Diodes are electrical components that allow current to flow through them in one direction. They are made up of two terminals, an anode and a cathode, and a semiconductor material in between. The semiconductor material is usually made up of two types of doped silicon. When a voltage is applied to the anode, the electrons in the semiconductor material move to the anode, creating an area of low potential, or a depletion region, between the anode and the cathode. This depletion region stops current from flowing from the cathode to the anode and allows current to only flow from the anode to the cathode. This allows the diode to act as a one-way valve for electrical current. Anode & Cathode This diagram shows the Diode with its two terminals; anode and cathode. The diode usually has a stripe to indicate which end is the Cathode (-) terminal. Light emmiting diodes (LEDs) are a special type of diode that produces light when current passes through it. The colour of the LED is defined by colour of the plastic that encases the compoent. Diodes come in two types; Germanium and Silicon. Germanium diodes are used for rectifying small signals, for example in early radios. They require only 0.2 volts, anode to cathode, to pass tiny amounts of current in one direction. Silicon diodes require 0.7 volts to open. Electrons pass from cathode to anode and 0.7 volts difference will be maintained over a wide range of current. Voltage Flow Here we get into the realms of confusion. On circuits, the cathode is regarding as positive, e.g. If you apply an A.C. signal to the anode, a positive voltage will be measured on the cathode. In the infancy of electronics, ‘conventional’ current is said to flow from anode to cathode, when in fact electrons travel from cathode to anode.