Overview of Power Semiconductor Switches

woundcallousSemiconductor

Nov 1, 2013 (3 years and 7 months ago)

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Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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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

Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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Diodes


On and off states controlled by the power circuit


Forward biased



conduction


Reverse biased



small leakage current flow until
break down voltage reached

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

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Thyristor in a Simple Circuit


For successful turn
-
off, reverse voltage required

Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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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

Generic Switch Symbol

Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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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

Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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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.

Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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MOSFETs


MOSFET is a voltage
-
controlled device


Easy to control by the gate


continuous application of
v
GS

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

Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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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

Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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IGBT


High impedance gate


requires small
amount of energy to switch the device


Current rating: ~1700 A


Voltage rating: 2~3 kV

Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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Comparison of Controllable Switches

Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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Review of Basic Electrical and Magnetic
Circuit Concepts

Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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Sinusoidal Steady State

Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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Three
-
Phase Circuit

Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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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


Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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Fourier Analysis

Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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Phasor Representation

Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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Response of
L

and
C

Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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Inductor Voltage and Current in Steady State

In steady
-
state, the average
inductor voltage (over one time
period) must be
zero
.

Copyright
©
2003

by John Wiley & Sons, Inc.

Chapter 2 Power Semiconductor
Switches: An Overview

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Capacitor Voltage and Current in Steady State

In steady
-
state, the average
capacitor current (over one
time period) must be
zero
.