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Message: <blockquote data-quote="laal" data-source="post: 8425544" data-attributes="member: 94459">Diodes - Surface Mountedn <a href="http://en.wikipedia.org/wiki/Electronics" target="_blank">electronics</a>, a diode is a two-<a href="http://en.wikipedia.org/wiki/Terminal_%28electronics%29" target="_blank">terminal</a> <a href="http://en.wikipedia.org/wiki/Electronic_component" target="_blank">electronic component</a> that conducts <a href="http://en.wikipedia.org/wiki/Electric_current" target="_blank">electric current</a> in only one direction. The term usually  refers to a semiconductor diode, the most common type today,  which is a crystal of <a href="http://en.wikipedia.org/wiki/Semiconductor" target="_blank">semiconductor</a>  connected to two electrical terminals, a <a href="http://en.wikipedia.org/wiki/P-N_junction" target="_blank">P-N junction</a>. A vacuum tube diode, now  little used, is a <a href="http://en.wikipedia.org/wiki/Vacuum_tube" target="_blank">vacuum tube</a> with two <a href="http://en.wikipedia.org/wiki/Electrode" target="_blank">electrodes</a>;  a <a href="http://en.wikipedia.org/wiki/Plate_electrode" target="_blank">plate</a> and a <a href="http://en.wikipedia.org/wiki/Cathode" target="_blank">cathode</a>.The most common function of a diode is to allow an electric current  in one direction (called the diode's forward direction) while  blocking current in the opposite direction (the reverse  direction). Thus, the diode can be thought of as an electronic version  of a <a href="http://en.wikipedia.org/wiki/Check_valve" target="_blank">check valve</a>. This unidirectional behavior is called <a href="http://en.wikipedia.org/wiki/Rectification_%28electricity%29" target="_blank">rectification</a>,  and is used to convert <a href="http://en.wikipedia.org/wiki/Alternating_current" target="_blank">alternating current</a> to <a href="http://en.wikipedia.org/wiki/Direct_current" target="_blank">direct current</a>, and extract <a href="http://en.wikipedia.org/wiki/Modulation" target="_blank">modulation</a>  from radio signals in radio receivers.However, diodes can have more complicated behavior than this simple  on-off action, due to their complex <a href="http://en.wikipedia.org/wiki/Non-linear" target="_blank">non-linear</a> electrical characteristics, which can  be tailored by varying the construction of their <a href="http://en.wikipedia.org/wiki/P-N_junction" target="_blank">P-N junction</a>. These are exploited in special  purpose diodes that perform many different functions. Diodes are used to  regulate voltage (<a href="http://en.wikipedia.org/wiki/Zener_diode" target="_blank">Zener diodes</a>), electronically tune radio and TV  receivers (<a href="http://en.wikipedia.org/wiki/Varactor_diode" target="_blank">varactor diodes</a>),  generate <a href="http://en.wikipedia.org/wiki/Radio_frequency" target="_blank">radio frequency</a> <a href="http://en.wikipedia.org/wiki/Oscillation" target="_blank">oscillations</a>  (<a href="http://en.wikipedia.org/wiki/Tunnel_diode" target="_blank">tunnel diodes</a>), and produce light (<a href="http://en.wikipedia.org/wiki/Light_emitting_diode" target="_blank">light emitting diodes</a>).Diodes were the first <a href="http://en.wikipedia.org/wiki/Semiconductor_device" target="_blank">semiconductor electronic devices</a>. The  discovery of crystals' <a href="http://en.wikipedia.org/wiki/Rectification_%28electricity%29" target="_blank">rectifying</a>  abilities was made by German physicist <a href="http://en.wikipedia.org/wiki/Ferdinand_Braun" target="_blank">Ferdinand Braun</a> in 1874. The first  semiconductor diodes, called <a href="http://en.wikipedia.org/wiki/Cat%27s_whisker_diode" target="_blank">cat's whisker diodes</a> were made of  crystals of minerals such as <a href="http://en.wikipedia.org/wiki/Galena" target="_blank">galena</a>.  Today most diodes are made of <a href="http://en.wikipedia.org/wiki/Silicon" target="_blank">silicon</a>,  but other <a href="http://en.wikipedia.org/wiki/Semiconductor" target="_blank">semiconductors</a> such as <a href="http://en.wikipedia.org/wiki/Germanium" target="_blank">germanium</a>  are sometimes used.<img src="http://lh5.ggpht.com/_8JZhVVmpICU/S8AZjg9mu8I/AAAAAAAAAJo/wzUpEHphSdY/smt%20diodes.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" />Types of  semiconductor diode in Mobile Phones Circuit<a href="http://en.wikipedia.org/wiki/Zener_diode" target="_blank">Zener diodes</a>Diodes that can be made to conduct backwards. This effect,  called  Zener breakdown, occurs at a precisely defined voltage, allowing  the  diode to be used as a precision voltage reference. In practical  voltage  reference circuits Zener and switching diodes are connected in  series  and opposite directions to balance the temperature coefficient  to near  zero. Some devices labeled as high-voltage Zener diodes are  actually  avalanche diodes (see above). Two (equivalent) Zeners in  series and in  reverse order, in the same package, constitute a  transient absorber (or <a href="http://en.wikipedia.org/wiki/Transorb" target="_blank">Transorb</a>, a registered trademark). The Zener  diode is named for Dr. <a href="http://en.wikipedia.org/wiki/Clarence_Melvin_Zener" target="_blank">Clarence Melvin Zener</a>  of Southern Illinois University, inventor of the device. <img src="http://lh5.ggpht.com/_8JZhVVmpICU/S8JtMtAA5vI/AAAAAAAAALM/3VjEEUWVrww/zener%20dioeds%20smt.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /><a href="http://en.wikipedia.org/wiki/Light-emitting_diode" target="_blank">Light-emitting diodes</a> (LEDs)In a diode formed from a <a href="http://en.wikipedia.org/wiki/Direct_bandgap" target="_blank">direct band-gap</a> semiconductor, such as <a href="http://en.wikipedia.org/wiki/Gallium_arsenide" target="_blank">gallium arsenide</a>, carriers that cross the junction emit <a href="http://en.wikipedia.org/wiki/Photons" target="_blank">photons</a> when they recombine with the majority  carrier on the other side. Depending on the material, <a href="http://en.wikipedia.org/wiki/Wavelength" target="_blank">wavelengths</a>  (or colors) from the <a href="http://en.wikipedia.org/wiki/Infrared" target="_blank">infrared</a> to the near <a href="http://en.wikipedia.org/wiki/Ultraviolet" target="_blank">ultraviolet</a>   may be produced. The forward potential of these diodes depends on the   wavelength of the emitted photons: 1.2 V corresponds to red, 2.4 V to   violet. The first LEDs were red and yellow, and higher-frequency diodes   have been developed over time. All LEDs produce incoherent,   narrow-spectrum light; “white” LEDs are actually combinations of three   LEDs of a different color, or a blue LED with a yellow <a href="http://en.wikipedia.org/wiki/Scintillator" target="_blank">scintillator</a>   coating. LEDs can also be used as low-efficiency photodiodes in signal   applications. An LED may be paired with a photodiode or  phototransistor  in the same package, to form an <a href="http://en.wikipedia.org/wiki/Opto-isolator" target="_blank">opto-isolator</a>.<img src="http://lh6.ggpht.com/_8JZhVVmpICU/S8AZ1cIgeDI/AAAAAAAAAJs/4hvVXk-dFms/Smt%20Led.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" />   <a href="http://en.wikipedia.org/wiki/Photodiode" target="_blank">Photodiodes</a>All semiconductors are subject to optical <a href="http://en.wikipedia.org/wiki/Charge_carrier" target="_blank">charge carrier</a> generation. This is typically an undesired   effect, so most semiconductors are packaged in light blocking material.   Photodiodes are intended to sense light(<a href="http://en.wikipedia.org/wiki/Photodetector" target="_blank">photodetector</a>),   so they are packaged in materials that allow light to pass, and are   usually PIN (the kind of diode most sensitive to light). A photodiode   can be used in <a href="http://en.wikipedia.org/wiki/Solar_cell" target="_blank">solar cells</a>, in <a href="http://en.wikipedia.org/wiki/Photometry_%28optics%29" target="_blank">photometry</a>, or in <a href="http://en.wikipedia.org/wiki/Optical_communication" target="_blank">optical communications</a>. Multiple photodiodes may be   packaged in a single device, either as a linear array or as a   two-dimensional array. These arrays should not be confused with <a href="http://en.wikipedia.org/wiki/Charge-coupled_device" target="_blank">charge-coupled devices</a>.</blockquote>

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