Diodes are semiconductor components that act as a one-way switch for current. Diodes allow current to flow easily in one direction but severely impedes current from flowing in the opposite direction.
Diodes have polarity, determined by an anode (positive lead) and the cathode (negative lead). Many diodes allow current to flow only when a positive voltage is applied to the anode.
They are also known as rectifiers because they change alternating current (AC) into pulsating direct current (DC). Diodes are rated according to their type, voltage, and current capacity.
Diodes are available in many configurations, such as:
Plastic case with a band
Plastic case with chamfer
Diodes are forward-biased when they allow current flow, when reverse-biased it does not permit current to flow and acts as an insulator.
A Diode circuit diagram symbol arrow points against the direction of electron flow.
The voltage applied to the anode is positive with respect to the cathode. Also, the voltage in the diode is higher than the threshold voltage, so it acts as a short circuit and allows current to flow.
If the cathode is made positive with respect to the anode, the diode is reversed-biased. It will then act as an open circuit; therefore, no current will flow.
What are diodes used for?
Reverse current protection
Blocking diodes are used in some electronic circuits for protection, such as, an accidental reverse connection problem:
Connecting a DC supply in a wrong way
As the flow of current in the wrong direction can damage other circuit components.
Simple Voltage Regulator
Voltage regulators are used to step down the input voltage to the required level and will keep it stable despite fluctuations in the supply. They can also regulate the output voltages, Zener diodes are usually used as a voltage regulator because it is designed to work in the reversed bias condition, but also behaves like normal signal diodes when in forward bias.