The Diode

A diode allows a current to flow through it in one direction only.

It has the symbol:

 

Remember circuit diagrams are drawn in conventional current. So the arrow on the diode symbol indicates the direction in which the conventional current can flow.

  • When the arrow of the diode is in the same direction as the conventional current flow it is said to be forward biased and current flows.

  • When the arrow of the diode is in the opposite direction to the conventional current flow it is said to be reversed biased and no current flows.

Diodes are used in electric circuits to protect electrical equipment. In electrical equipment such as radio or computers damage can be caused if the battery is connected the wrong way round. A diode in the circuit only allows the current to pass through when the battery is connected correctly. If the battery is connected the wrong way round no current passes through the diode and the electrical circuit for the equipment is protected from damage.

 

Current–Potential Difference graph for a Diode