Chapter 2 Overview of Power Semiconductor Devices

Electrónica de Potência© 2008 José Bastos

Chapter 2 Power Semiconductor Switches: An Overview

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Chapter 2 Overview of Power Semiconductor Devices

• Introduction• Diodes• Thyristors• Ideal switches• Bipolar transistors• MOSFETs• MOS-Controlled Thyristors• Comparison of controllable switches



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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



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Thyristor in a Simple Circuit

• For successful turn-off, reverse voltage required for an interval greater than the turn-off interval



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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



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Switching Characteristics (linearized)

Switching Power Loss is proportional to:• switching frequency• turn-on and turn-off times

cod tIVW

dtivW

ivtpdt

tdW

2

1

)()(



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• Small leakage current in off state• Small on state voltage• Short turn-on and turn-off• Large forward and reverse voltage• High on state current rating• Positive temperature coefficient• Small control power required to switch• Capability to survive rated voltage and rated current simultaneously

Switch: ideal characteristics



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Bipolar Junction Transistors (BJT) #1

• Used commonly in the past• Now used in specific applications• Replaced by MOSFETs and IGBTs



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Various Configurations of BJTs



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Conclusions BJTs



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MOSFETs #1

• Easy to control by the gate• Optimal for low-voltage operation at high switching frequencies• On-state resistance a concern at higher voltage ratings



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MOSFETs #2



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IGBT



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Conclusions IGBT



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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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MOS CONTROLLED THYRISTORS (MCT)



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Comparison of Controllable Switches



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Summary of Device Capabilities

Chapter 2 Overview of Power Semiconductor Devices

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