Relays and Optocouplers, Excellent Electronics Lecture by Great Scott

The relay is an electromechanical switch which is used for controlling the circuits.

The most common and basic construction of relay involves a coil and a switch. The coil can be energized to control the behavior of relay.

Difference between NO and NC

Very often the relays use the terms NO and NC with them. The abbreviation NO stands for normally open and it means the relay contacts are not opened when they are not energized. NC or normally closed switches mean that relays contacts are closed when they are not energized.

Voltage and Current limitations for relays

These are the values of voltage and current are usually labeled on the body of the relay itself or on the datasheet. Applying lower voltage to the relay doesn’t activate the switches. On the other side, the application of very high voltage will generate overcurrents thus damaging the relay.

Advantages and Disadvantages of Using a Relay

Advantages

  1. It switches big loads with lower power losses
  2. It provides a galvanic isolation

Disadvantages

  1. It is a slow device
  2. Its contacts wear out at the time

In this video, Great Scott delivers on basics of relay and why optocoupler is used with them.

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