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About information presented in this cross reference

The information presented in this cross reference is based on TOSHIBA's selection criteria and should be treated as a suggestion only. Please carefully review the latest versions of all relevant information on the TOSHIBA products, including without limitation data sheets and validate all operating parameters of the TOSHIBA products to ensure that the suggested TOSHIBA products are truly compatible with your design and application.
Please note that this cross reference is based on TOSHIBA's estimate of compatibility with other manufacturers' products, based on other manufacturers' published data, at the time the data was collected.
TOSHIBA is not responsible for any incorrect or incomplete information. Information is subject to change at any time without notice.

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Why is a photocoupler necessary?

1. Connecting circuits with different ground potentials

For example, when signals are exchanged between a circuit running with an AC line power supply and a telephone circuit, since their earth ground potentials are different, they cannot be connected to a common ground. Photocouplers are used for signal transmission to circuits with different ground potentials as these.

2. Preventing influence of common-mode noise

For example, when it is desired to control a large load, such as a motor and a solenoid, using a microprocessor operated based on weak signals, large common-mode noise produced by such a load may badly affect the operation of the microprocessor via the ground line. In such a case, by using a photocoupler capable of electrical separation, malfunction can be prevented.

3. Safety of the human body

Home electronics products are powered from the AC power line, and safety must be secured to prevent the human body from directly contacting this AC power line. Safety standards are defined in each country and it is compulsory for products to comply with such standards. For the purpose of electrical isolation such as electrical shock prevention, a photocoupler can be used as a safety standards-compliant component.