JPH083904B2 - Semiconductor laser drive circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a semiconductor laser drive circuit, and more particularly to a semiconductor laser drive circuit in an optical recording / reproducing apparatus.

[Conventional technology]

FIG. 5 is a block diagram showing a conventional semiconductor laser driving circuit disclosed in, for example, Japanese Patent Laid-Open No. 61-16044.
In the figure, 1 is a semiconductor laser such as a laser diode, 2 is a photodiode for monitoring the light output emitted from the semiconductor laser 1, and 3 is a current-voltage conversion circuit for converting the current output from the photodiode 2 into a voltage. Is. The photodiode 2 and the current / voltage conversion circuit 3 constitute a photoelectric conversion circuit 20 which converts the optical output of the semiconductor laser 1 into a voltage signal and outputs the voltage signal.
4 is a first peak hold circuit for peak-holding the high level of the voltage output of the conversion circuit 3, 5 is a second peak hold circuit for peak-holding the low level of the voltage output of the conversion circuit 3, and 6 is the first peak The output of the hold circuit 4 is input to one input terminal and the other input terminal 7 is input with a high-level reference voltage. A first amplifier, 8 is an output of the second peak hold circuit 5 is one input terminal. And a low level reference voltage is input to the other input terminal 9 of the second amplifier. These amplifiers 6 and 8 set the optical output of the semiconductor laser 1 according to the outputs of the first peak hold circuit 4 and the second peak hold circuit 5 and according to the set reference voltage. 10 is a first driver for converting the output of the first amplifier 6 into a drive current,
11 is a second driver that converts the output of the second amplifier 8 into a drive current, 12 is a modulation circuit to which the drive current output from the first driver 10 is input, and 13 is a modulation input terminal of the modulation circuit 12. is there. The modulation circuit 12 is a circuit that switches according to an input signal input from the modulation input terminal 13, and switches depending on the level of the input signal, and the first driver
It is designed to turn the 10 outputs on and off. Both the modulation circuit 12 and the second driver 11 are semiconductor lasers 1.
It is connected to the.

Next, the operation will be described. When the semiconductor laser 1 emits light during writing, the photodiode 2 receives the light emitted from the semiconductor laser 1 and outputs a current. The output current of the photodiode 2 is converted into a voltage change by the current-voltage conversion circuit 3 and supplied to the first peak hold circuit 4 and the second peak hold circuit 5, respectively. The first peak hold circuit 4 peak-holds the high level of the current-voltage conversion circuit 3, and the second peak hold circuit 5 peak-holds the low level. And the high and low levels that are peak-held are
It is supplied to a first amplifier 6 and a second amplifier 8, respectively.

The first amplifier 6 and the second amplifier 8 are feedback-controlled so that the voltages input from the hold circuits 4 and 5 become equal to the reference voltage set at the input terminals 7 and 9, respectively. There is. The outputs of the amplifiers 6 and 8 are input to the first driver 10 and the second driver 11, respectively, and converted into drive current. The drive current output from the first driver 10 is input to the modulation circuit 12 and is modulated by the input signal of the modulation input terminal 13. The output of the modulation circuit 12 is added to the output of the second driver 11 and supplied to the semiconductor laser 1 to drive the semiconductor laser 1.

6A shows the optical output level of the semiconductor laser 1 driven as described above, and FIG. 6B shows the current flowing through the semiconductor laser 1. In the figure, I _SIG is the current driven by the first driver 10, and I _DC is the second
This is the current driven by the driver 11 of. When the set reference voltage at the input terminal 7 of the first amplifier 6 is changed, only the high level is changed, and when the set reference voltage at the input terminal 9 of the second amplifier 8 is changed, only the low level can be changed. .

In such a conventional semiconductor laser drive circuit, it is necessary to set a large current variable range of each of the drivers 10 and 11 in order to correspond to recording / reproducing conditions of various optical recording media.

[Problems to be solved by the invention]

Since the conventional semiconductor laser drive circuit is configured as above, the maximum current value I of each driver is
_{SIG (max),} the total of I _{DC (max)} becomes a current value exceeding the absolute maximum rating of the emission power of the semiconductor laser, when expired systems rise time and the driving circuit of the circuit, it exceeds the rating of the semiconductor laser , Shorten the life of the semiconductor laser,
There were problems such as destruction.

The present invention has been made in order to solve the above-mentioned problems, and does not exceed the absolute maximum rating of the semiconductor laser even when the circuit is started up or is erroneously set. It is an object of the present invention to provide a semiconductor laser drive circuit that can be used with peace of mind without worrying about deterioration or destruction.

[Means for solving problems]

A semiconductor laser drive circuit according to the present invention includes a current detection circuit for detecting a current value driven by either one of a first driver and a second driver among currents flowing through a semiconductor laser, and a first or second driver. A current limiting circuit for limiting the current driven by the other driver by the output of the current detecting circuit, and driven by the other driver of the first or second drivers according to the output value of the current detecting circuit. It is configured so that the limit value of the generated current can be controlled.

[Action]

In the semiconductor laser drive circuit according to the present invention, the current detection circuit that detects the current value driven by one driver controls the limit value of the current driven by the other driver by the obtained output value. The total current flowing through the laser does not exceed a preset value, preventing damage to the semiconductor laser.

〔Example〕

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

In the description of this embodiment, the same or corresponding parts as those in FIG. 5 showing the conventional technique are designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 is a block diagram showing the basic configuration of an embodiment of the present invention. In the figure, 21 is the second driver 11
A current detection circuit for detecting the value of the current I _DC driven by, 22 is the current I driven by the first driver 10.
It is a current limiting circuit that limits _SIG . The current limiting circuit 22 is inserted between the first amplifier 6 and the first driver 10 and uses the output of the current detection circuit 21 as a control input.

FIG. 2 is a circuit diagram showing a part of the concrete circuit of the embodiment shown in FIG. 1. In the figure, the portions corresponding to the block elements shown in FIG. ing.

The current detection circuit 21 is composed of a resistor R1 connected between the emitter of the output transistor Q1 of the second driver 11 and the power supply, and the current limiting circuit 22 is the output terminal of the first amplifier 6 and the input of the first driver 10. The resistor R2 is connected between the terminals, and the diode D is connected between the input terminal of the first driver 10 and the output transistor Q1 of the second driver 11.

Next, the operation of the embodiment shown in FIGS. 1 and 2 will be described.

In the normal operation, the semiconductor laser 1 emits light and is controlled according to the reference voltage set to the input terminals 7 and 9 of the first amplifier 6 and the second amplifier 8 as in the conventional example.

Next, the case where the system is cut off during abnormal operation, for example, when the power is turned on or the emitted light of the semiconductor laser 1 does not return to the photodiode 2 will be described.

First, Fig. 3 (a) shows the input voltage V _H , V _L vs. output current I _SIG , I _DC characteristics of the first driver 10 and the second driver 11.
It shows in (b). In the figure, the output currents I _SIG and I _DC do not increase even if the input voltages V _H and V _L are increased, because they are limited by the power supply voltage of the circuit and the saturation of the transistors.
The currents at that time are I _{SIG (max)} and I _{DC (max)} . conventionally,
During abnormal operation, the total of the currents I _{SIG (max)} and I _{DC (max)} flows into the semiconductor laser 1 and the rating I of the semiconductor laser 1
_The semiconductor laser 1 was deteriorated or destroyed beyond the _{LD (max)} .

In this embodiment, when a voltage applied to the input of the second driver 11, the output current I _DC flows through the semiconductor laser 1. This current value is taken out by the current detection circuit 21 as a voltage and input to the current limiting circuit 22 as a control input voltage. The output voltage of the first amplifier 6 is input to the input terminal of the current limiting circuit 22, and in the voltage range lower than the control input voltage, the output current I of the first driver 10 is proportional to the input voltage.
_SIG will increase. However, when it becomes higher than the control input voltage, the output voltage of the current limiting circuit 22 becomes constant and the output current I _SIG of the first driver 10 is limited. As the output current I _DC of the second driver 11 increases, the control input voltage of the current limiting circuit 22 decreases, so that the first driver 10
The output current I _SIG limit value I _{SIG (LIMT)} also decreases.

Explaining with reference to FIG. 2, when a voltage is applied to the input of the second driver 11, an output current I _DC flows, and the terminal voltage V _I of the resistor R1 of the current detection circuit 21 is V _I = V _CC −R _I・ I _DC .

On the other hand, the first driver 10 side is proportional to the input voltage in the range in which the contact voltage between the resistor R2 of the current limiting circuit 22 and the diode D is driven at a voltage lower than V _I +0.6 [V]. Then, the output current I _SIG increases. However, when the contact voltage becomes V _I +0.6 [V], the diode D conducts, and the contact voltage does not rise above V _I +0.6 [V] and I _SIG
Is constant and limited.

Since the terminal voltage V _I of the resistor R1 decreases as the output current I _DC of the second driver 11 increases, the voltage V _I +0.6 [V] that limits the current of the first driver 10 also decreases and the output The limit value I _{SIG (LIMT) of the} current I _SIG will also be lowered.

The maximum current value flowing through the semiconductor laser 1 is the sum of the maximum current _{IDC (max) of} the second driver 11 and the limit value I _{SIG (LIMT)} of the output current of the first driver 10, and this value is the semiconductor laser. The semiconductor laser 1 is prevented from being deteriorated or destroyed by making it smaller than the maximum rated current I _{LD (max) of} 1.

FIG. 4 (a) shows the relationship between the input voltage V _L of the second driver 11 and the current I _LD of the semiconductor laser 1 of the conventional example.
Figure (b) shows the input voltage of the second driver 11 of this embodiment.
The relationship between V _{L and} the current I _LD of the semiconductor laser 1 is shown. In the figure,
The maximum current I _{SIG (max)} is being supplied by the first driver 10.

Although the current limiting circuit 22 is inserted in the first driver 10 side in the above embodiment, the current limiting circuit 22 may be provided in the second driver 11 side, on the contrary.

〔The invention's effect〕

As described above, according to the present invention, the current detection circuit that detects the current value driven by one of the first and second drivers and the other of the first and second drivers A current limiting circuit that limits the current driven by the driver by the output from the current detecting circuit is provided, and the limit value of the current driven by the other driver is controlled according to the output value of the current detecting means. Therefore, an overcurrent that exceeds the absolute maximum rating does not flow in the semiconductor laser, and there is an effect that it can be used safely without worrying about deterioration or destruction.

[Brief description of drawings]

FIG. 1 is a block diagram showing a semiconductor laser drive circuit according to an embodiment of the present invention, FIG. 2 is a specific circuit diagram of a part of the embodiment shown in FIG. 1, and FIG. 3 (a) is a first driver. Input voltage vs. output current characteristic diagram, FIG. 3 (b) is an input voltage vs. output current characteristic diagram of the second driver, FIG. 4 (a)
Is a conventional input voltage-semiconductor laser current characteristic diagram of the second driver, FIG. 4 (b) is an input voltage-semiconductor laser current characteristic diagram of the second driver of the embodiment, and FIG. 5 is a conventional semiconductor laser FIG. 6A is a block diagram showing a driving circuit, FIG. 6A is a light output waveform diagram of a semiconductor laser, and FIG.
FIG. 3 is a waveform diagram showing a current flowing through a semiconductor laser. 1 is a semiconductor laser, 2 is a photodiode, 3 is a current / voltage conversion circuit, 4 is a first peak hold circuit, 5 is a second peak hold circuit, 6 is a first amplifier, and 7 is a first input terminal. , 8 is a second amplifier, 9 is a second input terminal, 10 is a first driver, 11 is a second driver, 12
Is a modulation circuit, 13 is a modulation input terminal, 20 is a photoelectric conversion circuit,
21 is a current detection circuit and 22 is a current limiting circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A photoelectric conversion circuit for converting an optical output of a semiconductor laser into a voltage signal and outputting the voltage signal, and one of a high level peak and a low level peak of an output voltage of the photoelectric conversion circuit. A first peak hold circuit for holding, a second peak hold circuit for holding the other of the high level peak or the low level peak of the output voltage of the photoelectric conversion circuit, and the first peak hold circuit A first amplifier for controlling the output voltage to be equal to the first reference voltage, and a second amplifier for controlling the output voltage of the second peak hold circuit to be equal to the second reference voltage. Amplifier, a first driver that receives the output of the first amplifier to form a drive current, and a second driver that receives the output of the second amplifier to form a drive current. A bar and a modulation circuit that modulates and outputs one of the outputs of the first and second drivers according to a modulation input, and outputs the output of the first or second driver. In the semiconductor laser drive circuit of the optical recording / reproducing apparatus, the other output and the output of the modulation circuit are given to the semiconductor laser to emit light, and recording and reproduction are performed by the semiconductor laser.
A current detection circuit for detecting an output current of one of the first and second drivers, and an output current from the other driver of the first and second drivers according to the output of the current detection circuit. And a current limiting circuit for limiting the current.