JPS60234382A - Power loss stabilizing device for light-receiving element - Google Patents

Abstract

PURPOSE:To hold the power loss in the light-receiving element in a stabilized manner by a method wherein the quantity of light of the light-emitting element is subjected to a load-feedback control according to the current to run on the light-receiving element. CONSTITUTION:The current I to run on a light-receiving element 57 all runs on a load resistor RL, as the load resistor RL has a resistance lower sufficiently than the input impedance of an arithmetic amplifier 58. The voltage V of this load resistor RL is represented by a formula of V=IXRL. The difference between the reference voltage Vref and the voltage V of the load resistor RL is amplified in the arithmetic amplifier 58 and a control elemnt 54 is controlled by the output signal of the arithmetic amplifier 58. Accordingly, the current to run on a light-emitting element 53 is changed and the quantity of light emission is controlled so that the power loss in the light-emitting element 57 becomes constant. As a result, even in the case of the deterioration of the light-emitting element 57 and in the case when a shield is made to interpose between the light- emitting element and the light-receiving element and the quantity of incident light of the light-receiving element is changed, the power loss is automatically held at constant value, and moreover, manual adjustment is unnecessitated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a device for stabilizing power loss of a light-receiving element, which is applied to, for example, a life test of a runnostar, a photodiode, and the like.

[Technical background of the invention and its problems]

A life test of a light receiving element includes a test in which the power loss of the light receiving element is kept constant for a long period of time, and the initial characteristics are compared with the characteristics after being left unused.

FIGS. 1 and 2 show the conventional configuration of the above test. In FIG. 1, a light emitting element 11 and a variable resistor RF are connected in series between a power supply vcc1 and ground, and a power supply ■. Between c2 and ground is a light receiving element 12 facing the light emitting element 11.
and resistor R1 are connected in series. In FIG. 2, unlike FIG. 1, the resistor RE is fixed and the resistor 9 is variable. Figure 3 and Figure 4 are respectively Figure 1 and Figure 4.
This shows the specific circuit in Figure 2, and Figures 3 and 4.
In the figure, a light emitting diode is used as the light emitting element 11, and a phototransistor is used as the light receiving element 12. In such a configuration, when performing a life test, in FIGS. 1 and 3, the power loss of the light receiving element 12 is adjusted by varying the variable resistance RF on the light emitting side.
In FIGS. 2 and 4, after the power loss of the light receiving element 12 is adjusted by varying the variable resistor RL, the light receiving element 12 is left as it is for a long period of time.

By the way, in the above conventional life test, the light receiving element 1
After adjusting the power loss of 2 at the beginning of the test, it is rarely adjusted again. Therefore, during the test, the amount of light emitted from the light emitting element 1 changes due to changes in temperature, etc. If a shielding object such as dust enters between the light emitting element 1 and the light receiving element 12, the amount of light emitted from the light receiving element 12 changes. The problem is that the power loss varies.

Further, the power loss adjustment described above is performed manually each time the light receiving element is replaced, and furthermore, it is necessary to calculate the loss at that time. That is, the power loss of the light receiving element P = IoXVc, = IoX (V, , c2 - RLXIC)
However, (2, ■C: Current Vo□ flowing through the light-receiving element; determined by the voltage applied to the light-receiving element. In the case of Figures 1 and 3, the current Tc varies depending on the amount of light received.
1 voltage V. Since the value changes, it is necessary to perform calculations to account for losses. In the case of Figures 2 and 4, the current I flowing through the light receiving element is due to the sensitivity error of the light receiving element and the light amount error of the light emitting element.
. are different.

Therefore, the variable resistor RL is changed to obtain the voltage ■. is changing. The I--characteristic of the light-receiving element depends on the voltage V, and in this case as well, it is necessary to calculate the product of I and (2) in the set state. As described above, conventional devices have had various problems.

[Purpose of the invention]

This invention was made based on the above circumstances, and its purpose is to prevent the light emitting element from deteriorating or when a shielding object is interposed between the light emitting element and the light receiving element, and the amount of light incident on the light receiving element changes. The present invention also aims to provide a power loss electrification device for a light-receiving element in which the power loss is automatically maintained constant and does not require adjustment upon acquisition.

[Summary of the invention]

This invention maintains the power loss of the light receiving element constant by negative feedback controlling the light amount of the light emitting element according to the current flowing through the light receiving element. Examples will be described with reference to the drawings.

In FIG. 5, a light emitting element 53 is connected between connecting terminals 51 and 52, and a power source V is connected to this connecting terminal 51. 1
is connected. VtC between the connection terminal 52 and ground,
A control element 54 made of, for example, a current control element is connected thereto. On the other hand, a light receiving element 57 as an Fi test object is connected between the connecting terminals 55 and 56, and a power source VC2 is connected to the connecting terminal 55. A load resistor RL is connected between the connection terminal 56 and ground. An inverting input terminal of an operational amplifier 58 is connected to the connection point between the load resistor 9 and the connection terminal 56. A power supply 59 that generates a reference voltage vref is connected between the non-inverting input terminal of the operational amplifier 58 and the ground.
is connected, and the output terminal of this operational amplifier 58 is connected to the control element 54.

The operation in the above configuration will be explained. Light receiving element 57
Since the load resistance is sufficiently lower than the input impedance of the operational amplifier 58, all of the current flowing to RL flows to RL.

The voltage V of this load resistance RL is V=IXRL (1). The operational amplifier 58 amplifies the difference between the reference voltage vref and the voltage V across the load resistor 9, and the control element 54 is controlled by the output signal of the operational amplifier 58. Therefore, the light emitting element 53
The current flowing through the light emitting element 57 is changed, and the amount of light emitted is controlled so that the power loss of the light emitting element 57 is constant. For example, the light receiving element 5
When the current (light-receiving current) flowing through 7 is I+Δ, the conditions for each part are as shown in the table below.

K, which changes the amount of surface light, can be dealt with by changing the output voltage of the operational amplifier 58. In other words, the amount of light E is the output voltage of the Eoc operational amplifier, ', E = α · A (Vret'') -- (2). However, A is the amplification degree of the operational amplifier, and α is the proportionality constant. Considering the relationship between the table and equation (2) and the change in light amount, we get ΔE=-αAΔV (3). (3)
Transforming the equation using equation (1), ΔE−−αARL×
ΔI ・mm・ (4) According to equation (4), υ, the light receiving current is Δ■
If the amount of light E is increased by the amount of light E, the amount of light E will be attenuated. That is, the light emitting element 53 is controlled by negative feedback so as to suppress changes in the light receiving current.

Still, the power loss P of the light receiving element 57 is expressed as P=IX(Vc2-V)...=-(5). Generally, when the gain A of the operational amplifier is sufficiently large, the voltage between both input terminals of the operational amplifier is very small, and the following relationship holds: Vref-V (6). From equation (6), equation (5) becomes P=I
X (VC2-Vr,,)...(7). On the other hand, the light receiving electrician is calculated by equations (1) and (6).
RL=Vref. Substituting equation (8) into equation (7), the light receiving element 57
The power loss P is as follows. Equation (9) is ■. 2 is a fixed power supply, the stain force loss can be determined by the reference voltage vre and the load resistance R07.

FIG. 6 shows a specific example of the circuit shown in FIG. A light emitting diode is used as the light emitting element 53, and a phototransistor is used as the light receiving element 57.

A transistor is used as the current control element 54. The collector of the transistor 54 is connected to the connection terminal 52 via a resistor 61, and the emitter is grounded.

Further, the base is connected to the output terminal of the operational amplifier 58 via a resistor 62. A capacitor 63 for preventing oscillation is connected between both input terminals of this operational amplifier 68, and the non-inverting input terminal is grounded. Furthermore, the load resistor is connected between the connection terminal 56 and the power supply -V.

Incidentally, the distance between the light emitting diode 53 and the phototransistor 57 is set to a minimum of four meters, and the terminal 64 is used for voltage monitoring.

According to the embodiment described above, the current flowing through the light receiving element 57 is detected, and the amount of light emitted from the light emitting element 53 is controlled by negative feedback in accordance with the amount of change in the detected current.

Therefore, even if the light emitting element 53 deteriorates or if a shielding object such as dust is present between the light emitting element 53 and the light receiving element 57 and the amount of light incident on the light receiving element 57 changes, the power loss is automatically kept constant. Since it is retained, it is extremely convenient to apply to the life test of the light receiving element 57.

Further, since the power loss of the light receiving element 57 is uniquely determined by the load resistance 9 and the reference voltage vref, there is an advantage that adjustment is not required every time the light receiving element 57 as the test object is replaced.

Although the current control element is used as the control element 54 in the above embodiment, the present invention is not limited to this, and the voltage control element may be used as the light emitting element 5.
3 may be connected in parallel.

Furthermore, although the photodetection current was detected using resistor 9, a diode may be used in place of resistor 9.

It goes without saying that other modifications can be made without departing from the gist of the invention.

〔Effect of the invention〕

As detailed above, according to the present invention, power loss is automatically kept constant even when the amount of light incident on the light receiving element changes due to deterioration of the light emitting element or a shielding object is interposed between the light emitting element and the light receiving element. Therefore, it is possible to provide a device for stabilizing the power loss of a light-receiving element, which is maintained at a constant value, and which is difficult to manually adjust.

[Brief explanation of drawings]

Figures 1 and 2 are block diagrams schematically showing conventional life test equipment for light-receiving elements, Figures 3 and 4 are circuit diagrams of Figures 1 and 2, respectively, and Figure 5 is FIG. 6 is a schematic configuration diagram showing an embodiment of the power loss stabilizing device for a light receiving element according to the present invention, and FIG. 6 is a circuit configuration diagram specifically showing FIG. 5. 53... Light emitting element, 54... Control element, 57... Light receiving element, 58... Operational amplifier, RL... Resistor, Vr,
,,,. Reference voltage. Figure 1 Figure 2 Figure 3 Figure 4

Claims (6)

[Claims] (1) A light-emitting element, a light-receiving element disposed opposite to the light-emitting element, means for detecting a light-receiving current of the light-receiving element, and a means for detecting a light-receiving current of the light-receiving element; 1. A device for constant power loss of a light-receiving element, comprising means for controlling the amount of light emitted by negative feedback. (2) The device for stabilizing power loss in a light receiving element according to claim 1, wherein the means for detecting the light receiving current comprises a resistor. (3) The means for controlling the amount of light emitted by the light emitting element by negative feedback includes a control element connected to the light emitting element and an amplifier that amplifies the detected change in the light receiving current and controls the control element. A power loss equalizing device for a light receiving element according to claim 1. (4) The power loss stabilizing device for a light receiving element according to claim 3, wherein the control element is a current control element. (5) The power loss stabilizing device for a light receiving element according to claim 3, wherein the control element is a voltage control element. (6) Claim 3, wherein the amplifier is an operational amplifier to which a reference voltage is supplied to one input terminal.
A power loss constant device for a light-receiving element as described in 1.