CONTROLLABLE SWITCHES Overview

2011.10.06.2011.10.06. 11Power Electronics MScPower Electronics MSc

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

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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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Various Configurations of BJTs

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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 ratings2011.10.06.2011.10.06. 66Power Electronics MScPower Electronics MSc

Gate-Turn-Off Thyristors (GTO)

• Slow switching speeds

• Used at very high power levels

• Require elaborate gate control circuitry2011.10.06.2011.10.06. 77Power Electronics MScPower Electronics MSc

GTO Turn-Off

• Needs a turn-off snubber2011.10.06.2011.10.06. 88Power Electronics MScPower Electronics MSc

IGBT

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Mos Controlled Thyristor (MCT)

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Comparison of Controllable Switches

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Summary of Device Capabilities

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