Diodes provide a one-way street for current flow. They’re often used to convert AC to DC, in clipping and clamping circuits, as circuit protection, voltage limiter, and voltage regulator. Some even emit light. Diodes come in lots of different shapes and sizes each with their own specific use.
The circuit below shows a typical silicon diode. It is forward-biased and conducts current. So to do that it needs about 700 mV forward voltage to operate properly.
We get a reverse-biased diode if we turn it backward. This diode won’t conduct any current. Within limits of course.
If we apply too much voltage the diode conducts even while reverse biased. Going over this breakdown voltage limit can even destroy the diode.
Different types of diodes
Here’s a list of different diode types and their typical use.
- Rectifier diodesWidely used to turn AC into DC called rectification. Accepts higher voltage and current compared to signal diodes. Typical forward voltage between 600 and 1000 mV. A good example is the 1N4001.
- Signal diodesFast switching but can handle less current. Small in size and encapsulated in a glass container. A commonly used signal diode is the 1N4148.
- Schottky diodesLow forward voltage drop and a very fast switching. Forward voltage can be as low as 150 mV. High reverse leakage current.
- Zener diodesTypically used in reverse-biased mode as a (crude) voltage regulator or in waveform shaping circuits. Designed with a controlled reverse breakdown voltage called zener voltage (Vz). A typical group of zener diodes is the BZX55 series.
- Light emitting diodesThe LED we all know and love. When forward biased the special semiconductor material will produce photons with a specific spectral wavelenght. We see this as colored light. Forward voltages differ widely from 1 to 4 Volt. An LED needs a current limiting resistor in series to prevent excessive current flow from destroying it.