L6 semiconductor-power-switching-devices-3-130912210901-phpapp01

Semiconductor Power Switching Devices-3(Lecture-6)

R S Ananda Murthy

Associate Professor and HeadDepartment of Electrical & Electronics Engineering,

Sri Jayachamarajendra College of Engineering,Mysore 570 006

R S Ananda Murthy Semiconductor Power Switching Devices-3

TRIAC

MT2

MT1

G

Circuit Symbolof TRIAC

J1

J2

J3

Structure of TRIAC

+ indicates heavily doped region- indicates lightly doped region

MT1

MT2

G

J4ON

OFF

ON

OFF

MT2 positivew.r.t. MT1 andG positive w.r.t. MT1

Pulse triggered

MT2 negativew.r.t. MT1 andG negative w.r.t. MT1

Pulse triggered

MT1 MT2

GTRIAC is equivalent totwo SCRs in anti-parallel

Shorting of p1 region to n3 region due to MT2 metal contact,and the p2 region to the n2 region due to MT1 metal contactresults in two anti-parallel SCR structures: p1n1p2n2 andp2n1p1n3.


TRIAC used in ACVC

VRMS

Constant

f

AC

ACVCV,

AC

Variable

same as inputf

(a)

vivo

(b)

Triac+

−

R

+

−

vi

vo

tω

tω

(c)

0

Trigger

0

Trigger Trigger

π 2π

π 2π


Limitations of TRIAC as Compared to SCRs

Has lower dv/dt rating.Requires well designed R-C snubber connected across itto limit dv/dt .Has longer turn-off time.Has lower power handling capability.Typically used in small motor speed regulators,temperature control, illumination control, liquid levelcontrol, phase control circuits, power switches.Cannot be used in A.C. systems of frequency more than400 Hz.


Specifications of TRIAC BT139


Diac

MT1

MT2

P

N

P

J1

J2

MT1

MT2

MT1

MT2Structure and symbols of diac

Diacs are typically used to trigger TRIACS in ceiling fanregulators and light dimming circuits.


Typical Diac Specifications


Simple Fan Regulator Circuit using TRIAC

Diac DB2 is used to trigger TRIAC BT136.


Some High Power TRIACS

(Source: www.china-rectifier.com)


www.china-rectifier.com

Ratings of Some High Power TRIACS




Gate Turn Off Thyristor (GTO)

A

K

G

J1

J2J3

Buffer layer

A

K

G

Anode contact

Buffer layer structure Anode shorted structure

Anode short

A A

K K

GG

Circuit symbols of GTOIncreases reverse voltage

blocking capabilityDecreases reverse voltage

blocking capability

A

K

G

Inter digitized gate-cathode structure increases di/dt rating ofthe device and also improves turn-off performace of the device.


Static Characteristic of GTO

A

KG

Circuit Symbolof GTO

ON

OFF

= Latching Current= Holding Current

ForwardLeakageCurrent

SymmetricalGTO

AsymmetricalGTO


Control Characteristics of GTO

vo

iG

vo

+

−

iG

t

V

t

+

−

GTO

RV

GTO can be turned on by applying a positive gate currentpulse and turned off by applying a negative gate currentpulse.To prevent unwanted turn-off during transients, it isrecommended to apply a low value of continuous positivegate current as long as GTO has to be kept on.


GTO Compared with SCR

GTO SCR

Fully-controlled Semi-controlled

VON = 3-4 V VON =1.5-2 V

Higher IL and IH IL and IH very low compared to GTO

Assymetric GTO has very low VBR Has VBR ≈ VBO

Typically dv/dt = 1000 V/µs Typically dv/dt =200-500 V/µs

Turn-off Current Gain: 6-15 Not applicable

Max. operating frequency: 1-4 kHz Typcally operated at 50 or 60 Hz


Photographs of GTOs

Asymmetric Type Reverse Blocking Type




Stud Type GTO




Specifications of Asymmetric GTOs




Specifications of Symmetric GTOs




Next Lecture...

In the next lecture we will discuss some more powersemiconductor switching devices used in power electronics.

Thank You.


L6 semiconductor-power-switching-devices-3-130912210901-phpapp01

Engineering

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