JP2002171163A - Photoelectric sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric sensor which enables stable detection independently of a supplied power source voltage while restraining a consumption current of the whole circuit. SOLUTION: A projecting and receiving light circuit is constituted by connecting a light projecting element 10, a power source part 30 and a light receiving circuit 40 in series between a power source input terminal 1 and a ground terminal 2. A constant current circuit 20 is connected in series with the light projecting element 10 between the power source input terminal 1 and the power source part 30. Since the light projecting element 10 is connected in series with the light receiving circuit 40, a consumption current of the whole circuit can be restrained. The light projecting element 10 is driven by a prescribed constant current by the constant current circuit 20 independently of a power source voltage, so that the amount of a projection light is stabilized. Thereby stable detection is enabled while restraining the consumption current of the whole circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device, a light receiving circuit, and a constant voltage section for supplying a constant voltage to the light receiving circuit, which are connected in series between a power input terminal and a ground terminal. A photoelectric sensor.

[0002]

2. Description of the Related Art A conventional two-wire photoelectric sensor is disclosed in
No.-2131, a light projecting element and a light receiving circuit are connected in series to a DC power supply (see FIG. 3). This eliminates the need to supply a current to each of the light emitting element and the light receiving circuit, so that the current consumption of the entire circuit can be reduced.

[0003]

Generally, in a photoelectric sensor, the allowable range of the power supply voltage has a certain width of, for example, 12 to 24 V. However, in the conventional configuration described above,
If the power supply voltage is different, the current flowing into the circuit will be different, so that the light emission current supplied to the light emitting element will also be different according to the power supply voltage. For this reason, the amount of projected light differs depending on the power supply voltage, and there is a disadvantage that stable detection cannot be performed.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a photoelectric sensor capable of performing stable detection regardless of a supplied power supply voltage while suppressing current consumption of the entire circuit. To provide.

[0005]

According to a first aspect of the present invention, there is provided a photoelectric sensor according to the first aspect of the present invention, wherein a light emitting element, a light receiving circuit, and the light receiving circuit are provided between a power input terminal and a ground terminal. A constant current circuit that supplies a constant current to the light emitting element, between the power input terminal and the constant voltage unit, in a photoelectric sensor formed by serially connecting a constant voltage unit that supplies a constant voltage power to the photoelectric sensor. The feature is that it is arranged in series with the light emitting element.

[0006]

According to the first aspect of the present invention, since the light emitting element and the light receiving circuit are connected in series, the current consumption of the entire circuit is reduced as compared with the case where the light emitting element and the light receiving circuit are connected in parallel. Can be suppressed. Here, since the light emitting element is driven by the constant current circuit, it is driven by a predetermined light emitting current regardless of the power supply voltage, so that the projected light amount is stabilized. This enables stable detection while suppressing current consumption of the entire circuit.

[0007]

1 and 2 show an embodiment of the present invention.
It will be explained by. The photoelectric sensor, as shown in FIG.
A light-emitting element 10 composed of, for example, an LED, a power supply unit 30, and a light-receiving circuit 40 are connected in series between the power input terminal 1 and the ground terminal 2. A light emitting and receiving circuit in which a constant current circuit 20 is arranged in series with the light emitting element 10 is provided therebetween.

An FET 11 is connected to the light projecting element 10 in parallel. This operates so that a substantially constant drain current flows through the constant current circuit 20 irrespective of the load voltage (drain-source voltage). The constant current circuit 20 includes two transistors T1 and T2 and a resistor R1. The transistor T1 is connected so that, when the drain current of the FET 11 flows to the base, the collector current is taken from the output terminal of the light emitting element 10 and the emitter current flows to the resistor R1. On the other hand, when the emitter current of the transistor T1 flows through the base of the transistor T2,
It is connected so that a part of the drain current from the FET 11 is taken in as a collector current and an emitter current flows to the power supply unit 30.

The power supply unit 30 is a so-called constant voltage circuit, and supplies power having a predetermined voltage value to the light receiving circuit 40 (light receiving element) and the like regardless of the voltage of the power supply. Specifically, for example, 5 V is supplied as a drive voltage for driving an electronic component such as a transistor. The light receiving circuit 40 includes a light receiving element 41 composed of, for example, a photodiode and an OP amplifier 4.
2, the comparator 43, and the output transistor 44. The light receiving element 41 is disposed between the output terminal of the power supply unit 30 and the ground terminal 2. OP amplifier 42
The output terminal of the light receiving element 41 is connected to its input terminal, and the input terminal of the comparator 43 is connected to its output terminal. The output terminal of the comparator 43 is connected to the output transistor 44.

The operation of the photoelectric sensor having the above configuration will be described. When the power supply voltage Vcc is supplied to the light emitting / receiving circuit, the light emitting element 10 emits light. Of the light, the light received by the light receiving element 41 is amplified by the OP amplifier 42 as a light receiving signal corresponding to the light amount, and is compared with the reference voltage Vref by the comparator 43. Here, the reference voltage Vref is set to, for example, a light receiving signal level when a detected object does not exist. Therefore, when there is no detected object, the output transistor 44 is not driven. However,
When the detected object is present, the amount of light received by the light receiving element 41 decreases, and the light receiving signal level becomes equal to the reference voltage Vre.
The voltage f drops below f, and the comparator 43 and, consequently, the output transistor 44 are driven. The reference voltage Vr
ef can be created by another power supply circuit (not shown) based on the output of the power supply unit 30, for example.

Here, in the constant current circuit 20, the resistance R
Since the potential at both ends of 1 becomes the potential Vbe between the base and the emitter of the transistor T2, a fixed current Ir (Vbe / R1) flows regardless of the power supply voltage. Since the base current of the transistor T2 is extremely small, the emitter current of the transistor T1 and the current Ir can be regarded as equivalent. Also in the transistor T1, the base current is extremely small, so that the collector current and the emitter current are almost equal. Therefore, the light emitting current flowing through the light emitting element 10 is such that the collector current of the transistor T1 = emitter current = current Ir (Vbe / R1), and has a constant current amount regardless of the power supply voltage Vcc.
Note that, as shown in FIG. 2, even if the light projecting element is connected in series to the FET 11, the same effect as described above can be obtained.

As described above, the light emitting element 10 and the light receiving circuit 40
Are connected in series, the current consumption of the entire circuit can be suppressed. In addition, the light emitting element 10 is driven by the constant current circuit 20 at a predetermined constant current regardless of the power supply voltage, so that the projected light amount is stabilized. This makes it possible to perform stable detection while suppressing the current consumption of the entire circuit.

<Other Embodiments> The present invention is not limited to the above embodiments. For example, the following embodiments are also included in the technical scope of the present invention.
In addition to the following, various changes can be made without departing from the scope of the invention. (1) In the above embodiment, the constant current circuit 20 is composed of the transistors T1 and T2 and the resistor R1, but is not limited to this. For example, a constant current circuit using an IC (operational amplifier) or a constant current circuit using a Zener diode is used. There may be.

(2) In the above embodiment, the light projecting element 10 emits light at a constant current by the constant current circuit 20. However, for example, even if the light is pulsed by a switch circuit, the effect of the present invention can be achieved. Play.

[Brief description of the drawings]

FIG. 1 is a light emitting and receiving circuit diagram of a photoelectric sensor according to an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram thereof.

FIG. 3 is a circuit diagram of a light emitting and receiving circuit of a conventional photoelectric sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Power input terminal 2 ... Grounding terminal 10 ... Light emitting element 20 ... Constant current circuit 30 ... Power supply part 40 ... Light receiving circuit

Claims (1)

[Claims] 1. A photoelectric sensor comprising a light-emitting element, a light-receiving circuit, and a constant-voltage unit for supplying a constant voltage to the light-receiving circuit in series between a power input terminal and a ground terminal. A photoelectric sensor, wherein a constant current circuit for supplying a constant current to the light emitting element is arranged in series with the light emitting element between the power input terminal and the constant voltage section.