Types of thyristor

• The terms thyristor include all four-layer P-N-P-N devices used for control of power in AC and DC systems.
• The silicon controlled rectifier is the most popular member of the thyristor family. There are several other members of the thyristor family-like GTO, ETO, PUT, SUS, SCS, TRIAC, DIAC, etc.

Depending on the turn-off and turn-on capabilities and hence the physical structure, we categorize the thyristor into the following categories :

Major types of Thyristors :

• Silicon controlled thyristor or SCRs
• Bidirectional phase-controlled thyristor or BCTs
• Fast switching thyristor or SCRs
• Bidirectional triode thyristor or BCTs
• Light-activated silicon controlled rectifiers or LASERs
• Reverse conducting thyristor or RCTs
• FET controlled thyristor or FET-CDs
• Gate turn off thyristor or GTOs
• Emitter turn off thyristor or ETOs
• MOS turn off thyristor or MTOs
• Integrated gate commutated thyristors or IGCTs

In recent years, most development effort has gone into both continued integration of the gating and the control electronics into thyristor modules and the use of MOS technology to create gate structures integrated into the thyristor itself.

• Many variations of this theme are being developed and some technologies should rise above in the others in the years to come.

1. PUT :

• PUT full form is Programmable Uni Junction Transistor is a P-N-P-N device like SCR full meaning, but the major difference is that the gate is connected to n-types material near the anode as shown in the figure.
• PUT is used mainly in time delay, logic and also have SCR trigger circuits. Circuit symbol and I-V characteristics of a PUT are shown in the figure.
• In a PUT, Gate is always biased positive with respect to the cathode. When the anode voltage exceeds the gate voltage by about 0.7 V around, Junction j1 point gets forward biased and PUT turn on. When anode voltage becomes less than apply gate voltage, PUT is become turn off.

2. SUS :

• SUS full form Silicon Unilateral Switch is similar to a PUT  but with an inbuilt low voltage avalanche diode between gate and cathode as shown in the figure.
• Because of the presence of diode, SUS turns on for a fixed anode to cathode voltage unlike an SCR whose trigger voltage and/or current vary widely with changes in ambient temperature.
• SUS is used mainly in timing, logic, and trigger circuits. Its rating is about 20 V and 0.5 A. circuit symbol, equivalent circuit and I-V characteristic of a SUS are shown in the figure.

3. SCS :

• SCS full form silicon control switch. For example Four electrons thyristor. It has two gates, one anode gate (AG) like a PUT device and another cathode gate (KG) like an SCR.
• In other words, SCS is a four-layer, four terminal P-N-P-N devices; with anode A, cathode K, anode gate called AG, and cathode gate called KG to shown in the figure.
• SCS can be turned on by either gate. Circuit symbol and also I-V characteristics of an SCS are shown in the figure.
• When a negative pulse is applied to gate anode (AG), junction J1 is forward biased and at that time SCS is turned on.  A positive pulse at AG will reverse bias junction j1 and turn off the SCS.
• A positive pulse at gate kathode  (KG) turns on the device and a negative pulse at KG turns it off. 
• The application includes the timing, logic and triggering circuit, pulse generators, voltage sensors, oscillators.

4. Light-activated thyristors :

• The circuit symbol and I-V characteristics light activated thyristors, are also called LASCR, are shown in the figure. 
• LASCR is turned on by throwing a pulse of light on the silicon wafer of the thyristor. The pulse of the appropriate wavelength is guided by optical fibers to the special sensitive area of the wafer.
• If the intensity of light exceeds a certain value, the excess electron-hole pair is generated due to radiation and forward biased thyristor gets turned on.
• The primary use of light fired thyristor is in high voltage, high current application and also static reactive power compensation etc.
• A light fired thyristor has complete electrical isolation between the light triggering source and the high voltage anode-cathode circuit.
• Light-activated thyristors are available up to 6 kV and also 3.5 kA, with on state voltage drop of about around 2 V and with light triggering requirement of 5mW.

5. Diac ( Bidirectional thyristor diode) :

• Across-sectional view of a DIAC showing all its layers and junction is depicted shown in the figure.
• If voltage V12, with terminal 1 positive with respect to terminal 2, exceeds break over voltage  VB01, then structure P-N-P-N conducts. 
• The term Diac is obtained from capital letters called, DIode that can work on AC. To show in figure Diac has symmetrical breakdown characteristics.
• Its leads are interchangeable. Its turn on voltage is about 30 V.  When conducting, It acts like a low resistance with about 3 V drop across it to shown in figure.
• When not conducting, it acts as an open switch. A DIAC is sometimes called a gate less TRIAC.

6. SCR :

SCR stands for silicon controlled rectifier. It is basically four layered current controlling solid state device. SCRs can conduct current in only one direction, SCR can be triggered normally by the current which is applied to the gate terminal. To know more about SCR follow the link to know more about SCR (thyristor). I-V characteristics of a thyristor

7.Triac :

• SCR full form Silicon Control Rectifier is a unidirectional device that can conduct from anode to cathode only and not from cathode to anode while A Triac can conduct in both the directions. 
• A TRIAC is thus bidirectional thyristor with three terminals MT1, MT2, and Gate. It is used extensively for the control of power in the AC circuit. 
• The word Triac derived by combining the capital letters from the word TRIode and AC. When in operation, a Triac is equivalent to two SCRs connected in anti-parallel. The circuit symbol and its characteristics are shown in the figure.

PUT full form

What is the full form of PUT?

Answer : 

• Programmable Uni Junction Transistor

What does PUT mean?

In a PUT, G is always biased positive with respect to the cathode. When the anode voltage exceeds the gate voltage by near about 0.7 V, Junction gets forward biased and PUT turn on. When anode voltage becomes less than gate voltage, PUT is become turn off. 

It is a PNPN device like SCR, but the major difference is that the gate is connected to n-types material near the anode. 

PUT is used mainly in time delay, logic as well as SCR trigger circuits.

Explore more information:

1. MOSFET full form
2. JFET full form
3. BJT full form
4. IGBT full form
5. MCT full form
6. UJT full form

What is power transistor

Basic information : 

The power transistor is a transistor that used in high power amplifier and power supplies. Power transistors are suited for application where a lot of power is being used current and voltage. It is a junction transistor, is designed to handle high current and power and also used in audio and switching circuits. 

The power transistor is three terminal semiconductor device used to amplify and switch electronic signals and electrical power. They come in NPN, PNP, and Darlington (NPN or PNP) forms.

The structure and construction of a power transistor are entirely different from that of a single transistor but their characteristics and operation are almost the same. 

Power transistors, however, possess controlled characteristics. These are turned on when a current sign is given to base, or control, terminal. The transistor remains in the on-state so long as a control signal is present. When this control signal is removed, a power transistor is totally turned off.

There are four types of power transistor :

• Bipolar junction transistors (BJTs)
• Metal-oxide-semiconductor field-effect transistors (MOSFETs)
• Insulated gate bipolar transistors (IGBTs) 
• Static induction transistors (SITs)

How does a power transistor work? 

A power transistor can mainly do two different jobs such as work as an amplifier or as a switch. When it works as an amplifier, it takes in a tiny electric current at the input and produces a much bigger electric current at the output. 

When it works as switches a tiny electric current flowing through the input of transistor can make a much bigger current flow through the output of transistor. 

Why transistor is used in daily life application?

• High voltage gain
• Require low power supply voltage for operation
• Smaller size 
• No heating problem during operation 
• Solid state device 
• Mechanically so strong
• Easily portable

For detailed information

Read more >>  Power transistor application

Types of FDMA

FDMA is a continuous transmission method. Channel can use one phone circuit at any instant of time. 

Basically, there are two types of  FDMA multiple access methods. 

Types of FDMA : 

• FAMA 
• DAMA

FAMA - FAMA denoted as Fixed assignment multiple access. In FAMA the channel is assigned in a predetermined manner and distributed so that random changes in the capacity are not allowed.

DAMA -  DAMA denoted as Demand assignment multiple access. If there are multiple stations there is a change of capacity and after that, the channel can be allocated to the demand.

FAMA - FDMA :

FDMA deal with link accessing using different frequency band and by multiple stations. It is concerned with the logical link between the stations that are preassigned.

FAMA-FDMA is preassigned. It is not flexible in accordance with the change in traffic.

DAMA - FDMA :

Demand access signifies the allocation of satellite channel to a user on demand, rather than continuously. Therefore demand assignment multiple access is used for earth stations where the traffic conditions are continuously changing.

One demand allocation of channel greatly increases the number of simulations uses who can be served by the system.

For example, telephone voice users communicate at random times, some for less than a minute to voice users communicate at random times, some for less than a minute to several minutes.

If each user were allocated a fixed channel, most of the time the channel will be idle, resulting efficiency utilization of the entire system is low. Therefore demand allocation remarkably increases the number of telephone user served by the system.

Demand access system requires two different types of channel :

• Common signaling channel
• Communication channel

Full form of SCR

What is the full form of SCR?

Answer :

• Silicon Controlled Rectifier OR Semiconductor Controlled Rectifier

What does SCR mean? 

SCR is a four-layer semiconductor current controlling device. It has three terminals called Anode (A), Cathode (C), and Gate (G) and has three junction P-N-P-N.  

The first SCR was developed by a team of power engineers led by Gordon Hall. It was commercialized by Frank W. "Bill" Gutzwiller in 1957. 

It is a unidirectional device, meaning of that it passes electron in only one direction, from the cathode to the anode.

SCR is a General Electric's (GE) trade name for a type of thyristor used for power control in a DC system. SCR is one of the oldest methods of this thyristor family.  

At present, the use of SCR is so vast in recent years that over the years, the word thyristor has become synonymous with SCR. 

Explore more information:

1. MOSFET full form
2. JFET full form
3. BJT full form
4. IGBT full form
5. MCT full form
6. UJT full form

Full form related VLSI

VLSI - Very large scale integrated circuit  

ASIC - Application Specific Integrated Circuit

AVC - Advanced video coding Blu-Ray high-density disc used to store digital information

CABAC - Context-adaptive binary arithmetic coding

CB - Coding block
CLB - Configurable logic block

CIF - Common intermediate format

COE - Co-Efficient file format

CTB - Coding tree block

CTU - Coding tree unit

CU - Coding unit

DVD - Digital video disc

FPGA   Field Programmable gate array

GOP - Group of pictures
GA - Gate array

GPB - Generalized P and B- picture

HDL - Hardware description language

HDTV - High definition television

HEVC - High-efficiency video coding

ISO - International standardization organization
ICS - Integrated circuits   

ITU-T - International telecommunication union – telecommunication standardization sector

JCT-VC - Joint collaborative team on video coding

MPEG - Moving picture experts group

MPM - Most probable modes

MSE - Mean squared error
PLA - Programmable logic array

PB - Prediction block
PSM - Programmable multiplexer

PSNR - Peak signal to noise ratio

PU - Prediction unit

QCIF - Quarter CIF RGB   red green blue (Colour Space)

SAD - Sum of absolute differences
SOG - Sea of gate

TB - Transform block

TU - Transform unit

VHDL - VHSIC hardware description language

VHSIC - Very high speed integrated circuit

YCbCr - Luminance, blue chrominance, red chrominance colour space

YUV - Colour space that stores the luminance and chroma information of a pixel

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

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