1. Overview of Power Semiconductor Switches
Presently available power semiconductor switches can be divided into three groups according to their degree of controllability:
Diodes: ON and OFF states controlled by power circuits
Thyristors: latched on by a control signal but turned OFF by the power circuit
Controllable switches: turned ON and OFF by control signals

2. Diodes On and off states controlled by the power circuit
Forward biased – conduction
Reverse biased – small leakage current flow until break down voltage reached

3. Thyristors Semi-controlled device
Latches ON by a gate-current pulse if forward biased
Turns-off if current tries to reverse

4. Thyristor in a Simple Circuit
For successful turn-off, reverse voltage required

5. Generic Switch Symbol Idealized switch symbol
When on, current can flow only in the direction of the arrow
Instantaneous switching from one state to the other
Conduct large current with zero voltage drop in on-state
Block large forward and reverse voltages with zero current flow when off
Infinite voltage and current handling capabilities

6. Bipolar Junction Transistors (BJT)
BJT is a current-controlled device
A sufficiently large base current will turn the device ON
Base current must be supplied continuously to keep it in the ON state
Used commonly in the past
Now used in specific applications, replaced by MOSFETs and IGBTs

7. Various Configurations of BJTs
dc gain is in the order of 5-10 of one BJT
To achieve larger current gain, these devices are sometimes connected in the above configurations.

8. MOSFETs MOSFET is a voltage-controlled device
Easy to control by the gate – continuous application of vGS required to keep the device in the ON state
Faster switching speed (in the nanosecond range) than BJTs
Switching loss is lower compared to BJTs

9. Gate-Turn-Off Thyristors (GTO)
GTO as an ON/OFF switch
Once forward biased GTO can be turned ON by a gate pulse
GTO will stay ON
However, can be turned off by applying a negative gate-cathode voltage
Used at very high power levels
Require elaborate gate control circuitry

10. IGBT
High impedance gate – requires small amount of energy to switch the device
Current rating: ~1700 A
Voltage rating: 2~3 kV

11. Comparison of Controllable Switches

12. Review of Basic Electrical and Magnetic Circuit Concepts

13. Sinusoidal Steady State

14. Three-Phase Circuit

15. Steady State in Power Electronics
Voltage produced by an inverter in an ac motor drive
Often line currents drawn from the utility by the power electronic circuits are highly distorted as shown in b

16. Fourier Analysis

17. Phasor Representation

18. Response of L and C

19. Inductor Voltage and Current in Steady State
In steady-state, the average inductor voltage (over one time period) must be zero.

20. Capacitor Voltage and Current in Steady State
In steady-state, the average capacitor current (over one time period) must be zero.