The document discusses thyristors, which are semiconductor devices that can be used as electrically controlled switches. It provides details on: - The history and development of thyristors from the 1950s onward. - The basic construction of a thyristor, which consists of four layers of alternating P-type and N-type semiconductor material. - The three main modes of operation for thyristors - reverse blocking, forward blocking, and forward conducting. - Applications of thyristors onboard ships, including use in motor starters, variable frequency drives, converter circuits, and inverter circuits.

1. THYRISTOR
SASIVARNEN ALAM 005128
FADZRUL AFIQ ALAM 005115
NADEN SURYA ALAM 005114
HANS INDRAN ALAM 005108

2. HISTORY ON THYRISTOR???
• In 1950, the silicon controlled rectifier (SCR) or thyristor was
proposed by William Shockley.
• Developed in 1956 by power engineers at General Electric (G.E.)
• An earlier gas filled tube device called a thyratron provided a similar
electronic switching capability, where a small control voltage could
switch a large current.
• The term "thyristor" is derived from a combination of thyratron and
transistor

3. IMAGES ON THYRATRON
*A thyratron is a type of gas-filled
tube used as a high-power
electrical switch and controlled rectifier

4. What is a Thyristor???
• The Thyristor is a four-layered, three terminal semiconductor device,
with each layer consisting of alternately N-type or P-type material, for
example P-N-P-N.
• The main terminals, labelled anode and cathode, are across all four
layers. The control terminal, called the gate, is attached to p-type
material near the cathode.
• (A variant called an SCS—Silicon Controlled Switch—brings all four
layers out to terminals.)
• The operation of a thyristor can be understood in terms of a pair of
tightly coupled bipolar junction transistors, arranged to cause a self-
latching action

5. General Idea on a Thyristor
• Thyristor can produce half wave and full wave rectification just like
rectifier.
• Using a thyristor is better than diode for rectification.
• Particularly useful for controlling power circuits
• Simple to use, easy to build and cheap.
• The 3 terminals of a thyristor is known as Anode, Cathode and Gate.
• It is a bistable device.

6. Types of Thyristors
• There are four major types of thyristors:
Silicon Controlled
Rectifier
Gate Turn-off Thyristor
(GTO) &Integrated Gate
Commutated Thyristor
(IGCT)
MOS Controlled
Thyristor (MCT)
Static Induction
type Thyristor

7. Why use Silicon?
• Thyristors are usually manufactured from silicon although,in theory other
types of semiconductor could be used.
• Reasons for using silicon for thyristors:
 Able to handle the voltage and currents required for high power
application.
 Has good thermal properties.
 Well established and is widely used for variety of semiconductor
electronics, cheap and easy to use.

8. SILICON CONTROLLED
RECTIFIER

9. Lets talk about Silicon Controlled Rectifier
• Developed by Moll, Tanenbuam, Goldey and Holonyak of Bell Laboratories in 1956
• The name "silicon controlled rectifier" is General Electric's trade name for a type
of thyristor.
• The silicon control rectifier (SCR) consists of four layers of semiconductors, which
form NPNP or PNPN structures have three P-N junctions
• The anode terminal of an SCR is connected to the p-type material of a PNPN
structure, and the cathode terminal is connected to the n-type layer, while the gate
of the SCR is connected to the p-type material nearest to the cathode.
• An SCR consists of four layers of alternating p- and n-type semiconductor materials.
• Silicon is used as the intrinsic semiconductor, to which the proper dopants are added.
• The junctions are either diffused or alloyed (alloy is a mixed semiconductor or a
mixed metal).

11. SCR-Construction and Symbol
Physical diagram Equivalent schematic (c)Schematic symbol

12. Construction types for SCR

13. SCR looks like this

14. OPERATING PRINCIPLE

15. Operation mode of a SCR
Thyristors have three modes of operation:
• Reverse blocking mode — Voltage is applied in the direction that
would be blocked by a diode
• 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
• 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"

16. • Reverse Blocking Mode: In this mode, the SCR is reverse biased by
connecting its Anode terminal to negative end of the battery and by
providing its Cathode terminal with a positive voltage as in Figure (a).
This leads to the reverse biasing of the junctions J1 and J3, which in
turn prohibits the flow of current through the device, in spite of the
fact that the junction J2 will be forward biased. Further, in this state,
the SCR behavior will be identical to that of a typical diode as it
exhibits both the flow of reverse saturation current as well as the
reverse break-down phenomenon

17. • Forward Blocking Mode: Here a positive bias is applied to the SCR by
connecting its Anode to the positive of the battery and by shorting
the SCR cathode to the battery's negative terminal, as shown by
Figure 3b. Under this condition, the junctions J1 and J3 gets forward
biased while J2 will be reverse biased which allows only a minute
amount of current flow through the device

18. • Forward Conduction Mode: SCR can be made to conduct either (i) By
Increasing the positive voltage applied between the Anode and
Cathode terminals beyond the Break-Over Voltage, VB or (ii) By
applying positive voltage at its gate terminal. In the first case, the
increase in the applied bias causes the initially reverse biased junction
J2 to break-down at the point corresponding to Forward Break-Over
Voltage, VB. This results in the sudden increase in the current flowing
through the SCR , although the gate terminal of the SCR remains
unbiased.

19. How a Thyristor latches on?
1) With no current flowing into the gate, the thyristor is
switched off and no current flows between the anode and
the cathode.
2) When a current flows into the gate, it effectively flows
into the base (input) of the lower (n-p-n) transistor,
turning it on.
3) Once the lower transistor is switched on, current can flow
through it and into the base (input) of the upper (p-n-p)
transistor, turning that on as well.
4) Once both transistors are turned on completely
("saturated"), current can flow all the way through both
of them—through the entire thyristor from the anode to
the cathode.
5) Since the two transistors keep one another switched on,
the thyristor stays on—"latches"—even if the gate current
is removed.

20. APPLICATION ON BOARD
SHIPS

21. Several applications of Thyristor onboard
ships
•Motor starter (soft starter)
•Varying motor speed a.k.a Variable Frequency
Drive (VFD)
•Converter circuit
•Inverter circuit