The document discusses the silicon controlled rectifier (SCR), which is a thyristor used to control high voltages compared to transistors. It has a four-layer PNPN semiconductor structure with anode, cathode, and gate terminals. The SCR was developed in 1956 and can handle large power levels. It is used for applications like AC voltage stabilization, switching, inverters, power control, battery charging, and motor speed control due to advantages like high voltage/current handling and simple triggering. However, it can only control power during half cycles of AC and not at high frequencies.

1. Silicon controlled
rectifier

2. CONTENTS
• Introduction
• History
• Construction
• V-I Characteristics
• Switching on & off methods
• Application
• Advantages & Disadvantages
• Conclusion
• Reference

3. INTRODUCTION
• What is Silicon controlled rectifier ?
• SCR is actually a thyristor which is used to control the high voltage supply as compared to the
conventional transistors. It is a four layered P-N-P-N semiconductor three terminal device,
such that the entire four segments arranged in a single array. It has an anode, cathode and a
gate terminal.
• history of SCR
• The silicon controlled rectifier (SCR) or thyristor proposed by William Shockley in 1950 and
championed by Moll and others at Bell Labs was developed in 1956 by power engineers at
General Electric (G.E.), lead by Gordon Hall and commercialized by G.E.'s Frank W. "Bill"
Gutzwiller

4. FEATURES
 Missing Cycle Detection
Current Limiting
Over Current Trip
Shorted SCR Detection

5. ADVANTAGES OF SILICON CONTROLLED
RECTIFIER
• The silicon controlled rectifier (SCR) can handle large voltage, current
and power.
• It can be protected with the help of fuse.
• Easy to turn ON.
• Triggering circuit for silicon controlled rectifier (SCR) is simple.
• Simple to control.
• Low in cost.
• Able to control the AC power.

6.  The silicon controlled rectifier (SCR) is unidirectional devices, so it can control
power only in DC power during positive half cycle of AC supply. Thus only DC
power is controlled with the help of SCR.
 In AC circuit, it needs to be turned on each cycle.
 It cannot be used at higher frequencies.
 The gate current can not be negative.
Disadvantages of
silicon controlled
rectifier

7. COMPARISON BETWEEN SCR & TRIAC,DIAC
SCR
o The SCR is a unidirection device
• The terminal called are called anode –cathode
due to unilateral property.
• The gate current can be only in direction to turn
on scr.
• The applications are phase control ,protection of
power supplies etc.
• The reliability is more.
• Available in large rating.
• The charchteristic are lying in the first quadrant
only hence are nonsymmetrical.
•
TRIAC OR DIAC
• The triac conducts both the directions hence
bilateral device.
• The terminal are called MT1 & MT2 with
gate .
• For both the direction of gate current triac
conducts.
• The reliability is less.
• Not available in large ratings.
• The diac is used for triggering.
• The application are phase control, light
dimmer, motor control control etc

8. CONSTRUCTION
• FOUR LAYER DEVICE (ALTERNATE P-N JUNCTION )
• 3 TERMINALS
ANODE (TERMINAL CONNECTED TO OUTER P REGION)
CATHODE (TERMINAL CONNECTED TO OUTER N REGION)
TERMINAL CONNECTED TO INNER P REGION

9. WORKING
o Gate is open
Forward blocking mode –
1)When anode is positive with respect to cathode, with gate
circuit is open.
2) Junctions J1 , J3 are forward biased but junction J2 is reversed
bias.
3) SCR can be treated as an open switch.

10. REVERSE BLOCKING
MODE-
1)Cathode is made positive with respect to anode with gate open
2) Junction J1 & J3 are reverse biased but junction J2 are forwa
3) SCR can be treated as an open switch.

11. GATE IS CLOSED
1.Anode is positive with respected to cathode
& gate terminal too.
2.SCR is on state and behave like a closed switch.
3.Junctions J1 , J3 are forward biased but junction J2
is reversed bias.
Forward conduction mode -

12. V-I CHARACTERISTICS OF
SCR
Forward Characteristics (Forward Conduction)
•Anode is positive w.r.t. cathode
•When supply voltage is increased from zero, suddenly
the SCR starts conducting => break over voltage
•Voltage drops at this point suddenly as shown by the
dotted line.
•If proper gate current is made to flow, then SCR can
close at smaller supply voltage.

13. REVERSE CHARACTERISTICS
•Anode is negative w.r.t. cathode
•Initially the anode current retains
small (viz. leakage current)
Beyond a particular reverse
voltage, the SCR starts massive
conduction (avalanche) => Reverse
breakdown voltage

14. APPLICATION
• The silicon controlled rectifier (SCR) is used in AC voltage
stabilizers.
• The silicon controlled rectifier (SCR) is used as switch.
It is used in choppers.
• The silicon controlled rectifier (SCR) is used in inverters.
• The silicon controlled rectifier (SCR) is used for power
control.
• It is used for DC circuit breaker.
Silicon control rectifier (SCR) is used in battery charger.
• It is used to Adjust light dimmer.
• It is used to control motors speed.
• The SCR is used in pulse circuit.
• It is used for AC power control with solid relay.

15. CONCLUSION
• SCR is a power electronic device. It controls high voltages , current.
• Working in between 50 to 10k Hz frequency.
• Controlling of SCR is very easy. Triggering voltage is very less.

16. REFERENCE
1.https://www.pantechsolutions.net/powerelectroni
cs- tutorials/introduction-of-scr
2.https://www.brighthubengineering.com/commerci
al- electrical-applications/58051-characteristics-
and-applications-of-scr-thyristors/
3.https://www.pantechsolutions.net/powerelectroni
cs-tutorials/introduction-of-scr
4.https://en.wikipedia.org/wiki/Thyristor
5.https://www.brighthubengineering.com/commerci
al-electrical-applications/58051-characteristics-
and-applications-of-scr-thyristors/
6.http://www.circuitstoday.com/scr-applications
7.https://www.polytechnichub.com/advantages-
disadvantages-silicon-controlled-rectifier-scr/