Power electronics deals with controlling and converting electric power using solid-state electronics. It involves power equipment for generation, transmission and distribution as well as electronic devices and circuits for signal processing and control objectives. Some key developments include the mercury arc rectifier in 1900, silicon transistor in 1948, and thyristor or SCR in 1956. Power electronic converters are now used for applications like UPS, motor speed control, power transmission, and power supplies due to advantages like fast response, high efficiency and compact size, though they can generate harmonics and have low power factors requiring correction. Power electronic converters work by classifying and controlling the operation of power semiconductor devices like power diodes, SCRs, BJTs, MOSFETs

1. UNIT I
POWER SEMICONDUCTOR DEVICES
POWER ELECTRONICS

2.  Power Electronics deals with the application of solid
state electronics for the control and conversion of
electric power
 Power deals with the static and rotating power
equipment for the generation, transmission and
distribution
 Electronics deals with the solid state devices and
circuits for signal processing to meet the desired
control objectives
 Control deals with the steady state and dynamic
characteristics of closed loop system

3. History
 1900 - Mercury arc rectifier
 1900-1950 - Metal tank rectifier, ignitron,
phanotron, thyratron
 1948 - Silicon Transistor
 1956 - Thyristor or SCR
 1958 - Commercial Thyristor

4. Applications
 UPS and stand by power supplies for critical load
such as computers, medical equipments
 Power conversion for HVAC and HVDC
transmission system
 Speed control of motors which are used in
traction drives, textile mills, rolling mills, cranes,
lifts, pumps
 Power supplies for communication systems,
telephone exchanges, satellite systems

5. Advantages of Power Electronic
Controllers
 Fast dynamic response due to static devices
 High efficiency of conversion due to low losses in
electronic devices
 Compact size and light weight of the controllers
 Increased operating life and reduced
maintenance

6. Disadvantages
 It generates Harmonics. These harmonics affect
the performance
 Power factor is low. Hence power factor
correction is necessary to reduce reactive power
 For very simple conversion requirements, power
electronic converters may be costly

7. Block Diagram

8. Types of Power Electronic
Converters

9. Classification

10. Power Diodes

11. Switching Characteristics

12. Types of Power Diodes
General Purpose Diodes
 General purpose diodes handle power at the mains
frequency or below 1 KHz
 Turn off switching time is more
 Reverse recovery time is large i.e. about 25 μs
 Rating 1A/50V to 5kA/10kV
 Used in rectifiers and converters

13. Fast Recovery Diodes
 Reverse recovery time of the order of 25 – 100 ns
 Rating 1A / 50 V to 1 kA / 3kV with reverse
recovery time less than 5 μs
 For very high frequency applications p-i-n diodes
are used
 Used in inverters, choppers, SMPS, UPS, dc-dc
converters, resonant converter

14. Schottky Diodes:
In Schottky Diodes, pn junction is eliminated. A thin film of
metal is placed directly on the semiconductor.
Normally aluminium is deposited on n-type semiconductor.

15. Cut in voltage - 0.2 V
Reverse breakdown voltage – 50 V

17. Applications

18. Silicon Controlled Rectifier (SCR)

19. Construction of SCR
Symbol

21. SCR Characteristics and Modes of
Operation
1. Reverse blocking mode
2. Forward blocking mode
3. Forward conduction mode

23. Static V-I characteristic of a SCR

24. Latching Current

25. Holding Current

26. BJT

27. Input and Output Characteristics

28. BJT Switching Performance

29. Safe operating Area

30. MOSFET

32. Output Characteristics

33. Switching Characteristics

34. IGBT

35. V-I and Transfer Characteristics

37. GTO