izumi asked in Science & MathematicsEngineering · 2 months ago

# What are Optical isolation?

Funny as it sounds. I did try to google the answer, but I still don’t have a clue of what they are in general. All I know is they allow the trans omission of light in only one direction. But does anyone know why we use them and why it’s in an H-Bridge circuit. I basically want something in more detailed explanation.

Thank you, very much!

Relevance
• Dixon
Lv 7
2 months ago

What are optical isolators / what is optical isolation

Generally it is a pair of electrical components that have no electrical connection between them, ie they are electrically isolated from each other. However one can control the other by means of emitting light. They are usually put in a single package and sold as one device but there is still electrical isolation between the two components.

The most common case is a photo diode (where electrical current causes it to emit light) shining onto a photo transister (where incoming light causes electrons in the base region to jump up to the conduction band and become a base current).

The net result is something akin to a mechanical relay where the activation side can be at a completely different voltage to the switching side.

An H bridge can be used to make alternating direction load / source.

If the control signals are digital logic, this is an ideal situation to use opto isolators because the supply voltage for the H might be completely different to the logic levels. By using opto isolators we only need consider the transistors as conducting or non conducting because the base voltages are not influenced by the absolute voltage of the photodiodes.

• 2 months ago

not clear what you are asking. An optical isolator is an electronic device that is a LED combined with a photodiode or phototransistor in a package. Signals to the LED are coupled optically to the diode or transistor and cause an output. The optical isolation means the input and output can be at large voltage differentials, hence the word "isolator".

Look up the 4N25 for a typical partt