2. Partially controllable power semiconductor devices SCR, TRIAC, DIAC -- They are turned ON by applying gate signal. But these devices Department of ECE 9 GAT, Bengaluru Invention of thyristor Application of fast-switching fully-controlled semiconductor devices
Power Electronics Lab Manual (10ECL78) can not be turned OFF with the help of gate signals. They are turned off by load or by commutation. 3. Fully controllable power semiconductor devices Power BJT, MOSFET, IGBT, GTO -- These devices can be both turned ON and turned OFF by applying gate signals Based on Gate Signal: 1. Pulse gate requirement Example: SCR, GTO, SITH, MCT To Turn ON these devices, pulse voltage is applied as a control signal. Once the device is turned on, the gate pulse is not required and thus removed. 2. Continuous gate requirement Example: BJT, MOSFET, IGBT For these devices, continuous gate signal is required to maintain them in ON state. Based on Current Conduction Capability: 1. Unidirectional Current Devices Ex:- SCR, GTO, BJT, MOSFET, IGBT 2. Bidirectional Current Devices Ex:- TRIAC, RCT(Reverse Conducting Thyristor) Based on Voltage withstanding Ability: 1. Unipoloar voltage withstanding devices Ex:- BJT, MOSFET, IGBT 2. Bipolar voltage withstanding devices Ex:- SCR, GTO Power Diodes The power semiconductor diode or power diode , has a much larger PN junction area compared to small signal diode , resulting in a high forward current capability of up to several hundred amps (KA) and a reverse blocking voltage of up to several thousand volts (KV). Power diodes are of 3 types: 1) General purpose diode 2) High speed diode 3) Schottky diode. 1. Standard Diodes or General Purpose Diodes : Department of ECE 10 GAT, Bengaluru
Power Electronics Lab Manual (10ECL78) Standard or general purpose diodes have a comparatively high reverse recovery time, when compared to other diodes. Due to this reason they are used in applications which are not time sensitive and generally run on low speeds. Usually the reverse recovery time for general purpose diodes varies between 20 micro seconds to 30 micro seconds. Typical low speed applications for general purpose diodes include the power diode being used as a rectifier or in a converter, where the frequency input is quite low. 2. Fast Recovery Diodes: These are the type of power diodes which have a relatively faster reverse recovery time, which usually varies from 2 micro seconds to 5 micro seconds. With such a fast recovery time, they can be easily used in high speed switching applications w. Due to their property of fast reverse recovery, they are also comparatively expensive as compared to the general purpose diodes. 3. Schottky Diodes : The problem of charge storage in a pn-junction can be minimized to a great extent in a Schottky diode. A Schottky diode sets a barrier potential, i.e. a metal layer is deposited on n- type silicon. As the rectification depends upon the majority charge carriers, so this layer prevents the recombination of these majority charge carriers, and a fast recovery can also be achieved .
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