Types of power electronics converters

A term power electronics system in electronics science consists of one or more power electronic converters. A power electronic converters are made up of some power semiconductor devices controlled by the integrated circuit.

Broadly speaking power electronic converters can be classified into six types under :

• Diode rectifier
• AC to DC converters
• DC to DC converters
• DC to AC converters
• AC to AC converters
• Static switches

1. Diode Rectifier:

A diode rectifier is an electronic circuit convert AC current known as input voltage which periodically reverses direction to a fixed DC voltage which flows in only one direction. The input alternating voltage may be single phase or three phases. This process is known as rectification. 

Diode rectifiers find wide use in electric traction, battery charging, electroplating, electrochemical processing, power supplies, welding, and uninterruptible power supply systems.

2. AC-DC Converters  ( Phase Controlled Rectifiers ) :

AC to DC converter is electrical circuits that transform alternating current ( AC ) input into direct current ( DC ) output. These rectifier use line voltage for their communication. 

AC to DC converter is mainly used in power electronic applications where the power input is a 50 Hz or 60 Hz sine-wave AC voltage that requires power conversion for a DC output. 

It may be fed from one phase or three-phase source. It is used in DC drives, metallurgical and chemical industries, excitation systems for synchronous machines etc.

3. DC-DC Converters ( DC Choppers ) :

DC to DC converters is an electronic circuit or electromechanical device that converts a source of direct current from one voltage level to another one. It is also known as DC choppers. 

DC chopper circuit is needed to forced, load, commutation to turn off the thyristors. Thyristors are replaced by power transistors for the lower power circuit.

Classification of the chopper circuit is dependent upon the types of DC communication and also on the direction of power flow. It finds wide application in DC drives, subway cars, trolley trucks, battery driven vehicles etc.

4. DC-AC Converters ( Power Inverters ) :

DC to AC converters is an electronic circuit that changes direct current ( DC ) to alternating current ( AC ). DC to AC converter is also called power inverters. Output current may be variable current and variable frequency. 

This types of converter find wide use in induction motor and synchronous motor drives, induction heating, UPS, HVDC, and transmission etc. 

Power inverters use load, line, or forced commutation for turning off the thyristors. 

At present, the conventional thyristor is also being replaced by high power application and by power transistors in low power application.

5. AC-AC converters :

AC to AC converters is an electronic circuit converts an AC waveform to another AC waveform, where the output voltage and frequency can be set arbitrarily. In other words, it converts fixed AC input voltage into a variable AC output voltage. 

There are two types of AC to AC converters : 

• AC Voltage Controllers 
• Cyclo Converters 

AC voltage controllers convert fixed AC voltage directly to a variable AC voltage at the same frequency. It is based on either thyristors, TRIACs, SCRs, or IGBTs which converts a fixed voltage, fixed frequency alternating current electrical input supply to obtain a variable voltage in output delivered to a resistive load. 

The output voltage is controlled by varying the firing angle delay and turn off device is obtained by line communication. 

They are widely used for lighting control, speed control of fans, pumps etc.

Cyclo converters convert AC, power at one frequency into AC power of an adjustable but lower frequency without any direct current. It converts input power at one frequency to output power at a different frequency through one stage conversion. 

Line commutation is more common in cyclo converters so that forced and load commuted cyclo-converters are also employed. 

They are primarily used for slow speed large AC drives like rotary kiln etc.

6. Static switches :

The static switch is an electrical device that switches a load between two sources. Some switches are manual that an operator affects the transfer by throwing a switch, while others are automatic when they sense one of a source has lost or gained power.

The static switches are called AC static switches or DC static switches depending upon the input supply. 

Explore more information:

1. Advantages and disadvantages of power electronics converters

Full form of GTO

What is the full form of GTO?

Answer :

• Gate Turn Off ( Thyristor )

What does GTO mean? 

GTO is a special type of thyristor invented by General Electric with characteristics of a high power semiconductor device. 

GTO opposed to the normal thyristors because it is fully controllable switches which can be turned ON and OFF by their third lead is called as gate lead. 

MOSFET switching characteristics

The turn ON and OFF times of MOSFET gets affected by its internal capacitance and the internal impedance of the gate drive circuit but it does not affect during steady-state operation. 

To understand switching characteristics of MOSFET we can take the simple equivalent circuit for an n-type MOSFET is given below :

Turn ON Process :

• The gate voltage is made positive to turn ON the MOSFET. When the gate voltage has applied the gate to source capacitance C_GS starts charging.
• When the voltage reached through C_GS certain voltage level is called the Threshold voltage ( V_GST ) at the same time drain current I_D begins to increase. 
• The time needed to charge C_GS to the threshold voltage level is known as a turn-on delay time.
• The C_GS charges from threshold to the full gate (V_GSP) voltage. The time required for this charging is known as rising time (t_r).
• During this period, the drain current increases to its full value of I_D because of that the MOSFET is fully turned ON.
• MOSFET turn-on time is given by, 

t_ON = t_[d(on)] + t_r

• The turn-on time can be reduced using a low-impedance gate drive source. 

Turn OFF Process:

• The MOSFET can be turned off with a negative or zero gate voltage. Due to this, the gate to source voltage decreases from V_I to V_GSP.
• C_GS discharges from V_I to V_GSP gate voltage. The time required for this discharge is called a turn-off delay time, during which the drain current also begins to decrease.
• The C_GS continues to discharging and its voltage equals a threshold voltage (V_GST).
• The time required to discharge C_GS from V_GSP to V_GST is called fall time (t_f). The drain current will be zero when the voltage V_GS < V_GST then it is said to have turned off. 
• MOSFET turn-off time is given by,  

t_OFF = t_[d(off)] + t_f

MOSFET switching waveform is shown in the figure below : 

MOSFET characteristics

In general, any MOSFET shows three operating regions following below.

1. Cut-off Region 
2. Ohmic or Linear Region 
3. Saturation Region 

Cut-off Region :

It is a region where MOSFET will be OFF because there will be no current flow through it. In this region, MOSFET acts as an open switch and thus when they are required to function as electronic switches. 

Ohmic Region : 

Ohmic or Linear region is a region where the current increases as the value of the voltage increases. If MOSFET is used in this region, it can be used as amplifiers. 

Saturation Region : 

In this region, despite the increase in voltage, the MOSFET has it's current constant and occurs when the voltage exceeds the pinch-off value. Under this condition, the device acts as a closed switch that saturates the value of current flows. This operating region is therefore selected whenever MOSFET is required to perform a switching operation. 

Now that we know this, let us analyze the prejudice in which these regions are experienced for each type of MOSFET. 

The transfer and output characteristics of the power MOSFET following below :

Transfer characteristics :

• This feature shows the variation of the current  I_D of the drain as a function of the V_GS gate-source voltage. 
• V_GS is the minimum positive voltage to induce n-channel between gate and source. Therefore, for threshold voltage below V_GS, the device is in the off state, a magnitude of is of V_GST the order of 2  to 3 V. This is typical characteristics for n-type MOSFET. 

MOSFET output characteristics :

• The output characteristics of MOSFET shown in the figure indicate the variation of the drain current I_D as a function of the V_DS drain-source voltage with the V_GS gate-source voltage as a parameter.
• For a low V_DS value, the graph between I_D and V_DS is almost linear, indicating a constant value of on-resistance R_DS = V_DS/I_D.
• If V_DS is increased for a given V_GS, the output characteristics are relatively flat, indicating drain current is nearly constant.
• The output characteristics of the load line A and B intersect. A indicates fully on condition and B fully off condition. MOSFET works as a switch either at A or B.
• When power MOSFET is driven with large gate-source voltage, MOSFET is turned on, V_DS is small. Here, MOSFET acts as a closed switch is said to be ohmic region.
• When the device turns on, MOSFET traverses characteristics from cut off to the active region and then to the ohmic region.
• When MOSFET turn off, it takes a backward journey from ohmic region to cut off state.

What is MOSFET | History | Operation | Types | Applications

MOSFET Introduction :

The MOSFET, commonly known as Metal Oxide Semiconductor Field Effect Transistor, is one type of semiconductor device that is widely used in electronic devices to switch and amplify electronic signals. 

It is an integrated circuit core and can be designed and manufactured in one chip. MOSFET consists of four-terminal devices such as source (S), gate (G), drain (D), body (B). 

History of MOSFET :

1925 - Julius Edgar Lilienfield first established the basic principle of this type of transistor. 

1959 - MOSFET was invented on the basis of FET design by Dawon Kahng and Martin Atalla at Bell Labs. 

Operation of MOSFET : 

MOSFET's goal is to be able to control the voltage and current flow between source and drain. Its work depends upon the MOS capacitor and works almost like a switch. The surface of the semiconductor at the below oxide layer which can be located between the source and drain terminal. It can be inverted from p-type and n-type by applying positive or negative gate voltages. The holes present under the oxide layer with offensive force and holes are pushed downward with the substrate when we apply positive gate voltage. The depletion region is formed, populated by the bound negative charges which are associated with the acceptor atoms and therefore electrons reach the channel. The positive voltage also attracts electrons from the source of n+ and drain regions into the channel. If a voltage is applied between them, the current flows freely between the source and drain, and the electrons in the channel are controlled by the gate. If a negative voltage is applied, a hole channel is formed under the oxide layer instead of a positive voltage. 

Types of MOSFET : 

1. Depletion Mode MOSFET 
2. Enhancement Mode MOSFET 

The channel shows its minimum conductance when there is zero voltage on the gate terminal. Since the voltage on the gate is negative or positive, the channel conductivity will be reduced. This type of transistor is called MOSFET depletion mode.

The channel does not conduct when there is no voltage on the gate terminal. The device has good conductivity when more voltage applied to the gate terminal. This is called a MOSFET enhancement mode.

P-channel MOSFET : 

The MOSFET P-channel has a region of the P-channel between drain and source. The MOSFET P-channel consists of negative ions and therefore works with a negative voltage. When the negative voltage is applied to the gate, the electrons present under the oxide layer are pushed downward into the substrate with an excessive force. The depletion region is populated by the bound positive charges which are allied with the donor atoms. The negative voltage attracts holes from p+ source and also drain region into the channel region as well. 

N-channel MOSFET : 

The MOSFET N-channel has a region of the N-channel between source and drain. When we apply the gate voltage, the holes present in the oxide layer pushed downward with a repulsive force into the substrate. The depletion region is populated by the bound negative charges linked to the acceptor atoms. The positive voltage also attracts electrons from the n+source and drain region. If a voltage is applied between the drain and source, the current flows freely between the source and drain, and the electrons in the channel are controlled by the gate voltage. If a negative voltage is applied a hole channel will be formed under the oxide layer. 

MOSFET Application : 

• Used as a switch 
• Used in MOS integrated circuits 
• CMOS circuits 
• Switched-mode power supply ( SMPS )
• Inverters
• Used as a constant current source 

For detailed information :

Read more >> Applications of MOSFET

MOSFET Application

MOSFET is one of the important elements in the design of embedded systems used to control the loads as per requirements.

In applications such as switched-mode power supply, variable frequency drives and other power electronics applications where each device can switch thousands of watts, discrete devices are widely used. 

Different types of MOSFET applications are used as per requirement. 

Application of MOSFET : 

• Used as a switch 
• Used in a calculator
• Used in audio frequency power amplifier for the public address system
• Used in high-frequency amplifier for amplifying electronics signals in the electronic devices
• Used in MOS integrated circuits, CMOS circuits, and VLSI circuits
• Used in both analog and digital circuit
• Used in switched-mode power supplies and inverters
• Used as constant current sources
• Used in brushless DC motor drive
• Used in electronic DC relay
• Used in light intensity control
• Used in motor speed control 
• Used in a high-frequency generator
• Used in sound reinforcement 
• Used in automobile sound system

Explore more information:

1. BJT vs MOSFET

Applications of NPN transistor

NPN transistor with their function in amplifying currents they have many applications and between PNP and NPN, the only difference is the direction of voltage flow.

Let we check the applications of NPN transistor :

• Mostly used in switching applications.
• Used in applications where there is a need to sink current.
• Used in amplifying circuit applications, such as push-pull amplifier circuits. 
• It is used to amplify weak signals in the Darlington pair circuits. 
• Used in temperature sensors. 
• Used in very high-frequency applications.
• Used in logarithmic converters.

Characteristic of BJT

Before we check the characteristics you should know the BJT full meaning. It is helpful to view the characteristic curves of the transistor in graphical form is very similar to the graphical approach used with diodes. 

Now we can check it out the characteristics of BJT. 

BJT Input characteristics :

• A graph of base current I_B Vs base-emitter voltage V_BE gives input characteristics. 
• Since a transistor's base-emitter junction is like a diode I_B versus V_BE graph resembles a diode curve. 
• When collector-emitter voltage V_CE2 is more than V_CE1, base current, for the same V_BE, decreases as shown in the figure. 

BJT Output characteristics :

• A graph of collector current IC Vs collector-emitter voltage V_CE gives output characteristics.
• For zero base current, for example, I_B = 0, as  V_CE is increased, a small leakage (collector) current exists as shown in the figure.
• As the base current is increased from I_B = 0 to I_B1, I_B2 etc, collector current also rises as shown in Figure.

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

Difference between NPN and PNP transistor

Nowadays, the NPN transistor is the most commonly used of the two types. It can be used for amplification and switching application, NPN has higher electron mobility than PNP. Therefore, NPN bipolar transistor is often more favored compared to PNP transistor. Yet they have significantly different characteristics.

Main Difference :

The main difference between them is in their internal structure and also electrical current flow direction. 

Another 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. 

This is all about the main difference between transistor NPN and PNP which are used to design electrical and electronic circuits and various applications. So now let us check some other significant differences are described with the help of comparison between them.

Difference between NPN and PNP transistor

• NPN called for Negative-Positive-Negative type transistor and PNP called for Positive-Negative-Positive. 
• The one p-region is to sandwiched by two n-region, its called NPN transistor with two p-region sandwiched one n-region, called as PNP transistor.
• Both transistors are composed of different materials.
• NPN transistor is turned ON when the electron enters into the base, and the PNP transistor is turned ON when holes enter into the base.
• The current flows from the collector(C) to the emitter(E) in NPN transistor, while in a PNP transistor, the current flows from the emitter(E) to the collector(C).
• In an NPN transistor majority charge carrier electrons and minority charge carrier holes, while  In a PNP transistor majority charge carrier holes and minority charge carrier electrons.
• In an NPN transistor, the switching time is faster while PNP transistor switching time is to be lower.
• The ground signal of the NPN transistor is low, while high in PNP transistor.
• NPN transistor sources it, and PNP transistor sink current. 
• The emitter-base junction of both the transistor NPN and PNP is connected in a biased forward direction.
• Both the NPN and PNP transistor base junction is connected in reverse bias.
• For low current applications, BJT is preferred while MOSFET is suitable for high power functions. 

Difference between working principle :

• NPN transistor: When the current is increased to the base terminal, transistor switches ON and it performs from the collector terminal to the emitter terminal. When reducing the current to the base, the transistor switches ON and the flow of current is so slow. 
• PNP transistor: When the current exists at the base of the PNP transistor, and then the transistor turns OFF while there is no current flow at the base of the transistor then the transistor is switched ON.

What is analog signal processing

Analog signal processing process the signal which is not digitized. It is a defined signal having continuous value.

Common analog processing elements include capacitors, resistors, inductors, and transistors. Analog values are typically represented as a voltage, electric charge around the component in the electronic device. It includes classical radio, radar, TV, telephone, etc. 

Explore more information:

1. What is a digital signal processing
2. What is an analogue signal
3. What is Digital Signal
4. Application of DSP

Full form of technical terms related to power electronics

Full form of technical terms related to power electronics :

• Full form of UJT
• Full form of MCT
• Full form of BJT
• Full form of MOSFET
• Full form of IGBT
• Full form of GTO 
• Full form of SCR
• Full form of PUT 
• Full form of SUS
• Full form of SCS
• Full form of NSS
• Full form of OSS
• Full form of AUS
• Full form of VLR
• Full form of SITH
• Full form of SMPS
• Full form of HVDC
• Full form of UPS
• Full form of RMS
• Full form of TRIAC

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). 

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 :

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 I_C , I_E is receptively known as collector and emitter current and V_CB , V_EB is collector-base voltage and emitter-base voltage.
• Shown in figure current I_C , I_{E  ,} I_B 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 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 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