POWER ELECTRONICS LAB MANUAL, DR. B G SHIVALEELAVATHI, JSSATEB

Department of Electronics & Communication Engineering
JSSATE, BENGALURU1
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ECE/PEO-1 (Elementary Skills) To imbibe in students an ability to
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eclearinstructions.
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JSSATE, BENGALURU3
JSS ACADEMY OF TECHNICAL EDUCATION
(AFFILIATED TO VTU)
Uttarahalli-Kengeri Main Road, Mylasandra
Bangalore – 560060
DEPARTMENT OF ELECTRONICS &
COMMUNICATION ENGINEERING
POWER ELECTRONICS LAB MANUAL (10ECL78)
(VII SEM)
Dr. B. G. Shivaleelavathi,Professor,
Sunitha L Siraatti, Asst. Prof.,
Sangeetha K. N. Asst. Prof.,
E&C Dept.,
JSSATE, Bangalore.

JSSATE, BENGALURU4
INDEX
SERIAL
NO.
CONTENTS PAGE
NO.
1 Power Electronics lab syllabus 3
2 Static characteristics of MOSFET and IGBT 4 to 9
3 Static characteristics of SCR, TRAIC and DIAC 10 to 17
4 Controlled HWR and FWR using RC triggering circuit 18 to 25
5 SCR turn off using i) LC circuit ii) Auxiliary
Commutation
26 to 33
6 UJT firing circuit for HWR and FWR circuits 34 to 43
7 Generation of firing signals for thyristors / TRIACs using
digital circuits/microprocessor.
44 to 47
8 AC voltage controller using TRIAC-DIAC combination 48 to 50
9 Single phase Fully Controlled Bridge Converter with R
and R-L loads
51 to 73
10 Voltage (Impulse) commutated chopper both constant
frequency and variable frequency operations
74 to 83
11 Speed control of a separately exited DC motor. 84 to 89
12 Speed control of universal motor. 90 to 91
13 Speed control of stepper motor. 92 to 96
14 Parallel / Series inverter 97 to 105
15 spice-simulator.
16
17 Model questions 106
18 Viva questions 107
19 Bibliography 108

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POWER ELECTRONICS LAB
Subject Code: 06ECL78 IA Marks: 25
No. of Practical Hrs/Week: 03 Exam Hours: 03
Total no. of Practical Hrs: 42 Exam Marks: 50
1. Static characteristics of MOSFET and IGBT.
2. Static characteristics of SCR, TRIAC and DIAC.
3. Controlled HWR and FWR using RC triggering circuit
4. SCR turn off using i) LC circuit ii) Auxiliary Commutation
5. UJT firing circuit for HWR and FWR circuits.
6. Generation of firing signals for thyristors/ TRIACs using
digital circuits/microprocessor.
7. AC voltage controller using TRIAC-DIAC combination.
8. Single phase Fully Controlled Bridge Converter with R and R-L loads
9. Voltage (Impulse) commutated chopper both constant frequency and
variable frequency operations.
10. Speed control of a separately exited DC motor.
11. Speed control of universal motor.
12. Speed control of stepper motor.
13. Parallel / Series inverter.

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1) STATIC CHARACTERISTICS OF MOSFET AND IGBT
(i) STATIC CHARACTERISTICS OF MOSFET .
AIM: To plot input and transfer characteristics of an MOSFET and to find ON state resistance
and trans conductance.
APPARATUS:
1. 0 – 50V DC Voltmeter
3. 0 – 100mA DC Ammeter
4. Regulated power supply
5. n-channel MOSFET (IRF-840)
6. Resistance (500Ω/5W).
DEVICE SPECIFICATIONS: IRF 840.
1. VDss-Drain to Source Breakdown voltage : 400 Volts.
2. Rds (on)-On state Resistance : 0.55 ohms.
3. ID-continuous drain current-25° C : 10 Amps.
4. ID-continuous drain current-100° C : 6.3 Amps.
5. RJC-Max thermal resistance : 1° C/Watt.
6. PD Max-power dissipation@ 25° C : 125 watts.
CIRCUIT DIAGRAM:
ROCEDURE:
i) Transfer Conductance Characteristics:
Make the connections as shown in the circuit diagram including meters. Initially keep V1 and V2
minimum. Set VDD=VDS1=say 10V. Slowly vary VGG (VGS) and note down ID and VGS readings for
every 1 Volt and enter in the tabular column. The minimum gate voltage VGS that is required for
conduction to start the MOSFET is called Threshold Voltage VGS(Th). The Drain current depends on
magnitude of the Gate Voltage VGS which may vary from 2 to 5 Volts.
Repeat the same for different VDS and draw the graph of VGS V/s ID.

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ii) Tabular Column:
VDS1 (Volts) VDS2 (Volts)
VGS (Volts) ID (mA) VGS (Volts) ID (mA)
iii) Drain Characteristics:
Initially set VGG to VGS1=3.5 Volts. Slowly vary V1 and note down ID and VDS. For a particular
value of VGS1 there is a pinch off voltage (Vp) between drain and source.
If VDS is lower than Vp, the device works in the constant resistance region and ID is directly
proportional to VDS. If VDS is more than Vp, constant Id flows from the device and this operating
region is called constant current region.
Repeat the above for different values of VGS and note down VDS Vs ID.
Draw the graph of VDS Vs ID for different values of VGS.
iv) Tabular Column:
VGS1 (Volts) VGS2 (Volts)
VDS (Volts) ID (mA) VDS (Volts) ID (mA)

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WAVEFORMS :
Ohmic
ID
mA
0
GS4V
Active
GS3V
GS2V
GS1V
GS4V > GS3V > >VGS2 VGS1
DSV
voltsOutput Characteristics
DI
DSV
TransferCharacteristics
VGS(th)
RESULT:
∆VDS
1. RD = -------------- = ------------------------------ Ω.
∆ID
∆ID
2. Gm = -------------- = ------------------------------ mho.
∆VDS
CONCLUSION: We conclude that MOSFET is a voltage controlled device.

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(ii)) STATIC CHARACTERISTICS OF IGBT.
AIM: To plot the characteristics of IGBT.
APPARATUS:
3. 0 – 100mA DC Ammeter
4. Regulated power supply
5. Resistance (500Ω/5W).
6. IGBT (IRGBC-20S)
DEVICE SPECIFICATIONS: IRGBC 20S
1. Vce-Collector to emitter Voltage : 600 Volts.
2. Max Vce(on)-Collector to emitter Voltage : 3.0 Volts.
3. Ic-continuous collector current @ 25° C : 19 Amps.
4. ID-continuous collector current @ 100° C : 10 Amps.
5. Pd max-Maximum power dissipation : 60 Watts.
CIRCUIT DIAGRAM:
PROCEDURE:
i)Transfer Characteristics:
Make the connections as shown in the circuit diagram with meters.
Initially keep V1 and V2 minimum. Set V1=VCE1=say 10V. Slowly vary V2 (VGE) and note down IC
and VGE readings for every 1.0 Volt and enter in the tabular column. The minimum gate voltage
VGE which is required for conduction to start the IGBT is called Threshold Voltage VGE(Th). If VGE
is greater than VGE(Th) only very small leakage current flows from Collector to Emitter. If VGE is
greater than VGE(Th), the Collector current depends on magnitude of the Gate Voltage. VGE varies
from 4 to 8 Volts.

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Repeat the same for Vc and draw the graph of VGE V/S IC.
ii)Tabular Column:
VCE1 (Volts) VCE2 (Volts)
VGE (Volts) IC (mA) VGE (Volts) IC (mA)
iii) Collector Characteristics:
Initially set V2 to VGE1=5 Volts. Slowly vary V1 and note down IC and VGE. For a particular value
of VGE1 there is a pinch off voltage (Vp) between Collector and Emitter.
If VGE is lower than Vp, the device works in the constant resistance region and IC is directly
proportional to VGE. If VGE is more than Vp constant IC flows from the device and this operating
region is called constant current region.
Repeat the above for different values of VGE and note down VCE V/S IC.
Draw the graph of VCE V/S IC for different values of VGE.
iv) Tabular Column:
VGE1 (Volts) VGE2 (Volts)
VCE(Volts) IC (mA) VCE (Volts) IC (mA)

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WAVEFORMS:
COLLECTOR CHARACTERISTICS
TRANSFER CHARACTERISTICS
RESULT:
∆VCE
1. RON = -------------- = ------------------------------ Ω.
∆IC
2. VGSTh = ------------------------------ Volts
CONCLUSION:
We conclude that IGBT is a voltage controlled device.

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2) STATIC CHARACTERISTIC OF SCR, TRIAC & DIAC
(i) STATIC CHARACTERISTIC OF SCR
AIM: To plot the characteristics of an SCR and to find the forward resistance, holding current
and latching current.
APPARATUS:
1) 0 – 50V DC Voltmeter (Digital Multimeter)
2) 0 – 500mA DC Ammeter
3) 0 – 25mA DC Ammeter
4)Resistor (1kΩ/5w)
5)Regulated power supply
6)SCR (TYN616)
7)Rheostat
DEVICE SPECIFICATIONS: TYN 616
1. Vrrm : 600V.
2. It(rms) : 16 A.
3. It(av) : 10 A.
4. It(sm) : 160 A.
5. It : 128 A/µs.
6. di/dt : 100 A/µs.
7. Igt : 25 mA.
8. Vgt : 1.5 V.
9. IH : 40 mA.
10. IL : 70 mA.
11. tq : 70µs.
12. dv/dt : 500 V/µs.
CIRCUIT DIAGRAM:
Note: R1 is a rheostat of 1k (/2amp).

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PROCEDURE:
i). V-I Characteristics:
Make the connections as given in the circuit diagram. Now switch ON the mains supply to the unit
and initially keep VGG & VAA at minimum. Set load potentiometer R1 in the minimum position.
Adjust Ig to Ig1 say (2 to10) mA by varying VGG. Slowly vary VAA and note down VAK and IA
readings for every 5 volts and enter the readings in the tabular column. Further vary VAA till SCR
conducts, this can be noticed by sudden drop of VAK and rise of IA readings. Note down this
reading and tabulate. Vary VAA further and note down IA and VAK readings. Draw the graph of VAK
V/S IA.
Repeat the same for Ig = Ig2/Ig3 mA and draw the graph.
Tabular Column:
MODE 1, IG1=
VAA (volts) V AK2 (volts) I AK (mA)
To find latching current:
Apply about 20V between anode and cathode by varying VA. Keep the load rheostat R1 at minimum
position. The device must be in the OFF state with gate open. Gradually increase Gate voltage- VGG
till the device turns ON. This is the minimum gate current (Igmin) required to turn ON the device.
Adjust the gate voltage to a slightly higher value. The gate voltage should be kept constant in this
experiment. Now turn OFF the gate voltage. If the anode current is greater than the latching current
of the device, the device stays ON even after the gate switch is opened. Otherwise the device goes
into blocking mode as soon as the gate switch is opened. Note this anode current as the latching
current. Obtain more accurate value of the latching current by taking small steps of IA near the
latching current value.
Increase the anode current from the latching current level by VAA. Open the gate switch
permanently. The thyristor must be fully ON. Now start reducing the anode current gradually by
adjusting (increasing) R1. If the thyristor does not turns OFF even after the R1 at maximum
position, then reduce VAA. Observe when the device goes to blocking mode. Observe that for one
setting of R1 or VAA the anode current suddenly drops to zero. The anode current through the
device at this instant is the holding current of the device. Repeat the steps again to accurately get
the IH. Normally IH<IL.
MODE 2, IG2=
V AA (volts) V AK (volts) I AK (mA)

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WAVEFORMS:
RESULT: 1. The break over voltages : Vb1 = -------------- ; Ig1
: Vb2 = --------------- ; Ig2
Latching Current (IL)= ------------------------------------ amps
Holding Current(IH) = ------------------------------------- amps
∆ VAK
Forward Resistance Rf = ------------;
∆ IA
Rf = ------------------------------ Ω
CONCLUSION :
We conclude from the experiment that as the gate current increases the break over voltage
decreases.

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(ii) STATIC CHARACTERISTIC OF TRIAC.
AIM: To plot the characteristics of TRIAC.
APPARATUS:
1) 0 – 50V DC Voltmeter (Digital Multimeter)
2) 0 – 500mA Ammeter
3) 0 – 25mA Ammeter
4) Regulated power supply
5) Resistor (1kΩ/5w)
6) TRIAC(BT136-600)
7) Rheostat
DEVICE SPECIFICATIONS: BT136-600.
1. Vdrm : 600V.
2. Itrms : 4 A.
3. Itsm : 50 A.
4. It : 12.5 A.
5. di/dt : 10 A/µs.
6. Igt : 15 mA.
7. Vgt : 1.5 V.
8. IH : 13 mA.
9. IL : 50 mA.
10. dv/dt : 10 V/µs.
CIRCUIT DIAGRAM:

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PROCEDURE:
i) V-I Characteristics:
Make the connections as given in the circuit diagram including meters. Now switch ON the mains
supply to the unit and initially keep VTT & VGG at minimum. Set load rheostat R1 in the minimum
position. Adjust Ig-Ig1 say 10 mA by varying VGG. Slowly vary VAA and note down VT2T1 and IL
readings for every 5 Volts and enter the readings in the tabular column. Further vary VAA till
TRIAC conducts, this can be noticed by sudden drop of VT2T1 and rise of IL readings. Note down
this reading and tabulate. Vary VAA further and note down IL and VT2T1 readings. Draw the graph of
VT2T1 V/S IL. Repeat the same for Ig = Ig2/Ig3 and draw the graph.
To find latching current:
Apply about 20V between MT1 and MT2 by varying VAA. Keep the load rheostat R1 at minimum
position. The device must be in the OFF state with gate open. Gradually increase Gate Voltage VGG
till the device turns ON. This is the minimum gate current (Igmin) required to turn ON the device.
Adjust the gate Voltage to a slightly higher value. The gate Voltage should be kept constant in this
experiment. By varying VAA, gradually decrease anode current IL in steps. Open and close the Gate
voltage VGG switch after each step. If the load current is greater than the latching current of the
device, the device stays ON even after the gate switch is opened otherwise the device goes into
blocking mode as soon as the gate switch is opened. Note the latching current. Obtain more
accurate value of the latching current by taking small steps of IL near the latching current value.
Increase the Load current from the latching current level by load pot R1 or V1. Open the gate switch
permanently. The Triac must be fully ON. Now start reducing the anode current gradually by
adjusting R1. If the Triac does not turn OFF even after the R1 at maximum position, then reduce V1.
Observe when the device goes to blocking mode. The load current through the device at this instant
is the holding current of the device. Repeat the steps again to accurately get the IH. Normally IH<IL.
MODES
Modes MT2 MT1 G
Mode1 + - +
Mode2 + - -
M0de3 - + +
Mode4 - + -
Tabular Columns:
MODE 1, IG1=
V TT (volts) V T1T2 (volts) I T1T2 (mA)
MODE 2, IG2=

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MODE 3, IG3=
WAVEFORMS:
V-I characteristics
RESULT:
CONCLUSION:
We conclude that the sensitivity of the mode depends on minimum gate current required to turn on
the TRIAC. We found that mode1 is most sensitive where as mode 3 is least sensitive.
MODE 4, IG4=

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(iii) STATIC CHARACTERISTICS OF DIAC
AIM: To plot the characteristics of DIAC.
APPARATUS:
1) 0-60V DC Voltmeter
2) 0-250mA DC Ammeter
3) Resistor (1kΩ/5w)
4) Regulated power supply
5) DIAC (DB-3)
6) Rheostat
DEVICESPECFICATIONS: DB-3.
Breakdown Voltage: 32V±10%
Power: 0.5 Watts.
CIRCUIT DIAGRAM:
PROCEDURE:
Make the connections as given in the circuit diagram. Keep R2 at maximum resistance position and
do not change this throughout the experiment. Since the device is only a switching device and its
power rating is only 0.5 watts. Keep V1 potentiometer also at minimum position.
Next switch ON the unit and V1 power supply. Vary V1 in steps of 5V and note down the
corresponding Ammeter reading. Vary in steps of 5V up to 25 Volts. After that vary in steps of 1V.
At a particular value of voltage the device conducts. This can be noticed by the sudden increase of
ammeter reading. This is the device breakdown voltage. Vary V1 further and note down the
corresponding V/I readings in the tabular column.

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Tabular Columns:
FORWARD CHARACTERSTICS
WAVEFORMS:
RESULT :
VFBO = --------------- (V)
VRBO = --------------- (V)
CONLUSION :
We conclude that DIAC is a bi-directional device.
REVERSE CHARACTERSTICS

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3) CONTROLLED HWR AND FWR USING RC TRIGGERING CIRCUIT
(i)RC FIRING CIRCUIT – HALF WAVE RECTIFIER.
AIM: To study Resistance-Capacitance triggering of SCR in half wave mode.
APPARATUS:
Step down transformer (230–30V) , Load resistance (100Ω rheostat), Resistance (10KΩ
potentiometer, +100Ω/1W), Power Diodes (IN 4007), SCR (TYN616), CRO.
1. Vrrm : 600V.
2. It(rms) : 16 A.
3. It(av) : 10 A.
4. It(sm) : 160 A.
5. It : 128 A/µs.
6. di/dt : 100 A/µs.
7. Igt : 25 mA.
8. Vgt : 1.5 V.
9. IH : 40 mA.
10. IL : 70 mA.
11. tq : 70µs.
12. dv/dt : 500 V/µs.
CIRCUIT DIAGRAM :

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DESIGN:
It can be shown empirically that
RC ≥ 1.3T/2 ≈ 4/ω :
T = 1/f
f = 50Hz
R= R1 + R2
Vc = Vgt + Vd ;
where Vc is capacitor voltage , Vd is diode voltage drop.
At the instant of firing , Vc is assumed to be constant, the current Igt must be supplied by voltage
source through R, D2 and the gate cathode voltage.
Therefore maximum value of R is given by :
R= R1 + R2 ≤ (V- Vgt - Vd ) / Igt ;
Approximate values of R & C can be obtained from the above equations.
EXAMPLE :
RC = (4×π×50) / 2
Let Vgt = 1.5 V, Vd = 0.7 V
Then Vc = 1.5 + 0.7 = 2.2 V
Let Igt(max) = 10mA
R = R1 + R2 ≤ (V- Vgt - Vd ) / Igt ;
R ≤ (32 -1.5 - 0.7) / 10mA
≤ 2.97 KΩ;
&
RC ≥ 1.3T/2 ≈ 4/ω
C ≥ 1.3T/2 ≈ 4/ωR
= 1.3/(2 × 50 × 2.97 × 10-3
)
= 1.01× 10-6
F
Let C = 1µF, then
Let R2 = 100Ω/1W.
PROCEDURE:
i) R- Triggering
Make the connections as given in the connection diagram above. Connect a Rheostat of 100
ohms/1.7A between the load points. Vary the control potentiometer (R1) and observe the voltage
waveforms across load, SCR and at different points of the circuit.
We can vary the firing angle from 0° to 90° only in R triggering (you may have to disconnect the
capacitor to realize R triggering alone). In this triggering the synchronized firing angle can be
obtained easily and economically in the positive half cycle of the supply. But there is a draw back
that the firing angle can be controlled at the most at 90°, since the gate current is in phase with the
applied voltage. A resistor R2 is connected in series with the control potentiometer, so that the gate
current does not cross the maximum possible value Igmax

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Draw the waveform across the load and device for different values of firing angles.
ii) RC Triggering
Connect capacitor C to the R triggering circuit to realize RC triggering. Repeat the above
procedure and draw the waveform across the load and device for different values of firing angles.
Note here the firing can varied from 0° to (~)180°.
TABULAR COLUMN:
Firing angle
(degrees)
Theoretical Practical
α = sin-1
(Vn/Vp) 0
Vodc (Volts) Vodc (Volts)
Formula Used :
Vodc (theoretical) = Vm × (1+ cos α) / (2 π)
Note: Show sample calculations for design and Vodc (theoretical)

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WAVEFORMS :
Waveforms across Vc , Vload , Vscr , w.r.t to source

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RESULT :
CONCLUSION :
The average O/P voltage can be varied by varying the firing angle (α).
(ii)RC FIRING CIRCUIT – FULL WAVE.
AIM: To study Resistance- capacitance triggering of SCR in full wave mode.
APPARATUS:
potentiometer, 100Ω), Power Diodes (IN 4007), SCR (TYN616),CRO.
1. Vrrm : 600V.
2. It(rms) : 16 A.
3. It(av) : 10 A.
4. It(sm) : 160 A.
5. It : 128 A/µs.
6. di/dt : 100 A/µs.
7. Igt : 25 mA.
8. Vgt : 1.5 V.
9. IH : 40 mA.
10. IL : 70 mA.
11. tq : 70µs.
12. dv/dt : 500 V/µs.
CIRCUIT DIAGRAM : RC FIRING CIRCUIT – FULL WAVE.
NOTE :
A simple RC trigger circuit giving full-wave output voltage. Diodes D1 – D4 form a full-wave
bridge rectifier. Diode Bridge: In this circuit, the initial voltage from which the capacitor C charges
is almost zero. The capacitor C is set to this low positive voltage(upper plate positive) by the

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clamping action of SCR gate. When capacitor charges to a voltage equal to Vgt SCR triggers and
rectified voltage Vd appears across load as Vo.
DEISGN :
Same as for Half wave triggering
PROCEDURE:
Make the connections as shown in the circuit diagram above. Switch ON the unit. By varying the
potentiometer on the front panel, note down the voltage waveforms across the load( 100 Ohms/2A
rheostat) and also across SCR and capacitor. Infer on the control obtained with and without
capacitor connected to the circuit. Draw the waveforms across load, SCR and across capacitor.
TABULAR COLUMN:
Firing angle Theoretical Practical
(α)=sin-1
(Vn/Vp)0
FORMULA USED :
Vodc (theoretical) = Vm ×(1+ cos α)/( π)
Note :Show the sample calculations for design and Vodc (theoretical)

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WAVEFORMS :

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RESULT :
CONCLUSION :
We conclude that the average voltage in FW mode is greater than HW mode. The average O/P
voltage can be varied by varying the firing angle (α).
4) SCR TURN – OFF CIRCUITS USING
(a) LC CIRCUIT (b) AUXILIARY COMMUTATION
AIM: To rig up various turn off circuits for SCR by auxiliary commutation class D commutation.
APPARATUS:
Forced commutation study unit, DC power supply (0-30V/2A for Class E Commutation only),
Rheostats (50 ohms / 2A) – 2Nos, CRO, Probes and connecting wires.
DESCRIPTION :
FORCED COMMUTATION STUDY UNIT
This unit consists of two parts – (i) Power Circuit and (ii) Firing Circuit sufficient to study (a) Class
A Commutation – Self Commutation by load resonance. (b) Class B Commutation – Self
Commutation by LC circuit. (c) Class C Commutation – Complimentary SCR commutation. (d)
Class D Commutation – Auxiliary SCR commutation. (e) Class E Commutation – with an external
source of pulse for commutation.
POWER CIRCUIT:
This part consists of the following components to build different commutation circuits with
different values of commutation components.
a) 2 SCRs. b) a diode. c) 2 different values of commutation capacitors to get different value of
commutation capacitance by individual, series and parallel connections and d) a commutation
inductor with tappings at different points and a transistor for class E commutation. An unregulated
DC power supply of 24 Volts @ 2Amps is provided to use as DC input for commutation circuits.
FIRING CIRCUIT:
This part generates triggering pulses to fire two SCRs connected in different forced commutation
circuits. The frequency and duty cycle can be varied using respective potentiometers.

JSSATE, BENGALURU28
FRONT PANEL DIAGRAM:
FORCED COMMUTATION STUDY UNIT - FCU
U
POWER
TRIG - OUTPUT
CAT
T2
GATE
1T
OFF
ON
+
ON
E
S
FIRING CIRCUIT
FREQUENCY
MIN MAX
+
F
-
DUTY CYCLE
MIN MAX
C1 C2
T2
1LO L2 L3
T1
D
POWER CIRCUIT
C
B
RT
E
FRONT PANEL DETAILS:
1.Power : Power ON / OFF switch to the unit with built in indicator.
2.Frequency : Potentiometer to vary the frequency of commutation from 30Hz to
250Hz approximately.
3.Duty Cycle : Potentiometer to vary the duty cycle from 10% to 90%
approximately.
4.Trigger Output ON / OFF : On / Off switch for mains pulse T1
5. Gate / Cathode : Positive and negative points of trigger outputs to connect to gate and
cathode of SCRs.
6.T1 : Trigger output for SCR T1 – 200 µs pulse.
7.T2 : Trigger output for SCR T2 – 200 µs pulse.
8.Volts dc IN : 24V @ 2A unregulated DC supply is available at these terminals for DC
Source for the commutation power circuit.
9. ON : ON / OFF switch for DC supply.
10.Fuse : 2Amps glass fuse for DC power supply protection.
11. + : DC power supply point after switch and fuse.
12.D : Free wheeling diode – BYQ 28 – 200.
13.T1 & T2 : SCRs – TYN 612.
14.Tr : Transistor – TIP 122.
15. Commutation Inductance
L1 : 250µH
L2 : 500µH
L3 : 1µH @ 2A
16. Commutation Capacitance
C1 : 6.8µF / 100V
C2 : 10.0 µF / 100V

JSSATE, BENGALURU29
BACK PANEL DETAILS:
Main socket with built in fuse holder. The fuse holder has a spare fuse along with the fuse
in the circuit. If the fuse blows remove the blown fuse and replace with the spare fuse. Fuse – 1A
fast blow glass fuse.
DESIGN OF LC COMMUTATION CIRCUIT :
TON = π[LC]1/2
Let TON = 2 msec , C = 6.8 µF.
Then 2 x 10-3
= π [L x 6.8 x 10-6
]1/2
L = 590 H
PROCEDURE:
Switch on the mains to unit and observe the trigger outputs by varying frequency and duty cycle
potentiometer and make sure that the pulse output are proper before connecting to the power
circuit. Check the DC power supply between the DC Input points.
Check all the devices. Check the resistance between the Gate and Cathode of SCR’s. Check the
resistance between anode and cathode. Check the diode and its polarity. Check the transistor and its
polarity. Check the fuse in series with the DC input. Make sure that all the components are good
and firing pulse is correct before you start any commutation experiments.
(a)CLASS – A COMMUTATION: (SELF COMMUTATION BY RESONATING LOAD -LC)
The current reversing property of the load will force the device commutation. L,C and R values are
chosen such that the circuit is under damped.
Since the commutation elements carry load current on a continuous basis, these ratings are
generally high. For low frequency operation large value of L & C is required.
CIRCUIT DIAGRAM: CLASS–A COMMUTATION: (SELF COMMUTATION BY
RESONATING LOAD -LC)
PROCEDURE:
Make the interconnections in the power circuit as shown in the circuit diagram.
Connect trigger output T1 to gate and cathode of SCR T1. Switch on the DC Supply to the power
circuit and observe the voltage waveform across load by varying the frequency Potentiometer. Duty
cycle Potentiometer is of no use in this experiment.
Repeat the same for different values of L, C and R.

JSSATE, BENGALURU30
TABULAR COLUMN :
WHEN L = L1 AND C= C1
R (Ω) Ton ( msec) Tc ( msec)
WHEN L = L1 AND R= R1
C (µF) Ton ( msec) Tc ( msec)
WHEN R= R1 AND C= C1
L Ton ( msec) Tc ( msec)

JSSATE, BENGALURU31
WAVEFORMS:
T r i g g e r o u t p u t s :
T 1
T 2
Voltage across the gating pulse, Thyristor, voltge across capacitor, voltage across resistor
RESULT :
CONCLUSION :
We conclude that the SCRs can be commutated by using LC circuit also.

JSSATE, BENGALURU32
CLASS – B COMMUTATION: (SELF COMMUTATION BY AN LC CIRCUIT)
In this type of commutation, reverse voltage is applied to the thyristor by the over swinging of an
under damped LC circuit connected across the Thyristor.
Capacitor charges up to the supply voltage before the trigger pulse is applied to the gate. When the
thyristor is triggered, two currents flow, a load current through the external circuit and a pulse of
current through LC circuit and thyristor in opposite direction. This resonant current tends to turn
off the thyristor.
CIRCUIT DIAGRAM: CLASS – B COMMUTATION:(SELF COMMUTATION CIRCUIT)
PROCEDURE:
Make the interconnections in the power circuit as shown in the circuit diagram.
Connect trigger output T1 to gate and cathode of SCR T1. Switch on the DC Supply to the power
circuit and observe the voltage waveform across load by varying the frequency Potentiometer. Duty
cycle Potentiometer is of no use in this experiment.
Repeat the same for different values of L,C and R
WAVEFORMS:
O U T P U T A C R O S S " R "
o n ly fre q u e n c y v a ria tio n is p o s ib le
RESULT :
CONCLUSION :
Thus the SCR’s are commutated by LC circuit for class A and class B LC commutation circuits.

JSSATE, BENGALURU33
(ii) AUXILIARY VOLTAGE COMMUTATION: (Circuit same as Jones chopper)
PROCEDURE:
Make the connections as given in the circuit diagram. Connect T1 and T2 gate pulse from the
firing circuit to the corresponding SCR’s in the power circuit. Initially keep the trigger ON/OFF at
OFF position to initially charge the capacitor, this can be observed by connecting CRO across the
Capacitor. Now switch ON the trigger O/P switch and observe the voltage wave forms at different
frequencies of chopping and also at different duty cycles.
Repeat the experiment for different values of load resistance, commutation inductance and
capacitance. Compare the results with theoretical results.
PARAMETERS AND OBSERVATIONS:
1. Voltage wave form across capacitor.
2. Output voltage waveforms (across the load)
3. Output current waveforms (Through the shunt)
4. Voltage waveforms across Thyristors.
5. Study of variation of voltage and current waveforms with the variation of duty cycle
and frequency.
6. Study of effect of free wheeling diode in case of inductive loads.

JSSATE, BENGALURU34
5) UJT FIRUNG CIRCUIT(ACVC, HWR & FWR)
(i)UJT FIRING CIRCUIT – TWO SCRS(ACVC)
AIM: To fire two SCR using UJT firing circuit.
APPARATUS:
potentiometer, 3.3KΩ, 100Ω, 220 Ω, 500V/5W), Power Diodes (IN 4007), Zener diode ,SCR
(TYN616),Pulse transformer, CRO.
1. Vrrm : 600V.
2. It(rms) : 16 A.
3. It(av) : 10 A.
4. It(sm) : 160 A.
5. It : 128 A/µs.
6. di/dt : 100 A/µs.
7. Igt : 25 mA.
8. Vgt : 1.5 V.
9. IH : 40 mA.
10. IL : 70 mA.

JSSATE, BENGALURU35
11. tq : 70µs.
12. dv/dt : 500 V/µs.
CIRCUIT DIAGRAM :
DESIGN :
Let VBB =20V; VD = 0.7V;
Vc = VBB (1- e-t/RC
)
Vp = η VBB + VD ; (η = 0.65)
Since Vc = Vp of UJT
ηVz (1- e-T/RC
)
Therefore T = RC ln [1/(1-n)]
T = time period of output pulse .
The firing angle α is given by
α = ωT = ωRC ln [1/(1-n)]
ω = angular frequency.
Vodc(th) = Vm (1+ cosα) /2π
The leakage current drop across R1 should be small that when UJT is OFF it should not trigger i.e.,
VBB =I1eakage(RBB + R1+R2 )< SCR trigger voltage.
and R2 = 104
/( η VBB )
width of triggering pulse is R1 C = T2
When voltage drop across C reaches Vp voltage across R is VBB – Vp .
Therefore Rmax = (VBB - Vp ) / Ip
Rmin = (VBB - Vv )/Iv
PROCEDURE:
2.1. Firing of SCR using UJT.

JSSATE, BENGALURU36
Switch on the mains supply observe and note down the wave forms at the different points in the
circuit and also the trigger O/Ps – T1, & T1’.
Now, make the connections as given in the circuit diagram above ,using AC source, UJT
relaxation oscillator, SCR and suitable load(100ohms /2A rheostat). Switch ON the mains supply,
observe and note down the output waveforms across load and SCR. Draw the wave forms at
different firing angles as 120, 90 & 60 degrees. In the UJT firing circuit the firing angle can be
carried from 150° – 30° approximately.
This is one of the simplest methods of SCR triggering. We can also fire SCR’s in the different
power circuits as described earlier.
2.2. UJT Relaxation Oscillator:
To study oscillator using UJT, short Cf to the diode bridge rectifier to get filtered DC output. Now
we will get the equidistant pulses at the O/P of pulse transformer. The frequency of the pulse can be
varied by varying the potentiometer RC. Observe and note down the waveforms at different points
in the circuit.
TABULAR COLUMN:
Firing angle Practical Theoretical
(α)=sin-1
(Vn/Vp) Vorms (Volts) Vorms (Volts)
FORMULA USED :
Virms = Vm /√2
Vorms (theoretical) = Virms ×[( π- α)/(2 π) + (sin2α/2 π)]1/2
WAVEFORMS :

JSSATE, BENGALURU37
waveforms across rectifier (Vodc),zener (Vz), capacitor (Vc), resistor (Vr2), load(VL) ,SCR
(Vscr) with respect to source for α = 90 degrees.
RESULT :
CONCLUSION :

JSSATE, BENGALURU38
We conclude that the pulses obtained from UJT can be used to fire two SCRs also with the help of
a pulse transformer.
(ii)SYNCHRONIZED UJT FIRING CIRCUIT FOR HWR AND FWR TRIGGERING.
UJT FIRING CIRCUIT – HALF WAVE
AIM: To fire SCR for Half Wave using UJT firing circuit.

JSSATE, BENGALURU39
APPARATUS:
(TYN616),Pulse transformer, CRO.
1. Vrrm : 600V.
2. It(rms) : 16 A.
3. It(av) : 10 A.
4. It(sm) : 160 A.
5. It : 128 A/µs.
6. di/dt : 100 A/µs.
7. Igt : 25 mA.
8. Vgt : 1.5 V.
9. IH : 40 mA.
10. IL : 70 mA.
11. tq : 70µs.
12. dv/dt : 500 V/µs.
CIRCUIT DIAGRAM :
DESIGN:
Vc = VBB (1- e-t/RC
)

JSSATE, BENGALURU40
Vp = η VBB + VD ; (η = 0.65)
ηVz (1- e-T/RC
)
α = ωT = ωRC ln [1/(1-n)]
and R2 = 104
/( η VBB )
PROCEDURE:
1.1 . Firing of SCR using UJT.
circuit and also the trigger O/Ps – T1, & T1’. Make sure that the pulse transformer O/P T1 & T1’ are
proper and synchronized.
Now, make the connections as given in the connection diagram above ,using AC source, UJT
in the circuit.
TABULAR COLUMN:
(α)=sin-1
(Vn/Vp) Vodc (Volts) Vorms (Volts) Vodc
(Volts)
Vorms
(Volts)
Formula Used :
Vodc (theoretical) = Vm ×(1+ cos α)/(2 π)
WAVEFORMS :

JSSATE, BENGALURU41
(Vscr) with respect to source for α < 90 degrees.
RESULT :
CONCLUSION :
We conclude that the pulses obtained from UJT can be used to fire SCR.
(iii)UJT FIRING CIRCUIT – FULL WAVE
AIM: To fire SCR for Full Wave using UJT firing circuit.

JSSATE, BENGALURU42
APPARATUS:
(TYN616),CRO.
1. Vrrm : 600V.
2. It(rms) : 16 A.
3. It(av) : 10 A.
4. It(sm) : 160 A.
5. It : 128 A/µs.
6. di/dt : 100 A/µs.
7. Igt : 25 mA.
8. Vgt : 1.5 V.
9. IH : 40 mA.
10. IL : 70 mA.
11. tq : 70µs.
12. dv/dt : 500 V/µs.
CIRCUIT DIAGRAM :
DESIGN :
Vc = VBB (1- e-t/RC
)
Vp = η VBB + VD ; (η = 0.65)

JSSATE, BENGALURU43
ηVz (1- e-T/RC
)
α = ωT = ωRC ln [1/(1-n)]
and R2 = 104
/( η VBB )
PROCEDURE:
2.1. Firing of SCR using UJT.
circuit and also the trigger O/Ps – T1, & T1’.
Now, make the connections as given in the circuit diagram above ,using AC source, UJT
in the circuit.
TABULAR COLUMN:
(α)=sin-1
(Vn/Vp) Vodc (Volts) Vorms (Volts) Vodc
(Volts)
Vorms
(Volts)
FORMULA USED :
Vodc (theoretical) = Vm ×(1+ cos α)/( π)
WAVEFORMS :

JSSATE, BENGALURU44
(Vscr) with respect to source for α = 90 degrees.
RESULT :
CONCLUSION :
We conclude that the pulses obtained from UJT can be used to fire SCR
6) GENERATION OF FIRING SIGNALS USING DIGITAL FIRING CIRCUIT

JSSATE, BENGALURU45
AIM :To control firing angle /duty cycle using digital triggering.
APPARATUS:
Digital firing circuit, SCR’s( Single or any combination) loads, C.R.O, Probes etc.,
DIGITAL FIRING CIRCUIT:
This firing circuit generates isolated trigger pulses for the phase converter, Triac and DC
Chopper Power Circuits. The firing angle can be varied from 0-180° in steps of one degree and
duty cycle can be varied from 0- 100% in steps of 1% using a thumb wheel switch. The firing
scheme is based on ZCD, fixed frequency line synchronized clock generator, up/down counter, flip
flop and pulse Transformer isolation method.
DIGITALFIRINGCIRCUIT - DFC
ZCD
GENERATOR
CLOCK COUNTER LOGIC
CIRCUIT
A CGND
ACRef
180°
100%
F.A. / D.Cy
Fc
Oscillator
TP
NT
R
TRANSFORMER
PLUSETM
ON
OFF
GND
TRIGGERO/PS
T1
T2 2T '
T '1
MAINS
ISOLATION
1
2
INPUT
1) MAIN : Power ON/OFF switch to the unit with built-in indicator.
2) AC Ref : 10V AC reference input for synchronization.
3) GND : Ground point of the unit to observe the waveforms.
4) A : ZCD output.
5) C : Reset output for resetting the counter.
6) F.A/D.CY : Thumb wheel switch to set the firing angle from 0 to 1800
and Duty cycle
from 0 to 100%
7)1800
/ 100% : Switch to select 1800
(1ph converter) or 100% (chopper) mode
8)Fc Oscillator : Carrier frequency generator-5KHz.
9)R : 10 K ohms potentiometer to vary the no. of pulses from the clock
generator
10) Clock generator : A stable oscillator to generate clock input to the counter (180

JSSATE, BENGALURU46
pulses or 100 pulses) 3 stage.
11) Counter : 4bit up/down programmable counter.
12) Logic Circuit : Logic and modulator circuit to get TP,TN for 1ph converter and
TM, TA or chopper experiments.
Tp : Train of pulses for +ve cycle
TN : Train of pulses for –ve cycle.
TM : Pulse of 200µ sec for main SCR.
TA : Pulse of 200µ sec for auxiliary SCR.
13) TM ON
OFF : ON/OFF switch for main SCR14) Pulse Transformer
Isolation : Pulse transformer based isolation circuit with amplifier to isolate the Logic
circuit from the power circuit.
15) INPUT 1 and 2 : Input terminals to connect logic inputs.
16) Trigger O/Ps : Pulse Transformer isolated Trigger O/Ps –to
be connected to gate and cathode of SCRs.
T1 and T1
1
: Identical and isolated O/Ps for input-1,T2 and T2
1
: Identical and
isolated O/Ps for input-2
BLOCK DIAGRAM:
DigitalFrequency N-bit Flip-Flop
Logicckt.+ModulatorCounter (F/F)
+
Driver Stage
ZCD
CarrierFrequency
Oscillator
(~5kHz)
Oscillator
Preset
('N' no.ofcountingbits)
CLK max
minS
A A
B
B
T TFc
T
T
R Reset
LoadReset
CSync.
Signal(~8V)
Supply
DC5V
A¯
¯
En
DIGITALFIRINGCIRCUIT
A
P
N
AM

JSSATE, BENGALURU47
PROCEDURE: - Switch ON the mains supply to the unit. Observe AC reference signal and
compare it with ZCD O/P A and reset output C. Observe the carrier frequency oscillator o/p-5khz.
Now set the 1800
(Converter) mode. Observe the counter O/P keep the firing angle at 179°.
Adjust the potentiometer R in such a way that a very small pulse at the counter O/P is obtained.
Now vary the firing angle from 1800
to 00
step by step and observe the variation in trigger O/Ps TP
and TN. Connect TP and TN to 1 and 2 input of pulse Transformer isolation circuit and we will get
the pulse Transformer isolated and amplified outputs at T1 & T1
1
and T2 & T2
1
respectively.
Connect these Trigger O/Ps to gate and cathode of SCRs for different power circuits as given in the
table. Now set the 1800
-100% switch to 100% mode (chopper) keep the duty cycle at 99%. Adjust
the potentiometer ‘R’in such a way that a very small pulse output is obtained. Now vary the duty
cycle in steps from 99% to 1% and observe the counter O/P and also observe the time variation
between main pulse TM and auxiliary pulse-TA. Connect TM and TA to input 1 and 2 of pulse
transfer isolation.
TABLE
Experiment
TRIGGER I/P’S TRIGGER O/P’S
TP TN TM TA T1 T1
1
T2 T2
1
1)Single Ph-half wave converter.
2)1-ph-full wave converter.
3)1-ph-half controlled bridge
4)1-ph-Fully controlled bridge
5)1-ph.AC phase control
6)Triac (short T1-T2 +ve –ve)
7)Complimentary commutation
8)Auxiliary commutation
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
Table shows the useful Trigger inputs and Trigger outputs for different experiments.

JSSATE, BENGALURU48
WAVE FORMS:
0
1
P
e
2
Wt
3
0
A
F
A
F1
0
A
Wt
Wt
A
0
Wt
Wt
Wt
0
C
Down
0
Counting
16th pulse of
If
N pulse
A
0
Wta 2 3
0
B
Wt
0
B
Wt
Wt
Wt
0
C
0
G1
a 2 3
2
0
G
a+ 2
G = A,B, I1 c
G = A,B, I2 1
RESULT:
CONCLUSION :
7) AC VOLTAGE CONTROLLER USING TRIAC – DIAC COMBINATION

JSSATE, BENGALURU49
AIM : To fire TRIAC using DIAC.
APPRATUS REQUIRED :
Dimmer stat ,Isolator, Lamp Load, Resistor ,Potentiometer ,Capacitor,
DIAC( DB -3) ,TRIAC (BT-136), Power scope.
DEVICE SPECIFICATIONS: BT136-600.
1. Vdrm : 600V.
2. Itrms : 4 A.
3. Itsm : 50 A.
4. It : 12.5 A.
5. di/dt : 10 A/µs.
6. Igt : 15 mA.
7. Vgt : 1.5 V.
8. IH : 13 mA.
9. IL : 50 mA.
10.dv/dt : 10 V/µs.
DEVICE SPECFICATIONS: DB-3.
Breakdown Voltage: 32V±10%
Power: 0.5 Watts.
CIRCUIT DIAGRAM :
DESIGN FOR AC VOLTAGE CONTROLLER :

JSSATE, BENGALURU50
Time Constant = T =RC + (R+R1)C
T should exceed the time period of half a cycle for 50Hz mains.
T =(R+R1)>=10mSec.
The resistance R1 should limit the current value ,which prevents DIAC in conduction even after
capacitor has discharged.
Therefore, R1>VBBmax/Imax : R1>=VBDIAC/IDIAC
R1>32/100ma
R1>320 ohms
Therefore , Let C=0.47 microfarads
So, 0.00000047(320+R)=15mSec
R=31900-320
=31580 ohms
Choose a 100 kilo ohms potentiometer
PROCEDURE:
Make the connections as given in the circuit diagram. Switch ON the mains supply. Trigger the
TRIAC using DIAC firing circuit. Vary the firing angle potentiometer and observe the AC
voltmeter reading , waveform on the CRO & variation in lamp brightness and also note down the
voltage variation across the lamp.
For different positions ,we get different firing angle and for each setting note down the O/p voltage
ac voltmeter reading in tabular column. Plot the graph of firing angle Vs ac load voltage.
TABULAR COLUMN:
(α)=sin-1
(Vn/Vp) Vorms (Volts) Vorms (Volts)
Vrms = Vm /√2
Vorms = Vm [{(π-α)/(2π)} + {(sin 2α)/(2π)}]1/2
If α =00
; then
Vorms = Vm /√2 = Virms

JSSATE, BENGALURU51
WAVEFORMS:
waveforms across Vsupply, capacitor (VFBO), TRIAC (VTRIAC), load(VL) with respect to
source for α = 90 degrees.
RESULT:
CONCLUSION :
We conclude that power dissipation is less in case of DIAC firing circuit than UJT firing circuit.
DIAC firing circuit has a better firing angle control than the UJT firing circuit.

JSSATE, BENGALURU52
8) SINGLE PHASE CONTROLLED CONVERTER
1) SINGLE PHASE SEMI CONTROLLED CONVERTER
AIM :-To conduct a suitable experiment on half controlled(semi controlled) converter with
resistive and inductive load .
APPARATUS :-
Dimmer-stat, isolator, rheostat, inductor (transformer/isolator)resistors ,single phase converter
firing circuit, SCR converter module (power circuit module) .
SINGLE PHASE CONVERTER FIRING CIRCUIT
SINGLEPHASECONVERTERTRIGGERINGUNIT- SCT
ON / OFF
90°
60°
30°
0°
120°
150°
180°
TRIGGER
OUTPUTS
+ - FIRING ANGLE
T1
T '1
T2
T '2
GND
1 2 3
7654
TEST POINTS
POWER

JSSATE, BENGALURU53
1. Power :- Main ON/OFF switch with built in LED Indicator.
2. Firing angle :- Potentiometer to vary the firing angle from 180°
to 0°
3. ON/OFF :- Switch for trigger output with soft start feature.
4. Test points :- To observe the signals at various points in the logic
circuit for study purpose.
5. Trigger outputs :- T1 & T1
1
: For +ve Half Cycle.
T2 &T2
1
: For -ve Half Cycle.
This unit generates four line synchronized isolated triggering pulses to fire
thyristors connected in single phase (1) Half wave (2) Full wave (3) Half controlled Bridge (4)
Fully controlled Bridge and (5) AC phase control power circuit.
The firing circuit is based on Ramp-comparator scheme. Isolation is provided by
pulse transformer.
FEATURES :-
1. Work directly on 230V AC mains.
2. Gate drive current of 200mA to trigger wide range of devices.
3. Firing angle variation from 180° to 0° on a graduated scale.
4. Test points to study the logic circuit
5. Soft start and soft stop feature.
6. Neatly designed front panel.
This unit along with our SCR converter modules, rectifier diode modules, single
phase half controlled converter power circuit and single phase fully controlled
converter power circuit can be used to conduct power electronics experiments on
single phase.
BACK PANEL DETAILS :-
Mains socket with built in fuse holder.
Fuse -500mA. A spare fuse is also provided in the fuse holder.
INSTALLATION:
While operating, keep the equipment in well-aerated cool place. Avoid direct sunlight on the
equipment. Use a properly earth grounded outlet socket to connect to the equipment. This is so
because a floating earth ground will not provide a clean AC reference to the equipment. The power
input plug is situated on the back panel of the unit. Use the power cord provided along with the
equipment to the power outlet socket.
INPUT POWER SPECIFICATIONS:

JSSATE, BENGALURU54
Voltage : 215V -245V AC at 45 to 55Hz.
Current : 75mA (Max continuous) @ 230V AC.
500mA (Max surge).
Fuse : 500mA (Slow Blow) capsule type 20x 5mm.
Situated in the lower left corner of the equipment front panel is the power ON/OFF switch with
built in LED indicator. The LED glows when the switch is in ON position.
A fuse protects the equipment against over voltage and any short circuit. The fuse holder is an
integral part of the power inlet plug situated on the back panel. A spare fuse is provided in the fuse
holder. The power cord has to be removed from the plug, before you can access the fuse holder.
While replacing the fuse, pull off the holder smoothly.
Refer to figure shown below:
Power inlet plug
Pull here
Fuse holder
Power inlet plug/fuse holder
Remove and discard the blown off fuse and insert a new fuse in to the bay provided for it, replace
back the assembly in correct direction and press it until it flushes with the surface. Now connect
power cord back into the plug. Switch on the mains supply to the equipment. Observe the signals at
test points, trigger outputs and their phase sequence before connecting to the thyristor in the power
circuit. The built in pulse transformer based isolation between the trigger circuits and the power
circuit provides isolation up to a tune of 1000V.

JSSATE, BENGALURU55
5V1
1K+12V
10K
100K
1K
4K7
47K
-12V
100µF
OFF/ON
+12V
1N4007
1N4007
10K
1K
V1S
1K
0.1
100K
4K7
4K7
4K7
4K7
555
83 7
6
1 25
4
P
+12V
4K7
414812K
0.010.01
7VS
4K7
P
7V5
4K7
0.01 0.01
414812K
4K7
+12V
555
6
215
4
3 8 7
T1 T2
T3 4148
1K
1N4148
4K7
4148
2N2222
22K
1N4007
22K
1N4007
2N2222
IN41484148
+12V
+12V
7V5
4K7
100K
4148
1K
1K
741
3 4
6
7
+12V
100K
3
2
741
6
7
4
+12V
1K
T4
T5
6T
15V
0.75A
15V
1N4007
1N4007
1000µF
1000µF
25V
7812
7912
1000µF
25V
1000µF
25V 25V
+12V
GND
-12V
33 /5Wς
Vun
330
P/n1K 12V
BC107
SL-100
10K
22PF
GATE
1K8 5V1
CAT
GATE
CAT
T
5V11K8
1N4007
FIRINGANGLEPOT
CIRCUITDIAGRAM
+15V
+15V
100K
(75mA)
0
+12V
-12V
T7
1N4007
1'
T1
0.1µF
0.1µF

JSSATE, BENGALURU56
TEST POINTS
1
2
3
Vc 4
5
6
7
8
T1 & T1
T2 & T2
TRIGGER OUTPUTS

JSSATE, BENGALURU57
SERVICING DETAILS
SINGLE PHASE CONVERTER FIRING CIRCUIT :
a) Check the 3 pin Mains Cable used along with this unit
b) Check the Fuse in the Mains socket
c) Check the Mains Switch
d) Check the transformer
e) Check the firing angle potentiometer.
f) Check the ON/OFF switch
g) Check the zener diodes & IN4007 diodes at the output of the pulse transformer.
h) Check +12V & -12v power supply (Check 7812 &7912 regulators)
i) Check BC 107 & SL 100 transistors
j) Check 2N2222 transistors
k) Check 741/555IC’s
l) Check for any loose contacts.
SINGLE PHASE SEMI CONTROLLED CONVERTER POWER CIRCUIT :
SPECIICATIONS, 230V/5A
The circuit arrangement of a single-phase full converter is shown in fig. During the positive half
cycle, thyristor T1 and T1
1
are forward biased; and when these two thyristor are fired
simultaneously at wt=α, the load is connected to the input supply through T1 and T1
1
. In case of
inductive loads, during the period π ≤ wt ≤ (π+α), the input voltage is negative and the
freewheeling diode Dm is forward biased. Dm conducts to provide the conductivity of current in the
inductive load. The load current is transferred from T1 to Dm; and thyristor T1 IS turned off due to
line or natural commutation.
During the negative half cycle of the input voltage, thyristor T2 is forward
biased. The firing of thyristor T2 at wt= π+α will reverse bias Dm.
The diode Dm is turned off and the load is connected to the supply through T2 and T2
1
.
Figure shows the waveforms for input voltage, output voltage and Trigger Outputs.

JSSATE, BENGALURU58
This power circuit consists of four SCRs connected as semi- controlled bridge converter. A free
wheeling diode is provided to observe the effect of free wheeling diode on inductive loads.
Each device in the unit is mounted on an appropriate heat sink and is protected by snubber circuit.
Short circuit protection is achieved using glass fuses. A circuit breaker is provided in series with
the input supply for overload protection and to switch ON/OFF the supply to the power circuit.
The front panel consists of input and output terminals. The gate and Cathode of each SCRs brought
out on the front panel for firing pulse connection. Voltmeter and an Ammeter is mounted on the
front panel indicates the output voltage and current. A separate full wave bridge rectifier is
provided in the unit to get the DC supply for the field of DC Shunt Motors. The power circuit
schematic is printed on the front panel.
SPECIFICATIONS:
Input Voltage :15V to 230V AC.
Load current : 5 Amps maximum
Fuses : 6 Amps fast blow glass fuses.
Field supply : 220V ± 10%/2 Amps
MCB : Two pole 6 Amps/ 230V
Input terminals : To connect single phase input supply.
Output terminals(+&-) : To connect load.
Voltmeter(0 to 300V) : To indicate output voltage
Ammeter(0 to 5A) : To indicate output current.
Circuit breaker : 6 Amps AC power ON/OFF to the circuit and for
protection .
T1 & T2 : SCR – 16 TTS 12-16 A rms/1200Volts.
D1 & D2 : Diodes –SPR 16PB-16A/1200V
DM : Free wheeling diode –SPR 16PB-16A/1200V
Field(+ and -) : Field supply for DC motor for motor control
(with indicator) experiments.
BACK PANEL DETAILS:
Mains socket : For 230V AC mains supply to field supply bridge rectifier.
Fuse holders : 2 fuses in series with input AC supply, a fuse at the output and a fuse for
free wheeling diode.Fuse - 6 Amps
SINGLE PHASE POWER CIRCUIT
BLOCK DIAGRAM: :
230 V ,50Hz 0-230V
Isolation
Transformer
Power
Circuit
Load
Dimmer
Stat
Firing
circuit

JSSATE, BENGALURU59
1. Isolation Transformer:
To suit single phase 230V/50Hz supply, ratio 1:1, KVA rating to suit the load rating with
tapping at different voltages. Isolation of mains, phase and neutral with measurement circuit.
Serves the purpose of di/dt protection of SCR’s and safe measurement of waveforms by using
oscilloscope. Isolation of Electric noise with mains.
2. Power circuit:
Different power circuit configurations are possible using SCR’s and diode modules.
Half Wave Converter – 1SCR
Half Controlled Converter _ 2 SCRs & 2 Diodes
AC phase Control – 2 SCRs
3. Firing Circuit:
Each SCR of the above Power Circuit to be triggered using independently isolated outputs
using single phase converter firing unit. Trigger outputs phase sequence and variation to be
checked before with the power circuit. Phase sequence to be compared with the power circuits
phase sequence.
PROCEDURE :-
Switch on the mains to the circuit. Observe all the test points by varying the firing angle
potentiometer and trigger o/p’s ON/OFF switch. Then observe the trigger o/p’s and their phase
sequence .Make sure that all the trigger o/p’ sure proper before connecting to the power circuit..
Next connections in power circuit .Use a dimmer stat with a isolator and connect it to power
circuit. Connect the R-load between load points .Connect firing pulses from the firing circuit to
respective SCR’s .Switch ON the MCB trigger o/p’s and note down load voltage can be seen
.Repeat this same for R-L load and with and note down waveform.

JSSATE, BENGALURU60
TABULAR COLUMN:
(α)=sin-1
(Vn/Vp) Vodc (Volts) Vodc (Volts)
Vodc (th) = Vm (1+cos α) /π
Free Wheeling Diode, Resistive Load, and Resistive and Inductive load

JSSATE, BENGALURU61
WAVEFORMS:

JSSATE, BENGALURU62
RESULT:-
CONCLUSION :-
The output voltage at various firing angles are noted with R load and RL load and the difference
with and without free wheeling diode is observed. The relevant waveforms are traced.

JSSATE, BENGALURU63
(ii) SINGLE PHASE FULLY CONTROLEED CONVERTER
AIM: To Study the Single Phase Fully Controlled Converter on Resistance, Resistance &
Inductance Loads .
APPARATUS: Single Phase Converter Firing Circuit, Single Phase Fully controlled Power circuit,
Rheostat (150 Ohms/5A), Inductor(150 mH/5A), Power Scope, Connecting Wires etc.,
SINGLE PHASE CONVERTER FIRING CIRCUIT
SINGLEPHASECONVERTERTRIGGERINGUNIT- SCT
ON / OFF
90°
60°
30°
0°
120°
150°
180°
TRIGGER
OUTPUTS
+ - FIRING ANGLE
T1
T '1
T2
T '2
GND
1 2 3
7654
TEST POINTS
POWER
1. Power :- Main ON/OFF switch with built in LED Indicator.
2. Firing angle :- Potentiometer to vary the firing angle from 180°
to 0°
3. ON/OFF :- Switch for trigger output with soft start feature.
4. Test points :- To observe the signals at various points in the logic
circuit for study purpose.
5. Trigger outputs :- T1 & T1
1
: For +ve Half Cycle.
T2 &T2
1
: For -ve Half Cycle.
This unit generates four line synchronized isolated triggering pulses to fire
thyristors connected in single phase (1) Half wave (2) Full wave (3) Half controlled Bridge (4)
Fully controlled Bridge and (5) AC phase control power circuit.
The firing circuit is based on Ramp-comparator scheme. Isolation is provided by pulse transformer.

JSSATE, BENGALURU64
FEATURES :-
1. Work directly on 230V AC mains.
2. Gate drive current of 200mA to trigger wide range of devices.
3. Firing angle variation from 180° to 0° on a graduated scale.
4. Test points to study the logic circuit
5. Soft start and soft stop feature.
6. Neatly designed front panel.
This unit along with our SCR converter modules, rectifier diode modules, single
phase half controlled converter power circuit and single phase fully controlled
converter power circuit can be used to conduct power electronics experiments on
single phase.
BACK PANEL DETAILS :-
Mains socket with built in fuse holder.
Fuse -500mA. A spare fuse is also provided in the fuse holder.
INSTALLATION:
While operating, keep the equipment in well-aerated cool place. Avoid direct sunlight on the
input plug is situated on the back panel of the unit. Use the power cord provided along with the
Input power specifications:
Voltage : 215V -245V AC at 45 to 55Hz.
Current : 75mA (Max continuous) @ 230V AC.
500mA (Max surge).
Fuse : 500mA (Slow Blow) capsule type 20x 5mm.
Situated in the lower left corner of the equipment front panel is the power ON/OFF switch with
built in LED indicator. The LED glows when the switch is in ON position.
A fuse protects the equipment against over voltage and any short circuit. The fuse holder is an
holder. The power cord has to be removed from the plug, before you can access the fuse holder.
Refer to figure shown below:
Power inlet plug
Pull here
Fuse holder

JSSATE, BENGALURU65
Remove and discard the blown off fuse and insert a new fuse in to the bay provided for it, replace
back the assembly in correct direction and press it until it flushes with the surface. Now connect
power cord back into the plug. Switch on the mains supply to the equipment. Observe the signals at
test points, trigger outputs and their phase sequence before connecting to the thyristors in the power
circuit.
The built in pulse transformer based isolation between the trigger circuits and the power circuit
provides isolation up to a tune of 1000V.
Note that T1- T1
1
and T2- T2
1
are from different secondary. Therefore T1 –T1
1
will be in phase and
T2-T2
1
in the opposite phase.
The table below gives the usage of the trigger output against different experiments.
SL.NO EXPERIMENT TRIGGER OUTPUTS
T1 T1’ T2 T2’
1 I –Phase half wave converter *
2 I –Phase full wave converter * *
3 I –Phase half controlled converter * *
4 I –Phase full controlled converter * * * *
5 I –Phase AC, phase control * *
5V1
1K+12V
10K
100K
1K
4K7
47K
-12V
100µF
OFF/ON
+12V
1N4007
1N4007
10K
1K
V1S
1K
0.1
100K
4K7
4K7
4K7
4K7
555
83 7
6
1 25
4
P
+12V
4K7
414812K
0.010.01
7VS
4K7
P
7V5
4K7
0.01 0.01
414812K
4K7
+12V
555
6
215
4
3 8 7
T1 T2
T3 4148
1K
1N4148
4K7
4148
2N2222
22K
1N4007
22K
1N4007
2N2222
IN41484148
+12V
+12V
7V5
4K7
100K
4148
1K
1K
741
3 4
6
7
+12V
100K
3
2
741
6
7
4
+12V
1K
T4
T5
6T
15V
0.75A
15V
1N4007
1N4007
1000µF
1000µF
25V
7812
7912
1000µF
25V
1000µF
25V 25V
+12V
GND
-12V
33 /5Wς
Vun
330
P/n1K 12V
BC107
SL-100
10K
22PF
GATE
1K8 5V1
CAT
GATE
CAT
T
5V11K8
1N4007
FIRINGANGLEPOT
CIRCUITDIAGRAM
+15V
+15V
100K
(75mA)
0
+12V
-12V
T7
1N4007
1'
T1
0.1µF
0.1µF

JSSATE, BENGALURU66
TEST POINTS
1
2
3
Vc 4
5
6
7
8
T1 & T1
T2 & T2
TRIGGER OUTPUTS

JSSATE, BENGALURU67
SERVICING DETAILS
SINGLE PHASE CONVERTER FIRING CIRCUIT :
a) Check the 3 pin Mains Cable used along with this unit
b) Check the Fuse in the Mains socket
c) Check the Mains Switch
d) Check the transformer
e) Check the firing angle potentiometer.
f) Check the ON/OFF switch
g) Check the zener diodes & IN4007 diodes at the output of the pulse transformer.
h) Check +12V & -12v power supply (Check 7812 &7912 regulators)
i) Check BC 107 & SL 100 transistors
j) Check 2N2222 transistors
k) Check 741/555IC’s
l) Check for any loose contacts.
SINGLE PHASE FULLY CONTROLLED CONVERTER POWER CIRCUIT : SFC-
230V/5A
The circuit arrangement of a single-phase full converter is shown in fig. During the positive half
cycle, thyristor T1 and T1
1
are forward biased; and when these two thyristor are fired
simultaneously at wt=α, the load is connected to the input supply through T1 and T1
1
. In case of
inductive loads, during the period π ≤ wt ≤ (π+α), the input voltage is negative and the
freewheeling diode Dm is forward biased. Dm conducts to provide the conductivity of current in the
inductive load. The load current is transferred from T1 and T1
1
to Dm; and thyristor T1 and T1
1
are
turned off due to line or natural commutation.
During the negative half cycle of the input voltage, thyristor T2 and T2
1
are forward
biased. The firing of thyristor T2 and T2
1
simultaneously at wt= π+α will reverse bias Dm.
The diode Dm is turned off and the load is connected to the supply through T2 and T2
1
.
Figure shows the waveforms for input voltage, output voltage and Trigger Outputs.
A +
S H CF IE L D
O N
L IN E
R E C T IF IE R
~
+
~
-
1 P h. IN
N
L
-
T 1 T 2
V
D m
1 P h . F U L L Y C O N T R O L L E D C O N V E R T E R P O W E R C I R C U I T
T 1'T 2'
N
L
M C B
A M M E T E R
M E T E R
V O L T

JSSATE, BENGALURU68
This power circuit consists of four SCRs connected as fully controlled bridge converter. A free
wheeling diode is provided to observe the effect of free wheeling diode on inductive loads.
Each device in the unit is mounted on an appropriate heat sink and is protected by snubber circuit.
Short circuit protection is achieved using glass fuses. A circuit breaker is provided in series with
the input supply for overload protection and to switch ON/OFF the supply to the power circuit.
The front panel consists of input and output terminals. The gate and Cathode of each SCRs brought
out on the front panel for firing pulse connection. Voltmeter and an Ammeter is mounted on the
front panel indicates the output voltage and current. A separate full wave bridge rectifier is
provided in the unit to get the DC supply for the field of DC Shunt Motors. The power circuit
schematic is printed on the front panel.
SPECIFICATIONS:
protection .
T1,T1
1
,T2 & T2
1
: SCR – 16 TTS 12-16 A rms/1200Volts.
BACK PANEL DETAILS:
free wheeling diode.
Fuse - 6 Amps
SINGLE PHASE POWER CIRCUIT
Single ph AC
Input
Single Phase Experiments Block Diagram
Isolation
Transformer
Power
Circuit
Load
Firing
Circuit

JSSATE, BENGALURU69
1.Isolation Transformer :-
tappings at different voltages. Isolation of mains, phase and neutral with measurement circuit.
2.Power circuit :
Full Wave converter – 2 SCRs
Fully Controlled Converter – 4 SCRs
3. Firing Circuit :
phase sequence.
4. Load :
Load connection should include an ammeter and a current shunt for current waveform
measurements. Use freewheeling diodes wherever necessary.
Types of Loads: -
a) Resistance – ‘R’
b) Resistance and Inductive load ‘R’ & ‘L’.
c) Motor and Generator.
Note: In case of DC motor control, field excitation is separate. Field supply should be ON before
giving armature supply. It should be switched OFF only after switching off the armature supply.
Lamp load:
Due to di/dt limitation of SCR’s and since the initial inrush current
is 20 to 25 times more than load current in lamp loads and also since the cold resistance of the lamp
is very less, lamp loads can be used with large safety factors.
Precaution: Initially keep the input voltage low and firing angle at 1800
.Slowly increase the
voltage to the rated voltage and firing angle to 00
.

JSSATE, BENGALURU70
CIRCUIT DIAGRAM:
INSTRUCTIONS:
1. Check all the SCRs for performance before making the connections.
2. Check the firing circuit trigger outputs and its relative phase sequence.
3. Make fresh connections before you make a new experiment.
4. Preferably work at low voltages (20-30V) for every new connections. After careful verification it
can be raised to the maximum ratings. (This is to reduce damages due to wrong connections and
high starting current problems).
5. The thyristor has a very low thermal inertia as compared to machine and by any overload or
short circuit the SCR will immediately get damaged. Therefore do not switch ON the supply until
the instructor has checked the connections.
6. While observing the waveforms of two parameters on the oscilloscope, either differential input
oscilloscope should be used or special differential modules should be used with normal
oscilloscope. On normal oscilloscope, observation of wave forms can be done with respect to single
common point only. Ground connections of other probe must be avoided. It will lead to short
circuit if ground connections of both the probes are used since they are internally shorted. In no
case should oscilloscope input ground point be disconnected. This is a dangerous practice. Use 10:1
oscilloscope probe to see the waveforms at high voltages.
7. Do not make Gate & Cathode measurements when the power circuit is ON.
TABULAR COLUMN:
(α)=sin-1
(Vn/Vp) Vodc (Volts) Vodc (Volts)
Vodc (th) = 2Vm (cos α) /π

JSSATE, BENGALURU71
1. Input voltage waveform
2. Output Voltage waveform (across the load)
3. Output current waveform (through the shunt)
4. Voltage waveform across thyristors (make this measurement only if isolations is used)
5. Study of variation of voltage and current waveforms with the variation of firing angle.
6. Study of effect of freewheeling diode in case of inductive loads.
WAVEFORMS:
0
Wt
Wt
Wt
Wt
Vm
V
V=VmSin wt
2ππ π + αα
α π π + α
π20
T 1
2T
Vo
VOLTAGE WAVE FORMS

JSSATE, BENGALURU72

JSSATE, BENGALURU73
RESULT:
CONCLUSION:
The output voltage at various firing angles are noted with R load and RL load and the difference

JSSATE, BENGALURU74
SERVICING DETAILS:
Single-phase fully- controlled converter:
Power circuit: -
a) Check the devices – SCRs and diodes.
b) Check the fuse.
c) Check the MCB.
d) Check for any loose contacts.
e) Check the field supply bridge rectifier.

JSSATE, BENGALURU75
9) VOLTAGE COMMUTATED (IMPULSE COMMUTATED CHOPPER) BOTH
CONSTANT FREQUENCY AND VARIABLE FREQUENCY
AIM: To rig up DC Jones Chopper and to control O/P average DC Voltage both at constant
frequency and variable frequency and at different duty cycles.
APPARATUS:
DC chopper power circuit ,DC chopper firing circuit, DC Regulated power supply (0-30V/2A),
Rheostat (100hms/2A), CRO, connecting wires.
DESCRIPTION :
DC CHOPPER FIRING CIRCUIT:
This firing unit provides triggering pulses for the Thyristors in auxiliary commuted chopper circuit
configurations. It can be used for voltage commutation and current commutation chopper circuits
consisting of one main load carrying Thyristor and one auxiliary Thyristor and associated
commutation components.
DC – Chopper firing unit should be used together with our DC-Chopper power circuit to conduct
DC-DC chopper experiments on resistance, resistance and Inductance and motor load.
This firing circuit can also used for other chopper circuits also.
SPECIFICATIONS:
Power supply : 230V/50 Hz, single phase ac mains.
Output : Two pulse Transformer isolated trigger pulses for
main and auxiliary Thyristors.
Gate Drive current : 200 mA
Auxiliary Gate pulse width :100µsec.
Main Gate pulse width : Train of pulses
Test points : 1 to 8 provides signals at various points of the logic circuit.
Duty cycle : Variation from 10% to 90%.
Frequency : Variation from 30 Hz to 300 Hz. Approximately.
Control Voltage : Variation from 0 to 5V when the control switch is in INT position. External
control voltage can be used by putting the switch to EXT position.

JSSATE, BENGALURU76
DC - CHOPPER TRIGGERING UNIT - DCT
10%
TRIGGER
OUTPUTS
90%
DUTY CYCLE
Max.Min.
FREQUENCY
+ -
T M A IN
T A U X
G N D
1 2 3
7654
T E ST PO IN T S
PO W E R
Power : ON/OFF switch with built-in indicator.
Test points :1-7 test points for study of firing circuit.
Duty cycle : Potentiometer to vary the duty cycle from 10% to 90% when the control
switch is at INT position at the set frequency .
Frequency : Potentiometer to vary the operating frequency of the chopper from 30Hz to 300Hz
approximately.
ON/OFF : Switch for main thyristor trigger pulse with soft start feature.
Trigger Output TM : Main Thyristor Trigger pulse – Train of pulses.
Trigger Output TA. : Auxiliary Thyristor Trigger pulse of 100 µsec.
BACK PANEL DETAILS:
Main socket with built in fuse holder.
Fuse – 500mA.

JSSATE, BENGALURU77
NOTES:
1. The chopper cannot be tested without connecting the load.
2. The main thyristor T1 has to carry the resonant reversal current (along with load
current) there by increasing current rating requirements.
3. The discharging and charging time of commutation capacitor are dependent on the load
current and this limits the high frequency operation, especially at low load current.
4. The maximum value of the duty cycle is also limited to allow the commutation
capacitor to discharge and recharge.
5. The thyristor T1 must be ON for a minimum time of tr = π(LmC) to allow the charge
reversal of the capacitor and tr is fixed for a particular circuit design. This imposes
minimum duty cycle limit and hence minimum output voltage.
6. The firing circuit provides the trigger pulses in the following range:
Duty cycle: 10% to 90%
Frequency: 30Hz to 300Hz.
When the frequency is varied, the duty cycle is maintained constant at the set value. For example if
the duty cycle is 50% at 50 Hz and you have now selected the frequency to vary from 50 Hz to 100
Hz, the duty cycle still remains 50% at 100Hz.
The range of chopping frequency/duty cycle provided is no guarantee that any chopper power
circuit will work for the full range. The limits of operation of a given power circuit depend on
various factors like (a) the turn off requirement of the main thyristor (which should be less than the
available turn off time) (b) the peak load current (c) the input DC voltage (d) The source and load
inductance (e) The commutation circuitry – the value of C and Lm, etc.,
The function of firing circuit is only to provide properly sequenced and accurately timed trigger
pulse in the said range. The trigger pulse for the main thyristor T1 is a continuous train of pulses
for the whole of the ‘ON’ time kT (where k is the duty cycle). This train of pulses will be followed
by the firing pulse for commutation thyristor, also known as Auxiliary thyristor, T2. This auxiliary
trigger pulse is a single pulse whose width is approximately 100 microseconds.
INSTALLATION:
While operating, keep the equipment in well-aerated cool place. Avoid direct sunlight on to the
input plug is situated on the back panel of the unit. Use the power card provided along with the
INPUT POWER SPECIFICATIONS:
Voltage : 215 – 245 A/C at 45 to 55 Hz.
Current : 75mA (Max. continuous)@ 230V A/C.
500mA (Max. surge.)
Fuse : 500mA (Slow Blow) Capsule type 20 x 5mm.
Situated in the lower left corner of the equipment font panel is the power ON/OFF switch with
built-in in LED indicator. The LED glows when the switch is in ON position.

JSSATE, BENGALURU78
A fuse protects the equipment against over Voltages and any short circuit. The fuse holder is an
holder. The power card has to be removed from the plug, before you can access the fuse holder.
Refer to the figure shown below.
Power inlet plug
Pull here
Fuse holder
Remove and discard the blown off fuse and insert a new fuse in to the bay provided for it, Replace
back it the assembly in correct direction and press it until it flushes with the surface. Now connect
the power card back into the plug. Switch on the mains supply to the equipment. Observe the test
point’s signals, Trigger outputs and their phase sequence before connecting to the thyristors in the
power circuits.
DESIGN FOR JONES CHOPPER (VGE COMMUTATED CHOPPER)
Ic = Cdv/dt; -(1);
Ic = capacitor current
v=Voltage across capacitor
for constant load current ; equation can be
Ic = CVs/tc or C = tcIo/Vs
tc= commutating circuit time>tq(device turn-off time)
i.e,tc>tq ; so now let tc = tq + ∆t
tq for TY612 is 70 µSec which is almost equal to100 µSec
Let ∆t= 20 µSec
Therefore tc = 120µSec
Let Vs= 30v; Ic =2 A.
Therefore c = 120 µSec x 2/30
= 4 x 2 µF = 8 µF.
Choose C = 10 µF.

JSSATE, BENGALURU79
Ic = {VsSin (Wot)}/Wo L ;
Wo = 1/[LC] ½
Icp = Vs/WoL<=Io
<=Vs[(C/L)] ½
,
L>=[ (Vs/Io)]2
C >= [ (30/2)]2
8 x 10-6
>=1.8mH
Select L= 2mH or 8mH.
WAVEFORMS:
15 TP1
0
10V
5 TP2
5V
0 TP3
D C - C H O PPER FIRIN G CIRC U IT - TEST PO IN TS
5V
0 TP4
5V
0 TP5
0 TP6
5V
T P 7
T
T A
M
JONES CHOPPER POWER CIRCUIT: 30V/2A:
This unit consists of two SCR’s two diodes and L C commutation circuit to construct Jones chopper
power circuit. Each device in the unit is mounted on an appropriate hear sink and is protected with

JSSATE, BENGALURU80
an RC snubber circuit. All the components are independent and their connections are brought out
to front panel. The cathode and gate of each SCR is brought out ob to separate terminals for firing
pulse connection. A switch and a fuse are provided in series with the input DC Supply.
The devices and components can also be used to build different chopper circuits. Integrated
Thyristor Controller –ITC 08 and DC chopper firing unit DCT provided triggering pulses for this
power circuit.
SPECIFICATION:
30V @ 2.0 Amps.
+
+
-
DC INPUT
L
L'
C com
TM
TA DFW
D1
OUTPUT
+
-
RECTIFIER
~
+
~
-
230 VAC
FIELD
SCR DC - CHOPPER POWER CIRCUIT - SDCP
M
C
B
VDC IN : Terminal to connect DC input 10V to 30V DC.
ON : ON/OFF switch for the input DC supply to the power circuit.
Fuse : In series with the DC input for short circuit protection –2 Amps.
T1 & T2 :SCR’s – TYN 616
D1 & D2 : diodes – BYQ 28 200.
C : Commutation Capacitor – 10uF/100V.
L1-0-L2 : Commutation Inductor 500-0-500 Micro henry/2 Amps.

JSSATE, BENGALURU81
CIRCUIT DIAGRAM:
PROCEDURE :
To begin with switch ON the DC Chopper firing unit. Observe the test point Signals and Trigger
output signals by carrying Duty cycle and Frequency Potentiometer by keeping the control switch
into INT position. Be sure the trigger Outputs are proper before connecting to the power circuit.
Now make the interconnections in the power circuit as given in the circuit diagram. Connect DC

JSSATE, BENGALURU82
supply from a variable DC source. Initially set the input DC supply to 10 Volts. Connect a
Resistive load. Connect respective trigger outputs from the firing circuit to the respective SCRs in
the Power circuit. Initially keep[ the ON/OFF switch in the firing circuit in OFF position.
Switch ON the DC supply. Apply Main SCR trigger pulses by pressing the ON/OFF Switch to ON
position. Observe the voltage waveforms across load. We can observe the chopped DC waveform.
If the commutation fails we can see only the DC voltage. In that case switch OFF the DC supply,
Switch OFF pulses and check the connections and try again. Observe the voltage across load,
across Capacitor, across Main SCR and auxiliary SCR by varying Duty cycle and frequency
Potentiometer. Now vary the DC supply up to the rated voltage (30V DC). Draw the waveforms at
different duty cycle and at different Frequency. Connect Voltmeter and Ammeter and note down
values in the table.
TABULAR COLUMNS:
Sl.
No.
V in
Volts
Ton
Secs.
Toff
Secs.
Duty
cycle
Vo(volts)
Practical
Vo(volts)
Theoretical
INSTRUCTIONS:
1. Check all the SCR’s for performance before making the connections.
2. Check the firing circuit Trigger output and its relative phase sequence
3. Make fresh connection before you make a new experiment.
4. Preferably work at low voltages for every new connections. After careful verification
it can be raised to the maximum ratings (This is to reduce damages due to wrong
connections and high starting current problems)
5. The Thyristor has a very low thermal inertia as compared to machine and by any over
load or short circuit the SCR will immediately get damaged. Therefore do not switch
ON the supply until the instructor has checked the connections.
6. While observing the waveform of two parameters on the oscilloscope observation of
waveforms can be done with respect to single common point only. Ground connection
of other probe must be avoided. It will lead to short circuit if ground connections of

JSSATE, BENGALURU83
both the probes are used. Since they are internally shorted. In no case should
oscilloscope input ground point be disconnected. This is a dangerous practice. Use
10:1 oscilloscope probe to see the waveforms at high voltages.
7. Do not make Gate & cathode measurements when the power circuit is on
1. Voltage wave form across capacitor.
2. Output voltage waveforms (across the load)
3. Output current waveforms (Through the shunt)
4. Voltage waveforms across Thyristor.
5. Study of variation of voltage and current waveforms with the variation of duty cycle
and frequency.
6. Study of effect of free wheeling diode in case of inductive loads.
PRECAUTIONS:
1.In case of DC motor control, field excitation is separate. Field supply must be ON
before giving armature supply. It should be OFF only after switching off the armature
supply. Without field supply load current is too high which is limited by armature
resistance.
2.In case lamp load, due to di/dt limitation of SCR’s and since the initial inrush current
is 20 to 25 times more than load current, it can be done only with large safety factor.
3.Chopper cannot be tested without connecting load.
RESULT:
CONCLUSION :
The chopper has been verified and tested .It is found that Vo(prac) = Vo(theor)

JSSATE, BENGALURU84
10) SPEED CONTROL OF SEPARATELY EXCITED DC MOTOR:
SPECIFICATIONS:
protection .
T1,T1
1
,T2 & T2
1
: SCR – 16 TTS 12-16 A rms/1200Volts.
BACK PANEL DETAILS:
free wheeling diode.
Fuse - 6 Amps

JSSATE, BENGALURU85
1.Isolation Transformer :-
tappings at different voltages. Isolation of mains, phase and neutral with measurement circuit.
2.Power circuit :
Full Wave converter – 2 SCRs
Fully Controlled Converter – 4 SCRs
3. Firing Circuit :
phase sequence.
4. Load :
Load connection should include an ammeter and a current shunt for current waveform
measurements. Use freewheeling diodes wherever necessary.
Types of Loads: -
a) Resistance – ‘R’
b) Resistance and Inductive load ‘R’ & ‘L’.
c) Motor and Generator.
Note: In case of DC motor control, field excitation is separate. Field supply should be ON before
giving armature supply. It should be switched OFF only after switching off the armature supply.
Lamp load:
Due to di/dt limitation of SCR’s and since the initial inrush current
is 20 to 25 times more than load current in lamp loads and also since the cold resistance of the lamp
is very less, lamp loads can be used with large safety factors.
Precaution: Initially keep the input voltage low and firing angle at 1800
.Slowly increase the
voltage to the rated voltage and firing angle to 00
.
INSTRUCTIONS:
1. Check all the SCRs for performance before making the connections.
2. Check the firing circuit trigger outputs and its relative phase sequence.
3. Make fresh connections before you make a new experiment.

JSSATE, BENGALURU86
4. Preferably work at low voltages (20-30V) for every new connections. After careful verification it
can be raised to the maximum ratings. (This is to reduce damages due to wrong connections and
high starting current problems).
5. The thyristor has a very low thermal inertia as compared to machine and by any overload or
short circuit the SCR will immediately get damaged. Therefore do not switch ON the supply until
the instructor has checked the connections.
6. While observing the waveforms of two parameters on the oscilloscope, either differential input
oscilloscope should be used or special differential modules should be used with normal
oscilloscope. On normal oscilloscope, observation of wave forms can be done with respect to single
common point only. Ground connections of other probe must be avoided. It will lead to short
circuit if ground connections of both the probes are used since they are internally shorted. In no
case should oscilloscope input ground point be disconnected. This is a dangerous practice. Use 10:1
oscilloscope probe to see the waveforms at high voltages.
7. Do not make Gate & Cathode measurements when the power circuit is ON.
8. Vary the firing and note down Vodc, Iodc and speed N in RPM
TABULAR COLUMN:
Firing on the
Pottetiometer
Deg
Firing angle Practical Theoretical N Speed in RPM
(α)=sin-1
(Vn/Vp)
Vodc (th) = 2Vm (cos α) /π
1. Input voltage waveform
2. Output Voltage waveform (across the load)
3. Output current waveform (through the shunt)
4. Voltage waveform across thyristors (make this measurement only if isolations is used)
5. Study of variation of voltage and current waveforms with the variation of firing angle.
6. Study of effect of freewheeling diode in case of inductive loads.
7. Fro various firing note the speed on the digital meter on the motor panel.

JSSATE, BENGALURU87
WAVEFORMS:
0
W t
W t
W t
W t
V m
V
V =V m Sin w t
2 ππ π + αα
α π π + α
π20
T 1
2T
V o
V O LTA G E W A V E FO R M S

JSSATE, BENGALURU88

JSSATE, BENGALURU89
RESULT:
CONCLUSION:
The output voltage at various firing angles are noted with DC Motor as load and the difference

JSSATE, BENGALURU90
11) SPEED CONTROL OF UNIVERSAL MOTOR
Motor Specification: 0.5HP/220V AC/DC
AIM: To Control the speed of the Universal through (i) AC-DC Power converter (FCR) and
(ii)AC Voltage Controller
Apparatus: Universal Motor, Isolation Transformer, dimmer-stat, Fully controlled bridge
rectifier (FCR), ACVC, FCR Firing Circuit.

JSSATE, BENGALURU91
Procedure: Make the inter connections in the power circuit as in the circuit for FCR and ACVC,.
Switch on the the firing circuit and observe the trigger pulses. Make sure that the firing pulses are
proper before connecting to the power circuit. Then connect the trigger output from the firing
circuit to the corresponding SCR’s/TRIAC. In the power circuit initially set AC input to 30V.
Switch on the MCB. Switch on the trigger. First observe the output across R load by varying the
potentiometer. If the output wave form is proper then you can connect the motor and increase the
input voltage to the rated value i.e., 230V gradually. Vary the firing angle and note O/P voltage
and speed of the motor
Table (Fully Controlled Rectifier
Firing on the
Potentiometer
Deg
(α)=sin-1
(Vn/Vp)
Table (ACVC)
Firing on the
Potentiometer
Deg
(α)=sin-1
Vn/Vp) Vodc (Volts) Vodc (Volts)

JSSATE, BENGALURU92
12) SPEED CONTROL OF STEPPER MOTOR:
STEPPER MOTOR CONTROLLER
This is Micro controller based controller circuit to accurately generates pulses to energizes the
stepper motor winding in the desired sequence . Power transistor based driver circuit to driver
circuit to drive the stepper motor. From this controller we can set the speed of the stepper motor in
RPM, set the number of steps motor can move .We can set the direction of rotation forward and
reverse direction. We can also set half step and full step mode.
1.Mains :Power ON/Off Switch to the unit with built-in indicator.
2.Display :Seven segment 5 digit display to display the parameter and values
3.Key board :
a)Set :To set the Parameter.
b)INC :To increment the set parameter values.
c)DEC :To decrement the set parameter values.
d)ENT :To enter the set values.
e)RUN/STOP :To start and stop the stepper motor. .(Built in)
4.+v : 5v/2 amps DC supply for stepper motor.(Built in)
5.+5v :5 v for control circuit .(Built in)
6.GND :Supply ground point
7.FUSE :2 amp fast below glass fuse for short circuit protection.
8.A1,A2,B1 & B3: Outpoints to connect to the A1,A2,B1 &B3 leads of stepper motor.
9.LED’s :To indicate the status of output.
BACK PANNEL DETAILS:
Mains socket with built in fuse holder and a spare fuse.
PROCEDURE:-
Connect A1, A2, B1 and B2 leads of stepper motor to the corresponding output terminal points.
And two common terminal to +V supply. Switch ON the mains supply to the unit. Check the
power supplies. The unit display S – 00. Now press SET. Then the display shows rpm(revolutions
per minute). If you press ENT now the speed mode is set and it displays 00. Then press INC Key to
set the rpm. When the display shows rpm, if you press INC/DEC it goes to STEP mode or vice
versa.
After setting the Speed in rpm/ no of steps, press ENT Key. Then the parameter values is entered
and it shows set direction of rotation. Press INC/DEC changes the direction of rotation. Then press
ENT Key to set the direction of rotation.
Then it displays Half step or Full step mode. Pressing INT/DEC will changes to HALF Step/ FULL
Step mode or vice versa. Press ENT Key to set the Half step or Full step mode.

POWER ELECTRONICS LAB MANUAL, DR. B G SHIVALEELAVATHI, JSSATEB

POWER ELECTRONICS LAB MANUAL, DR. B G SHIVALEELAVATHI, JSSATEB

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