Showing posts with label Power transistor. Show all posts
Showing posts with label Power transistor. Show all posts

What is PNP transistor

PNP transistor structure :

PNP transistor consisting of a layer of N-doped semiconductor between two layers of p-doped material. In the collector output, a small current leaving the base is amplified. If its base is pulled low relative to the emitter, the PNP transistor is ON. The emitter-base region is biased forward in this type of transistor so that holes are injected into the base as a minority carrier. The base is very thin and most holes cross the collector's reverse biased base-collector junction. 

PNP potential barrier : 

 In PNP transistor as more electrons and holes flow in the region of depletion, the number of positive and negative ions is reduced and the region of depletion becomes narrow. The energy loss in overcoming the barrier potential results in a voltage drop across the PN junction equal to the barrier potential in the range of 0.7 V for Si and 0.3 V for Ge. 


PNP transistor works : 

 When you have a small current running from emitter to base of the transistor a PNP transistor will turn ON. When you say turn ON, means that the transistor will open up a channel between emitter and collector and this channel can carry a much larger current. As discussed, we need two depletion layers with specific barrier potential required to diffuse the depletion layer. According to the barrier potential most common type of transistor used is silicon because it is the most abundant element on the earth after oxygen. 

What is NPN transistor

NPN transistor structure : 

The transistor in which one p-type region is placed between two n-type regions is known as the NPN transistor. The p region has access to 'holes' mobile carrier of positive charge, and n region has access of electrons mobile carrier of negative charge. The charge carriers diffuse and some electrons fall into p-type holes are fitted with n-type electrons. This leaves some atoms with a negative charge in the p region, and some atoms with a positive charge in the n region. The atoms are fixed in place and they are charged but mobile is not charged. This creates a potential for space charge between regions, which forces mobile carriers near the junctions between regions away from the junction, leaving depletion layers at the junctions without mobile carriers.

NPN potential barriers : 

Since they do not have mobile charge carriers, the depletion layers are insulators, potential barriers. If you bias a positive n region with respect to the p region adds to the potential for space charging and increase the barrier potential and no current flows. So region n is called a collector. 

p region is called as a base because one way of making an NPN transistor starts with p material and n material are diffused into it to make other regions.

NPN transistor works : 

Electrons at the base are in a potential field that attracts them to the collector. Most of these electrons are collected due to the proper design, leaving only a few to flow out of the base connection. The proportion of collected electrons out of emitted electrons is called as an alpha. 

NPN transistor current gain : 

The overall effect of NPN transistor is that a small base current controls a much larger collector current. If we take the emitter current as 1, the collector current is alpha, and the base current is 1 - alpha. This is known as Kirchoff's Current Law. The current gain from base to collector called beta which is alpha / (1-alpha). 

If alpha is 0.95 beta is 0.95 / 0.05 = 19 ( a very poor design )
If alpha is 0.99 beta is 0.99 / 0.01 = 99 ( ok design )
If alpha is 0.999 beta is 0.999 / 0.001 = 999 ( Excellent design ) 

What is IGBT

Let us find out the full meaning of IGBT and some more information on IGBT to know more about it. 

Full information about IGBT :

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

IGBT is also known as metal oxide insulated gate transistor (MOSFET device), also called a conductively modulated field-effect transistor (COMFORT). It was also initially called an insulated gate transistor called IGT. 
Several merits of IGBT process is high input impedance compare to PMOSFET and has low on-state power loss as in a BJT. All these merits have made it IGBT is very popular among all power electronics system engineers.

IGBT is a three-terminal semiconductor device (emitter, base, collector) with huge bipolar current-carrying capability.

These terminals as an emitter, collector, and gate. IGBT has a CMOS input and bipolar output characteristic and voltage-controlled bipolar device. This device is apt for several applications such as DC and AC motor drive, UPS system, power supply, PWM (pulse width modulated), SMPS (Switched-mode power supplies) and drives for solenoids.

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 the various value of gate-emitter voltages VGE1, VGE2 etc.

IGBT meaning

The term IGBT full form Insulated Gate Bipolar Transistor is a solid-state device. It is introduced on the 1980s. A power transistor characteristics of both MOSFET as well as BJT  are used in IGBT. So it makes used advantages of both power MOSFET and BJT, the IGBT has been introduced. IGBT can be used much more application like electric cars, digital stereo power amplifier, SMPS, UPS, PWM, home application and uses in many more power circuits. IGBT advantages are that it can improve dynamic performance and efficiency.

IGBT symbol

IGBT stands for Insulated Gate Bipolar Transistors a three terminal device. It combined with BJT and MOSFET. It can be used as an electronic switch.

Schematic symbol diagram :
MOSFET                  BJT                              IGBT

MOSFET symbol

N-channel and P-channel both are Metal oxide field effect transistor ( MOSFET ). It is a four terminal device. MOSFET has four terminal called G called gate, D called drain, S called source and B called base. MOSFET full form source terminal is frequently connected so making it a three-terminal device like a Field effect transistor. It is most commonly used in the analog and digital circuit.

Schematic diagram symbol :

N-channel                        P-channel

Advantages and disadvantages of FET

The term FET full form is the Field Effect Transistor. We all know the real fact is all MOSFET are FETs but not all FETs are MOSFET. It is used in amplifier in the oscilloscope, electronics voltmeter, multiplexer, chopper, etc. This article gives information about advantages and disadvantages of FET to know more about FETs.

Advantages of FET :
  • FET has a high input impedance of several megaohms 
  • FET has less effect by radiation than BJT
  • Temperature stable than BJT
  • Less noise compare to BJT
  • Can be fabricated with fewer processing
  • Smaller in size
  • Longer life
  • High efficiency
  • It can be used low frequency application
  • Uni-polar device
  • Voltage control device
  • They have better thermal stability
  • They have voltage control device
Disadvantages of  FET :
  • They are more costly than junction transistor
  • Smaller gain bandwidth product compare to BJT
  • Transconductance is low hence voltage gain is low
  • It has lower switching time compare to BJT
  • Special handling is required during installation
  • When FET performance degrades as frequency increases. This due to the feedback by internal capacitance
Explore more information:

Advantages and disadvantages of MOSFET

The term MOSFET full form is Metal-Oxide-Semiconductor-Field-Effect-Transistor. MOSFET is a one types of power transistor device mostly used in VLSI circuit, CMOS digital circuit, microprocessor, and memory devices etc. This article gives information about the advantages and disadvantages of  MOSFET to know more about MOSFET.

Advantages of MOSFET :
  • Ability to scale down in size
  • It has low power consumption to allow more components per chip surface area
  • MOSFET has no gate diode. This makes it is possible to operate with a positive or negative gate voltage
  • It read directly with very thin active area
  • They have high drain resistance due to lower resistance of a channel
  • Physical size is less than 4 mm^2 when it is a package form
  • It is widely used than JFET
  • The enhancement type MOSFET find wide application in digital circuitry
  • They support high speed operation compare to JFETs 
  • They have high input impedance compare to JFET
  • It is easier to fabricate MOSFET than JFET
  • They can easy to manufacture
Disadvantages of  MOSFET :
  • Has a short life
  • Required repeated calibration for accurate dose measurement
  • They have very susceptible to overload voltage, hence due to installation special handling is to be required 

Explore more information:

BJT modes of operation

The Bipolar junction transistor (BJT) is a junction transistor. It can be operated in three modes. The operation of the transistor in these modes is listed below :
  • Cute of mode
  • Saturation mode
  • Active mode
1. Cut of mode :
  • In cut of mode both of emitter to base and collector to base are reversed biased. 
  • In reverse bias condition, there is no current flow through the device, so there is no current flowing in the transistor.
  • So in this mode transistor is OFF state.
  • In off state mode of a transistor can be used switching operation for switch off application.
2. Saturation mode :
  • In saturation mode, both of collector to base and emitter to base is forward bias. 
  • In forward bias condition, current flow through the device, so electric current flow through the transistor.
  • So in this mode, free electrons flow from both of device emitter to base and collector to base.
  • In this mode huge current flow to the base of a transistor so at this stage transistor in going to saturation mode and that will be on ON state and acts as a closed switch.
So finally we conclude that above two modes of operation transistor as an ON/OFF switch.

 3. Active mode :
  • In Active mode one junction Collector to a base reverse mode and other junction emitters to base forward bias.
  • So in this type of mode, it can be used as amplification of current.
Conclusion: So we can conclude that the transistor work as an ON/OFF switch when it is in saturation and cut off modes whereas it works as an amplifier of current in active mode.

Application of BJT

Biploar Junction Transistor (BJT) can be most commonly used in analog and digital circuit Here this article gives some application of BJT to better understand this topic.
  • It is used digital circuit design 
  • It is used as amplifying circuit
  • It is used as amplifying circuit
  • It is also used sound amplifier
  • It is used as a oscillator
  • It can used as modulator
  • It can be used as multivibrator
  • It is used in electronics switch
  • It is used timer as well as time delay circuit
  • It can be also used in demodulator or detector
  • Analog circuit
  • High frequency application
  • Switching device
  • Microwave device
  • Robotics application
  • Darling-ton pair circuit
  • Heavy motor to control current flow

Advantages and disadvantages of BJT

The term BJT full form is called as Bipolar Junction Transistor. It is one type of power transistor. It is used in the amplifier, multi-vibrator, oscillator, modulator, demodulator, etc. This article gives information about the advantages and disadvantages of BJT to know more about BJT.

 Advantages of  BJT : 
  • They have a better voltage gain
  • They have a high current density
  • They have a low forward voltage 
  • It can be operated in low to high power application
  • BJT has a large gain bandwidth
  • BJT shows better performance at high frequency
Disadvantages of BJT :
  • BJT has a low thermal stability
  • BJT is most effective by radiation
  • BJT has more noise produced
  • BJT has a low switching frequency
  • BJT has a very complex control
  • The switching time is not very fast compared to a high alternating frequency of current and voltage 

BJT symbol

NPN and PNP both are Bipolar junction transistor (full form of BJT). It is three terminal electronics device n b called Base, e called Emitter and c called Collector. It is back to back connection of two P-N junction diode. The terminal are emitter are highly doped, base are lightly doped and collector are moderately doped region.

Schematic diagram symbol :

NPN                                          PNP

What is NPN and PNP transistor

What is an NPN transistor?

 NPN transistors are three-terminal, a three-layer device that can function as either amplifiers or electronic switches. 

In NPN transistor one p-type material is placed between two n-types materials is known as Negative-Positive-Negative type transistor. 

It amplifies the weak signals to enter into the base and produces strong amplify signals at the collector end. In NPN transistor, the direction of movement of an electron is from the emitter to collector region due to which current constitutes in the transistor. 

 What is a PNP transistor? 

 PNP transistors also are three-terminal, a three-layer device that opposite to NPN transistor where a positive DC voltage is applied to the emitter.  

 In PNP transistor one n-type material is placed between two p-type materials is known as Positive-Negative-Positive type transistor.  

 PNP transistor uses a small base current and a negative base voltage to control a much larger emitter-collector current. PNP transistor, the emitter is more positive with respect to the base and also a collector. 

 The main difference between these two types of transistors is that the holes are more important carriers for PNP transistors, while electrons are more important carriers for NPN transistors. 
Both NPN and PNP transistor are the same in some way and related to each other but they may have differed from each other too. 

 You can also check it out the difference between NPN and PNP transistor
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