Different types of thyristors and their applications

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.

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.

Applications
 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.
What is a Thyristor?

Applications
Thyristor
Circuit Symbol
 Thyistor circuit symbol is as given below. It has three terminals Anode,
cathode and gate.

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”.

Applications
Thyristor Layer Diagram

Applications
 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).

Applications
 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.

Applications
 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,
o The potential VAK is removed or
o 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.

Applications
Thyristor Switching Circuits
1. DC Thyristor Circuit.
2. AC Thyristor circuit.
 The two types of thyristor switching circuits are

Applications
DC Thyristor Circuit

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.

Applications
AC Thyristor Circuit

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.

Applications
Types of
Thyristors
 Based on turn on and turn off capabilities the thyristors are classified
into the following types:
o Silicon controlled thyristor or SCRs
o Gate turn off thyristors or GTOs
o Emitter turn off thyristors or ETOs
o Reverse conducting thyristors or RCTs
o Bidirectional Triode Thyristors or TRIACs
o MOS turn off thyristors or MTOs

Applications
Types of
Thyristors
o Bidirectional phase controlled thyristors or BCTs
o Fast switching thyristors or SCRs
o Light activated silicon controlled rectifiers or LASCRs
o FET controlled thyristors or FET-CTHs
o Integrated gate commutated Thyristors or IGCTs
 Based on turn on and turn off capabilities the thyristors are classified
into the following types:

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.

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.

Applications
(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.

Applications
(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.

Applications
Applications
 Variable speed motor drives
 High power inverters and traction

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.

Applications
GTO Application on Variable Speed Drive

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.

Applications
Emitter Turn OFF
Thyristor

Applications
 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.
Emitter Turn OFF Thyristor

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.

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.

Applications
Operating Characteristics of ETO in Solid State Circuit
Breaker

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.

Applications
Reverse Conducting Thyristors or
RCTs

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

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.

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.

Applications
Bidirectional Triode Thyristors or
TRIACs

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.

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.

Applications
Application in Domestic light dimmer

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.

Different types of thyristors and their applications

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