For instance, a diode's forward-direction voltage drop varies only a little with the current, and is more so a function of temperature this effect can be used as a temperature sensor or as a voltage reference. However, diodes can have more complicated behavior than this simple on–off action, because of their nonlinear current–voltage characteristics. As rectifiers, diodes can be used for such tasks as extracting modulation from radio signals in radio receivers. This unidirectional behavior is called rectification and is used to convert alternating current (AC) to direct current (DC). As such, the diode can be viewed as an electronic version of a check valve. The most common function of a diode is to allow an electric current to pass in one direction (called the diode's forward direction), while blocking it in the opposite direction (the reverse direction). A common variant of a diode is a light-emitting diode, which is used as electric lighting and status indicators on electronic devices. The obsolete thermionic diode is a vacuum tube with two electrodes, a heated cathode and a plate, in which electrons can flow in only one direction, from cathode to plate.Īmong many uses, diodes are found in rectifiers to convert alternating current (AC) power to direct current (DC), demodulation in radio receivers, and can even be used for logic or as temperature sensors. Today, most diodes are made of silicon, but other semiconducting materials such as gallium arsenide and germanium are also used. The discovery of asymmetric electrical conduction across the contact between a crystalline mineral and a metal was made by German physicist Ferdinand Braun in 1874. Semiconductor diodes were the first semiconductor electronic devices. It has an exponential current–voltage characteristic. It has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other.Ī semiconductor diode, the most commonly used type today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals. The filament itself may be the cathode, or more commonly (as shown here) used to heat a separate metal tube which serves as the cathode.Ī diode is a two- terminal electronic component that conducts current primarily in one direction (asymmetric conductance). Electron flow is the reverse of conventional current flow. In most diodes, a white or black painted band identifies the cathode into which electrons will flow when the diode is conducting. The square silicon crystal can be seen between the two leads. The anode is on the right side the cathode is on the left side (where it is marked with a black band).
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