JPS58151081A - Laser power source circuit - Google Patents

Abstract

PURPOSE:To prevent faults, by restricting the supply current when the temperature of a semiconductor laser exceeds the fixed value. CONSTITUTION:A drive circuit 4 is automatically controlled 3 by comparing 301 the output of a photo detector 2 in the neighborhood of the laser element 1 with the reference voltage. By the resistor 401 and the capacitor 402 of a circuit 4, the rapid increase of the base potential of the element 403 is prevented, and accordingly the sudden current rushing into the laser element 1 is prevented. On the other hand, when the detection temperature 7 decreases to less than the set value, the output is inversed 601, and then the command to turn the laser element OFF is given resulting in protection operation 6. Next, an AND gate 501 receives this command and the external command which is interlocked with the mechanical operation, and accordingly operates switch elements 502-504 resulting in the control of the current of the drive circuit 4. By a resistor 506 and a capacitor 507, the rapid increase of the base potential of the element is prevented, and accordingly the sudden current into the laser element 1 is prevented. By this constitution, the laser current does not continue to increase with temperature, thus rush current is not generated at the time of throw-in of the power source, and therefore the breakdown of the laser element can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser power supply circuit that automatically controls a constant force and prevents a laser element from being destroyed due to temperature rise.

Generally, the output of a semiconductor laser is highly temperature dependent, and in order to obtain stable output, it is necessary to detect a portion of the laser output and perform automatic control. However, the temperature characteristics of semiconductor lasers are negative, that is, the output decreases as the temperature rises. Therefore, in conventional automatic control circuits, the laser current continues to increase in proportion to the temperature rise. There was a problem in that the heat loss of the laser increased over time, and eventually exceeded the allowable amount of heat loss for the semiconductor laser, resulting in destruction of the semiconductor laser.

It is an object of the present invention to provide a laser power supply circuit that solves these problems and makes it possible to realize a semiconductor laser with fewer failures.

First, the basic circuit configuration of the laser power supply circuit according to the present invention will be explained.

FIG. 1 is a block diagram showing the basic circuit configuration of a laser power supply circuit according to the present invention, in which 1 is a laser element made of a semiconductor, 2 is a photodetector for detecting the laser output of the laser element 1, and 3 is an optical 1 is an automatic control circuit that compares the signal voltage from the detector 2 with the reference voltage E to keep the laser output constant; 4 is a drive circuit for driving the laser element 1; Means is provided to prevent the generation of inrush current at times. 5 turns on the laser output according to a command from the protection circuit 6 and an external command.

An output control circuit 7 that turns off or limits the output is a temperature detector that detects the temperature of the laser element 1 or its vicinity and inputs the detection signal to the protection circuit 6.

FIG. 2 shows an example of a specific circuit configuration based on the basic circuit configuration of the present invention.Next, the present invention will be specifically explained with reference to FIG. .

The automatic control circuit 3 mainly consists of a differential input amplifier 301, and a drive circuit so that the voltage detected by the photodetector 2 connected to one terminal is compared with the reference voltage of the ten terminals so that the laser output is always constant. Control 4. 302 is a Zener diode for passing an appropriate bias current to the photodetector 2 connected to one terminal. A resistor 401 and a capacitor 402 are connected to the base of the transistor 403 in the drive circuit 4.
A time constant circuit is provided, which prevents a sudden rise in the base potential of the transistor 403 and prevents a rush current from flowing into the laser element 1 when the power is turned on.

On the other hand, the electric potential of the comparator 601 in the sampling circuit 6 changes depending on the temperature due to the temperature characteristics of the temperature detector 7, and when the electric potential of the electric power falls below the set electric potential of the - electric power, the output of the comparator 601 changes. Inverted output control circuit 5
A low level command signal is issued to turn off the laser element 1.

The AND gate 501 of the output control circuit 5 is connected to the command signal of the protection circuit 6 and the command signal AND from the outside linked to a device operation switch, etc., and then the transistor 502 is connected.
, 503, 504 are operated in a switching manner. That is, when the pace potential of the transistor 502 becomes high level, the transistor 502 is turned off, and the F run raster 503 is turned on (0FF1), and the transistor 504 is turned on to supply current to the drive circuit 4. Conversely, transistor 5020
When the pace becomes low level, transistor 502 turns on,) transistor 503 turns on,) transistor 504
is turned OFF, cutting off the current of the drive circuit 4. In addition,
The time constant circuit made up of the resistor 506 and the capacitor 507 prevents the transistor 5040 pace potential from rising rapidly.
This is to prevent a sudden increase in the output current when the transistor 504 is turned OFF and ON, and to prevent a rush current from flowing into the laser element 1. Furthermore, a Zener diode 505 connected to the emitter of the transistor 502 is provided to align the output level of the AND gate 501 and the switching level voltage of the transistor 5o2. Furthermore, in this implementation example, the collector of the transistor 503 is directly grounded, but if the collector is grounded through a resistor, the switching operation of the transistor 504 will be more complete, and the output limiting operation will be more effective. It can be done reliably.

As explained above, the laser power supply circuit of the present invention is not only an automatic control circuit that controls the output of the laser at a constant level, but also a circuit that stops driving the laser when the temperature of the laser element exceeds a predetermined value, or supplies power to the laser. Since the laser current is limited, the laser current does not continue to increase in proportion to the temperature rise as in the conventional case, and it also prevents rush current from flowing into the laser element when the power is turned on. This reduces the probability that the laser element will be destroyed.

Therefore, according to the laser power supply circuit of the present invention, it is possible to realize a long-life semiconductor laser with a low failure rate.

Note that the laser power supply circuit of the present invention can be easily applied to protection circuits for other elements by replacing the temperature detector 7 with another detector.

[Brief explanation of the drawings] Figure 1 is a professional diagram showing the basic circuit configuration of the present invention;
The figure is a diagram showing an example of a specific circuit based on the present invention. DESCRIPTION OF SYMBOLS 1... Laser element, 2... Photodetector, 3... Automatic control circuit, 4... Drive circuit, 5... Output control circuit, 56... Protection circuit, 7... Temperature Detector.

Claims (1)

[Claims] (11) In a laser power supply circuit equipped with an automatic control circuit for keeping the laser output of a semiconductor laser constant, the tIL flow supplied to the semiconductor laser when the temperature of the semiconductor laser exceeds a predetermined value. (2) A patent characterized in that the current limiting means includes means for preventing rush current from flowing into the laser element when the power is turned on. A laser power supply circuit according to claim (1).