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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.
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What are Form A contacts and Form B contacts in a photorelay? Also, what are A, B, and C connections? What is the difference?

Form A contact, Form B contact

<Form A contact, Form B contact>

For Form A contacts, the output side is turned on while a current at a certain level or higher flows at the input side. This type of contact is also referred to as "Normally open".
For Form B contacts, the output side is in the Off-state while a current at a certain level or higher flows at the input side, and the output side turns into the On-state when a current at the input side comes to a certain level or lower. This type of contact is also referred to as "Normally closed".

Form A connection, Form B connection, and Form C connection

<A connection, B connection, and C connection>

In A connection, both AC and DC load currents can be handled, and in B and C connections,  DC load currents can be handled. In A connection, photorelays can also be used without AC signal switch and polarity. In C connections, since MOSFETs are connected in parallel, compared with A connections, DC load currents twice as large can be handled.

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