ECEstream: Diode

Tunnel Diode

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The tunnel diode has a region in its voltage current characteristic where the current decreases with increased forward voltage, known as its negative resistance region. This characteristic makes the tunnel diode useful in oscillators and as a microwave amplifier.</div>
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<b>Tunnel Diode Symbol</b></div>
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<img alt="Tunnel Diode Symbol" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEglUODc7tKNgMq55Z7IzNkc3aafFgXarAmimEOlSL5yW4E5O5AF7duzyRj8MD2HHI3WvaskEOEJU3ZUyaNvOKBOJMe8nMYHmLLz0zscsjxDzuEUHuZZ4wM8-WEa9imo3F7c1p_kq1NZ6I5t/s1600/tunnel+diode+symbol.png" title="Tunnel Diode Symbol" /></div>
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<b>Tunnel Diode Characteristic</b></div>
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<img alt="Tunnel Diode Characteristic" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiL05L91-ydRgIhH7j6UctF5vt6IA79adryDW1-ZIkrMgVASStesqC0iEN7_X75JEjXTUVmVHp4wFqvcZeWQNL6gxcUKjq7zo0gGHUrKMdj7G2vxz2hqNAFZEUryYlixKc942Pyd0lioYIO/s1600/Tunnel+Diode+Characteristic.png" title="Tunnel Diode Characteristic" /></div>
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Tunnel Diode

The tunnel diode has a region in its voltage current characteristic where the current decreases with increased forward voltage, known as i...

Zener Diode

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The zener diode uses a <a href="http://www.ecestream.com/2014/11/p-n-junction.html" target="_blank">p-n junction</a> in reverse bias to make use of the <a href="http://www.ecestream.com/2014/11/the-zener-effect.html" target="_blank">zener effect</a>, which is a breakdown phenomenon which holds the voltage close to a constant value called the zener voltage. It is useful in zener regulators to provide a more constant voltage, for improvement of regulated power supplies, and for limiter applications.</div>
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<b>Zener Diode Symbol</b></h4>
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<img alt="Zener Diode Symbol" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiGYCF7OD0U4-S0xYmUfsxK23JzbyUZah_4Nd75xIPASIEl0gO6nHsT7piDXd9pJJ0isE1-gJpd0DP9Ur140yPu_iWLBMWIeVMFDjYpdmC071zkVEmJGAtj4hMlcTZhZgXc-E5chyImpyZM/s1600/Zener+diode+symbol.png" title="Zener Diode Symbol" /></div>
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<b>Zener Current Characteristics</b></h4>
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<img alt="Zener Current Characteristics" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhMRGkdmaEYhhyphenhyphenuZdyxdrHn-SPnmHqsirHQEHU_zKmkB_QVKmY4rRuDJSEpBO0kgqqyvdS6U32qovsAFVfu9iEJ7Kl5TBWUFfHQ_v6GF-MsQ3iBzrUEZLE-t7bhQXDdsz1pfkPJqJVm9_yp/s1600/Zener+Effect.png" title="Zener Current Characteristics" /></div>
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Zener Diode

The zener diode uses a p-n junction in reverse bias to make use of the zener effect , which is a breakdown phenomenon which holds the vol...

The Zener Effect

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With the application of sufficient reverse voltage, a <a href="http://www.ecestream.com/2014/11/p-n-junction.html" target="_blank">p-n junction</a> will experience a rapid avalanche breakdown and conduct current in the reverse direction. Valence electrons which break free under the influence of the applied electric field can be accelerated enough that they can knock loose other electrons and the subsequent collisions quickly become an avalanche. When this process is taking place, very small changes in voltage can cause very large changes in current. The breakdown process depends upon the applied electric field, so by changing the thickness of the layer to which the voltage is applied, zener diodes can be formed which break down at voltages from about 4 volts to several hundred volts.</div>
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<img alt="Zener Effect" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhMRGkdmaEYhhyphenhyphenuZdyxdrHn-SPnmHqsirHQEHU_zKmkB_QVKmY4rRuDJSEpBO0kgqqyvdS6U32qovsAFVfu9iEJ7Kl5TBWUFfHQ_v6GF-MsQ3iBzrUEZLE-t7bhQXDdsz1pfkPJqJVm9_yp/s1600/Zener+Effect.png" title="Zener Effect" /></div>
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The Zener Effect

With the application of sufficient reverse voltage, a p-n junction will experience a rapid avalanche breakdown and conduct current in the...

PIN Diode

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The PIN diode has heavily doped p-type and n-type regions separated by an <a href="http://www.ecestream.com/2014/11/intrinsic-semiconductor.html" target="_blank">intrinsic</a> region. When reverse biased, it acts like an almost constant capacitance and when forward biased it behaves as a variable resistor.</div>
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The forward resistance of the intrinsic region decreases with increasing current. Since its forward resistance can be changed by varying the bias, it can be used as a modulating device for AC signals. It is used in microwave switching applications.</div>
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<b>Symbol</b></h4>
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<img alt="Symbol of PIN Diode" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhKf1SLMe-BYGm_jMT531OE8hpK9NwF-e3ljQAHnlYfShyphenhyphenCBh-m8BIRt_raDi5ccuBjAJ1CC1HRmABhi9Z7XWJ1ECxP0Mf6rXxu17B5QcI3n0RWqTR1U2bMooC3NHxMarjTwqJlEKU5uIYt/s1600/PIN+diode.jpg" title="Symbol of PIN Diode" /></div>
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PIN Diode

The PIN diode has heavily doped p-type and n-type regions separated by an intrinsic region. When reverse biased, it acts like an almost c...

P-N Junction Diode

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The nature of the p-n junction is that it will conduct current in the forward direction but not in the reverse direction. It is therefore a basic tool for <i>rectification</i> in the building of <i>DC power supplies</i>.</div>
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<b>Symbol</b></h4>
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<img alt="Symbol of PN Junction Diode" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEisjNKYhsomZNJWOrmXZeYxDVeAvoaYbudpbpzxMpKHqEqlvmUxnaj6j694yq-s8YM3AQcDmBGlwuVZzI5GU5ZpZRWgeCPCXqaccMYZkb5As__-x31cMU0dRujYmlI3HStDo1wTi3_uMyMh/s1600/pndiod5.png" title="Symbol of PN Junction Diode" /></div>
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<b>Forward Biased P-N Junction</b></h4>
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Forward biasing the p-n junction drives holes to the junction from the p-type material and electrons to the junction from the n-type material. At the junction the electrons and holes combine so that a continuous current can be maintained.</div>
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<img alt="Forward Biased P-N Junction" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEimildxogkwMrqharM3U6tugk1eABptzDWlglob4BbXH9BdsN7XUHiDrdSf7SmhrO8xiGbbpx5MTmFQMyhBiDXwrQokLGh9a2WwCFxu_45hSRkRu-asA6XZly0ofXnwd5CyEBC2G4uPqQZv/s1600/forward+biased+PN+diode.png" title="Forward Biased P-N Junction" /></div>
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<b>Reverse Biased P-N Junction</b></h4>
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The application of a reverse voltage to the p-n junction will cause a transient current to flow as both electrons and holes are pulled away from the junction. When the potential formed by the widened depletion layer equals the applied voltage, the current will cease except for the small thermal current.</div>
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<img alt="Reverse Biased P-N Junction" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj8ovZ-Iw6iyhVQqqqc2sfLIRlFlBwz0psADpijaqYHf64Fl-d0aHJIr5MYhaKw5YW4ZiB2DVpO_473R5-YIuSubqk5LXCom18Sut_q5xEVKKtnWtQMFTLgESSDQfyVzw3qNbgItxvAdl6p/s1600/reverse+biased+pn+diode.png" title="Reverse Biased P-N Junction" /></div>
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<b>The P-N Junction Diode Characteristics</b></h4>
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<img alt="P-N Junction Diode Characteristics" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhaMAx3qMktn63W8DXhwWBwVliHi_gwLoR8chFIivj7w0PEfUJDkfYERrlMc5IdpiJfVyNKr3EaEVfiO3rwKmhqwKjtFSbhIqibrdytkkfq7xy4TkATwfD_BLYpFaOxXuf25EMMVyfDi_PL/s1600/PN+diode+characteristics.png" title="P-N Junction Diode Characteristics" /></div>
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P-N Junction Diode

The nature of the p-n junction is that it will conduct current in the forward direction but not in the reverse direction. It is therefore ...

Photodiodes

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A photodiode consists of an active p-n junction which is operated in reverse bias. When light falls on the junction, a reverse current flows which is proportional to the illuminance. The linear response to light makes it an element in useful photodetectors for some applications. It is also used as the active element in light-activated switches.</div>
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<img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhviK_gXvVL-VT2ZmPEEXkqMjMfGKOpY3usHR3LlgJQ_vhqT0UcoEApPjdkwLsMkxSuB4ejLPW8XvC4cY1zJ5TX40SuBZEDprnZpcRmAIIGSPIPbTICNjV_047b2l4pIeb3wiMk8NaC9GOT/s1600/Photodiode_operation.png" /></div>
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<b>Photodiode Mechanism</b></div>
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The mechanism of the photodiode is like that of a (miniaturized) solar cell. Their response time is fast, on the order of nanoseconds. As light detectors, they are reverse biased - the reverse current is linearly proportional to the illuminance striking the diode. They are not as sensitive as a phototransistor, but their linearity can make them useful in simple light meters.</div>
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<img alt="Photodiode Symbol" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhKe6zmGbEVUbWBTmxH7sqBQGN9ZbV32zbumhe9EYLESxIIJBlI0nEQReHuRwmkpj0eJBfDrYux1Aoqh9EyJAkux2g5hOSeAiKTurxe8jPFyLu_MMYa97R4Iz6DSsMncBCAGCCAuWTpOK-y/s1600/Photodiode_symbol.png" title="Photodiode Symbol" /></div>
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<b>Photodiode Characteristics</b></div>
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The reverse current through a photodiode varies linearly with illuminance once you are significantly above the dark current region.</div>
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<img alt="Photodiode Characteristics" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh_Xht-Thx5rBpOPiH_EGrHwqB96wKR5Xf8NEJ-p0P5ABhqQGCmRDKmPPx3mgJzVOrF33FbqkWpu-wfy7ORNxyNadl_mIa8nkm7hqSz85txGDJIYS_nMZAd9PrLPiu7tt84hu2iAG5Et0Gw/s1600/Photodiode_charcteristics.png" title="Photodiode Characteristics" /></div>
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Photodiodes

A photodiode consists of an active p-n junction which is operated in reverse bias. When light falls on the junction, a reverse current flo...

Light Emitting Diodes (LEDs)

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The best known of all opto-electronic devices is the so called LED (light-emitting diode), which emits a fairly narrow bandwidth of visible (usually red, orange, yellow or green) or invisible (infrared) light when its internal diode junction is stimulated by a forward electric current/voltage (power). LEDs have typical power-to-light energy conversion efficiencies some 10 to 50 times greater than of a simple tungsten lamp and have very fast response times (approximately 0.1 us compared with tens or hundreds of milliseconds for a tungsten lamp), and are thus widely employed as visual indicators and as moving light displays.</div>
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<b>Operation</b></div>
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The operation of LED is based on the phenomenon of electroluminance, which is the emission of light from a semiconductor under the influence of an electrical field. The recombination of charge carriers takes place in a forward P-N junction as the electrons cross from the N-region and recombine with holes existing in P-region. Free electrons are in the conduction band of energy levels, while holes are in the valence energy band. Therefore, the electrons  are at high energy levels than the holes. For the electrons to recombine with the holes,they must give some of their energy. Typically, these electrons give up energy in the form of heat and light.</div>
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<img alt="Light Emitting Diode Operation" border="0" height="449" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhYjZk8HJrJbbRyYnVCPzr2wf1tcyIJ2r6AraFd5hFaCLYJkjdUhyphenhyphenJvRqs0WKqQf8JFbIP4h5ztotlqyMmTJ4F8GcxjW5Qo044L6hIjQiZYVM-16uDVv-a4ALVO1BQtc_m6sV3yrD_UDvr1/s1600/PnJunction-LED.png" title="Light Emitting Diode Operation" width="640" /></div>
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In silicon and germanium diodes, most of the electrons give up their energy in the form of heat. However, with GaAsP, and GaP semiconductors, the electrons give up their energy by emitting photons. If the semiconductor is transluscent, the light will be emitted and the junction becomes a source of light, i.e., a <i>light-emitting diode</i> (LED). LEDs emit no light when reverse biased. In fact, operating LEDs emit no light when reverse biased. In fact, operating LEDs in reverse bias mode will quickly destroy them.</div>
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LEDs are manufactured with domed lenses so as to reduce the reabsorption problem. LEDs are always encased in order to protect their wires. LEDs made from GaAs emit invisible infrared light, LEDs constructed of GaAsP tend to emit either red or yellow light. The GaP LEDs give either red or green light. LEDs can be manufactured to produce light of virtually any colour. Table 1 provides  a list of common compound semiconductors and the light they produce. In addition, the typical range of forward bias voltage for each is listed.</div>
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<b><i>Table 1. Light-Emitting Diodes</i></b></div>
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<b>Colour</b></div>
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<b>Construction</b></div>
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<b>Typical Forward
  Voltage Voltage in Volts</b></div>
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Amber</div>
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AllnGaP</div>
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2.1</div>
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Blue</div>
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GaN</div>
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5.0</div>
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Green or red</div>
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GaP</div>
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2.2</div>
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Yellow</div>
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  <td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; height: 17.5pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 76.5pt;" valign="top" width="102"><div align="center" class="MsoNormal" style="text-align: center;">
GaAsP</div>
</td>
  <td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; height: 17.5pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 2.75in;" valign="top" width="264"><div align="center" class="MsoNormal" style="text-align: center;">
2.2</div>
</td>
 </tr>
<tr style="height: 17.5pt; mso-yfti-irow: 6;">
  <td style="border-top: none; border: solid windowtext 1.0pt; height: 17.5pt; mso-border-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 1.0in;" valign="top" width="96"><div align="center" class="MsoNormal" style="text-align: center;">
Red</div>
</td>
  <td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; height: 17.5pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 76.5pt;" valign="top" width="102"><div align="center" class="MsoNormal" style="text-align: center;">
GaAsP</div>
</td>
  <td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; height: 17.5pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 2.75in;" valign="top" width="264"><div align="center" class="MsoNormal" style="text-align: center;">
1.8</div>
</td>
 </tr>
<tr style="height: 17.5pt; mso-yfti-irow: 7;">
  <td style="border-top: none; border: solid windowtext 1.0pt; height: 17.5pt; mso-border-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 1.0in;" valign="top" width="96"><div align="center" class="MsoNormal" style="text-align: center;">
White</div>
</td>
  <td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; height: 17.5pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 76.5pt;" valign="top" width="102"><div align="center" class="MsoNormal" style="text-align: center;">
GaN</div>
</td>
  <td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; height: 17.5pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 2.75in;" valign="top" width="264"><div align="center" class="MsoNormal" style="text-align: center;">
4.1</div>
</td>
 </tr>
<tr style="height: 17.5pt; mso-yfti-irow: 8; mso-yfti-lastrow: yes;">
  <td style="border-top: none; border: solid windowtext 1.0pt; height: 17.5pt; mso-border-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 1.0in;" valign="top" width="96"><div align="center" class="MsoNormal" style="text-align: center;">
Yellow</div>
</td>
  <td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; height: 17.5pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 76.5pt;" valign="top" width="102"><div align="center" class="MsoNormal" style="text-align: center;">
AllnGaP</div>
</td>
  <td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; height: 17.5pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 2.75in;" valign="top" width="264"><div align="center" class="MsoNormal" style="text-align: center;">
2.1</div>
</td>
 </tr>
</tbody></table>
<br />
<div style="text-align: justify;">
</div>
<div class="MsoNormal" style="text-align: justify;">
<o:p><b>Light Circuit Symbol</b></o:p></div>
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The below figure shows a circuit symbol for a LED. The arrows indicate radiation emitted by the diode.</div>
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<img alt="LED Symbol" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjrX47jr9DzvsAg39fxQwcaMmywjqBfZBklO6hIcZ1fNRG4UXHzPJggL7mvTEAERgQPqR2wP5UVGTVWKTLR9swRHK74LmG-qzRw9PdeXPlKKl-8ZZEXU5ZE_qqNF7QDYvAUtw5E3-K1OHTm/s1600/LED-Circuit-Symbol.jpg" title="LED Symbol" /></div>
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<br /></div>
<div class="separator" style="clear: both; text-align: justify;">
<b>LED Operating Characteristics</b></div>
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The below figure give two curves used to determine LED operating characteristics. The V-I curve is practically applicable in burglar alarms. Forward bias of approximately one volt is needed to give significant forward current. The second figure is used to represent a radiant power-forward current curve. The output power produced is very small and thus the efficiency in electrical-to-radiant energy conversion is very less.</div>
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<br /></div>
<div class="separator" style="clear: both; text-align: center;">
<img alt="LED Operating Characteristics" border="0" height="314" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhUsYumIsi0IKcucdBp_14AMEGimiQ3dR1cfdgLBlujg8mg415nO0UfW5JxmpbaZEI2lusDnIg1e82PizyZzocn9X8INlI84OQ0a_dZCwzULZk-FMybHXD4zeZGA5wB7gHSh_OyZXN-9F-V/s1600/LED-Characteristics.jpg" title="LED Operating Characteristics" width="640" /></div>
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<br /></div>
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<b>Advantages of LEDs:</b></div>
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</div>
<ol style="text-align: left;">
<li>LEDs are miniature in size and can be stacked together to form numeric and alphanumeric displays in high density matrix.</li>
<li>Smooth control of light intensity from an LED because light output from an  LED is a function of current flowing through it.</li>
<li>LEDs are economical and have a high degree of reliability.</li>
<li>LEDs are rugged and can, therefore, withstand shocks and vibrations.</li>
<li>LEDs can be operated over a with temperature range (0-70<span style="font-size: 11pt; line-height: 115%; vertical-align: super;"><span style="font-family: inherit;">o</span></span>C).</li>
<li>The switching time is less than 1 ns. So they are very suitable where dynamic operation of large number of arrays is involved.</li>
<li>LEDs are available in different colours like red, yellow, green and amber.</li>
<li>They need moderate power. They are used where low dc power is available.</li>
<li>They occupy small area.</li>
<li>LED can be driven by transistor-transistor logic (TTL).</li>
</ol>
<ol>
</ol>
<span style="text-align: justify;">The </span><b style="text-align: justify;"><i>drawbacks</i></b><span style="text-align: justify;"> of LEDs are that they may get damaged by overvoltage or overcurrent. They have wide optical bandwidth compared to the LASER. Their temperature depends on the radiant output power and wavelength. LEDs are not suited for large area displays, primarily because of their high cost. For large displays, devices using gas filled plasma are used.</span></div>

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