PPT on thyristor

1. PRESENTATION
ON
THYRISTOR
BY : ARPITA BANIK

2. POWER SEMICONDUCTOR DEVICES
• Power semiconductor devices can be divided broadly into three types:
• a) Power diodes: Power diodes are of three types.
1) General purpose diode 2) High speed or fast recovery diode
3) schottky diode.
• b) Transistors: Power transistors are of four types.
1) BJTs 2) MOSFETs 3) IGBTs 4) SITs.
• c) Thyristors: Thyristors are of following types.
1) SCR: Silicon Controlled Rectifier
2) DIAC: Diode on Alternating Current
3) TRIAC : Triode for Alternating Current
4) SCS: Silicon Control Switch
5) SUS: Silicon Unilateral Switch
6) SBS: Silicon Bidirectional Switch

3. 7) SIS: Silicon Induction Switch
8) LASCS: Light Activated Silicon Control Switch
9) LASCR: Light Activated Silicon Control Rectifier
10) SITH: Static Induction Thyristor
11) RCT: Reverse Conducting Thyristor
12) GTO: Gate Turn-Off Thyristor
13) MCT: MOSFET Controlled Thyristor
14) ETO: Emitter Turn-On Thyristor

4. LIMITATION OF POWER SEMICONDUCTOR DEVICES
Power semiconductor devices, like Schottky diode, MOSFET exhibit very fast
switching responses, controlled essentially by the charging of the device capacitances.
– However, forward voltage drops of these devices increases quickly with
increasing breakdown voltage.
Power semiconductor devices like BJT, IGBT can exhibit high breakdown voltage
relatively low forward voltage drop.
– But they can have longer switching times due to stored minority charges.

5. INTRODUCTION TO THYRISTOR
• Thyristor,a three terminal,four layer solid state semiconductor device, each layer
consisting of alternately N-type or P-type material, i.e;P-N-P-N that can handle
high currents and high voltages with better switching speed and improved
breakdown voltage.
• Name ‘thyristor’, is derived by a combination of the capital letters from
THYRatron and transISTER.
• Thyristor has characteristics similar to a thyratron tube which is a type of gas
filled tube used as a high energy electrical switch and controlled rectifier.
• But from the construction view point, a thyristor (pnpn device) belongs to
transistor (pnp or npn device) family.
• This means that thyristor is a solid state device like a transistor and has
characteristics similar to that of a thyratron tube.
• Thyristor (famous as Silicon Control Rectifier-SCR) can handle high currents and
high voltages.
• Typical rating are 1.5KA & 10KV which responds to 15MW power handling
capacity.

6. THYRISTOR SCHEMATIC REPRESENTATION

7. TWO TRANSISTOR MODEL OF THYRISTOR
Ic=αIE+ICBO
Where,Ic=Collector Current
α= Collector emitter current gain
IE=Emitter current
ICBO=Collector-base junction leakage
current
IC1= α1IA+ICBO1
IC2= α2IK+ICBO2
IA=IC1+IC2= α1IA+ICBO1+ α2IK+ICBO2
IK=IA+IG
IA =
α2IG + ICBO1 +
ICBO2
1 − (α1 + α2)

8. THYRISTOR OPERATION PRINCIPAL
Thyristors have three operating modes :
1) Forward blocking mode
2) Forward conducting mode
3) Reverse blocking mode

9. THYRISTOR V-I CHARACTERISTICS

10. THYRISTOR TURN-ON METHODS
• Thyristor turning ON is also known as Triggering.
• With anode positive with respect to cathode, a thyristor can be turned ON by
any one of the following techniques :
• Forward voltage triggering
• Gate triggering
• dv/dt triggering
• Temperature triggering
• Light triggering

11. GATE TRIGGERING METHOD OF THYRISTOR
Effects of gate current on forward blocking voltage

12. dv/dt TRIGGERING METHOD OF THYRISTOR
• Ic=dQ/dt
• =d/dt(cj.va)
• =cj dva/dt + va dcj/dt
• =cj dva/dt with dcj/dt=0

13. TURN-ON CHARACTERISTICS OF THYRISTOR

14. TURN-OFF OR COMMUTATION OF THYRISTOR
• Commutation can be classified as
• Natural commutation
• Forced commutation
• Forced commutation techniques are:
1) Class A commutation: Load commutation
2) Class B commutation: Resonant-pulse commutation
3) Class C commutation: complementary commutation
4) Class D commutation: Impulse commutation
5) Class E commutation: External pulse commutation
6) Class F commutation: Line commutation

15. THYRISTOR TURN-OFF CHARACTERISTICS

16. THYRISTOR PROTECTION
Thyristor protection techniques are as follows:
1) di/dt protection
2) dv/dt protection
Snubber Circuit:

17. THANK YOU