JPH02168678A - Photocoupler - Google Patents

Abstract

PURPOSE:To prevent the malfunction of a photocoupler without adding any external circuit which can raise the threshold voltage of malfunctions to noise of a different phase by connecting a plurality of light emitting elements between input terminals. CONSTITUTION:This photocoupler is provided with three light emitting diodes 1A-1C connected in series between input terminals TI1 and TI2 and a phototransistor 2 which converts received rays of light from the diodes 1A-1C into electric signals and outputs the electric signals to output terminals TO1 and TO2 and the diodes 1A-1C and transistor 2 are housed in a container 3 so as to prevent light getting into and leaking out of the container 3. Therefore, no malfunction take place even when noise of a different phase is inputted between the input terminals TI1 and Tl2 to nearly 3.3V when the voltage VP necessary for the light emitting operation of each diode 1A-1C is 1.1V. Namely, the threshold voltage of malfunctions can be raised against noise of a different phase.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a photocoupler, and particularly to a photocoupler used for improving out-of-phase noise characteristics.

[Conventional technology]

The configuration of a conventional photocoupler is shown in FIG.

This photocoupler has input terminals T1. , one light emitting element 6 connected between TI2 and the output terminal T○1. One light-receiving element 7 connected between To2 is assembled into one container 3B, and input terminals T1. , T1. The configuration is such that electrical signals from the terminals are transmitted to the output terminals TO, ,'ro2.

In the photocoupler, the light emitting element 6 has an input terminal 'rr,
, 'r, x2 Since the light emission changes only in response to the current flowing due to the out-of-phase signal input to the input terminal T I 1
, T I 2 can be removed. Therefore, photocouplers have excellent common-mode noise characteristics and are widely used for purposes such as noise removal, level conversion, and high-voltage insulation.

The light emitting element 6 of this photocoupler is made of AJ2GaAs.
, GaAs, GaAsP, or the like are used, and the voltage (P) required to cause these light-emitting diodes to emit light is usually as low as 1.1 to 1.6V.

[Problem to be solved by the invention]

The conventional photocoupler described above is composed of one light-emitting element 6 and one light-receiving element 7, and the voltage VP required to cause the light-emitting element 6 to emit light is usually 1.1 to 1.6V, which is a low input terminal. When out-of-phase noise higher than the voltage VF is input to TTI and TI2, the light emitting element 6 changes its light emission and malfunctions.

In order to compensate for this drawback, it is common practice to add an external circuit such as a resistor to the outside of the photocoupler to increase the voltage V required to cause the light emitting element 6 to emit light. However, there is a drawback that the area on the mounting board increases due to the external circuit.

An object of the present invention is to provide a photocoupler that can prevent malfunctions due to out-of-phase noise without adding an external circuit.

[Means to solve the problem]

The photocoupler of the present invention includes a plurality of light emitting elements connected in series between input terminals, each of which emits light when a predetermined voltage is applied thereto, and a light receiving element that receives light from each of these light emitting elements and converts it into an electrical signal. It has

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

In this embodiment, three light emitting diodes I~1c and these light emitting diodes IA~1c are connected in series between the input terminals T r t and T I2, each of which emits light when a predetermined voltage is applied thereto. The phototransistor 2 receives the light from 1c, converts it into an electric signal, and outputs it to the output terminal TO3T02.

Each of these light emitting diodes IA to 1o is arranged so that the emitted light reaches the light receiving surface of the phototransistor 2, and these light emitting diodes IA... It is housed in a container 3 to prevent light leakage.

In this embodiment, input terminals T1. Since three light emitting diodes IA-1c are connected in series between the input terminals T I 1. T
Malfunction does not occur even if out-of-phase noise of up to nearly 3.3 V is input between I2, that is, the threshold voltage for malfunction with respect to out-of-phase noise can be increased.

FIG. 2 is a circuit diagram showing a second practical example of the present invention.

In this embodiment, input terminal T1. , TI2, three light emitting diodes IA to 1c are connected in series, and a third input terminal TI connected to the connection point of the light emitting diode IB and IC is provided, and these inputs can be adjusted according to external circuit conditions, etc. Terminal T1. ~TI, and the number of light emitting diodes is 1.
It has the advantage that it can be selected from three types: 1, 2, and 3.

Further, in this embodiment, the light receiving portion is constituted by a photodiode 4 for receiving light and a transistor 5 for amplifying the output signal of the photodiode 4, thereby increasing the sensitivity.

Note that in these embodiments, the input terminal TI.

Although the number of light emitting diodes connected in series between T I 2 was set to three, the number can be increased or decreased depending on the operating voltage of the external circuit, the voltage VF necessary for the light emitting operation of the light emitting diodes, etc.

In addition to GaAs, Aj'Ga
As, GaP, GaAsP, etc. may be used, and these may be combined.

〔Effect of the invention〕

As explained above, the present invention has a configuration in which a plurality of light emitting elements are connected in series between input terminals, thereby increasing the threshold voltage for malfunction due to out-of-phase noise. This has the effect of preventing malfunctions without causing any problems.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams showing first and second embodiments of the present invention, respectively, and FIG. 3 is a circuit diagram showing an example of a conventional photocoupler. ■A~1゜...Light emitting diode, 2...Phototransistor, 3, 34.3m...Container, 4...Photodiode, 5...Transistor, 6...Light emitting element, 7
... Light receiving element, T11-TI, ... Input terminal, To
! ~TO3...Output terminal.

Claims (1)

[Claims] It is characterized by having a plurality of light emitting elements connected in series between input terminals, each of which emits light when a predetermined voltage is applied thereto, and a light receiving element that receives light from each of these light emitting elements and converts it into an electrical signal. A photocoupler.