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What is a photocoupler?

Latest Updated:10/01/2007

Question:

What is a photocoupler?

Answer:

A photocoupler is a type of optical junction element that combines a light-emitting element and a light-receiving element in one package. (Figure 1 shows an example of a cross-section of a Renesas Electronics photocoupler, and Figure 2 shows a sample internal perspective diagram.) Another type of integrated product is a photo interrupter (which features a light-emitting element and a light-receiving element placed facing each other, so that object detection is performed when an object passes between the two elements and blocks off the light).
Generally, a LED is used as the light-emitting element, and a photo transistor, photo MOSFET, or photo IC is used as the light-receiving element. Depending on the light-receiving element that is used, there are types of a photo transistor output, optical MOSFET output, photo IC output, and so on.
Figure 3 shows several equivalent circuits.

<Features>
A photocoupler has the following features because of exchanging electrical signal into optical signal for transmission.

(1) Discrete insulation can be achieved electrically between the input and output.

(2) Electrical signals from DC to high frequency can be transmitted and the transmission is one-way as well.

(3) Compact compared to relays, etc.


Renesas Electronics manufactures a wide range of photocouplers, including photo transistor outputs, optical MOSFETs, and photo IC outputs.

Figure 1.  Photocoupler Cross-Section Diagram


Figure 2.  Sample Internal Perspective Diagram of Photocoupler


Figure 3.  Photocoupler Types

Suitable Products
Photocouplers / Optocouplers