Editing Diode (section)

==Applications==

===Radio demodulation===
[[File:Simple envelope detector.svg|thumb|300x300px|A simple [[envelope detector|envelope demodulator]] circuit.]]
The first use for the diode was the demodulation of [[amplitude modulation|amplitude modulated]] (AM) radio broadcasts. The history of this discovery is treated in depth in the [[crystal detector]] article. In summary, an AM signal consists of alternating positive and negative peaks of a radio carrier wave, whose [[amplitude]] or envelope is proportional to the original audio signal. The diode [[rectifier|rectifies]] the AM radio frequency signal, leaving only the positive peaks of the carrier wave. The audio is then extracted from the rectified carrier wave using a simple [[electronic filter|filter]] and fed into an audio amplifier or [[transducer]], which generates sound waves via [[Loudspeaker|audio speaker]].

In microwave and millimeter wave technology, beginning in the 1930s, researchers improved and miniaturized the crystal detector. [[#Point-contact diodes|Point contact diodes]] (''crystal diodes'') and [[#Junction diodes|Schottky diodes]] are used in radar, microwave and millimeter wave detectors.<ref name="skyworks_01"/>

===Power conversion===
{{Main article|Rectifier}}
[[File:ACtoDCpowersupply.png|250px|thumb|Schematic of basic AC-to-DC power supply]]

[[Rectifier]]s are constructed from diodes, where they are used to convert [[alternating current]] (AC) electricity into [[direct current]] (DC). Automotive [[alternator (auto)|alternators]] are a common example, where the diode, which rectifies the AC into DC, provides better performance than the [[Commutator (electric)|commutator]] or earlier, [[electrical generator|dynamo]]. Similarly, diodes are also used in ''[[Cockcroft-Walton generator|Cockcroft–Walton]] [[voltage multiplier]]s'' to convert AC into higher DC voltages.

===Reverse-voltage protection===
Since most electronic circuits can be damaged when the polarity of their power supply inputs are reversed, a series diode is sometimes used to protect against such situations. This concept is known by multiple naming variations that mean the same thing: reverse voltage protection, reverse polarity protection, and reverse battery protection.

===Over-voltage protection===
Diodes are frequently used to conduct damaging high voltages away from sensitive electronic devices. They are usually reverse-biased (non-conducting) under normal circumstances. When the voltage rises above the normal range, the diodes become forward-biased (conducting). For example, diodes are used in ([[stepper motor]] and [[H-bridge]]) [[motor controller]] and [[relay]] circuits to de-energize coils rapidly without the damaging [[voltage spike]]s that would otherwise occur. (A diode used in such an application is called a [[flyback diode]]). Many [[integrated circuits]] also incorporate diodes on the connection pins to prevent external voltages from damaging their sensitive [[transistors]]. Specialized diodes are used to protect from over-voltages at higher power (see [[#Types of semiconductor diode|Diode types]] above).

===Logic gates===
{{Main|Diode logic}}
[[Diode logic|Diode–resistor logic]] constructs [[logical conjunction|AND]] and [[logical disjunction|OR]] [[logic gate]]s. [[Functional completeness]] can be achieved by adding an active device to provide [[Inverter (logic gate)|inversion]] (as done with [[diode–transistor logic]]).

===Ionizing radiation detectors===
In addition to light, mentioned above, [[semiconductor]] diodes are sensitive to more [[energy|energetic]] radiation. In [[electronics]], [[cosmic ray]]s and other sources of ionizing radiation cause [[noise]] [[pulse]]s and single and multiple bit errors. This effect is sometimes exploited by [[particle detector]]s to detect radiation. A single particle of radiation, with thousands or millions of [[electron volt]], s of energy, generates many charge carrier pairs, as its energy is deposited in the semiconductor material. If the depletion layer is large enough to catch the whole shower or to stop a heavy particle, a fairly accurate measurement of the particle's energy can be made, simply by measuring the charge conducted and without the complexity of a magnetic spectrometer, etc. These semiconductor radiation detectors need efficient and uniform charge collection and low leakage current. They are often cooled by [[liquid nitrogen]]. For longer-range (about a centimeter) particles, they need a very large depletion depth and large area. For short-range particles, they need any contact or un-depleted semiconductor on at least one surface to be very thin. The back-bias voltages are near breakdown (around a thousand volts per centimeter). Germanium and silicon are common materials. Some of these detectors sense position as well as energy. They have a finite life, especially when detecting heavy particles, because of radiation damage. Silicon and germanium are quite different in their ability to convert [[gamma ray]]s to electron showers.

[[Semiconductor detector]]s for high-energy particles are used in large numbers. Because of energy loss fluctuations, accurate measurement of the energy deposited is of less use.

===Temperature measurements===
A diode can be used as a [[temperature]] measuring device, since the forward voltage drop across the diode depends on temperature, as in a [[silicon bandgap temperature sensor]]. From the Shockley ideal diode equation given above, it might ''appear'' that the voltage has a ''positive'' temperature coefficient (at a constant current), but usually the variation of the [[Saturation current|reverse saturation current]] term is more significant than the variation in the thermal voltage term. Most diodes therefore have a ''negative'' temperature coefficient, typically −2 mV/°C for silicon diodes. The temperature coefficient is approximately constant for temperatures above about 20 [[kelvin]]. Some graphs are given for 1N400x series,<ref>{{cite web |url=http://www.cliftonlaboratories.com/1n400x_diode_family_forward_voltage.htm |title=1N400x Diode Family Forward Voltage |website=cliftonlaboratories.com |access-date=2013-12-19 |archive-url=https://web.archive.org/web/20130524153406/http://www.cliftonlaboratories.com/1n400x_diode_family_forward_voltage.htm |archive-date=2013-05-24}}</ref> and CY7 cryogenic temperature sensor.<ref>[http://www.omega.com/Temperature/pdf/CY7.pdf Cryogenic Temperature Sensors]. omega.com</ref>

===Current steering===
Diodes will prevent currents in unintended directions. To supply power to an electrical circuit during a power failure, the circuit can draw current from a [[Battery (electricity)|battery]]. An [[uninterruptible power supply]] may use diodes in this way to ensure that the current is only drawn from the battery when necessary. Likewise, small boats typically have two circuits each with their own battery/batteries: one used for engine starting; one used for domestics. Normally, both are charged from a single alternator, and a heavy-duty split-charge diode is used to prevent the higher-charge battery (typically the engine battery) from discharging through the lower-charge battery when the alternator is not running.

Diodes are also used in [[electronic keyboards|electronic musical keyboards]]. To reduce the amount of wiring needed in electronic musical keyboards, these instruments often use [[keyboard matrix circuit]]s. The keyboard controller scans the rows and columns to determine which note the player has pressed. The problem with matrix circuits is that, when several notes are pressed at once, the current can flow backward through the circuit and trigger "[[Keyboard (computing)#Control processor|phantom keys]]" that cause "ghost" notes to play. To avoid triggering unwanted notes, most keyboard matrix circuits have diodes soldered with the switch under each key of the [[musical keyboard]]. The same principle is also used for the switch matrix in solid-state [[pinball machine]]s.

===Waveform clipper===
{{Main article|Clipper (electronics)}}
Diodes can be used to limit the positive or negative excursion of a signal to a prescribed voltage.

===Clamper===
{{Main article|Clamper (electronics)}}
[[File:DiodeClamp.png|150px|thumb|This simple diode clamp will clamp the negative peaks of the incoming waveform to the common rail voltage]]
A diode [[Clamper (electronics)|clamp circuit]] can take a periodic alternating current signal that oscillates between positive and negative values, and vertically displace it such that either the positive or the negative peaks occur at a prescribed level. The clamper does not restrict the peak-to-peak excursion of the signal, it moves the whole signal up or down so as to place the peaks at the reference level.

===Computing exponentials and logarithms===
The diode's exponential current–voltage relationship is exploited to evaluate [[exponentiation]] and its [[inverse function]] the [[logarithm]] using analog voltage signals (see {{Slink|Operational amplifier applications|Exponential output|Logarithmic output}}).

===Oscillator===
It is possible to modify a regular semiconductor diode like 1N4148 to give it a negative differential resistance by injection of calibrated current pulses ,the diode being reversely biased  near its avalanche zone .After this treatment the diode associated with an L/C circuit can oscillate , the frequency set by the L/C circuit .The maximum frequency depends on the diode used .With a 1N4148 oscillation can go up to 100 Mhz  (see https://www.researchgate.net/publication/384043395_Another_way_to_create_negative_differential_resistance_Author)