POORNIMA COLLEGE OF ENGINEERING
EXPERIMENT NO: 8 OBEJECTIVE:
Study and test 3-phase diode bridge rectifier with R and RL
loads. Study the effect of filters.
APPEARTUS REQURIED:
1) 230 V power supply2) 3-Phase uncontrolled bridge convertor
Trainer Kit3) CRO4) Connecting Leads
CIRCUIT DIAGRAM:
THEORY:
RESISTIVE LOAD
Single-phase diode rectifiers require a rather high transformer
VA rating for a given dc output power. Therefore, these rectifiers
are suitable only for low to medium power applications. For power
output higher than 15 kW, three-phase or poly-phase diode
rectifiers should be employed. There are two types of three-phase
diode rectifier that convert a three-phase ac supply into a dc
voltage, namely, half (star) rectifiers and bridge rectifiers., the
diodes and the transformers are considered to be ideal, i.e. the
diodes have zero forward voltage drop and reverse current, and the
transformers possess no resistance and no leakage inductance.
Furthermore, it is assumed that the load is purely resistive, such
that the load voltage and the load current have similar
waveforms.
RLE LOAD
This type of load may represent a dc motor or a battery. Usually
for driving these loads a variable output voltage is required. This
requirement has to be met by using a variable ac source (e.g. a 3
phase variable) since the average output voltage of an uncontrolled
rectifier is constant for a given ac voltage. It will also be
assumed in the following analysis that the load side inductance is
large enough to keep the load current continuous. The relevant
condition for continuous conduction will be derived but analysis of
discontinuous conduction mode will not be attempted. Compared to
single phase converters the cases of discontinuous conduction in 3
phase bridge converter are negligible.
OPERATION OF THREE-PHASE BRIDGE RECTIFIERS
The circuit of a three-phase bridge rectifier is shown in Fig.
The diodes are numbered in the order of conduction sequences and
the conduction angle of each diode is 2/3. The load current is
assumed to be continuous at least one diode from the top group (D1,
D3 and D5) and one diode from the bottom group (D2, D4 and D6) must
conduct at all time. It can be easily verified that only one diode
from each group (either top or bottom) conducts at a time and two
diodes from the same phase leg never conducts simultaneously. Thus
the converter has six different diode conduction modes. These are
D1D2, D2D3, D3D4, D4D5, D5D6 and D6D1. Each conduction mode lasts
for /3 rad and each group diode conducts for 120 and each arms
diode conducts from after180o.
Shows voltages across different diodes and the output voltage in
each of these conduction modes. The time interval during which a
particular conduction mode will be effective can be ascertained
from this table. For example the D1D2 conduction mode will occur
when the voltage across all other diodes (i.e. vba, vca and vcb)
are negative. This implies that D1D2 conducts in the interval 0 t
/3 as shown in Fig. The diodes have been numbered such that the
conduction sequence is D1 D2 D3 D4 D5 D6 D1---. When a diode stops
conduction its current is commutated to another diode in the same
group (top or bottom). This way the sequence of conduction modes
become, D1D2 D2D3 D3D4 D4D5 D5D6 D6D1 D1D2 The output dc voltage
can be constructed from this conduction diagram using appropriate
line voltage segments as specified in the conduction table.
The input ac line currents can be constructed from the
conduction diagram and the output current. For example
ia = io for 0 t /3 and 5/3 t 2 ia = - io for 2/3 t 4/3 ia = 0
otherwise.
THE RMS VALUE OF THE OUTPUT VOLTAGE
WAVEFORMS
RESULTWe have study of three phase uncontrolled bridge converter
and draw various wave forms.PRECAUTION1) To make connection should
be according to circuit diagram.2) Connecting leads should not
loose.3) Connecting circuit should be check to be respected lab
faculty after complete connection Diagram.4) Power Supply should
not be ON during connecting leads to experimental kit.5) Power
supply should be OFF after performance of allotted practicalVIVA
QUESTIONS:Fill in the blank(s) with the appropriate word(s). i)
Three phase full wave uncontrolled rectifier uses _________ diodes.
ii) Three phase full wave uncontrolled rectifier does not require
________ wire connection. iii) In a three phase full wave
uncontrolled rectifier each diode conducts for _______ radians. iv)
The minimum frequency of the output voltage ripple in a three phase
full wave rectifier is _________ times the input voltage frequency.
v) The input ac line current of a three phase full wave
uncontrolled rectifiers supplying an R L E load contain only
________ harmonics but no ________ harmonic or __________
component. vi) A three phase full wave uncontrolled rectifier
supplying an R L E load normally operates in the ________
conduction mode.
Answers: (i) six; (ii) neutral; (iii) 2/3; (iv) six; (v) odd,
tripler, dc; (vi) continuous.
EXPERIMENT NO: 9
OBEJECTIVE:
Study and obtain waveforms of single-phase half wave controlled
rectifier with and without Filters. Study the variation of output
voltage with respect to firing angle.
APPEARTUS REQURIED:
1) 230 V power supply2) 1-Phase half bridge convertor Trainer
Kit3) Oscilloscope 4) Multimeter5) Connecting Leads
CIRCUIT DIAGRAM:
PROCEDURE:
Make sure that there should not be any connections by patch cord
on the board 1. Rotate the firing control Potentiometers 1 and 2 in
full counter clockwise direction and also switch set at
Potentiometer 1 side. 2. Switch On the power supply 3. Measure the
AC voltage (Vrms) by voltmeter between point 0V-15V and calculate
Em by Em =1.414 X Vrms. 4. Switch Off the power. 5. Connect the
circuit of half wave rectifier as shown figure 6 using 2 mm patch
cords.6. Switch On the power supply 7. Connect the Oscilloscope and
voltmeter across the load. 8. Vary the firing control Potentiometer
and set on 30, 60, 90, 120 and 150 firing angles using equation 9.
Observe the output waveforms and note the readings of voltage
across load on different firing angles. 10. Observe the waveform
across the SCR1 when firing angle is 90. 11. Calculate the average
load current IDC and power PDC from measured load voltage Vo. 12.
Plot the input signal, gate pulse, and drop signal across SCR and
output waveforms when firing angle is 90. THEORY
R LOADThe thyristor conducts only when the anode is positive
with respect to cathode and a positive gate signal is applied,
otherwise, it remains in the forward blocking state and blocks the
flow of the load current At t = 0 when the input supply voltage
becomes positive the thyristor T becomes forward biased. However,
unlike a diode, it does not turn ON till a gate pulse is applied at
t = . During the period 0 < t , the thyristor blocks the supply
voltage and the load voltage remains zero. Consequently, no load
current flows during this interval. As soon as a gate pulse is
applied to the thyristor at t = it turns ON. The voltage across the
thyristor collapses to almost zero and the full supply voltage
appears across the load. From this point onwards the load voltage
follows the supply voltage. The load being purely resistive the
load current io is proportional to the load voltage. At t = as the
supply voltage passes through the negative going zero crossing the
load voltage and hence the load current becomes zero and tries to
reverse direction. In the process the thyristor undergoes reverse
recovery and starts blocking the negative supply voltage.
Therefore, the load voltage and the load current remains clamped at
zero till the thyristor is fired again at t = 2 + . The same
process repeats there after. The average DC output voltage across
load is given by
VDC = Em (1+cos )/2Average current is given byIDC = Em (1 + cos
)/2RAnd, the DC output power isPDC = VDC X IDC
(a) For R Load (30o) (b) For R Load (90o)
RESULTStudy and obtain waveforms of single-phase half wave
controlled rectifier with and without Filters. Study the variation
of output voltage with respect to firing angle.
PRECAUTION1) To make connection should be according to circuit
diagram.2) Connecting leads should not loose.3) Connecting circuit
should be check to be respected lab faculty after complete
connection Diagram.4) Power Supply should not be ON during
connecting leads to experimental kit.5) Power supply should be OFF
after performance of allotted practicalVIVA QUESTIONS:Fill in the
blank(s) with appropriate word(s) i) In a single phase fully
controlled converter the _________ of an uncontrolled converters
are replaced by ____________. ii) In a fully controlled converter
the load voltage is controlled by controlling the _________ of the
converter. iii) A single phase half wave controlled converter
always operates in the ________ conduction mode. iv) The voltage
form factor of a single phase fully controlled half wave converter
with a resistive inductive load is _________ compared to the same
converter with a resistive load. v) The load current form factor of
a single phase fully controlled half wave converter with a
resistive inductive load is _________ compared to the same
converter with a resistive load.
Answers: (i) diodes, thyristors; (ii) firing angle; (iii)
discontinuous (iv) poorer; (v) better.EXPERIMENT NO: 10
OBEJECTIVE:
Study and obtain waveforms of single-phase half controlled
bridge rectifier with R and RL Loads.
APPEARTUS REQURIED:
1) 230 V power supply2) 1-Phase half bridge convertor Trainer
Kit3) Oscilloscope 4) Multimeter5) Connecting Leads
CIRCUIT DIAGRAM:
PROCEDURE:
Make sure that there should not be any connections by patch cord
on the board 1. Rotate the firing control Potentiometers 1 and 2 in
full counter clockwise direction and also switch set at
Potentiometer 1 side. 2. Switch On the power supply 3. Measure the
AC voltage (Vrms) by voltmeter between point 0V-15V and calculate
Em by Em =1.414 X Vrms. 4. Switch Off the power. 5. Connect the
circuit of half wave rectifier as shown figure 6 using 2 mm patch
cords.6. Switch On the power supply 7. Connect the Oscilloscope and
voltmeter across the load. 8. Vary the firing control Potentiometer
and set on 30, 60, 90, 120 and 150 firing angles using equation 9.
Observe the output waveforms and note the readings of voltage
across load on different firing angles. 10. Observe the waveform
across the SCR1 when firing angle is 90. 11. Calculate the average
load current IDC and power PDC from measured load voltage Vo. 12.
Plot the input signal, gate pulse, and drop signal across SCR and
output waveforms when firing angle is 90. THEORY
R LOAD
The thyristor conducts only when the anode is positive with
respect to cathode and a positive gate signal is applied,
otherwise, it remains in the forward blocking state and blocks the
flow of the load current At t = 0 when the input supply voltage
becomes positive the thyristor T becomes forward biased. However,
unlike a diode, it does not turn ON till a gate pulse is applied at
t = . During the period 0 < t , the thyristor blocks the supply
voltage and the load voltage remains zero. Consequently, no load
current flows during this interval. As soon as a gate pulse is
applied to the thyristor at t = it turns ON. The voltage across the
thyristor collapses to almost zero and the full supply voltage
appears across the load. From this point onwards the load voltage
follows the supply voltage. The load being purely resistive the
load current io is proportional to the load voltage. At t = as the
supply voltage passes through the negative going zero crossing the
load voltage and hence the load current becomes zero and tries to
reverse direction. In the process the thyristor undergoes reverse
recovery and starts blocking the negative supply voltage.
Therefore, the load voltage and the load current remains clamped at
zero till the thyristor is fired again at t = 2 + . The same
process repeats there after. The average DC output voltage across
load is given by
VDC = Em (1+cos )/2Average current is given byIDC = Em (1 + cos
)/2RAnd, the DC output power isPDC = VDC X IDC
R-L LOAD
As in the case of a resistive load, the thyristor T becomes
forward biased when the supply voltage becomes positive at t = 0.
However, it does not start conduction until a gate pulse is applied
at t = . As the thyristor turns ON at t = the input voltage appears
across the load and the load current starts building up. However,
unlike a resistive load, the load current does not become zero at t
= , instead it continues to flow through the thyristor and the
negative supply voltage appears across the load forcing the load
current to decrease. Finally, at t = ( > ) the load current
becomes zero and the thyristor undergoes reverse recovery. From
this point onwards the thyristor starts blocking the supply voltage
and the load voltage remains zero until the thyristor is turned ON
again in the next cycle. It is to be noted that the value of
depends on the load parameters. Therefore, unlike the resistive
load the average and RMS output voltage depends on the load
parameters. Since the thyristors does not conduct over the entire
input supply cycle this mode of operation is called the
discontinuous conduction mode.
WAVEFORM:
(a) For R Load (b) For R-L Load
RESULTStudy and obtain waveforms of single-phase half controlled
bridge rectifier with R and RL Loads.
PRECAUTION1) To make connection should be according to circuit
diagram.2) Connecting leads should not loose.3) Connecting circuit
should be check to be respected lab faculty after complete
connection Diagram.4) Power Supply should not be ON during
connecting leads to experimental kit.5) 6) Power supply should be
OFF after performance of allotted practical
VIVA QUESTIONS:Fill in the blank(s) with appropriate word(s) i)
In a single phase fully controlled converter the _________ of an
uncontrolled converters are replaced by ____________. ii) In a
fully controlled converter the load voltage is controlled by
controlling the _________ of the converter. iii) A single phase
half wave controlled converter always operates in the ________
conduction mode. iv) The voltage form factor of a single phase
fully controlled half wave converter with a resistive inductive
load is _________ compared to the same converter with a resistive
load. v) The load current form factor of a single phase fully
controlled half wave converter with a resistive inductive load is
_________ compared to the same converter with a resistive load.
Answers: (i) diodes, thyristors; (ii) firing angle; (iii)
discontinuous (iv) poorer; (v) better.
EXPERIMENT NO: 11
OBEJECTIVE:
Study and obtain waveforms of single-phase full controlled
bridge converter with R and RL loads. Study and show rectification
and inversion operations.
APPEARTUS REQURIED:
1) 230 V power supply2) 1-Phase half bridge convertor Trainer
Kit3) Oscilloscope 4) Multimeter5) Connecting Leads
CIRCUIT DIAGRAM:
(a) 1-phase Full wave convertor with R Load(b) 1-phase Full wave
convertor with RL Load (RECTIFICATION)
(c) 1-phase Full wave convertor with RL Load (INVERSION
MODE)
PROCEDURE:
Make sure that there should not be any connections by patch cord
on the board.1. Rotate the firing control Potentiometer in full
clockwise direction. 2. Switch On the power supply 3. Measure the
AC voltage (Vrms) by voltmeter between point 0V-15V and calculate
Em by Em =1.414 X Vrms. 4. Switch Off the power supply 5. Connect
the circuit of fully-controlled bridge rectifier as shown figure 11
using 2 mm patch cords. 6. Switch On the power supply 7. Connect
the Oscilloscope and voltmeter across the load. 8. Vary the firing
control Potentiometer and set on 30, 60, 90, 120 and 150 firing
angles using equation 9. Observe the output waveforms and note the
readings of voltage across load on different firing angle. 10.
Connect the Oscilloscope one by one across SCR1, SCR2, and SCR3
& SCR4 and observe the waveform when firing angle is 90
respectively. 11. Calculate the average load IDC current and power
PDC from measured loadvoltage Vo. 12. Plot the input signal, gate
pulse, and drop signal across SCR and output waveforms when firing
angle is 90.
THEORY:
A single-phase fully controlled bridge circuit with resistive
load consists of four thyristor as shown in figure. During the
positive half cycle when terminal P is positive w.r.t.Q, thyristors
T1 and T2 are in the forward blocking state and when these
thyristors fire simultaneously at t = , the load is connected to
the input through T1 and T2 Thyristors T1 and T2 are fired together
while T3 and T4 are fired 180 after T1 and T2. From the circuit
diagram of Fig it is clear that for any load current to flow at
least one thyristor from the top group (T1, T3) and one thyristor
from the bottom group (T2, T4) must conduct. It can also be argued
that neither T1T3 nor T2T4 can conduct simultaneously. For example
whenever T3 and T4 are in the forward blocking state and a gate
pulse is applied to them, they turn ON and at the same time a
negative voltage is applied across T1 and T2 commutating them
immediately. Similar argument holds for T1 and T2. For the same
reason T1T4 or T2T3 can not conduct simultaneously. Therefore, the
only possible conduction modes when the current i0 can flow are
T1T2 and T3T4.
R LOAD
A single-phase fully controlled bridge circuit with resistive
load consists of four thyristor as shown in figure. During the
positive half cycle when terminal P is positive w.r.t.Q, thyristors
T1 and T2 are in the forward blocking state and when these
thyristors fire simultaneously at t = , the load is connected to
the input through T1 and T2. During negative half cycle i.e., after
t = , thyristor T3 and T4 are in the forward blocking state, and
simultaneous firing of these thyristors reverse biases the
previously
conducting thyristors T1 and T2. These reverse biased thyristors
turn off due to line or natural commutation and the load current
transfers from T1 and T2 to T3 and T4. The voltage and current
waveforms are shown in figure.
The average DC voltage across load isVDC = Em (1+cos )/ The
average load current isIDC = Em (1+cos )/R Therefore, the DC output
power isPDC = VDC XIDC
RLE LOADThe circuit diagram of a single phase fully controlled
bridge converter. It is one of the most popular converter circuits
and is widely used in the speed control of separately excited dc
machines. Indeed, the RLE load shown in this figure may represent
the electrical equivalent circuit of a separately excited dc
motor.
WAVE FORMS:
(a) For RL Load (RECTIFICATION MODE) (b) For RL Load (INVERSION
MODE)
RESULTStudy and obtain waveforms of single-phase full controlled
bridge converter with R and RL Loads. Study and show rectification
and inversion operations.
PRECAUTION1) To make connection should be according to circuit
diagram.2) Connecting leads should not loose.3) Connecting circuit
should be check to be respected lab faculty after complete
connection Diagram.4) Power Supply should not be ON during
connecting leads to experimental kit.5) Power supply should be OFF
after performance of allotted practical
VIVA QUESTIONS:
Fill in the blank(s) with the appropriate word(s). i) A single
phase fully controlled bridge converter can operate either in the
_________ or ________ conduction mode. ii) In the continuous
conduction mode at least _________ thyristors conduct at all times.
iii) In the continuous conduction mode the output voltage waveform
does not depend on the ________ parameters. iv) The minimum
frequency of the output voltage harmonic in a single phase fully
controlled bridge converter is _________ the input supply
frequency. v) The input displacement factor of a single phase fully
controlled bridge converter in the continuous conduction mode is
equal to the cosine of the ________ angle.
Answer: (i) continuous, discontinuous; (ii) two; (iii) load;
(iv) twice; (v) firing.
EXPERIMENT NO.:2
OBJECTIVE:Study and plot V-I Characteristic of SCR
APPARATUS REQUIRED:
1. SCR Characteristic Trainer2. 2mm Patch cords3. Power
Supply
CIRCUIT DIAGRAM:-
PROCEDURE:1. Connect terminal1 to terminal 4, terminal 2 to
terminal 8 and terminal 3 to terminal 12 as shown in figure 11.2.
Connect Voltmeter across terminal 7 and 8 and Ammeter across
terminal 9 and10 as shown in figure 12.3. Make short terminals 5
and 6.4. Rotate the knob P1 and P2 fully in counter clockwise.5.
Switch ON the power supply.6. Set the value of Anode Voltage at 35V
by using the knob P1.7. Now Increases gate current Ig gradually by
varying knob P2 and observe it.8. At certain value of gate current,
voltmeter reading falls down to almost zero.This action indicates
the firing of SCR.9. Note the gate current value at this position
(firing of SCR).10. Keep the gate current constant by shorting
terminal 9 with 10 and connect Ammeter to the terminal 5 and 6 (as
in figure 13).
11. Rotate the potentiometer P1 fully in counter clockwise.12.
Rotate knob P1 (from initial position to its maximum limit)
gradually and record Anode current for respective value of anode
voltages.13. Plot the graph between anode voltage Va and anode
current Ia.
THEORY-
Introduction:-The Silicon Controlled Rectifier (SCR) is a
semiconductor device that is a member of a family of control
devices known as Thyristors. The SCR is a three lead device with an
anode and a cathode ( us with a standard diode) plus a third
control lead or gate .
Reverse Blocking Mode: When cathode is made positive with
respect to anode with switch S open , thyristor is reverse
biased.Junctions j1,j3 are seen to be reverse biased whereas
junction j2 is forward biased. The device behaves as if two diodes
are connected in series with reverse voltage applied across them. A
small leakage current of the order a few milliamperes (or a few
microamperes depending upon the SCR rating) flows. This is reverse
blocking mode, called the off-state,of the reverse blocking mode is
shown by OP. If the reverse voltage is increased, then at a
critical breakdown level, called reverse breakdown voltage VBR , an
avalanche occurs at J1 and J3 and the reverse current increases
rapidly. A large current associated with VBR gives rise to more
losses in the SCR. This may lead to thyristor damage as the
junction temperature rise. It should, therefore, be ensured that
maximum working reverse voltage, across a thyristor does not exceed
VBR. Reverse avalanche region is shown by PQ. When reverse voltage
applied across a SCR is less than VBR, the device offers high
impedance in the reverse direction. The SCR in the reverse blocking
mode may therefore be treated as an open switch.Note that I-V
characteristic after avalanche breakdown during reverse blocking
mode is applicable only when load resistance is present, a large
anode current associated with avalanche breakdown at VBR would
cause substantial voltage drop across load and as a result , I-V
characteristic in third quadrant would bend to the of vertical line
at VBR .
Forward blocking mode: When anode is positive with respect to
the cathode, with gate circuit open thyristor is said to be forward
biased. It is seen from this figure that junctions J1,J3 are
forward biased but junction J2 is reverse biased. In this mode, a
small current, called forward leakage current, flows . M represents
the forward blocking mode of SCR. AS the
forward leakage current is small, SCR offers high impedance.
Therefore, a SCR can be treated as an open switch even in the
forward blocking mode.
Forward conduction mode: When anode to cathode forward voltage
is increased with gate circuit open, reverse biased junction J2
will have an avalanche breakdown at a voltage called forward break
over voltage VBO. After this breakdown, thyristor gets turned on
with point M at once shifting to N and then to a point anywhere
between N and K. Here NK represents the forward conduction mode. A
SCR can be brought from forward blocking mode to forward conduction
mode by turning it on by applying (1) a positive gate pulse between
gate and cathode or (2) a forward break over voltage across anode
cathode. Forward conduction mode NK shows that voltage drop across
thyristor is of the order of 1 to 2 V depending upon the rating of
SCR. It may also be seen from NK that voltage drop across SCR
increase slightly with an increase in anode as voltage drop across
SCR is quit small. This small voltage drop VT across the device is
due to ohmic drop in four layers. In forward conduction mode,
thyristor is treated as a closed switch.
APPLICATION
Power electronic systems are virtually in every electronic
device. For example, around us:DC/DC converters are used in most
mobile devices (mobile phone, pda.) to maintain the voltage at a
fixed value whatever the charge level of the battery is. These
converters are also used for electronic isolation and power factor
correctionAC/DC converters (rectifiers) are used every time an
electronic device is connected to the mains (computer,
television...) AC/AC converters are used to change either the
voltage level or the frequency (international power adapters, light
dimmer). In power distribution networks AC/AC converters may be
used to exchange power between utility frequency 50 Hz and 60 Hz
power grids. DC/AC converters (inverters) are used primarily in UPS
or emergency light. During normal electricity condition, the
electricity will charge the DC battery. During blackout time, the
DC battery will be used to produce AC electricity at its output to
power up the appliances.
OBSERVATION TABLE:
S.NO.ANODE VOLTAGE Va VANODE CURRENT Ia MA ( Ig = MA)
1
2
3
4
5
6
7
8
9
10
RESULT:
We have Study and plot V-I Characteristic of SCR.
PRECAUTION1) To make connection should be according to circuit
diagram.2) Connecting leads should not loose.3) Connecting circuit
should be check to be respected lab faculty after complete
connection Diagram.4) Power Supply should not be ON during
connecting leads to experimental kit.5) Power supply should be OFF
after performance of allotted practical
VIVA QUESTIONS:
Q:1 What is holding current .Q:2 What is latching current. Q:3
Fill in the blank(s) with the appropriate word(s) i. A thyristor is
turned on by applying a ________________ gate current pulse when it
is ________________ biased. ii. Total turn on time of a thyristor
can be divided into ________________ time ________________ time and
________________ time. iii. During rise time the rate of rise of
anode current should be limited to avoid creating local
________________. iv. A thyristor can be turned off by bringing its
anode current below ________________ current and applying a reverse
voltage across the device for duration larger than the
________________ time of the device. v. Reverse recovery charge of
a thyristor depends on the ________________ of the forward current
just before turn off and its ________________.
EXPERIMENT NO.:3
OBJECTIVE:
To study the V-I Characteristic of DIAC with positive, negative
biasing and plot the curve between V & I.
APPARATUS REQUIRED:
1. DIAC Characteristic Trainer2. 2mm Patch Cord3. Power
Supply
CIRCUIT DIAGRAM:
PROCEDURE:POSITIVE BIASING:1. Make the connections as shown in
the above figure.2. Connect the +35V DC supply to the circuit by
connecting the point 1 with point 4 with the help of patch cord.3.
Rotate the potentiometer P1 in fully anti-clock wise direction.4.
Now connect point 2 with point 8 to make the grounds common.5.
Connect the voltmeter across the DIAC. For that connect the +Ve
terminal of Voltmeter with the point 7 and connect the -Ve terminal
of the voltmeter with the point 8.6. Now connect the Ammeter in the
circuit for that connect the +Ve terminal of the ammeter to the
point 5 and connect the -Ve terminal of the Ammeter to the point
6.7. Connect the mains cord to the trainer & switch On the
supply.8. Here you will observe that there is no current flow in
the circuit and as well as no voltage across the DIAC.9. Increase
the voltage across the DIAC in steps of 1V by rotating the
potentiometer P1 in clockwise direction and note down the readings
for Voltage and Current in the following table.10. Now plot the VI
curve for taken readings.
NEGATIVE BIASING:10. Now connect the -35V DC supply to the
circuit by connecting the point 3 with point 4 with the help of
patch cord.11. Repeat the process from step 3 to step 9.12. Now
plot the VI curve for taken readings.
THEORY
A cross - sectional view of a diac showing all layer and
junction in fig. If voltage V12 with terminal 1 positive with
respect to terminal 2, exceed break over voltage Vbo1 and structure
P1N2P2N3 conduct. In case terminal 2 positive with respect to
terminal 1and when V21 exceeds break over voltage Vbo2 and
structure N1P1N2P2 conduct. The term DIAC is obtained from capital
letters. DIode works an AC.
The DIAC, or diode for alternating current, is a trigger diode
that conducts current only after its breakdown voltage has been
exceeded momentarily. When this occurs, the resistance of the diode
abruptly decreases, leading to a sharp decrease in the voltage drop
across the diode and, usually, a sharp increase in current flow
through the diode. The diode remains "in conduction" until the
current flow through it drops below a value characteristic for the
device, called the holding current. Below this value, the diode
switches back to its high-resistance (non-conducting) state. This
behavioris bidirectional, meaning typically the same for both
directions of current flow. DIACs have no gate electrode, unlike
some other thyristors they are commonly used to trigger, such as
TRIACs. Some TRIACs contain a built-in DIAC in series with the
TRIAC's "gate" terminal for this purpose. DIACs are also called
symmetrical trigger diodes due to the symmetry of their
characteristic curve. Because DIACs are bidirectional devices,
their terminals are not labeled as anode and cathode but as A1 and
A2 or MT1 ("Main Terminal") and MT2.
DIAC is basically a two terminal parallel inverse combination of
semiconductor layer that permits triggering in either direction.
The characteristic of the device clearly demonstrated that there is
breakdown voltage in either direction
DIAC CHARACTERISTICS:
Volt-ampere characteristic of a diac is shown in figure. It
resembles the English letter Z because of the symmetrical switching
characteristics for either polarity of the applied voltage.The diac
acts like an open-circuit until its switching or breakover voltage
is exceeded. At that point the diac conducts until its current
reduces toward zero (below the level of the holding current of the
device). The diac, because of its peculiar construction, does not
switch sharply into a low voltage condition at a low current level
like the SCR or triac. Instead, once it goes into conduction, the
diac maintains an almost continuous negative resistance
characteristic, that is,voltage decreases with the increase in
current. This means that, unlike the SCR and the triac, the diac
cannot be expected to maintain a low (on) voltage drop until its
current falls below a holding current level.
OBSERVATION TABLE:
FORWARD BIASING:
S.NO.ANODE VOLTAGE Va (V)ANODE CURRENT Ia (MA )
1
2
3
4
5
6
7
8
9
10
REVERSE BIASING:
S.NO.ANODE VOLTAGE Va (V)ANODE CURRENT Ia (MA )
1
2
3
4
5
6
7
8
9
10
APPLICATION:
Trigging for TRIAC
RESULT:
We have study the VI Characteristic of DIAC with positive,
negative biasing and plot the curvebetween V & I.
PRECAUTION1) To make connection should be according to circuit
diagram.2) Connecting leads should not loose.3) Connecting circuit
should be check to be respected lab faculty after complete
connection Diagram.4) Power Supply should not be ON during
connecting leads to experimental kit.5) Power supply should be OFF
after performance of allotted practical
VIVA QUESTIONS:
(1) Fill in the blanks with the appropriate word(s).
(i) The width of the space charge region increases as the
applied ______________ voltage increases. (ii) The maximum electric
field strength at the center of the depletion layer increases
Within the reverse voltage. (iii) Reverse saturation current in a
power diode is extremely sensitive to ___________ variation.
(iv) Donor atoms are _____________________ carrier providers in
the p type and _________________ carrier providers in the n type
semiconductor materials. (v) Forward current density in a diode is
__________________________ proportional to the life time of
carriers.
Answer: (i) Reverse, (ii) increase, (iii) temperature, (iv)
Minority Majority, (v) inversely
EXPERIMENT NO.:4
OBJECTIVE:
To study the V-I Characteristic of TRIAC with positive &
negative biasing and plot the curve between V & I
APPARATUS REQUIRED:
1. TRIAC Characteristic Trainer2. 2mm Patch Cords3. Power
supply
CIRCUIT DIAGRAM:
PROCEDURE:
VI Characteristic with Positive Biasing1. Make the connections
as shown in the above figure. 2. of patch cord. 3. Rotate both the
potentiometers in fully anti-clock wise direction. 4. Now connect
point 4 with point 9 to make the grounds common. 5. Connect the
Point 3 with point 13 to give a supply of 15V for gate current. 6.
Now connect the positive & negative terminal of Ammeter to
point 6 and point 7 respectively to measure Anode Current. 7.
Connect the positive & negative terminal of Voltmeter to point
8 and point 9 (Gnd) respectively to measure Anode Voltage. 8.
Connect the point 10 with point 11. 9. Connect the mains cord to
the trainer & switch On the power supply.10. Rotate the pot P1
and increase the anode voltage slowly. Here you will see that the
anode current will be zero for all the values of anode voltage. 11.
Now remove the Ammeter between points 6 & 7 & connect
across the point 11 and 10 respectively.
12. Set the value of gate current near about 0.5mA using pot P2.
13. Rotate the potentiometer P1 in fully anti-clock wise direction.
14. Now again connect the ammeter across the point 6 and point 7,
and short the point 10 and 1115. Now rotate the P1 slowly in
clockwise direction & note the readings for Va (Anode Voltage)
and corresponding Ia (Anode Current) in the following observation
table. Note: For a proper value of gate current there will be a
breakdown in the TRIAC. At breakdown condition there will be sudden
increment in the anode current (Ia) and simultaneously a decrement
in the anode voltage (Va). 16. If breakdown is not achieved then
increase the gate current slightly (by .05mA) and repeat steps 13
to 15 and check for breakdown condition. Note: Rotate the pot P2 as
precise as you can to observe breakdown of TRIAC. 17. Observe the
gate current for which breakdown is achieved and plot the graph
between Va & Ia. Note: Here you will observe that the value of
Ia will be zero for the insufficient gate current.
V-I Characteristic with Negative Biasing
18. Now connect the -35V DC supply to the circuit and repeat the
process from step 1 to step 12. 19. Repeat steps 3 to 13. 20.
Observe the gate current for which breakdown is achieved and plot
the graph between Va & Ia.THEORY
An SCR is a unidirectional device as it can conduct from anode
to cathode only and it cannot be conduct from cathode to anode. A
triac can however conduct both directions. The TRIAC is a
bidirectional, three terminal semiconductors for controlling
current in either direction. The term TRIAC is obtained from
capital letters. TRIode works an AC Below is the schematic symbol
for the TRIAC shown in fig.
Fig: Schematic Symbol
Notce the symbol looks like two SCRs in parallel (opposite
direction) with one triggers or gate terminal. The main or power
terminals are designated as MT1 and MT2. 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 then the right SCR
conducts. Minimum holding current, Ih, must be maintained in order
to keep a TRIAC conducting. A TRIAC operates in the same way as the
SCR however it operates in both a forward and reverse direction. To
get a quick understanding of its operation refer to its
characteristic curve below and compare this to the SCR
characteristic curve. It can be triggered into conduction by either
a PLUS (+) or MINUS (-) gate signal.. Obviously a TRIAC can also be
triggered by exceeding the break
over voltage. This is not normally employed in TRIAC operation.
The break over voltage is usually considered a design limitation.
One other major limitation, as with the SCR, is dV/dt, which is the
rate of rise of voltage with respect to time. A TRIAC can be
switched into conduction by a large dV/dt. Typical applications are
in phase control, inverter design, AC switching, relay replacement,
etc.
TRIAC CHARACTERISTICS:
OBSERVATION TABLE:
S.NOFORWARD BIASING:REVERSE BIASING
ANODE VOLTAGEVa (V)ANODE CURRENTIa (MA )ANODE VOLTAGEVa (V)ANODE
CURRENTIa (MA )
1
2
3
4
5
6
7
8
9
10
APPLICATION
Power electronic systems are virtually in every electronic
device. For example, around us:DC/DC converters are used in most
mobile devices (mobile phone, pda.) to maintain the voltage at a
fixed value whatever the charge level of the battery is. These
converters are also used for electronic isolation and power factor
correctionAC/DC converters (rectifiers) are used every time an
electronic device is connected to the mains (computer,
television...) AC/AC converters are used to change either the
voltage level or the frequency (international power adapters, light
dimmer). In power distribution networks AC/AC converters may be
used to exchange power between utility frequency 50 Hz and 60 Hz
power grids. DC/AC converters (inverters) are used primarily in UPS
or emergency light. During normal electricity condition, the
electricity will charge the DC battery. During blackout time, the
DC battery will be used to produce AC electricity at its output to
power up the appliances.
RESULT:
We have study the VI Characteristic of TRIAC with positive &
negative biasing and plot the curve between V & I
PRECAUTION1) To make connection should be according to circuit
diagram.2) Connecting leads should not loose.3) Connecting circuit
should be check to be respected lab faculty after complete
connection Diagram.4) Power Supply should not be ON during
connecting leads to experimental kit.5) Power supply should be OFF
after performance of allotted practicalVIVA QUESTION
1) Fill in the blank(s) with the appropriate word(s) i. A
thyristor is turned on by applying a ________________ gate current
pulse when it is ________________ biased. ii. Total turn on time of
a thyristor can be divided into ________________ time
________________ time and ________________ time. iii. During rise
time the rate of rise of anode current should be limited to avoid
creating local ________________. iv. A thyristor can be turned off
by bringing its anode current below ________________ current and
applying a reverse voltage across the device for duration larger
than the ________________ time of the device. v. Reverse recovery
charge of a thyristor depends on the ________________ of the
forward current just before turn off and its ________________.
EXPERIMENT NO.:5
OBJECTIVE:
Find output and tranfer characteristics of MOSFET. APPEARTUS
REQURIED
1. MOSFET Trainer Kit2. Connecting Leads3. Voltmeter4.
Ammeter
CIRCUIT DIAGRAM:-
Fig. Cicuitdigram of MOSFET
PROCEDURE:
1. Connect +35 V, +15 V DC power supplies & Ground at their
indicated position in the circuit by patch cords. 2. Rotate both
the potentiometer P1 and P2 fully in counter clockwise direction
and keep the toggle switch at off position. 3. Connect +ve terminal
of Ammeter to terminal 3 and ve terminal of Ammeter to Drain
terminal to measure drain current ID (mA). 4. Connect a 2mm patch
cord between terminal 2 and Gate terminal. 5. Connect +ve terminal
of voltmeter to terminal 1 and -ve terminal to ground to measure
gate voltage VGS. 6. Switch On the power supply & toggle
switch. 7. Vary potentiometer P1 and set a value of gate voltage
VGS at some constant value (3.8V, 3.9 V, 4 V...............5V). 8.
Disconnect voltmeter between terminal 1 and ground. 9. Now connect
voltmeter between terminal 4 and ground. 10. Vary the potentiometer
P2 so as to increase the value of drain voltage VDS from zero to 35
V in step and measure the corresponding values of drain current Id
for different constant value, gate voltage VGS in an observation
table. 11. Repeat the procedure from step 7 for different sets of
gate voltage VGS. 12. Plot a curve between drain voltage VDS and
drain current ID, 10 using suitable scale with the help of
observation table. This curve is the required drain
characteristic.
THEORY:-
The metaloxidesemiconductor field-effect transistor (MOSFET) is
a device used for amplifying or switching electronic signals. In
MOSFETs, a voltage on the oxideinsulated gate electrode can induce
a conducting channel between the two other contacts called source
and drain. The channel can be of n-type or p-type and is
accordingly called an nMOSFET or a pMOSFET (also commonly nMOS,
pMOS). It is by far the most common transistor in both digital and
analog circuits, though the bipolar junction transistor was at one
time much more common. FET with an oxide coating between gate and
channel is called a MOSFET (metaloxide semiconductor field effect
transistor) the figure below shows the oxide, insulating the gate
from the channel. MOSFET is voltage controlled device &
required only small input current. Its switching speed is very
high; it is used in low power high frequency converter. But it has
the problem of electrostatic discharge so require special care in
handling.
Here drain current is cut-off until the gate to source voltage
reaches a specific magnitude. So, current control in n-channel is
effected by +ve source to gate voltage If VGS is set to zero,
voltage applied between D & S of the device, the absence of
nchanne will result in current zero amperes With VDS some +ve
voltage, VGS at zero volts & terminal is directly connected t
source there are in fact two reverse biased p-n junction between
the n-doped & psubstrat to oppose any significant flow between
drain & source Now of VGS & VDS is set at some +ve voltage
greater then zero, hence established Dgat at +ve potential with
respect to source. As VGS is increase, then significant increase in
drain current (ID) is called threshold voltage & given by VT.
Since channel is non-existence with VGS= 0V and enhanced by the
application of +ve gate-to-source voltage so this type of MOSFET is
called enhancement type. So with increase in VGS, drain current
increase. If we hold VGS constant & increase in level of VDS
then ID will eventually reach saturation level.
APPLICATION:
AC to DC (rectification)DC to AC (inversion)DC to DC
(chopping)AC to ACOBSERVATION TABLE:
RESULT:We have draw the output characteristics of MOSFET.
PRECAUTION6) To make connection should be according to circuit
diagram.7) Connecting leads should not loose.8) Connecting circuit
should be check to be respected lab faculty after complete
connection Diagram.9) Power Supply should not be ON during
connecting leads to experimental kit.10) Power supply should be OFF
after performance of allotted practicalVIVA QUESTIONS:
Fill in the blank(s) with the appropriate word(s). i) A single
phase fully controlled bridge converter can operate either in the
_________ or ________ conduction mode. ii) In the continuous
conduction mode at least _________ thyristors conduct at all times.
iii) In the continuous conduction mode the output voltage waveform
does not depend on the ________ parameters. iv) The minimum
frequency of the output voltage harmonic in a single phase fully
controlled bridge converter is _________ the input supply
frequency. v) The input displacement factor of a single phase fully
controlled bridge converter in the continuous conduction mode is
equal to the cosine of the ________ angle.
Answer: (i) continuous, discontinuous; (ii) two; (iii) load;
(iv) twice; (v) firing.
EXPERIMENT NO.:6
OBJECTIVE:
Find output and tranfer characteristics of IGBT. APPEARTUS
REQURIED
1. IGBT Trainer Kit2. Connecting Leads3. Voltmeter4. Ammeter
CIRCUIT DIAGRAM:-
Circuit diagram of IGBT
Out put characteristics Transfer characteristics
PROCEDURE :
1. Rotate the potentiometer P1 fully in clockwise direction and
P2 fully in counter clockwise 2. direction. 3. Connect Ammeter
between point d and e to measure collector current Ic (mA). Connect
a 2mm patch cord between point a and b.4. Connect voltmeter between
point c and ground to measure the Gate voltage VGE and between
point f and ground.5. Switch On the power supply.6. Vary the
potentiometer P1 in counterclockwise direction to set the gate
voltage VGE (between 4.8V and 5.6V). 7. Vary the potentiometer P2
in clockwise direction so as to increase the value of
collector-emitter voltage VCE from 0 to 35V in step and measure the
corresponding values of collector current Ic for different constant
value of gate voltage VGE in an Observation Table 1. 8. Rotate the
potentiometer P2 fully in the counterclockwise direction and
potentiometer P1 fully in clockwise direction. 9. Repeat the
procedure from step 6 for different sets of gate voltage VGE. 10.
Plot a curve between collector-emitter voltage current (VCE) and
Collector current Ic using suitable scale with the help of
observation Table 1. This curve is the required collector
characteristic.
THEORY:-
BASIC STRUCTURE:
The insulated gate bipolar transistor (IGBT) combines the
positive attributes of BJTs and MOSFETs. BJTs have lower conduction
losses in the On-state, especially in devices with larger blocking
voltages, but have longer switching times, especially at turn-Off
while MOSFETs can be turned on and off much faster, but their
on-state conduction losses are larger, especially in devices rated
for higher blocking voltages. Hence, IGBTs have lower on-state
voltage drop with high blocking voltage capabilities in addition to
fast switching speeds and has become the most favored power device
in Industrial application.
The vertical cross sectional structure of an IGBT is shown in
Figure 1 having four alternate p-n-p-n layers with three terminals
Emitter, Collector and Gate. A heavily doped p+ substrate has a
lightly doped n-type drift region grown on to it by epitaxial
process. Then the p-type emitter is diffused with two subsequent
n-type layers over doping windows. The performance of an IGBT is
closer to that of a BJT rather than a MOSFET. The circuit symbol of
an IGBT are shown in the below Figure 2. When the gate is positive
with respect to the emitter and this voltage is beyond the
threshold value, an n channel is induced in the p-region of a
MOSFET. These charge carriers forward bias the base-emitter
junction of the p-n-p transistor and holes are injected into the
n-type drift region. These injected holes cross the reverse biased
collector junction of the p-n-p transistor and constitute the
collector current. This collector current is the base current for
the np- n transistor, which is properly biased in the active
region. This amplifying collector current flows from the n-p-n
transistor to the base of the p-n-p transistor, hence a positive
feedback exits and the device turns ON
WORKING:-
When a positive voltage is applied to the collector terminal
with the gate short circuited (VGE = 0) to the emitter terminal,
the upper junction (J2) becomes reverse biased and the device
operates in forward blocking mode i.e. there is no current flow
between collector and emitter. If we set a positive voltage to VGE
& VCE then a current (Ic) will flow in collector terminal. For
a value less than the threshold level the collector current of an
IGBT is 0mA.If we hold VGE constant and increasing the VCE then Ic
will reach a saturation level. So with increase in VCE and keeping
the VGE to the threshold value the collector current (Ic) will
reach the saturation level. Further increase in Gate voltage the
value of collector current will increase. The V-I characteristics
of the IGBT is given below
APPLICATION:
AC to DC (rectification)DC to AC (inversion)DC to DC
(chopping)AC to ACOBSERVATION TABLE:S.No.Collector Voltage
VCECollector Current Ic (mA) at constant value of Gate Voltage VGE
(volt)
VGE = VVGE = VVGE = V
1
2
3
4
5
6
7
RESULT:We have drawn the output characteristics of IGBT.
PRECAUTION1) To make connection should be according to circuit
diagram.2) Connecting leads should not loose.3) Connecting circuit
should be check to be respected lab faculty after complete
connection Diagram.4) Power Supply should not be ON during
connecting leads to experimental kit.5) Power supply should be OFF
after performance of allotted practical
VIVA QUESTION
1) Fill in the blank(s) with the appropriate word(s) i. A
thyristor is turned on by applying a ________________ gate current
pulse when it is ________________ biased. ii. Total turn on time of
a thyristor can be divided into ________________ time
________________ time and ________________ time. iii. During rise
time the rate of rise of anode current should be limited to avoid
creating local ________________. iv. A thyristor can be turned off
by bringing its anode current below ________________ current and
applying a reverse voltage across the device for duration larger
than the ________________ time of the device. v. Reverse recovery
charge of a thyristor depends on the ________________ of the
forward current just before turn off and its ________________.
EXPERIMENT NO.: 8
OBJECTIVE:
Study And Test Firing Circuit For SCR- UJT Firing Circuits.
APPEARTUS REQURIED
IGBT Trainer Kit Connecting Leads Voltmeter Ammeter
CIRCUIT DIAGRAM:-
PROCEDURE:
1. Connect Ammeter between point c and b to measure
Anode-cathode current IAK (mA). 2. Connect Ammeter between point f
and e to measure the gate Current IG (mA).3. Connect voltmeter
between point a and ground to measure the anodecathode voltage VAK
. 4. Rotate the potentiometer P1 fully in clockwise direction and
P2 fully in counter clockwise direction. 5. Switch On the power
supply.6. Vary the potentiometer P2 in clockwise direction so as to
increase the anode to cathode voltage. Set this voltage above
11V.7. Vary the potentiometer P1 in counterclockwise direction so
as to increase the value of gate current in step and measure the
corresponding values of anode to cathode current IAK in an
Observation Table 1.8. Initially there will not be any current flow
across the SCR while varying the gate current the ammeter connected
at point c and d suddenly increases and the voltmeter connected at
point e and ground will suddenly decrease. This shows that the SCR
is triggered. 9. Now vary the P1, there will not be any effect in
the anode-cathode voltage and current of SCR. To repeat the
experiment switch off the power supply and follow the procedure
from step 4
THEORY:The UJT is often used as a trigger device for SCRs and
TRIACs. The diode-resistance, resistance, resistance-capacitance
and the diode-resistance capacitance circuit produce prolonged
pulses, so power dissipation is more at the gate. The power loss
can be limited by the use of this UJT in the firing circuit. Pulse
triggering is preferred as it offers several merits over R and RC
triggering. Gate characteristics wide spread; pulses can be
adjusted easily to suit such a wide spectrum of gate
characteristics. The power level in pulse triggering is low as the
gate drive is discontinuous; pulse triggering is therefore more
efficient. The resistor and capacitor connected to the emitter form
an RC timing circuit. Normally, the value of capacitor is fixed and
the value of resistor is of potentiometer type. The charging rate
of the capacitor depends on the value of the resistor and since the
resistor is variable the RC time constant can be controlled.
When the voltage across the capacitor is equal to more than the
peak voltage VP of the UJT, it starts conducting. Since the UJT has
a negative resistance, its voltage starts decreasing up to the
valley voltage, and the capacitor discharges up to the valley
voltage. This repetitive process produces a train of pulses at its
output is shown in figure 2. From the output voltage waveform it is
clear that the output pulses has a very small width and that a long
relaxation time exits between the two pulses. Therefore it is said
that the device is relaxed in this duration and is called the
relaxation oscillator.
OBSERVATION TABLE:Set VAK = +12VS.NoGate current IG(mA)Anode to
cathode current IAK(mA)Anode to cathodevoltage VAK(V)
1
2
3
4
5
6
7
RESULT:We study and test firing circuit for SCR- UJT firing
circuits.
PRECAUTION6) To make connection should be according to circuit
diagram.7) Connecting leads should not loose.8) Connecting circuit
should be check to be respected lab faculty after complete
connection Diagram.9) Power Supply should not be ON during
connecting leads to experimental kit.10) Power supply should be OFF
after performance of allotted practicalVIVA QUESTIONS:
Fill in the blank(s) with the appropriate word(s). i) A single
phase fully controlled bridge converter can operate either in the
_________ or ________ conduction mode. ii) In the continuous
conduction mode at least _________ thyristors conduct at all times.
iii) In the continuous conduction mode the output voltage waveform
does not depend on the ________ parameters. iv) The minimum
frequency of the output voltage harmonic in a single phase fully
controlled bridge converter is _________ the input supply
frequency. v) The input displacement factor of a single phase fully
controlled bridge converter in the continuous conduction mode is
equal to the cosine of the ________ angle.
Answer: (i) continuous, discontinuous; (ii) two; (iii) load;
(iv) twice; (v) firing.
EXPERIMENT NO.7OBJECTIVE: Find UJT static emitter
characteristics and study the variation in peak point and valley
pointAPPARATUS REQUIRED:1. UJT traner kit2. Voltmeter-2nos(0-20v)3.
Ammeter(0-30ma)4. patchcords5. Powersupply-2no (0-30v,2A)
CIRCUIT DIAGRAM:-
Circuit diagram of UJT
THEORY-
The static emitter characteristic (a curve showing the relation
between emitter voltage VEand emitter current IE) of aUJTat a given
inter base voltage VBBis shown in figure. From figure it is noted
that for emitter potentials to the left of peak point, emitter
current IEnever exceeds IEo. The current IEocorresponds very
closely to the reverse leakage current ICoof the conventional BJT.
This region, as shown in the figure, is called the cut-off region.
Once conduction is established at VE= VPthe emitter potential
VEstarts decreasing with the increase in emitter current IE. This
Corresponds exactly with the decrease in resistance RBfor
increasing current IE. This device, therefore, has a negative
resistance region which is stable enough to be used with a great
deal of reliability in the areas of applications listed earlier.
Eventually, the valley point reaches, and any further increase in
emitter current IEplaces the device in the saturation region, as
shown in the figure. Three other important parameters for the UJT
are IP, VVand IVand are defined below:Peak-Point Emitter Current.
Ip. It is the emitter current at the peak point. It represents the
rnimrnum current that is required to trigger the device (UJT). It
is inversely proportional to the interbase voltage VBB.Valley Point
Voltage VVThe valley point voltage is the emitter voltage at the
valley point. The valley voltage increases with the increase in
interbase voltage VBB.Valley Point Current IVThe valley point
current is the emitter current at the valley point. It increases
with the increase in inter-base voltage VBB.The static emitter
characteristic (a curve showing the relation between emitter
voltage VEand emitter current IE) of aUJTat a given inter base
voltage VBBis shown in figure. From figure it is noted that for
emitter potentials to the left of peak point, emitter current
IEnever exceeds IEo. The current IEocorresponds very closely to the
reverse leakage current ICoof the conventional BJT. This region, as
shown in the figure, is called the cut-off region. Once conduction
is established at VE= VPthe emitter potential VEstarts decreasing
with the increase in emitter current IE. This Corresponds exactly
with the decrease in resistance RBfor increasing current IE. This
device, therefore, has a negative resistance region which is stable
enough to be used with a great deal of reliability in the areas of
applications listed earlier. Eventually, the valley point reaches,
and any further increase in emitter current IEplaces the device in
the saturation region, as shown in the figure. Three other
important parameters for the UJT are IP, VVand IVand are defined
below:Peak-Point Emitter Current. Ip. It is the emitter current at
the peak point. It represents the rnimrnum current that is required
to trigger the device (UJT). It is inversely proportional to the
interbase voltage VBB.Valley Point Voltage VVThe valley point
voltage is the emitter voltage at the valley point. The valley
voltage increases with the increase in interbase voltage VBB.Valley
Point Current IVThe valley point current is the emitter current at
the valley point. It increases with the increase in inter-base
voltage VBB.
OBSERVATION TABLE:
Sr. noVoltage(volt)Current(ma)
1
2
3
4
5
6
7
RESULT: Study the UJT static emitter characteristics and study
the variation in peak point and valley point Special Features of
UJT.The special features of a UJT are : 1. A stable triggering
voltage (VP) a fixed fraction of applied inter base voltage VBB. 2.
A very low value of triggering current. 3 A high pulse current
capability. 4. A negative resistance characteristic. 5. Low
cost.
Lab Manual
POWER ELECTRONICS-III LAB (5EE7)
DEPARTMENT OF ELECTRICAL ENGINEERING
INSTRUCTIONS
BEFORE ENTERING THE LAB Come prepared with theory related to the
practical to be performed in the lab. Bring completed practical
file on every turn. Carry lab copy for noting down readings.
WHILE WORKING IN THE LAB Adhere to experimental schedule as
instructed by the faculty concerned. Get the previously performed
practical checked by the faculty. Get the result of the current
practical checked by the instructor in the lab copy. Students must
work on their assigned experiment kit/computer on respective turn
of their lab. Students are responsible for the experiment
kit/computer system and attached peripherals they are working on
respective turn of his/her lab. They should immediately intimate
any fault or malfunctioning of these to the concerned faculty
member. Strict action (including penalty) will be taken against the
student found stealing any equipments from the lab. The experiment
kits/instruments and lab instruction sheets must be got duly issued
from the lab instructor at the commencement of the lab and must be
returned in working condition at the end of lab.
LAB ETHICSDos: Shut down the computer experiment kits and
instruments before leaving the lab. Keep the bags outside lab. Be
punctual. Maintain decorum in the lab. Utilize lab hours for
experiments. Get your pen drives scanned by the lab in-charge
before using in the lab.
Donts: External material is not permitted in the lab. Mobile
phone is not permitted in the labs. Dont litter in the lab. Dont
delete and make any modification in the setup/configuration files.
Students are not permitted to carry any lab equipments outside the
lab.
MARKING /ASSIGNMENT SCHEME
Total Marks:75Sessional Marks:45Practical Marks:30Sessional
Marks break up-AttendanceRecordPerformanceViva
1010520
Lab Plan and Time Distribution
Lab Plan: Total no. of Experiments: 11 No. of turns required :
3
Distribution of Lab hours: (Please change the distribution as
per the lab timings) - the line written in parenthesis needs to be
deleted while finalizing this lab instruction sheet Explanation of
Experiment & Logic:20 Minutes Performing the Experiment:50
Minutes File Checking:05 Minutes Viva/Quiz:05 Minutes Solving of
Queries:10 Minutes
Power Electronisc-IIIMr. Nemi Chand KoliTechnical Officer-EE