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
2011.10.06.2011.10.06. 22Power Electronics MScPower Electronics MSc
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
2011.10.06.2011.10.06. 99Power Electronics MScPower Electronics MSc
Mos Controlled Thyristor (MCT)
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Comparison of Controllable Switches
2011.10.06.2011.10.06. 1111Power Electronics MScPower Electronics MSc
Summary of Device Capabilities
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