Optocoupler / Optoisolator

[tonilopezmr]

When a microcontroller with low voltage wants to control high voltages and current you need to isolate the low voltage circuit (cold) to the high voltage circuit (hot) to not burn the low voltage circuit.

Problem example:

This circuit has the problem of link the negative part of the battery with 220v AC wich it is a dangerous connection because high voltage could reach the cell and exploit it. Optocoupler / Optoisolator will protect the battery isolating hot side from the cold side.

Optocoupler schematic

MOC3041 schematic which is zero-crossing

How it works

Optocoupler has a diode in the cold side which emit infrared light when it is exciting, on the cold side there is a TRIAC composed by photo transistors or photo diacs which is open while the diode isn't excited, when the diode emit infrared light to the photo transistors, it closes the HOT circuit and turn on the 220v bulb for example.

This is an example of using optocoupler for switch on/off a 220v bulb with TRIAC controlled by 5v.

References

First time I read about optocouplers
Video Using a TRIAC to Switch AC line power
Optocoupler MOC3021 datasheet
Optocoupler MOC3041 zero crossing datasheet