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Jawaharlal Nehru Engineering College
Laboratory Manual
POWER ELECTRONICS
For
TE-EEP Students
 Author JNEC, Aurangabad
PREFACE
It is my great pleasure to present this laboratory manual for third year engineering
students for the subject of Power Electronics keeping in view the vast coverage required for
visualization of concepts of basic equipments.
As a student, many of you may be wondering with some of the questions in your mind
regarding the subject and exactly that has been tried to answer through this manual.
Faculty members are also advised that covering these aspects in initial stage itself will
greatly relieve them in future, as much of the load will be taken care by the enthusiastic
energies of the students, once they are conceptually clear. Students are advised to thoroughly
go through this manual rather than only topics mentioned in the syllabus as practical aspects
are the key to understanding and conceptual visualization of theoretical aspects covered in the
books.
Good Luck for your Enjoyable Laboratory Sessions.
HOD-EEP
Subject Index
Lab Exercise.

Study of V-I characteristics of SCR, DIAC, TRIAC.

Study of V-I characteristics of power semiconductor devices: GTO, MOSFET, IGBT.

Study of R firing circuit.

Commutation circuits: Class A, B, C, D.

Study of 1-ph half controlled and full controlled converter. (R & RL Load)

Application of phase control using SCR/TRIAC.

Study of chopper circuit.

Study of Series Inverter.

Study of UPS.
Experiment No:- 2
Aim: Study of V-I characteristics of power semiconductor devices:, MOSFET.
Apparatus: Voltmeter (0-25v), Voltmeter (0-5v), Milliammeter (0-25mA),
Theory:
1) Explain the constructional details of MOSFET
2) Explain the working of MOSFET.
3) Mention various types of MOSFET and applications of MOSFET.
Procedure:
1) Study the circuit provided on the front panel of the kit.
2) Connect voltmeter Vgs , Vds and Milliammeter Id in circuit.
3) Keep Vgs=0 vary Vdd note Vds and Id.
4) Repeat step 3 for Vgs= 1v, Vgs=2V etc.
5) Plot drain characteristics between Vds and Id for fixed value of Vgs.
6) Keep Vdd= Constant and vary Vgs and note Vgs and Id.
7) Plot transfer characteristics in between Vgs and Id.
Observation:
1) Drain Characteristics
Vdd
Vds
Id
Vgs
Id
0v
1v
2v
2) Transfer Characteristics
Vgg
0v
1v
2v
Conclusion:
The Enhancement type N-channel MOSFET becomes ON when gate voltage applied Vgs is Positive
and is found to be ____ V.
Experiment No:- 4
Aim :- To study various Commutation circuits: Class A, B, C, D.
Appartus:- Trainer Kit, CRO, Probes, Supply, ETC.
Theory: - Explain the working of different commutating circuit.
Procedure:A) Class A or Self commutation by resonating the load.
2.
3.
Connect the circuit as shown using the F.T.O SCR.
Trigger the F.T.O SCR. The “C” first charges with top plate positive to a voltage higher
then the supply and than tries to force current back through SCR, thus turning it “OFF”.
Progressively increase the value of C till the SCR commutates. The series and parallel
combinations of L1 and L2 may also be tried.
Thus here reverse voltage is applied to the load carrying SCR from the over swing
of an undamped LC resonant circuit containing the load in series with SCR. Turn-off
time is determined by period of LC circuit. Inverters, of this class are most suitable for
frequencies above 400Hz, but at lower frequencies weight, size and cost of the
resonant circuit, which carries full load current, become prohibitive. Current through
SCR is nearly sinusoidal and hence of low di/dt. However, load regulation is poor and
voltage across the SCR can be high under condition of heavy load.
B) Class B or Self commutation by an LC circuit.
Here reverse voltage is applied to the load carrying SCR from the overswing of an
undamped series LC resonant circuit connected across the SCR.
The turn off time is determined by period of LC circuit.
1.
Connect as per shown in the given circuit, using the F.T.O. SCR and put on the supply. “C”
charges up with the top plate positive.
2. Trigger SCR:- Now current flows in two directions. The load current flows through SCR
and a pulse of current flows through the resonant LC circuit and “C” charges up in the
reverse polarity. The resonant circuit current again reverses and attempts to flow
through the SCR in the oppose direction to loose current. The SCR will turn off if this
reverse resonant circuit current is greater than the load current. Progressively
increases “C” till SCR commutates. Advantages of this class are simplicity, good load
regulation and max. SCR voltage not exceeding the supply voltage. Disadvantage is high
initial di/dt through SCR. This type is mainly used for DC to DC conversion, DC motor
control and regulated DC power supplies.
C) Class-C or commutation through charged commutation switched by an another load SCR.
Here reverse voltage is applied, when another load carrying SCR is switched. The turnoff time is usually determined by time constant of the capacitor and the load. Inverters of
this class are more useful below 1000Hz. Regulation is good and SCR voltage is limited to
double the supply voltage. However, the initial di/dt is very high.
D) Class-D or commutation through charged capacitor switched by an auxillary SCR.This is
again the same setup as C
The circuit then has chopper configuration and has been used to control DC motor of a battery
powered vehicle.
E) Class-D Alternative version:Refer to d) section of the circuit plate
1) Connect the circuit as per shown in the circuit diagram and put on the supply.
2) Use normal SCR for SCR1 and F.T.O SCR for SCR2.
3) Trigger SCR2 “C” charges with upper plate +ve. As soon as “C” charges, SCR2 turns off due
to lack of holding current.
4) Now trigger SCR1, The current flows in two paths: Load current flows in the 250Ω load and
commutating current flows through C-SCR1-L and D and the charge on C reverses,and is
held at –ve peak because of diode D.
5) Now trigger SCR2- This places”C” across SCR1 Thus turning it “off”. Progressively increases
“c” till this happens.
This class of inverter is very versatile as both time ratio and pulse width control can be
rapidly incorporated. Load regulation is very good.
F) Class-e or External pulse source commutation .
Here the reverse voltage is applied to the load carrying SCR from an external pulse source,
which may be applied either across the SCR or in series with it. The turn off time is equal to
width of applied pulse.
In the setup, when SCR is triggered, current flows in the load. To turn the SCR off, base
drive is applied to transistor T1. This connects the auxillary supply across the SCR in
opposition, turning it off.
G) Class F- A.C line commutation:Here reverse voltage is applied to the load carrying SCR,the ac voltage is produced across
the load. The off time and the conducting time is determined by the frequency of the ac
voltage and the triggering angle of load carrying SCR.
Conclusion:Thus we have studied various types of commutation circuits.
Experiment No:- 6
Aim: To study fan control using SCR, and lamp dimmer using TRIAC. (Phase control using
SCR and TRIAC.)
Apparatus: Circuit board, connecting wires.
Theory:
1)
2)
3)
4)
Explain the working of fan control and lamp dimmer with respect to their circuits.
Give the specifications of various components used in the circuit.
Explain how phase control is achieved using SCR and TRIAC.
Explain how triggering of TRIAC is achieved using DIAC.
Procedure:
1. Make connections as per Circuit diagram.
2. Observe the variation in light intensity in case of lamp dimmer and speed of fan in case of
fan regulator.
3. Switch off the mains and remove connections
Circuit diagram:
Lamp Dimmer:
Fan Regulator:
Conclusion:
Thus we have studied phase control using SCR & TRIAC.
Experiment No:-7
Aim: To study Chopper circuit.
Apparatus:
Chopper kit, Connecting wires, CRO
Theory :
Explain in detail how resistive chopper circuit works.
Procedure:
1.
Short "+15 V DC EXT" to "+15 V DC INT".
2. Connect G1-G1T, K1-K1T, G2-G2T and K2-K2T.
3.
Connect L1 on the "Commutation components" panel for COM-L in the
power circuit.
4.
Similarly, connect "C1" for COM-C.
5.
Put the switch in the SCR1 gate circuit to “off”.
6. Connect "Load Voltage Divider" across "Load R" and the oscilloscope at the terminals
indicated.
7.
Connect multimeter 250 V DC range across the load.
8.
Connect the ac mains and put on.
9.
Turn "Pulse Width" potentiometer fully anticlockwise.
10. Put on the switch in the SCR1 gate circuit. The chopper will start operating.
11.
Observe the variation in the waveform by rotating "Pulse Width"
knob clockwise, also note changes in the output voltage shown on the meter. Calculate
max/min output voltage ratio.
12.
Repeat step 2 by changing various values of COM-C.
Observations:
Sr.
Ton( sec)
Toff( sec)
o/p voltage
No.
observed
observed
observed
Duty cycle
Calculation:
Conclusion:
1.
Duty cycle
= Ton / (Ton + Toff)
2.
Output Voltage Vo = Vs*
Thus, we have studied chopper with resistive load.
Experiment No:- 8
Aim: To study of Series Inverter.
Apparatus: Trainer kit, multimeter, general purpose CRO, CRO probes.
Theory:
1.
2.
3.
4.
5.
Explain the working of inverter circuit.
Explain various types of inverter circuit.
Explain how series inverter works.
Advantages and Disadvantages.
Its applications.
Procedure:
1. Connect G to G1 .
2. Connect Load voltage divider across the load terminals and CRO across the indicated
terminals.
3. Connect one current sensing resistor between lower end of C and SCR anode.
4. Connect DC supply turn Freq pot fully anticlockwise and put on.
5. Connect RL1 across Load terminals
6. Connect DC supply and put ON.
7. Observe the changes in various waveforms by changing trigger ar output frequency by
changing ratio Fr/Fo.
Conclusion:
From overall observations we may conclude that, series inverter used extensively in induction
heating and florescent lighting.
Experiment No:-9
Aim :- To study UPS
Appartus:- Trainer Kit of UPS.
Theory:- Explain the working of different types of UPS.
Main Power
Supply
N/ON
Rectifier
Inverter
N/Off
Battery
1) Explain various types of power supply.
2) Explain UPS system.
3) Explain different types of UPS.
4) Applications of UPS.
Conclusion:
Thus we have studied UPS system and its various applications.
Load
Experiment No:-10
Experiment Name: Study of V- I Characteristics of TRIAC.
Aim: To study the V-I characteristics of TRIAC.
Apparatus Required:
1. NV6532 TRIAC Characteristic Trainer
2. 2mm Patch cords.
Circuit Diagram:
Theory: An TRIAC is a device which can be turned on through the gate pulse for both positive and
negative values of VAK and turned off using power circuit i.e., turn on is controlled but turn off is
uncontrolled in a TRIAC. The voltage at which the TRIAC gets into conduction state is called forward
breakover voltage(VBO) for positive voltages and reverse breakover voltage (VBR) for negative voltgaes.. If
the gate current is increased then the forward breakover and reverse breakover voltages will be
reduced. The current at which the TRIAC turns on is called latching current (IL). Once the TRIAC is turned
on , no need of the gate pulse i.e., gate pulse can be removed once the device is turned on. The
minimum current required for the device to keep the thyristor on is holding current(IH). The ratio of
latching to holding currents will be 3-5. When the gate current is increased, the breakover voltage values
will be reduced.
Procedure:
1. Connect the circuit as per the connection diagram.
2. Keep the gate current a fixed value (Ig1).
3. By varying the anode to cathode voltage note the voltage (Vak) and current (Ia).
4. Note the forward breakover voltage(VBO), latching current (IL) and holding current(IH).
5. Change the gate current value (Ig2, Ig3) and repeat steps 3 and 4.
6. Plot the graph between Vak and Ia , denoting IL, IH, VBO's.
Precautions:
1. While changing the gate current, first make the Vak equal to zero and then vary Ig.
2. Avoid double connections if possible.
3. The connections should be proper and tight.
Model Graph:
Observation Table:
Result:
V-I characteristics of TRIAC are obtained.
Conclusion:
1. When the gate current is increased, the forward breakover voltage and reverse breakover voltages are
reduced and the values are........
2. The ratio of latching to holding current is ......