Chapter 2 Overview of Power
Semiconductor Devices
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 2 Power Semiconductor
Switches: An Overview
2-1
Diodes
• On and off states controlled by the power circuit
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 2 Power Semiconductor
Switches: An Overview
2-2
Diode Turn-Off
• Fast-recovery diodes have a small reverse-recovery time
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 2 Power Semiconductor
Switches: An Overview
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Thyristors
• Semi-controlled device
• Latches ON by a gate-current pulse if forward biased
• Turns-off if current tries to reverse
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 2 Power Semiconductor
Switches: An Overview
2-4
Thyristor in a Simple Circuit
•
For successful turn-off, reverse voltage required
for an interval greater than the turn-off interval
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 2 Power Semiconductor
Switches: An Overview
2-5
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
• Zero voltage drop in on-state
• Infinite voltage and current handling capabilities
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 2 Power Semiconductor
Switches: An Overview
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Switching Characteristics (linearized)
Switching Power Loss is
proportional to:
• switching frequency
• turn-on and turn-off times
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 2 Power Semiconductor
Switches: An Overview
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Bipolar Junction Transistors (BJT)
• Used commonly in the past
• Now used in specific applications
• Replaced by MOSFETs and IGBTs
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Chapter 2 Power Semiconductor
Switches: An Overview
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Various Configurations of BJTs
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Chapter 2 Power Semiconductor
Switches: An Overview
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MOSFETs
• Easy to control by the gate
• Optimal for low-voltage operation at high switching frequencies
• On-state resistance a concern at higher voltage ratings
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 2 Power Semiconductor
Switches: An Overview
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Gate-Turn-Off Thyristors (GTO)
• Slow switching speeds
• Used at very high power levels
• Require elaborate gate control circuitry
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by John Wiley & Sons, Inc.
Chapter 2 Power Semiconductor
Switches: An Overview
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GTO Turn-Off
• Need a turn-off snubber
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Chapter 2 Power Semiconductor
Switches: An Overview
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IGBT
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Chapter 2 Power Semiconductor
Switches: An Overview
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MCT
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Switches: An Overview
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Comparison of Controllable Switches
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Switches: An Overview
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Summary of Device Capabilities
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by John Wiley & Sons, Inc.
Chapter 2 Power Semiconductor
Switches: An Overview
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