Diodes

A diode is the simplest form of semiconductor. Diodes are a discrete component that allows current to flow in one direction only. The direction that current is allowed to pass is called the forward bias. The direction that current is not allowed to pass is called the reverse bias. A diode has two leads: for forward bias, the current comes in at the anode (positive lead) and out at the cathode (negative lead).

Rectification

A common use for diodes is rectification - that is, the changing of alternating current into direct current. (An alternating current (AC) is one which flows alternately in opposite directions around a circuit, while a direct current (DC) is one that always flows in one direction only.)

A rectifying circuit can be found in the transformers used with many types of equipment that require a mains alternating current to be converted into a smaller direct current - eg electronic keyboards or mobile phone chargers.

The circuit diagrams show the two methods of rectification.

Full wave rectification:

Half wave rectification:

Light emitting diode

Light emiting diode (LED)

A light-emitting diode or LED is a special kind of diode that glows when electricity passes through it. The LED is made from a semi-conducting material called gallium arsenide phosphide. LEDs can be bought in a range of colours. In common with all diodes, the LED will only allow current to pass in one direction. The current required to power an LED is usually 25 mA.

Seven-segment LED displays

Seven-segment LED display

A seven-segment LED is a special type of LED display used in digital clocks, video recorders and microwave ovens.