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CHAPTER 1:
OVERVIEW OF POWER
ELECTRONIC DEVICES
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SCR
Structure
Terminals
Operation
Symbol
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SCR
pnpndevices
(thyristor)family
Terminals
Gate(G)
Anode(A)
Cathode(C).
Applications
relay control
time-delaycircuit
regulatedpower supplier
staticswitches
motor control
chopper inverter
batterycharges
phase control
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the anode must be positive with respect to
the cathode and no gate signal junctionj1
andj3are forward biased andj2is reversed
biased.
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cathode positive with respect to the anode,
j2is forward-biased andj1 andj3are
reverse biased. Again only leakage current
flows.
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Using 2 transistor (NPN and PNP).
From 0 ke t1 ,Vgate = 0V.
Vb2 =Vgate =0V
Base current, Ib2 =0 and Ic2 almost same to Ic0. Base current for Q1 , Ib1=Ic2=Ic0.
The current too smal to on the Q1.
So that, both transistor will OFF .
The resistance for each transistor are highbetween the collector and emitter.
So that, the circuit will open.
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When t= t1, Vg is trigger to the gate terminal.
The value is enough to onQ2(Vbe2=Vg).
Current collector Q2 will increase and will on
Q1(Ib1=Ic2).
When Q1 on,Ic1 will increase and also increase the Ib2.
Ib2 at Q2 increase and it also increase the Ic2.
This process is called Regeneration Concept where the
current collector for each transistor will increase and this
will make the process continuous for each transistor.
The resistance between anode and cathode is low.
So that, the anode current (IA) is almost same with the
cathode current (IK).
In this condition, we can assume that the SCR will on.
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Forward Breakover voltageMinimum forward voltage, gate being open, SCR
starts conducting to turn ON (50 500V)
Holding current
Minimum anode current, to maintain SCR in the
ON state
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Latching Current
Minimum anode current required
maintaining SCR in ON state immediately
after SCR has been turn on and gate currenthas been removed
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Reverse Breakover Voltage
Maximum reverse voltage can applied to
SCR without conducting in reverse direction
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Forward current rating
Maximum anode current that SCR is capable
of passing without destruction
Gate triggering voltageMinimum values of gate voltage at which
SCR is turned ON
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Gate triggering current
Resulting gate current
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Increase the forward biased voltage more or
equal to forward breakdown
Trigger positive supply when the device in
forward biased condition, Gate controlmethod are trigger with
(i)DC signal
(ii)AC signal
(iii)beat signal
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Method to off SCR
1)natural Commutation
2)Reverse Bias Turn Off3)Get turn Off.
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#To turn off SCR, the anode-cathodecurrent must be reduced to less than
the holding current, Ih
Requirement to off SCR1) Cut off the current connection of SCR.
2) Short anode and cathode.
3) Switch off the positive voltage supply at anode.4) Change the polarity of anode to negative.
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GTO
Structure
Terminals
Operation
Symbol
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4 layers of semi-conductor material
Has 3 terminals, anode, cathode and Gate.
Behave like normal thyristor, but can be
turned off using gate signal.However turning off is difficult. Need very
large reverse gate current (normally 1/5 of
anode current).
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- Can turn on by giving positive supply to the gate.
- GTO still function without positive supply.
- GTO can turn off by supply negative supply at
the gate and this will cause negative Ig flow
drastically.- Negative Ig only flow in just a few microsecond.
-When Ig reach the maximum level, current at
anode will fall down and VAK voltage will
increase
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i. Tractionii. inverters
iii. motor drives
iv. pulsed power
v. distribution lines
vi. induction heating
vii. flexible ac transmission
systems
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TRIAC
Structure
Terminals
Operation
Symbol
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http://en.wikipedia.org/wiki/File:TRIAC_(smial).jpg5/25/2018 Et502 Power Electronic
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Has three terminal semiconductor for controlling
current in either direction.
The symbol looks like two SCRs in parallel(
opposite direction) with one trigger or gateterminal.
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n
n n
p
n
p
n
MT2
MT1G
The main or power terminals are designated
as MT1 and MT2 .
Bidirectional electronic switch which can
conduct current in either direction when it is
triggered (turned on). Doesn't have any
polarity.
When the voltage on the MT2 is positive
with regard to MT1 and a positive gate voltage
is applied, the left SCR conducts.
When the voltage is reversed and a negativevoltage is applied to the gate, the right SCR
conducts.
Minimum holding current, Ih, must be
maintained in order to keep a triac conducting.
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Operates in the same way as the SCR however it
operates in both a forward and reverse
direction.
It can be triggered into conduction by either (+)
or (-) gate signal.
TRIAC is capable of conducting current in both
directions and assuring that it switches "off"
during the brief zero-crossing of current can be
difficult.
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Application
1) Phase control
2) Inverter design
3) AC switching
4) Relay replacement
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Two main categories of transistors: bipolar junction transistors(BJTs)and
field effect transistors (FETs).
Transistors have 3 terminals where the
application of current (BJT)or voltage (FET)tothe input terminal increases the amount ofcharge in the active region.
The physics of "transistor action" is quite
different for the BJT and FET.
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In analog circuits, transistors are used inamplifiers and linear regulated powersupplies.
In digital circuits they function aselectrical switches, including logic gates,random access memory (RAM), andmicroprocessors
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BJT
Structure
Terminals
Operation
Symbol
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http://upload.wikimedia.org/wikipedia/commons/5/5a/Transistors.agr.jpghttp://upload.wikimedia.org/wikipedia/commons/5/5a/Transistors.agr.jpg5/25/2018 Et502 Power Electronic
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A bipolar transistoressentially consists ofa pair of PN Junctiondiodesthat are joinedback-to-back.
There are thereforetwo kinds of BJT, theNPNand PNPvarieties.
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The three layers of the sandwich areconventionally called the Collector, Base,andEmitter.
The term bipolar was tagged onto thename to distinguish the fact that both
carrier types play important roles in the
operation
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-Energy levels in an NPN
transistor under no externallyapplying voltages.-In each of the N-type layersconduction can take place bythe free movement of electronsin the conduction band.In the P-type (filling) layer
conduction can take place bythe movement of the free holesin the valence band.-However, in the absence of anyexternally applied electric field,we find that depletion zones
form at both PN-Junctions, sono charge wants to move fromone layer to another.
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What happens when weapply a moderate voltagebetween the collectorand base parts.
The polarity of theapplied voltage is chosen
to increase the forcepulling the N-typeelectrons and P-typeholes apart.
This widens the depletionzone between thecollector and base and sono current will flow.
In effect we havereverse-biassedthe Base-Collector diode junction.
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Apply a relatively smallEmitter-Base voltage whosepolarity is designed toforward-bias the Emitter-Basejunction.
This 'pushes' electrons from theEmitter into the Base regionand sets up a current flowacross the Emitter-Baseboundary.
As a result the electrons whichget into the Base move swiftlytowards the Collector andcross into the Collector region.
Hence a Emitter-Collectorcurrent magnitude is set by thechosen Emitter-Base voltage
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Some electron fall into a hole
-Some of free electronscrossing the Base encounter a
hole and 'drop into it'.
-As a result, the Base region
loses one of its positive
charges (holes).
-The Base potential would
become more negative
(because of the removal of the
holes) until it was negative
enough to repel any more
electrons from crossing theEmitter-Base junction.
The current flow would then
stop.
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Normal operation B-E junction forward biased; B-C junction reverse
biased.
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fet
FET
Structure
Terminals
Operation
Symbol
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FET Field Effect Transistor-are unipolar transistors since their operationdepends primarily on a single carrier type.
There are two main types of FETs:
a) Junction Field-Effect Transistor (JFET)
b) Metal Oxide Semiconductor Field Effect Transistor
(MOSFET)
The JFET and MOSFET are voltage controlled devices:
that is a small change in input voltage causes a large
change in output current.
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FET operation involves an electric field which
controls the flow of a charge (current ) through
the device.
Bipolar transistor employs a small input current
to control a large output current.
The source, drain, and gate terminal of the FET
are analogous to the emitter, collector, and base
of a bipolar transistor .
N-channel and P-channel refer to the materialwhich the drain and source are connected.
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The JFET channel is controlled
by the size of the depletionregion of the reverse-biased PN
junction.
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Identify the characteristics of FET
Identify the characteristics of FET
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MOSFET have two types:
a) Depletion type MOSFET ( DE MOSFET)
b) Enhancement type MOSFET (EN MOSFET)
The channel is controlled by the action of the electric
field.
DE MOSFET is similar to JFET.
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DE MOSFET- Depletion & Enhancement mode MOSFET
(MOSFET Ragam Susutan & Peningkatan)
Gate voltage can be varied through both negative and positive values. Voltage is positive valueDE MOSFET will operate in depletion mode.
Voltage is negative valueDE MOSFET will operate in enhancement
mode.
The channel has connection from drain and source. The current drain can
flow even the voltage gate ,VGS =0.
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-Has no PN junction at
the gate
- SiO2 is used to separate the
Gate terminal with the channel.
- Cause the gate current is
smaller than JFET.
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EN MOSFET- Enhancement mode MOSFET (MOSFETRagam Peningkatan)
Operate if the voltage gate,VGS is large.
The channel has no connection from drain and source. The current drain
cant flow if the voltage gate ,VGS =0.
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Until one level, the depletion area will cover
all the channel and the current ID cannot
flow.
# VGS , depletion area , and the ID
current will
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Types FET BJT
Input Resistance -Big
109-1011
-Small
103- 105
Current flow - unipolar - bipolar Operate device - Voltage-operated
device
- Current-operated
device
Power gain - Higher than BJT - Lower than FET
Power requirement - FET digital circuitneed much less
power
- BJT circuit needmore power
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Insulated Gate Bipolar Transistor have three terminals. The terminals are
collector(C), gate (G) and emitter (E).
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combines features from both the MSOFET
and BJT.
useful in high voltage and high current
switching applications
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APPLICATION
electric cars
Trains
variable speed refrigerators air-conditioners
stereo systems with switching amplifiers
switched-mode power supplies
traction motor control
induction heating
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