Seminar on THYRISTOR with PPT and PDF Report: Large semiconductor diode can be considered as a predecessor to thyristors. The advent of thyristors started the field new power electronics. P-N-P-N switch concept’s introduction in the year of 1956 was one among initial advancement. This switch concept was published by J.L. Moll and others in Bell laboratories. Very fast, engineers recognized its importance to control and power conversion. After this recognition, within a time period of nine months announced a commercial silicon control rectifier and year of an announcement was 1957. The initial commercial silicon rectifier had a blocking voltage of 300V and had 25A of continuous current carrying capacity. Silicon controlled rectifiers is another name for thyristors. Many other machines in a huge number which has similar features like a thyristor have been developed. Few examples of such devices are mentioned below:

  • Inverter grade fast thyristor
  • Silicon controlled switch (SCS)
  • Light-activated silicon controlled switch (LASCR)
  • Asymmetrical thyristor (ASCR)
  • Reverse conducting thyristor (RCT)
  • Diac
  • Triac
  • Gate turn off thyristor (GTO)

Seminar THYRISTOR with PPT and PDF Report

If we observe thyristor from an operational point of view and from a constructional point of view then it has following features:

  • It is a four layer device
  • It has three terminals
  • It is also a minority carrier semi-controlled machine

The thyristor can be operated with a current signal but it is difficult to turn off device without interrupting main current. It has feature of conducting current in only one direction and blocking voltage in both directions. Because of internal latch-up technique, it gives very low forward voltage drop. If we compare thyristors with BJT then thyristors have longer switching times.

Constructional features of a thyristor:

Circuit symbol of thyristor is shown below:

Fig1: circuit symbol of a thyristor

The schematic construction of a thyristor has lightly doped  layer which is sandwiched between p-type layers. These p-type layers have doing levels which are higher by two orders of magnitude. The p-layer which is in bottom has connections of gate terminal.

Steady-state characteristics of a thyristor:

Characteristics which come under steady-state characteristics are mentioned below:

  • Static output i-v characteristics of a thyristor
  • Thyristor gate characteristics

Thyristor ratings:

Few specifications of thyristor which are related to its steady-state characteristics are found in datasheet of a manufacturer and those are mentioned below:

  • Voltage ratings
  • Current ratings
  • Gate specifications
  1. Voltage ratings: Parameters related to voltage ratings are mentioned below:
  • Peak working forward OFF state voltage
  • Peak repetitive off state forward voltage
  • Peak non-repetitive off state forward voltage
  • Peak working reverse voltage
  • Peak repetitive reverse voltage
  • Peak non-repetitive reverse voltage
  1. Current ratings: Parameters which come under current ratings are mentioned below:
  • Maximum RMS current
  • Maximum surge current
  • Maximum squared current integral
  • Latching current
  • Holding current
  • Maximum forward voltage drop
  • Average power dissipation
  1. Gate specifications: Parameters which are under gate specifications are:
  • Gate current to trigger
  • Gate voltage to trigger
  • Nontriggering gate voltage
  • Peak reverse gate voltage
  • Average gate power dissipation
  • Peak forward gate current

Switching characteristics:

Switching characteristics of a thyristor are:

  • Turn on switching characteristics
  • Turn off switching characteristics
  1. Turn on switching characteristics: In this, transition time is known as thyristor turn of time. It is divided into three distinct intervals and they are:
    • Delay time
    • Rise time
    • Spread time

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