MADE BY ANANDHUU

1. SEMINAR ON
THYRISTOR
• GUIDED BY: PRESENTED BY:
LEKSHMIPRIYA S MIDHUN M
CLASS NO. 34
REG.NO.20200399
Dept. of Electronics and communication

2. Introduction
 Thyristerisa three terminal device having Gate
Anode and Cathode.
 Anode Ispositive and Cathode isnegative terminal
 Gate terminal fora controlling input signal

3. SCR/Thyristor
A thyristor is normally four layer three-terminal
device.
 Four layers are formed by alternating n –type and
p –type semiconductor materials.
 Consequently there are three p –n junctions formed
in the device.
 It is a bistable device.
The three terminals of this device are called anode
(A), cathode (K) and gate (G) respectively.

4. Structure on the physical and electronic level, and the
thyristor symbol.

5. • Thyristors have three states:
1.Reverse blocking mode – Voltage is applied in the
direction that would be blocked by a diode.
2.Forward blocking mode – Voltage is applied in the
direction that would cause a diode to conduct, but the
thyristor has not been triggered into conduction.
3.Forward conducting mode – The thyristor has been
triggered into conduction and will remain conducting
until the forward current drops below a threshold value
known as the "holding current“.

6. Thyristor discovery
• The idea for the thyristor was first described by Shockley in 1950.
• It was referred to as a bipolar transistor with a p-n hook-collector.
• The mechanism for the operation was analysed further in 1952 by
Ebers.
• Then in 1956 Moll investigated the switching mechanism of the
thyristor.
• Development continued and more was learned about the device
such that the first silicon controlled rectifiers became available in
the early 1960s where it started to gain a significant level of
popularity for power switching.

7. Basic Operating Principle ofThyristor
The basic working principle in the SCR is that as the
triggering or the biasing is applied at the terminal gate
then the conduction begins.
 As it is a unidirectional device the current will be in a
single direction.
 It resembles the operation of the diode but the only
difference is that this can withstand the high amount of
voltages and powers.

8. Basic Construction of Thyristor
 An SCR is constructed with the four layers that consist of the P-type
and the N-type semiconductor material.
 These are layered in such a way that it tends to form three junctions
that are J1, J2, and J3.
 The three terminals that are attached to it are known as anode,
cathode, and gate.
 SILICON CONTROLLED RECTIFIERS (SCR) A silicon controlled
rectifier is a semiconductor device that acts as a true electronic
switch.
 It can change alternating current and at the same time can control the
amount of power fed to the load.
 SCR combines the features of a rectifier and a transistor.

9. Construction of Thyristors
• Thyristors can be understood with the help
of two transistor analogy.
• The collector of one transistor is connected to the base of the
second transistor while the collector of the second transistor is
connected to the base of the first transistor.
• Thus, total four layers of semiconductor material are connected
to each other and total three junctions are formed.
• In thyristors, there are three terminals that are anode, cathode
and gate. Gate terminal provides the controlling voltage.

10. Types of Thyristor
• There are various semiconductor devices which can be
classified under the thyristor family. Some of the most
used devices are SCR, DIAC, TRIAC, GATT etc..

11. Characteristics of Thyristors
• The characteristics curve of Thyristors is shown in the diagram below.
With the help of characteristics curve, we can understand its working
in forward biased mode and reversed biased mode in a detailed
manner.

13. Advantages of Thyristors
1.Better Efficiency: Thyristors possess better efficiency than
transistors, thus it is used in various application of electronics.
2.Low cost of Fabrication: The cost of fabrication of thyristors
is low and thus it is economical to use in various electronics
circuits for switching operation.
3.Ability to be controlled: This is the robust characteristics of
the thyristor as because of the gate terminal the thyristor can be
controlled.
4.High Reliability: The thyristor is the highly reliable device, and
thus is used as a significant part in HVDC transmission.

14. Disadvantages of Thyristor :
It can not be negative.
It can not be used higher frequency.
It can not be easily turn off.
In the AC circuit, it need to be turn on each cycle.
Gate current can not be negative.

15. Applications of Thyristors
1.Rectification Purpose: The thyristors are used for rectification of AC
signal. Thus, when the controlled signal is given to rectifier it converts AC
into DC.
2.Relay Control: Thyristors are used in relay control.
3.Phase Control: The phase controller used thyristors for providing phase
correction in the circuit.
4.HVDC transmission: They are also used in high voltage DC transmission.
5.Control of temperature, level and Position: Due to its robust controlling,
it can be used for controlling the temperature, level, position and
illumination.

16. CONCLUSION
• It is a power elelctronic device.
• It controls high voltage and current.
• Working in between 50 to 10khz frequency.
• Controlling is very easy.
• Triggering voltage is very less.