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. 
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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.

Difference between IGBT and SCR

Before we learn about the difference between IGBT and SCR first let us check out what is full form of IGBT and what is the full form of SCR. We already know that IGBT process is high input impedance like PMOSFET and has low on-state power loss as in a BJT, but in  thyristor (SCRs) are usually chosen so that their break over voltage is so far beyond the greatest voltage expected to be experienced from the power source, so that it can be turned on only by an intentional voltage pulse applied to the gate terminal. 

So here this article gives information about the difference between IGBT and Thyristor  called (SCR)  to know more detail about IGBT and thyristor :

Difference between IGBT and Thyristor


 Meaning : 

 IGBT called an Insulated gate bipolar transistor, While Thyristor also called SCR known as silicon controlled rectifier.

 Definition :

 IGBT : IGBT has been developed by combining the best qualities of both BJT called bipolar junction transistor and PMOSFET called power metal-oxide field-effect transistor. Thus does IGBT process is very high input impedance like PMOSFET and has low on-state power loss as in a BJT. Insulated gate bipolar transistor is totally free from the second breakdown problem present in BJT. All these merits have made it IGBT very popular among in all power electronics engineers. 

 Thyristor: The terms thyristor called SCR denotes a family of semiconductor devices used for power control in dc and ac systems. One of the oldest members of the thyristor family called SCR silicon control rectifier (SCR) is the most widely used for the device. 

 Terminals : 

 IGBT Has three-terminal known as a collector(C), emitter(E), and gate(G) whereas SCR (thyristor) has three terminals known as the gate(G), an anode(A), and the cathode(C).  

 Layers : 

 IGBT is a semiconductor device with four alternating layers called (P-N-P-N) and they are controlled by a metal-oxide-semiconductor (MOS) gate structure whereas SCR (thyristor) is three-terminal four-layer device.

 Junction : 

 IGBT has only one PN junction, while SCR (thyristor) consist of three PN junctions.

Application :

 IGBT are most commonly used medium power application such as dc and ac motor drive, UPS system, power supplies, relays and contactors, where SCR (Thyristor) is most commonly used to a converter, is used to convert an alternating power into alternating power of different frequency and amplitude. Both device IGBT and SCR are used in high power applications and control currents.

IGBT used for always needs a continuous supply of gate voltage whereas Gate of the SCR (thyristor) only needs a pulse to change into conducting mode.

Advantages and disadvantages of power electronic converters

Power electronics system is a subject that mainly focuses on the application of electronic principles into the situation that is rated at power level rather than signal level and also deal with the apparatus and equipment working on the principle of electronics. So now let us talk about the advantages and disadvantages of power electronics converters to know more details about power electronics.

Advantages of power electronic converter :

  • Long life
  • Small size 
  • High efficiency because of loss is low in power semiconductor devices
  • High reliability of power-electronic converter system
  • Can handle large output current
  • Less maintenance due to the absence of any moving part
  • Fast dynamic response of the power electronic system as compared to the electro-mechanical converter systems
  • Fewer weight results in less floor space and therefore lower installation cost
  • Low thermal dissipation
  • Mass production of power semiconductor devices have resulted in a lower cost of the converter equipment
  • Reduce the fluctuation in power fed to grid
  • Reduce acoustical noise from the wide turbine
  • High-quality power to the grid
  • Flexibility in operation

Disadvantages of power electronic converter :

  • Complected design
  • Regeneration of power is difficult in power electronic systems
  • AC to DC and AC converter operate at a low input power factor under certain operating conditions. In order to avoid a law pf, some special measures have to be adopted
  • Power electronic controllers have low overload capacity. As such, Increase the cost of power electronic controller
  • Power electronic converter circuits have a tendency to generate harmonics in the supply system as well as in the load circuit

Advantages and disadvantages of IGBT

The term IGBT full form is Insulated Gate Bipolar Transister. IGBT has been developed by combining the best qualities of both BJT and PMOSFET. Thus IGBT process is high input impedance like PMOSFET and has low on-state power loss as in a BJT. All these merits have made it IGBT very popular among power electronics engineers. This article give the information about some advantages and disadvantages of IGBT to know more details about IGBT.

Advantages of IGBT :
  • Simple drive circuit
  • Low on-resistance
  • High voltage capacity
  • Fast switching speed
  • Easy of drive
  • Low switching loss
  • Low on stage power dissipation
  • Low gate drive requirement
  • High switching speed
  • High input impedance 
  • Voltage control device
  • Smaller snubber circuit requirement
  • It has Superior current conduction capability 
  • It is easy to turn ON and OFF
  • It has excellent forward and reverse blocking capabilities
  • Switching frequency is higher than the BJT
  • Enhanced conduction due to bipolar nature
  • IGBT has a very low on-state voltage drop due to superior on-state current density and conductivity modulation. So the cost can be reduced and a smaller chip size is possible
Disadvantages of IGBT :
  • Latching up problem
  • It can't block high reverse voltage
  • High turn off time
  • Cost is high
  • The speed of the switching is lower to a power MOSFET and higher to a BJT. So the collector current following due to the minority charge carriers root the turnoff speed to be very slow. There is a chance of latch-up due to the internal structure of the PNPN thyristor device

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Difference between IGBT and MOSFET

An IGBT is essentially a MOSFET controlling a bipolar junction power transistor with both transistors are integrated on a single piece of silicon. 

MOSFET find a most important application in high frequency switching application, varying from few watts to few kWs, While IGBT possesses high input impedance like a MOSFET and has low on-state power loss as in a BJT.

With the rise in temperature, the increase in on-state resistance in MOSFET is much pronounced than it is in IGBT devices. So, on-state voltage drop and losses rise rapidly in MOSFET compare to IGBT, with rising in temperature.

So here this article gives information about the difference between IGBT and MOSFET to know more details about it.

Difference between IGBT and MOSFET 


  • IGBT modules are their higher voltage and current handling capability as compared to a comparable price of MOSFET. 
  • Both IGBT and MOSFET are voltage control devices and IGBT has a BJT like conduction characteristics. 
  • Terminals of IGBT are known as an emitter, collector, and gate, whereas MOSFET terminals are gate, source and drain. 
  • IGBT has a better power handling than MOSFET. 
  • IGBT has a lower forward voltage drop as compared to MOSFET.  
  • MOSFET has a long history than IGBT.
  • MOSFET used in a condition of high light-load efficiency, dv/dt on the diode is a limited and wide line and load conditions where IGBT used in full load efficiency, high dv/dt handled by a diode and high power levels around 3 kW.
  • IGBT is extremely tolerant to electrostatic discharge and overloads whereas MOSFET are vulnerable to ESD as the high impedance technology won't allow for voltage dissipation. 
  • MOSFET used in medium to ultra-high-power applications such as SMPS and VFDs and IGBT used in switching and amplifying weak electronic signals in electronic devices. 
  • IGBT has PN junction whereas MOSFET doesn't have that. 

Explore more information:
  1. Difference between IGBT and Thyristor
  2. NMOS vs PMOS

Applications of IGBT

 IGBT is used in order to allow power flow in the ON state and to stop power flow in the OFF state. It is used mostly in medium to high power applications for example induction heating, switched-mode power supply, traction motor control. 

How IGBT used :

There are some applications of IGBT full form is Insulated Gate Bipolar Transistor are following below :
  • IGBT is most commonly used in power application such as DC and AC motor drive, UPS system, power supply and drive for solenoid.
  • Though IGBT is somewhat more expensive than BJT full form, yet IGBT are becoming popular because of lower gate drive requirement, lower switching losses and also smaller snubber circuit requirement
  • IGBT used in an unregulated power supply (UPS) system.
  • The IGBT is used combines an isolated gate FET for the control input and bipolar power transistor as a switch in a single device
  • It is also used in inverter
  • IGBT is fitted in the of resonant mode converter circuits. Optimized IGBT is accessible for both low conduction loss and low switching loss
  •  Inductive heating cookers
  • IGBT used in power distribution
  • Electric vehicle motor drives
  • The IGBT used in switched-mode power supplies (SMPS)
  • Solar inverter
  • IGBT used in due-mode or E-auto automobile system
  •  IGBT used in  solar and wind power generation plant

Characteristics of IGBT

The circuit of figure circuit diagram shows the various parameters pertaining in the IGBT characteristics. 

Static I-V or output characteristics of an IGBT (n channel type) show the plot of conduct collector current IC versus collector-emitter voltage VCE for various value of gate emitter voltages VGE1, VGE2 etc. These characteristics are shown in figure static I-V characteristics.


In the forward directions, the shape of the output characteristics is similar to that of BJT. But here the controlling parameter is gate emitter voltage VGE because IGBT is a voltage-controlled device is when the device is of junction J2 to block the forward voltage and in case reverse voltage appears across collector and emitter junction J1 blocks it. In static I-V characteristics, VRM is the maximum reverse breakdown voltage.

The transfer characteristics of an IGBT is a plot of collector current IC vs gate emitter voltage VGE as shown in figure transfer characteristics. This characteristic is identical to that of power MOSFET when VGE is less than the threshold voltage VGET, IGBT is in the offset.

Output Characteristics :


  • These connection are made as shown in the circuit diagram.
  • Now increase the VCE voltage to the maximum position.
  • When slowly increase the voltage across the VGE at certain voltage IGBT is turned on stop varying the voltage at that point.
  • Then reduce the voltage  VCE to the minimum position.
  • Now vary VCE voltage slowly, correspondingly note down the VCE and IC readings and plot the graph.

Transfer characteristic :


  • These connections are made as shown in the circuit diagram.
  • In these characteristics when increase the voltage  VCE voltage to the maximum position.
  • When slowly increase increase the voltage across VGE and note down the voltage VGE and current IC value and plot graph. 
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