This is passive semiconductor device that allows (usually) the flowing of current only in one direction (this is called a rectifier). It doesn't obey Ohm law (i.e. it's not linear) and if you put it in a circuit, it won't have a Thevenin equivalent.

The main parameters for a diode are

  • the forward voltage drop
  • the leaking current

but you can consider also

  • maximum forward current
  • capacitance
  • reverse recovery time

The schematics element is the following


with the arrow indicating the flow of current; usually there is a drop of 0.6V between anode and catode.

A diode in a circuit can be used as

  • signal rectifier
  • gates
  • clamps and limiter
  • non-linear element

see this video with a couple of examples.


A Zener diode behaves differently from a normal diode: has a reverse-breakdown current pre-determined and can be used as a voltage regulator. In other words, it allows flow in both directions, it's like having two diodes in parallel with different voltage drops.

  • What is a zener diode? Video
  • Video about using it with OpAmp


Are another kind of diode with lower forward voltage drop and fast switching speed but with greater leakage current.