JPS60187074A - Automatic light quantity control circuit of laser diode - Google Patents

Abstract

PURPOSE:To operate the titled circuit at constant light quantity with a simple circuit constitution by a method wherein a Zener diode is connected between a base of P-N-P transistor the emitter of which is connected to positive polarity power supply and an output terminal of processing amplifier. CONSTITUTION:When light quantity radiated from a laser diode LD is reduced corresponding to the ambient temperature rise, monitor current IM is reduced to lower the positive polarity power supply +V side potential of a processing amplifier 14 seen from a negative polarity power supply -V resultantly lowering the potential at the output terminal end of the amplifier 14. Therefore, the base current IB of a P-N-P transistor 12 is increased to increase the driving current IL of LD resultantly increasing the light quantity radiated from LD. Besides, when only the voltage from power supply +V is supplied and the voltage from power supply -V is not supplied, the current IB is not supplied, resultantly the current IL is not supplied at all by means of providing a Zener diode Z with Zener voltage almost equivalent to the voltage with the larger absolute value out of power supply +V, -V between a base of TR12 and an output terminal of the amplifier 14.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an automatic light amount adjustment circuit for a laser diode,
In particular, the present invention relates to improvements in automatic light power control circuits (APCs) for operating laser diodes with constant light power.

The light source of an optical pickup (hereinafter referred to as optical PU) used to optically extract information from information recording carriers such as video discs (VD) and digital audio discs (DAD) is a laser diode (hereinafter referred to as LD). ) is often used.

The performance required of these light sources is firstly that the temperature of the light is at a point, and secondly that the emitted light be of a single wavelength.
Thirdly, the pattern of emitted light is circular (elliptical), and fourthly, it is stable against external shadows.

However, in general, LDs have a learning point in that the wavelength and optical output vary greatly in response to changes in hybridization.

In other words, as shown in Figure 1, when the horizontal axis is the LD drive current (forward current) and the laser light output is the vertical axis, and the drive current is gradually increased, the light suddenly increases from a certain current value. It exhibits characteristics like a curved body that emits light, and after the light is emitted it becomes 0.
．． A slope of 2 to 0.3 mW/mA increases the light output.

However, when the influence of temperature is added to this relationship, as the temperature increases, the optical output decreases with the same drive current, and as the temperature decreases, the optical output increases. At the same time, the wavelength also changes, but in the operating temperature range of the light P[J mentioned above, it does not change significantly, so the optical output is generally taken up as a bigger problem.

This change in optical output directly results in a change in the gain of the servo and a change in the amplitude of the read signal, which has a negative effect on the optical PU and its surroundings, so it is important to prevent the optical output from changing even if the temperature changes as much as possible. Special measures must be taken.

Due to its structure, an LD emits a laser beam from both sides of a semiconductor chip. The light amounts of the laser beams on both sides are in a proportional relationship. Taking advantage of this, in the optical PU, one of the laser beams is used to read the +kk information, the other is directly received by the photodiode to monitor the output light intensity, and the servo system is configured so that the light intensity is constant. ing. The circuit used for this purpose is the nine APC mentioned above.

In particular, many LDs produced as light sources for optical PUs have a built-in PIN 7 photodiode for monitoring in the same package, and as soon as an APC is connected, the LD can be used as a light source.
It has been devised so that it can be operated with a constant amount of light.

The performance requirements for this person's PC are: firstly, it must always maintain a constant light output even when the external temperature changes, and secondly, since LDs are extremely susceptible to overcurrent, sudden changes in the power supply Do not allow overcurrent to flow through the LD even if there is an interruption. Thirdly, do not allow overcurrent to flow through the LDK even if the power supply voltage is rising or falling. An APC that uses a power source is required to have a function that can protect the LD from overcurrent even when only one side of the power source is turned on.

Generally, the forward current of LD is 50 to 100
mA, and the forward voltage drop is approximately 2V.

That is, the power consumption per unit is about 0.41 to 0.2 W.

If this amount of power is consumed by a semiconductor chip several hundred micrometers square, the temperature rise of the semiconductor chip will be negligible, and as mentioned earlier, LDs may suffer from unstable output due to temperature changes. In addition, the LD semiconductor chip can be mounted directly on the gold JFA package without using an insulator, with sufficient consideration given to the heat dissipation effect.

Furthermore, in order to reduce costs, a PIN photodiode for monitoring is also mounted on the same package, so one electrode of the LD and one electrode of the PIN photodiode for monitoring become a common terminal.

In this case, there is not much difference in the structure of the PIN photodiode, but since there are various differences in the structure of the LD, two types are generally used. That is,
The anode of the LD shown in Figure 2 and the cathode of the PIN 7 Otodiode are common. □The LD shown in Figure 3
There are two types, although the cathode of PIN7 and the cathode of PIN7 Otodiode are common.

In this case, since the monitor PIN7 autodiode is used by applying a negative voltage (reverse bias) to the anode, the one in Figure 3 does not require a power supply with both positive and negative polarities, so the APC is used first. Only the positive and negative power supplies mentioned in
It is required that a function is added to protect the LD even if it becomes NK.

Further, a PIN photodiode also generates an electromotive force when exposed to light without applying a voltage, regardless of the PN junction, and this electromotive force is proportional to the amount of light applied. Therefore, depending on the idea, PIN7 Otodai Auto for monitoring without bias.

At this time, a positive polarity power supply can be used to configure an APC.

However, when the PIN photodiode is used without applying a reverse bias, the only carrier movement is drift (diffusion), so the response frequency is extremely low.
The APC response frequency cannot be set too high.

When using the PIN photodiode ignoring this response frequency, the PIN photodiode may be used as a voltage source or as a current source. In the former case, the linearity of the input and output is guaranteed when the output voltage is approximately 0.4V or less, and since the linearity cannot be obtained with a voltage higher than that, the operational amplifier is used with one side power supply. If the operating point (1
1, half of the source voltage), making circuit configuration extremely difficult. In the latter case, a dedicated operational amplifier is required as a current/voltage conversion circuit, which is disadvantageous in terms of cost.

Generally VD-? DAD players have both positive and negative polarity power supplies inside, so even when using such an LD as a light source, the PIN photodiode is not used without bias, and the APC power supply also has positive and negative polarity power supplies. Power source is used.

Next, the configuration of a conventional APC using a bipolar power source will be explained with reference to FIG.

ν1j, the collector is connected to the positive polarity power supply (10V),
Output 1 NPN transistor (1) as a spike current prevention circuit (1) whose base is connected to the negative polarity power supply (-V)
The emitter of 1□) is connected to the collector of a second NPN transistor (2) for current control, and this second NPN
The emitter of the transistor (2) is connected to the anode of the LD sealed in the package (3) via the first resistor, and the collector and base of the second NPN transistor (2) are connected to the anode of the LD sealed in the package (3). is connected to the resistor (R2). In addition, the anode of the PIN photodiode attached to the package (3) that resonates with the grounded cathode of the LD is connected to the negative terminal of the operational amplifier (4) which uses only the negative polarity power supply (-V). A variable resistor (6) and an operational amplifier (4) are connected between the terminal and the negative power supply (-V).
A reference power source (5) is provided between the positive terminal and the negative power source (-■). Further, the base of the second NPN transistor (2) and the output terminal of the operational amplifier (4) are connected by a third resistor (R, ).

In the laser diode automatic optical iM rectifier circuit consisting of such a circuit 11g, the first NPN) transistor (1
, ) does not generate a spike voltage when the positive polarity power supply (10V) rises suddenly, and only generates a positive polarity power supply when the absolute value of the voltage of the negative polarity power supply (-■) exceeds a certain value. It functions to transmit the voltage of (10■) to the next. The package (3) is a light source in which an LD and a PIN photodiode for monitoring are sealed, and the light output from the LD is the output current of the PIN photodiode, which is 1. is proportional to.

Now, if we consider a case where the ambient temperature drops and the amount of light emitted from the LD increases, as the amount of light increases, the monitor current I will also increase in proportion to the amount of light emitted from the variable resistor (Rv).
The negative polarity power supply (
-V) increases.

The output of the arithmetic intensifier (4) is co=A x (Eg-I, xRv) V/2, where A is the amplification factor.
R8 is the voltage of the reference power source (5).

Now, as IM increases, the output eo of the operational amplifier (4) approaches the potential of the negative power supply. increases, and the second NP
N) Since the base potential of transistor (2) decreases,
The emitter current of the second ONPN transistor (2), that is, the drive current of the LD is reduced, and the light emitted from the LD is also reduced. That is, the amount of emitted light settles to the level before the temperature drops.

However, in this circuit configuration, the spike current prevention circuit (1) including the first ONPN transistor (11) causes a slow start, and the voltage of the positive power supply applied to the collector of the second NPN transistor (2) is negative polarity. It is always applied after the voltage of the 'a source. In other words, when only the voltage of the positive polarity power supply is applied, the LD
A circuit is added to the spike current prevention circuit (1) to prevent the spike current from operating. If there is no circuit to control this, and only the voltage from the positive polarity power supply is applied without the voltage from the negative polarity power supply, the second NPN) transistor (
In case 2), there is no sudden conduction and there is no control by an operational amplifier, so an overcurrent will flow through the LD. Furthermore, there is a problem in that when the power supply is turned on and off, the second NPN transistor (2) suddenly turns on and off, causing a cycle current that may cause damage to the LD.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned nine points, and is an automatic laser diode that can operate an LD with a constant light intensity with a simple circuit configuration and prevents spike currents and overcurrents from flowing to the LD. The purpose of this invention is to provide a light amount adjustment circuit.

[Summary of the invention]

That is, the present invention comprises a PNP transistor whose emitter is connected to a positive power supply via a first resistor, a capacitor and a second resistor interposed between the positive power supply and the base of the PNP transistor. A parallel circuit, a regulated laser diode whose anode is connected to the collector of the PNP transistor, and a PIN7 otodiode that shares the grounded cathode of this regulated laser diode, the cathodes of the PIN photodiodes input to the positive terminals. an operational amplifier whose power source is only the negative polarity power source, a variable resistor installed between the positive terminal and ground, a reference power source installed between the negative terminal of the operational intensifier and the ground, and a PNP) It is equipped with a series circuit of a Zener diode and a third resistor provided between the base of the transistor and the output terminal of the operational amplifier, and the Zener voltage of the Zener diode is the absolute value of the positive or negative polarity power supply voltage. This is an automatic light amount adjustment circuit for a laser diode that is special in that it is set almost equal to a large voltage.

[Embodiments of the invention]

Next, the automatic light amount adjustment circuit (A
An example of the PC) will be explained with reference to FIG.

That is, the collector of the PNP transistor aa whose emitter is connected to the positive power supply (10V) via the first resistor (-) is connected to the anode of the LD sealed in the package (I3) and the PNP transistor is connected to the anode of the LD sealed in the package (I3). The base of the transistor α2 is connected to a capacitor (C) and a second resistor (-) connected in series from a positive polarity power supply (10). In addition, the anode of the PIN7 autodiode enclosed in package a3, which also includes the grounded cathode of the LD, is connected to the positive terminal of the operational amplifier I which uses only the negative polarity power supply (-■), and this positive terminal and the negative polarity A variable resistor is connected between the polarity power supply (-V), and a negative terminal of the operational amplifier ← and the negative polarity power supply (-
A reference power source α [present] is provided between the two terminals V) and V). Furthermore, the base of the transistor (PNP) and the operational amplifier (1
A Zener diode (Z) and a third
A resistor (R3) is provided in series.

With such a circuit configuration, if R2>几, , R2>bird are satisfied, the base current (B) of the PNP transistor α becomes almost equal to the current flowing through the resistor (R2).

Now, if we consider a case where the emitted light from the LD decreases due to a rise in ambient temperature, when the emitted light decreases, the monitor current I,
also decreases, and the operational amplifier (1
4) Since the potential on the positive power supply (+V) side decreases, the potential at the output terminal of the operational amplifier α also decreases, the base current of the PNP transistor α4 increases, and the drive current of the LD increases. However, the amount of emitted light from the LD also increases, returns to the level before the temperature rise, and the emitted light from the LD is kept constant.

Also, if only the voltage from the positive polarity power supply (+■) is applied and the voltage from the negative polarity power supply is not applied, then the positive or negative polarity is connected between the base of the transistor ring and the output terminal of the operational amplifier (PNP). By providing a Zener diode (Z) with a Zener voltage whose absolute value is approximately equal to a large voltage among the voltages of the positive power supplies (+V) and (-V), the current B does not flow, and therefore the current I does not flow either.

In addition, since a capacitor (C') is provided in parallel to the second i resistor 1 (R2), the spike current accompanying the intermittent power supply voltage is reduced by the time constant determined by CxfL3 when the power is turned on. is charged, and after the voltage of (C) exceeds the voltage between the base and emitter of transistor α2 (PNP), lL gradually begins to flow, and only after (C) is sufficiently charged, lL reaches the specified current. and starts operating as an APC. Also, when the power is turned off, the PNP transistor (121) does not turn off suddenly, but the base current gradually decreases due to the time constant determined by Cx.
No spike current occurs.

〔Effect of the invention〕

As mentioned above, the automatic laser diode of the present invention
The t adjustment circuit is composed of a small number of circuit components, and no spike current occurs even when the power supply is interrupted, and when the positive or negative power supply is not connected, no current flows through the LD.
D can be preserved.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the relationship between laser diode drive current and optical output, Figures 2 and 3 are diagrams showing the relationship between laser diode and P
This is a diagram showing the connection of the IN 7 photodiode, Figure 2 is an explanatory diagram showing the state where the anode of the laser diode and the cathode of the PIN 7 photodiode are common, and Figure 3 is the connection between the cathode of the laser diode and the PIN photodiode. FIG. 4 is a wiring diagram of an example of a conventional laser diode automatic light amount adjustment circuit, and FIG. 5 is an example of an embodiment of the laser diode automatic light amount adjustment circuit of the present invention. It is a wiring diagram. 1.2...NPN) transistor 3.13 package 4,14... operational amplifier 5.
15...Reference power supply 6.16...Variable resistor 12...P
NP) transistor Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] a PNP transistor whose emitter is connected to the positive power supply via a first resistor;
NP) A parallel circuit of a capacitor and a second resistor interposed between the bases of the transistor; 1) NP) a diode to be adjusted whose anode is connected to the collector of the transistor; and a laser for adjustment. A photodiode that shares the grounded cathode of the diode, an operational amplifier powered only by a negative power supply whose positive terminal is input to the cathode of the photodiode, and a variable resistor provided between the positive terminal and ground. a reference power supply provided between the negative terminal of the operational amplifier and ground; and a series circuit of nine Zener diodes and a third resistor provided between the base of the PNP transistor and the output terminal of the operational amplifier. The automatic light amount adjustment circuit for a laser diode is characterized in that the Zener voltage of the Zener diode is set to be approximately equal to a voltage having a large absolute value among the voltages of the positive or negative polarity power supply.