. The resistance value becomes substantially infinite when reaching the value to be set, and the resistance value becomes substantially zero when the drive signal input through the time constant circuit reaches the value at which the semiconductor laser is turned off. And a switching means to be performed.

(Operation) Switching of the driving current of the semiconductor laser is performed via a time constant circuit. Further, the drive current of the semiconductor laser is controlled without passing through the time constant circuit.

Embodiment An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing a configuration example of an embodiment of the present invention. In this figure, the same parts as those in FIG. 3 are designated by the same reference numerals. In this figure, the difference from FIG. 3 is that the time constant circuit 4 is connected to the base terminal which is the input of the switching element 3 for ON / OFF controlling the semiconductor laser 2.

The semiconductor laser on / off drive signal drives the switching element 3 after passing through the time constant circuit 4. And
When the switching element 3 is turned on and the emitter current flows, the base voltage of the current control transistor 1 drops and the emitter current also stops flowing. Therefore, no current flows through the semiconductor laser 2. When the switching element 3 is turned off and the emitter current stops flowing, the base voltage of the current control transistor 1 rises and the emitter current also starts flowing. Therefore, current also flows in the semiconductor laser 2. In this way, by the input of the time constant circuit 4,
The current of the semiconductor laser 2 is switching-controlled. Further, the value of the current flowing through the semiconductor laser 2 changes according to the light output control signal applied to the base of the current control transistor 1, and the light output also changes correspondingly.

By doing so, the control signal from the light output control unit 5 is not affected by the time constant circuit 4, and the response speed of control of the light output is improved. That is, the slow start and the high-speed response of the light output control are compatible with each other, and as a result, it is suitable for high frequency driving.

FIG. 2 is a circuit diagram showing a concrete circuit example of the time constant circuit 4. In this case, the time constant circuit is composed of the capacitor C and the resistor R. By selecting the time constant determined by C and R, the rise of the drive current of the semiconductor laser 2 can be made gentle (slow start), and the semiconductor laser 2 can be protected.

The transistors shown in FIGS. 1 and 2 are NPN type and P type by adjusting the direction of voltage, the circuit configuration, and the like.
It is possible to use any of the NP type.
The emitter or collector of the transistor may be connected to the anode of the semiconductor laser 2. It is also possible to use a FET instead of a transistor.

(Effect of the Invention) As described in detail above, in the present invention, the time constant circuit is arranged at the input of the switching element so that the optical output control signal does not pass through the time constant circuit.

Therefore, without sacrificing the response speed to the light output control signal, it is possible to realize the light output control circuit that can always slow start the semiconductor laser and protect the semiconductor laser when the semiconductor laser is turned on.

[Brief description of drawings]

FIG. 1 is a block diagram showing the constitution of an embodiment of the present invention, FIG. 2 is a circuit diagram showing the detailed constitution of the present invention, and FIGS. 3 and 4 show the constitution of a conventional optical output control circuit. FIG. 5 is a circuit diagram showing a circuit configuration of a conventional light output control circuit. 1 ... Current control transistor 2 ... Semiconductor laser 3 ... Switching element, 4 ... Time constant circuit

Claims (1)

[Scope of utility model registration request] 1. A drive current control means (1) capable of increasing or decreasing a drive current supplied to a semiconductor laser (2) according to a control signal supplied to an input section, and an optical output of the semiconductor laser (2). A light output detection means for outputting a signal according to, so that the output signal of the light output detection means is a constant value, by giving a control signal to the input portion of the drive current control means (1),
In a light output control circuit for stabilizing a light output when driving a semiconductor laser, a time constant circuit (4) for receiving a drive signal for turning on / off the semiconductor laser (2), and an input of the drive current control means (1) Voltage (V _EE ) such that the drive current to the semiconductor laser (2) becomes zero at the input section and the input section.
, The resistance value of which changes according to the value of the drive signal input via the time constant circuit (4), and the change of the resistance value is the time constant. When the drive signal input through the circuit (4) reaches a value for turning on the semiconductor laser (2), the resistance value becomes substantially infinite, and the resistance is input through the time constant circuit (4). A light output control circuit, comprising: a switching means (3) for making the resistance value substantially zero when a drive signal reaches a value for turning off the semiconductor laser (2).