Different Types Of Thyristors And Their Applications

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Types Of Thyristors And Their Applications
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Types Of Thyristors And Their Applications
Introduction

• Thyristor is a small device which can control
  large amounts of voltage and power. Thyristors
  are used as current reversal to turn off the
  device. Actually, it takes direct current so it
  is very difficult to apply to the device. Lets
  learn Types Of Thyristors And Their Applications
  in details.

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Types Of Thyristors And Their Applications
What is a Thyristor?

• A thyristor is a four layer solid-state
  semiconductor device with P and N type material.
• Whenever a gate receives a triggering current.
• It starts conducting until the voltage across
  the thyistor device is under forward bias.
• So it acts as a bistable switch under this
  condition. 
• To control the large amount of current of the two
  leads.

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Types Of Thyristors And Their Applications
What is a Thyristor?

• We have to design a three lead thyristor by
  combining the small amount of current to that
  current.
• This process is known as control lead.
• If the potential difference between the two leads
  is under breakdown voltage.
• Then a two lead thyristor is used to switch on
  the device.

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Types Of Thyristors And Their Applications
Thyristor Circuit Symbol

• Thyistor circuit symbol is as given below. It has
  three terminals Anode, cathode and gate.

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Types Of Thyristors And Their Applications
Different States in a Thyristor

• There are three states in a thyristor

• Reverse blocking mode In this mode of operation,
  the diode will block the voltage which is
  applied.
• Forward blocking mode In this mode, the voltage
  applied in a direction makes a diode to conduct.
  But conduction will not happen here because the
  thyristor has not triggered.
• Forward conducting mode The thyristor has
  triggered and current will flow through the
  device until the forward current reaches below
  the threshold value which is known as Holding
  current.

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Types Of Thyristors And Their Applications
Thyristor Layer Diagram
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Types Of Thyristors And Their Applications
Thyristor Layer Diagram

• Thyristor consists of three p-n junctions namely
  J1, J2, and J3.
• If the anode is at a positive potential with
  respect to the cathode and the gate terminal is
  not triggered with any voltage.
• Then J1 and J3 will be under forward bias
  condition.
• While J2 junction will be under reverse bias
  condition.
• So J2 junction will be in the off state (no
  conduction will take place).

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Types Of Thyristors And Their Applications
Thyristor Layer Diagram

• If the increase in voltage across anode and
  cathode beyond the VBO (Breakdown voltage).
• Then avalanche breakdown occurs for J2.
• Then thyristor will be in ON state (starts
  conducting).
• If a VG (Positive potential) is applied to the
  gate terminal.
• Then a breakdown occurs at the junction J2 which
  will be of low value VAK.

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Types Of Thyristors And Their Applications
Thyristor Layer Diagram

• The thyristor can switch to ON state, by
  selecting a proper value VG.
• Under avalanche breakdown condition.
• The thyristor will conduct continuously without
  taking consideration of gate voltage, until and
  unless,

• The potential VAK is removed or
• Holding current is greater than the current
  flowing through the device.

• Here VG Voltage pulse which is the output
  voltage of the UJT relaxation oscillator.

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Types Of Thyristors And Their Applications
Thyristor Switching Circuits

• The two types of thyristor switching circuits are

1. DC Thyristor Circuit.
2. AC Thyristor circuit.

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Types Of Thyristors And Their Applications
DC Thyristor Circuit
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Types Of Thyristors And Their Applications
DC Thyristor Circuit

• When connected to the DC supply, to control the
  larger DC loads and current we use thyristor.
• The main advantage of thyristor in a DC circuit
  as a switch gives a high gain in current.
• A small gate current can control large amounts of
  anode current.
• So the thyristor is known as a current operated
  device.

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Types Of Thyristors And Their Applications
AC Thyristor Circuit
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Types Of Thyristors And Their Applications
AC Thyristor Circuit

• When connected to the AC supply,
• Thyristor acts differently because it is not same
  as DC connected circuit.
• During one half of a cycle,
• Thyristor used as an AC circuit causing it to
  turn off automatically due to its reverse biased
  condition.

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Types Of Thyristors And Their Applications
Types of Thyristors

• Based on turn on and turn off capabilities the
  thyristors are classified into the following
  types

• Silicon controlled thyristor or SCRs
• Gate turn off thyristors or GTOs
• Emitter turn off thyristors or ETOs
• Reverse conducting thyristors or RCTs
• Bidirectional Triode Thyristors or TRIACs
• MOS turn off thyristors or MTOs

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Types Of Thyristors And Their Applications
Types of Thyristors

• Based on turn on and turn off capabilities the
  thyristors are classified into the following
  types

• Bidirectional phase controlled thyristors or BCTs
• Fast switching thyristors or SCRs
• Light activated silicon controlled rectifiers or
  LASCRs
• FET controlled thyristors or FET-CTHs
• Integrated gate commutated Thyristors or IGCTs

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Types Of Thyristors And Their Applications
Silicon Controlled Rectifier (SCR)

• A silicon controlled rectifier is also known as
  thyristor rectifier.
• It is a four layered current controlling solid
  state device.
• SCRs can conduct current in only one direction
  (unidirectional devices).
• SCRs can be triggered normally by the current
  which is applied to the gate terminal.

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Types Of Thyristors And Their Applications
Gate Turn Off Thyristors (GTOs)

• One of the special types of high power
  semiconductor devices is GTO (gate turn-off
  thyristor).
• The gate terminal controls the switches to be
  turned ON and OFF.

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Types Of Thyristors And Their Applications
Gate Turn Off Thyristors (GTOs)

• If positive pulse applied between the cathode and
  gate terminals, then the device will be turned
  ON.
• Cathode and gate terminals behave as a PN
  junction and there exists a small voltage
  relatively between the terminals.
• It is not reliable as an SCR.
• To improve the reliability we must maintain a
  small amount of positive gate current.

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Types Of Thyristors And Their Applications
Gate Turn Off Thyristors (GTOs)

• If negative voltage pulse applied between the
  gate and cathode terminals, then the device will
  turn OFF.
• To induce the gate cathode voltage some of
  forward current is stolen.
• which in turn induced forward current may fall
  and automatically GTO will transition to the
  blocking state.

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Types Of Thyristors And Their Applications
Applications

• Variable speed motor drives
• High power inverters and traction

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Types Of Thyristors And Their Applications
GTO Application on Variable Speed Drive

• There are two main reasons for adjustable speed
  drive is process energy conversation and control.
  
• It provides smoother operation.
• High frequency reverse conducting GTO is
  available in this application.

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Types Of Thyristors And Their Applications
GTO Application on Variable Speed Drive
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Types Of Thyristors And Their Applications
Emitter Turn OFF Thyristor

• The Emitter turn OFF thyristor is one type of the
  thyristor.
• It will turn ON and turn OFF by using MOSFET.
• It includes both the advantages of the MOSFET and
  GTO.
• It consists of two gates- one gate is used to
  turn ON
• Another gate with a series MOSFET is used to turn
  OFF.

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Types Of Thyristors And Their Applications
Emitter Turn OFF Thyristor
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Types Of Thyristors And Their Applications
Emitter Turn OFF Thyristor

• If a gate 2 is applied with some positive
  voltage.
• It will turn ON the MOSFET which is connected in
  series with the PNPN thyristor cathode terminal.
• The MOSFET connected to the thyristor gate
  terminal will turn OFF when we applied positive
  voltage to gate 1.
• The drawback of MOSFET connecting in series with
  gate terminal is that total voltage drop
  increases from 0.3V to 0.5V and losses
  corresponding to it.

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Types Of Thyristors And Their Applications
Applications

• ETO device is used for the fault current limiter
  and solid-state circuit breaker.
• Because of its high capability current
  interruption, fast switching speed, compact
  structure and low conduction loss.

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Types Of Thyristors And Their Applications
Operating Characteristics of ETO in Solid State
Circuit Breaker

• When compared to electromechanical switchgear the
  solid-state circuit breakers can provide
  advantages in lifetime, functionality and speed.
• During Turn off transient we can observe the
  operating characteristics of an ETO semiconductor
  power switch.

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Types Of Thyristors And Their Applications
Operating Characteristics of ETO in Solid State
Circuit Breaker
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Types Of Thyristors And Their Applications
Reverse Conducting Thyristors or RCTs

• The normal high power thyristor is different from
  reverse conducting thyristor (RCT).
• RCT is not able to perform reverse blocking
  because of the reverse diode.
• If we use freewheel or reverse diode then it will
  be more advantageous for these types of devices.
• The diode and SCR will never conduct and they
  simultaneously cannot produce heat.

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Types Of Thyristors And Their Applications
Reverse Conducting Thyristors or RCTs
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Types Of Thyristors And Their Applications
Applications

• RCTs or reverse conducting thyristors
  applications in frequency inverters and changers.
• Used in AC controller by using Snubbers circuit.

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Types Of Thyristors And Their Applications
Application in AC Controller by Using Snubbers

• Protecting the semiconductor elements from over
  voltages is by arranging the capacitors and
  resistors in parallel to the switches
  individually.
• So the components are always protected from the
  over voltages.

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Types Of Thyristors And Their Applications
Bidirectional Triode Thyristors or TRIACs

• TRIAC is a device for controlling current and it
  is a three terminal semiconductor device.
• It is derived from the name called Triode for
  Alternating Current.
• Thyristors can conduct only in one direction, but
  TRIAC is able to conduct in both directions.
• There are two options to switch AC waveform for
  both halves- one is using TRIAC and the other is
  back to back connected Thyristors.
• To switch ON one half of the cycle, we use one
  Thyristor and to operate other cycle we use
  reverse connected Thyristors.

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Types Of Thyristors And Their Applications
Bidirectional Triode Thyristors or TRIACs
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Types Of Thyristors And Their Applications
Applications

• Used in Domestic light dimmers.
• Used in Small motor controls.
• Used in electric fan speed controls.
• Used in controlling of small domestic AC power
  appliances.

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Types Of Thyristors And Their Applications
Application in Domestic light dimmer

• By using the chopping parts of AC voltage the
  light dimmer will works.
• It allows lamp to pass only the parts of the
  waveform.
• If dim is more than chopping of the waveform is
  also more.
• Mainly the power transferred will determine the
  brightness of the lamp.
• Typically TRIAC is used to manufacture the light
  dimmer.

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Types Of Thyristors And Their Applications
Application in Domestic light dimmer
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Types Of Thyristors And Their Applications
Conclusion
This is all about Types of Thyristors and their
applications. We have seen many types of
thyristors , overview of circuits and
applications in different fields.
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