Full form of technical terms related to power electronics

What is BJT

BJT full form is a bipolar junction transistor that uses both electron and hole charge carriers. For their operation, BJT uses two junctions between two semiconductor-type such as n-type and p-type. 

BJTs are manufactured in two types, NPN and PNP, and are available as individual components, or fabricated in integrated circuits, in large numbers. The function of a BJT is to amplify current that can be used as amplifiers or switches. These functions offer a wide range of electronic equipment applications, including computers, TVs, mobile phones, audio amplifiers, industrial control, and radio transmitters. 

Meaning of BJT :

  • A bipolar junction transistor is a three layer, two junction NPN or PNP semiconductor device with one p-region sandwiched by two n-region and two p-region sandwiched one n-region. It has three terminal named collector (C), Emitter(E), and base(B). 
    meaning of BJT
    Figure of  BJT
  • The current flow in the device takes place due to movement both holes and electrons. 
  • An emitter is indicated by an arrowhead indicating the direction of emitter current. No arrow is associated with base or collector. 

Schematic diagram symbol of BJT :
diagram symbol of BJT
NPN                                                  PNP  

Types of  BJTs  :


 There are two types of junction transistor :

 1. NPN transistor 
2. PNP transistor 

 This article gave brief details about NPN and PNP transistor like working principle, advantages and application to better understand this topic.

The working principle of NPN transistor : 


  • This circuit is NPN types of BJT transistor shown in the figure there are two types of current flow IC , IE is receptively known as collector and emitter current and VCB , VEB is collector-base voltage and emitter-base voltage.
  • Shown in figure current IC , IE  , IB current going into the transistor is and the sign is taken as positive and if current goes out sign is taken as negative.
NPN transistor

 NPN transistor Application:

  • Use as an amplifier
  • Use as a Darling-tone pair
  • Use as a switch

The working principle of PNP transistor :


  • In P-N-P junction transistor, emitter current enter through the emitter terminal shown in the figure. 
  • When using any BJT device, the junction of emitter-base is forward biased and the junction of the collector-base is in reverse biased.
So conclude that BJT can be operated in the different mode of BJT like cut off, saturated and active mode.
PNP transistor

PNP transistor application :

  • Used in darling-ton pair circuit
  • Used in heavy motors to control current flow
  • Used as switch
  • Used as a robotic workshop
  • Used in the amplifying circuit

Difference between BJT and MOSFET

BJT and MOSFET both transistors are useful for amplification and switching applications. Yet, they have many similarities and also different characteristics. As a result, one or the other may be better suited to specific electronics applications. 

Difference between BJT and MOSFET


  • A BJT has a negative temperature coefficient device, so current sharing resistors are necessary during parallel operation of BJT's while in MOSFET has a positive temperature coefficient for resistance makes the parallel operation of MOSFET is easy.
  • BJT, with a decrease in resistance at that time rise in temperature, the current increases. This increased current over the same area results in hot spot and breakdown of the BJT because of negative temperature coefficient occurs, the secondary breakdown does occur, Whereas in MOSFET device secondary breakdown does not occur, because it has a positive temperature coefficient. 
  • BJT stands for bipolar junction transistor, and MOSFET stands for metal oxide semiconductor field-effect transistor.
  • BJT is a bipolar device, MOSFET is a uni-polar power electronics device.
  • A BJT has three terminals called an emitter, base, and collector, whereas a MOSFET  also has a three-terminal called the gate, source, and drain. 
  • BJT current a controlled device while MOSFET is a voltage-controlled device.   
  • BJT's are used for low current applications, while MOSFETs are used for high power applications.      
  • BJT has a low input impedance (a few kilo-ohms), a MOSFET has a high input impedance  (megaohm).  
  • In the analog and digital circuits, MOSFET is considered to be more commonly used compare to  BJT now these days. 
  • MOSFET's in higher voltage ratings have much more conduction loss.
  • BJTs are available with ratings up to 1200 V and  800 A, and MOSFETs are available with ratings upon 500 V and 140 A. 
  • BJT depends on the current at the base terminal and the MOSFET depends on the voltage at the oxide-insulated gate electrode. 
  • MOSFET structure is more complex than BJT. 
Explore more information:

Full form of SMPS

What is the full form of SMPS?


Answer :

  • Switched-Mode Power Supply / Switching Mode Power Supply 


What does SMPS mean?



SMPS is one type of power supply unit uses a switching regulator to convert electrical power efficiently, mainly used in computers to convert the voltage into an acceptable range of power. It also uses a great power conversation technique to reduce the overall power loss.

IGBT construction

Before knowing about the construction of IGBT one question you should be clear about is  What is full form of IGBT?

IGBT Structure :


Illustrates the basic structure of an IGBT.  IGBT is constructed virtually in the same way as a power MOSFET construct. There a major difference in the substrate. The n+ layer subtract at the drain in a MOSFET is now substituted in the IGBT by a p+ layer substrate called collector C. Like a power  MOSFET, an IGBT has also thousands of structure cells connected appropriately on a single chip of silicon.
                      

In the IGBT p+ substratum injects holes into n-layer so-called as injection layer. The n-layer is called the region of drift. As in other semiconductor devices, the n-layer thickness determines IGBT's capacity to block voltage. Layer p is called the IGBT body region. the n- layer between p+ and p regions accommodates the pn- junction of the depletion layer, Example- junction J2.

IGBT switching characteristics

How IGBT Switching characteristic works?


Switching characteristics of an IGBT during turn-on and turn-off are sketched in fig. Turn-on time is defined as the time between the instant of forward blocking to forward on the state. Turn-on time is composed of delay time tdn and rise time ton =  tdn +tr.

  • The delay time is defined as the time for the collector-emitter voltage to fall from VCE to 0.9 VCE. Here VCE is the initial collector emitter voltage.
  • Time tdn may also be defined as the time for the collector current to rise from its initial leakage current ICE to 0.1 Ic. Here Ic is the final value of collector. The rise time tr is the time during which collector-emitter voltage falls from  VCE.
  • It is also defined as the time for the collector current to rise from 0.1 IC to its final value IC. After time ton, the collector current  IC is and the collector-emitter voltage fall to a small value called conduction drop is said to be VCES where subscript S denotes saturated value.

  • The turn-off time is somewhat complex.
  • It consists of three intervals : (i) delay time , (ii) initial fall time and (iii) final fall time.
  • toff = tdf +tf1+tf2.
  • The delay time is the time during which gate voltage fall forms VGE to threshold VGET.
  • As VGE falls to VGET during tdf, the collector current falls from Ic to 0.9 Ic . At the end of tdf, the collector-emitter voltage begins to rise.
  • The first fall time tf1 is defined as the time during which collector current fall from 90 to 20 % of its initial value of current IC, or the time during which collector-emitter voltage rise from VCES to 0.1 VCE.
  • The final fall time tf2 is the time during which collector current fall from 20 to 10% of  Ic or the time during which collector-emitter voltage rise from 0.1  VCE to final value  VCE has shown in  figure.

Applications of power electronics

The era of modern power electronics began with the invention of silicon controlled rectifier by cell bell laboratories in 1956. Its prototype was introduced by GEC in 1957 and subsequently, GEC introduced SCR based systems commercially in 1958.

 Since then, There has been the development of many new power semiconductor devices. Today power electronics systems incorporate power semiconductor devices as well as microelectronic integrated circuits.

 The terms converter system, in general, is used to denote a static device that converts DC to AC or AC to DC. Conventional power controller based on thyratrons and mercury arc controller using power semiconductor devices in almost all applications. 

 The development of new power semiconductor device new circuit topology with their improved performance and their fall in price have opened up a wide field for the new application of power electronic converter. It is said to power semiconductor devices can be regarded as the muscle and the microelectronics as the intelligent brain in the modern power electronic systems.

Some of the typical applications are:

  • Domestic and theater lighting.
  • Generation and transmission control.
  • Power supplies can be used laboratories and uninterruptible power for important loads.
  • An industrial application like chemical device, paper, and steel industries.

Some other application of power electronics :

  • Aerospace supplies: Space shuttle power supplies, satellite power supplies, aircraft power systems.
  • Commercial: Advertising, heating, elevators, light dimmers, uninterruptible power supplies, flashers, and industrial lasers.
  • Industrial area: Transformer tap changers, blowers and fans, pumps and compressor, industrial laser, cement mills, rolling mills, textiles mills, cement mills, welding, arc, and industrial furnaces. 
  • Residential area: Cooking, vacuum cleaner, lighting, air-conditioning, space heating, refrigerators, electric-door openers, dryers, fans, food warmer trays, personal computers, light dimmer, food mixer, electric blanket.
  • Telecommunication device: Power supplies (DC and UPS device), battery chargers.
  • Transportation: Electric vehicles, electric locomotives, streetcars, trolley buses, Battery chargers, subways, automotive electronics.
  • Utility Process: VAR compensation, HVDC, static circuit breakers, fans, and boiler feed pumps, supplementary energy system.
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