BEL-PET

POWER ELECTRONICS TRAINERr

EXPERIMENTAL MANUAL
BEL-PET POWER ELECTRONICS TRAINER V-24.0

…. A MESSAGE FROM

Today’s system designers are faced with tomorrow’s problems. BASIC ELECTRONICS is
one of the important subject need to teach while learning electronics.
It is our vision to provide you with the product you need for training ensuring lasting
reliability & quality.

OUR MOTTO;
- Light years ahead – refers to leadership.

As leaders in our industry in India, We are totally committed to servicing as the standard
against which all are measured in the areas of

• Design • Quality • Value • Delivery • Support.

We are truly light years ahead of our competition in this area. That means that you our
valued customers are guaranteed satisfaction.

As you will move through this manual you will quickly discover that We have a complete,
truly innovative & superior training products we are so committed to quality that we back our
products with a complete comprehensive warranty.

AKADEMIKA LAB SOLUTIONS

Sr. No. 15/8/1, Unit No.9, Kruti Industrial Estate, Opp.
Karishma Society, Off Karve Road, Kothrud, Pune,
Maharashtra- 411038
INDIA
Contact No.:+91-7447438443
Email: lab@akademika.in
www.akademika.in

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SAFETY RULES

• Read carefully and follow the instructions mentioned in this manual. This user manual
includes all the important points about the installation, use and the maintenance of the
product. Keep this manual always with you, for quick reference.

• After unpacking the product, arrange all the accessories in proper order, so that their
integrity is checked with the packing list. Also, ensure that the accessories have no
visible damage.

• Before connecting the power supply to the kit, be sure that the jumpers and the
connecting chords are connected correctly, as per the experiment.

• This kit must be employed only for the use for which it has been conceived, i.e. as
educational kit and must be used under the direct survey of expert personnel. Any
other use is inadvisable and dangerous too. The manufacturer cannot be considered
responsible for eventual damages due to improper, wrong or unreasonable uses.

• In case of any fault or malfunctioning in the trainer kit, turn off the power supply. Please
do not tamper the kit. If you require our service, kindly contact the service centre for
technical assistance.

• The kits are liable to malfunction/under-perform if they are not operated under standard
environmental conditions of temperature and humidity.

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WARRANTY
This kit is warranted against defects in workmanship and materials. Any failure due to defect
in either workmanship or material should occur under normal use within a year from the
original date of purchase, such failure will be corrected free of charge to the purchaser by
repair or replacement of defective part or parts. When the failure is result of user’s neglect,
natural disaster or accident, we would charge for repairs, regardless of the warranty period.
The warranty does not cover include perishable items like connecting chords, crystals, etc.
and other imported items.

Conditions and Limitations

The warranty is void and inapplicable if the defective product is not brought or sent to our
authorized service center or sales outlet within the warranty period. Defective product will
be Akademika Lab Solutions sole judgment. The defective product will be replaced with a
new one or repaired, without charge or with charge.

In the warranty period if the service is needed, the purchaser should get in touch with the
service center or the sales outlet. The purchaser should return the product to the service
center or the sales outlet at his or her sole expense. The loss and damage in transit will be
outside the preview of this warranty. A returned product must be accompanied by a written
description of the defects. Type and Model No. of the kit has to be mentioned specifically.
We return the product to the purchaser at our expense. In case the warranty does not cover
the product on Akademika Lab Solutions judgment, we would repair the product after
obtaining prior permission from purchaser who would receive an estimate statement about
the repairing charges. In such cases, Akademika Lab Solutions bares the transporting
expenses required to send back all the repaired products for the moment, and then repairs
and transporting expenses will be charged against the purchaser by the statement of
accounts.

When the authorized sales agents sell our products, they must notify the purchaser of the
warranty contents, but they have no rights to stretch the meaning of original warranty
contents or to offer an additional warranty. Akademika Lab Solutions does not provide any
other promise or suggestive warranty and hold no liability for the damage caused by
negligence, abnormal use or natural disaster. Akademika Lab Solutions is not responsible
for the damages even if it is notified of above dangers in advance as well.

For more special service or overall repairs, maintenance and up gradation of products, be
sure to contact our service center or the sales outlet.

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INDEX

Sr. Chapter Page

No. No.
1 Technical Specifications 6

2 Functional Block 7

3 Introduction 8

401 Experiment No-1 9

02 Simple DC to AC Inverter
501 Experiment No-2 15
02 Dc to Dc Converter (Dual Converter)
601 Experiment No-3 21
02 Low Voltage Lamp Flasher (Using PUT & SCR)
701 Experiment No-4 25
02 Led Flasher with SCR and UJT
801 Experiment No-5 29
02 Lamp Dimmer Using DIAC and TRIAC
901 Experiment No-6 35
02 Half Wave Control Rectifier
1001 Experiment No-7 39
02 Full Wave Control Rectifier
1101 Experiment No-8 43
02 Ac Power Flasher Using SCR
1201 Experiment No-9 47
02 SCR Triggering Using 555
1301 Experiment No-10 53
02 SCR Time Delay Relay
14 Experiment No-11 57
DC Chopper
15 Experiment No-12 61
Switched Mode Controller/ Rectifier
16 Experiment No-13 65
SCR Turn ON Methods
17 Experiment No-14 71
SCR Firing Circuits

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18 Experiment No-15 77
Time delay Circuit.
19 Experiment No-16 81
AC Voltage Controller

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TECHNICAL SPECIFICATIONS

• Characteristics study of different types of power

• AC supply, ranging from0~30VAC/50Hz, DC supply of +12V
• electronics Devices i.e. thyristors ( SCR, TRIAC, DIAC ), UJT,
• MOSFET, etc.
• Application study of different types of power electronics
• Devices i.e. thyristors (SCR, TRIAC, DIAC ) and MOSFET
• Different gate-pulsing circuits (turn-on methods)
• Different commutation circuits (turn-off methods)
• Different IC's for gate triggering circuits
• Provision of freewheeling diodes
• Resistor bank
• Capacitor bank
• Inductor bank
• Potentiometer bank
• Interconnection points
• Interconnection cords

• Accessories

BEL-PET Quantity

1 Short Links PCS2 Patch cord Male To Male 15

2 Long Links PCS2 Patch cord Male To Male 5
3 EXPT Manual 1
4 PET Power Supply 1
5 Power cord 1
6 Single Strand Wire 2mtr 1

Note: Reading Tables and Graphs provided in this manual are taken on sample trainer board
hence actual readings and graphs may differ from the readings and graphs shown
in this manual. Readings and graphs in this manual are to be treated as sample only
for reference purpose to get idea of characteristics of the respective component.

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FUNCTIONAL BLOCK

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INTRODUCTION

Akademika Lab Solutions’ BEL-PET Power electronics Trainer kit” is a compact single board
unit in wooden casing it provides hands on experimentation in the area DC to AC converter,
DC to DC converter, Diac, Triac, etc. It broadly deals with controlling the flow of electrical
power using electronic switching devices.

This kit it is possible to embark on any formative path, in fact, starting from simple
experiments, it makes you grow in experience and complexity up to being able to deal with
competence and master the fundamental elements which makes the Basic electronics
based .

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EXPERIMENT
NO. 1

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EXPERIMENT NO: 1

NAME:-

Simple DC to AC Inverter

OBJECTIVE:-

Study of simple DC to AC converter

THEORY:-

In one simple inverter circuit, DC power is connected to a transformer through the centre
tap of the primary winding. A switch is rapidly switched back and forth to allow current to
flow back to the DC source following two alternate paths through one end of the primary
winding and then the other. The alternation of the direction of current in the primary winding
of the transformer produces alternating current (AC) in the secondary circuit.

The electromechanical version of the switching device includes two stationary contacts and
a spring supported moving contact. The spring holds the movable contact against one of
the stationary contacts and an electromagnet pulls the movable contact to the opposite
stationary contact. The current in the electromagnet is interrupted by the action of the switch
so that the switch continually switches rapidly back and forth. This type of electromechanical
inverter switch, called a vibrato or buzzer, was once used in vacuum tube automobile radios.
A similar mechanism has been used in door bells, buzzers and tattoo guns. As they became
available with adequate power ratings, transistors and various other types of semiconductor
switches have been incorporated into inverter circuit designs.

PROCEDURE:-

• Make sure that power supply must be OFF.

• Refer to the circuit diagram and carry out the following connections.
• Connect power supply in proper polarity to kit BEL-PET.
• Connect M1 and M2 terminals in the MOSFET bridge circuit to 4 OT winding of
transformer i.e. pin no.11 and 12 respectively, you should not connect HPWM & LPWM
anywhere. It is connected internally in circuit.
• After connecting all connections power supply should be ON.
• Check the PWM pulses at HPWM and LPWM and vary the POT 6 to change the duty
cycle of PWM.
• For perfect o/p keep POT 6 at Minimum position that give 50% duty cycle at o/p.
• Then observe the o/p at M1 & M2, you will get AC square wave.

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• Also observe the waveform on the other winding of Transformer .you can observe same
waveform in step down mode

CIRCUIT DIAGRAM:-

M2

M1

As per the above connection for 40T , you can also do same connections for different
values.

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OBSERVATION:-
CAPTURED WAVEFORM
• DC Input(12VDC)

• HPWM,LPWM

• Motor O/P M1 &M2(AC across motor O/P)

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• Transformer TX1 output across 10T step down AC

• Transformer TX1 output across 20T step down AC

• Transformer TX1 output across 25T step down AC

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EXPERIMENT
NO. 2

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EXPERIMENT NO: 2

NAME:-

DC To DC Converter (Dual Converter)

OBJECTIVE:-

Study of DC TO DC converter (dual converter)

THEORY:-

Dc-dc power converters are employed in a variety of applications, including power supplies
for personal computers, office equipment, spacecraft power systems, laptop computers, and
telecommunications equipment, as well as dc motor drives. The input to a dc-dc converter
is an unregulated dc voltage Vg. The converter produces a regulated output voltage V,
having a magnitude (and possibly polarity) that differs from Vg. For example, in a computer
off-line power supply, the120 V or 240 V ac utility voltage is rectified, producing a dc voltage
of approximately 170 V or 340 V, respectively. A dc-dc converter then reduces the voltage
to the regulated 5Vor 3.3 V required by the processor ICs. High efficiency is invariably
required, since cooling of inefficient power converters is difficult.
The ideal dCconverterexhibits100%efficiency; inpractice, efficiencies of 70% to 95% are
typically obtained. This is achieved using switched-mode, or chopper, circuits whose
elements dissipate negligible power. Pulse-width modulation (PWM) allows control and
regulation of the total output voltage. This approach is also employed in applications
involving alternating current, including high-efficiency dc-ac power converters (inverters and
power amplifiers), ac-ac power converters, and some ac-dc power converters (low-
harmonic rectifiers). A basic dc-dc converter circuit known as the buck converter.

PROCEDURE:-

A. For Positive Output

I. Without Load.
• Make sure that power supply must be OFF.
• Refer block diagram & carry out the following connections.
• Connect power supply in proper polarity to kit BEL-PET.
• Connect M1 & M2 terminal in MOSFET bridge CKT to 4 OT winding of transformer. i.e.
pin no.11 & 12 resp.
• Now select 1 OT winding of transformer and connect pin no.1 to GND.
• Next pin no 2 is connected to the anode of diode 1N5819 from diode bank.
• Cathode of same diode is connected to the terminal of 10uF/63V capacitor.
• Connect -ve terminal of capacitor to the GND.

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• Observe the Amplitude of AC square wave at 4 OT winding & 2 OT winding.

• Put pot 6 at MAX position for without load condition & observe the O/P voltage &
compare with load value.
• Observe the DC O/P at the terminal of capacitor .we get DC value is less than 12V DC
which is used as input in MOSFET Bridge.
• Hence we obtain DC to DC conversion using Dual conversion method.
II. With Load.
• Repeat the same procedure for With Load experiment, just connect resistive 560E/2W
load across the capacitor.
• Observe the O/P across the load, you will get the ripples at the O/P.
• If the voltage is less, then vary the pot 6 of PWM section to change the duty cycle. It will
compensate the difference in the load value.& the actual value when load is connected.

B. For Negative Output

I. Without Load
• Repeat the steps (1) to (4) from previous expt.
• Select 1OT winding of transformer & connect pin 2 to GND.
• Next pin no 1 to be connected to the cathode of diode 1N5819 from diode bank.
• Anode of same diode is connected to the -ve terminal of 10uF/63V capacitor & +ve
terminal to the GND.
• Observe DC –ve voltage at –ve terminal of capacitor.

II. With Load

• Repeat the same procedure for with load condition, just connect resistive load
560E/2W load across the capacitor.
• Observe the O/P across the load; you will get ripples at the O/P.

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CIRCUIT DIAGRAM

OBSERVATION:-
Captured Waveform
A. Without Load
• DC Input (+12V)

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• AC Signal at 10T of transformer

• DC output across capacitor (~2VDC)

B. With Load(560ohm/2W)

• DC output across Resistance (load) with ripples.

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A. Without Load
• DC input & AC signal is same as that of experiment NO.2.
• DC output across capacitor(`-2V DC).

C. With Load (560OHM/2w)

• DC output across load with ripples.

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EXPERIMENT
NO. 3

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EXPERIMENT NO: 3

NAME:-

Low Voltage Lamp Flasher (Using PUT & SCR)

OBJECTIVE:-

Study of low voltage lamp flasher (using PUT & SCR)

THEORY:-

A "two-wire" circuit and simply connects in series with the load and battery. The two resistors
on the base of the PNP set a threshold voltage and when power is applied the capacitor
begins charging toward this voltage. When the capacitor voltage is high enough the two
transistors begin to conduct. The current flow causes the voltage across the circuit to drop
slightly and this drop causes a drop in the threshold voltage. The lower threshold voltage
causes even more current and this positive feedback causes the circuit to rapidly turn on. It
stays on until the capacitor discharges at which point a reverse process causes the circuit
to suddenly switch off.

PROCEDURE:-

• Refer the circuit diagram carry out the following connections.

• Connect power supply in proper polarity to the kit BEL-PET.

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CIRCUIT DIAGRAM:-

OBSERVATION:-

• Led will flash continuously with same ON & OFF Time.

• When we replace R5=R6=10K then LED will go ON for ½ second & OFF for same
time.

CAPTURED WAVEFORM:-

• Waveform across PUT.

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• Waveform across SCR1

• Waveform across SCR2

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EXPERIMENT
NO. 4

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EXPERIMENT NO: 4

NAME:-

LED Flasher with SCR and UJT

OBJECTIVE:-

Study of LED flasher with SCR and UJT

THEORY:-

The Q1 will give the period of time of pulse for trigger. The work of SCR for drive LED. The
circuit will pull current 2 mA from just Battery 9V. When the schedule is Flasher keep 12
time per second The SCR use at have 6A 50V.
LED flashers are great fun for the novice or seasoned builder
In modern times, analog circuits such as the astable BJT multivibrator or a 555 timer IC
driving 4017 decade counter(s) are being replaced with small microprocessor-based circuits
such as the PIC Microcontroller. The QRP/SWL Home Builder web site has featured a
number of multivibrator and LED flasher circuits over the past decade and each year at least
40 - 50 emails are received requesting help, specific designs or calling for more projects.
Thus, another page of LED flasher circuits was added and building these circuit was quite
enjoyable.
Lower LEDS were used for all the experiments. The 2N3904 transistor was used exclusively
and the schematics do not indicate this part. By request, this web page these circuit using
a lot of math.

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PROCEDURE:-

1. Refer the circuit diagram & carry out the following connection.
2. Connect power supply in proper polarity to the kit.

CIRCUIT DIAGRAM:-

OBSERVATION:-
• When pot R1 is at minimum position, LED will remain ON.
• As we increasing pot R1, OFF time of LED will increase and ON time of LED is for
½ second.

CAPTURED WAVEFORM:-
• Waveform at point E of UJT (2N2646) at R1=13K waveform across LED.

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• A waveform at R1=50K.

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EXPERIMENT
NO. 5

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EXPERIMENT NO: 5

NAME:-

Lamp Dimmer Using DIAC and TRIAC

OBJECTIVE:-
Study of lamp dimmer using diac and triac

THEORY:-

Dimmers are devices used to vary the brightness of a light. By decreasing or increasing the
RMS voltage and hence the mean power to the lamp it is possible to vary the intensity of
the light output. Although variable-voltage devices are used for various purposes, the term
dimmer is generally reserved for those intended to control resistive incandescent, halogen
and more recently compact fluorescent (CFL) lighting. More specialized pulse-width
modulation equipment is needed to dim fluorescent, mercury vapor, solid state and other
arc lighting. Dimmers range in size from small units the size of a normal light switch used
for domestic lighting to high power units used in large theatre or architectural lighting
installations. Small domestic dimmers are generally directly controlled, although remote
control systems (such as X10) are available. Modern professional dimmers are generally
controlled by a digital control system like DMX or DALI. In newer systems these protocols
are often used in conjunction with ethernet. In the professional lighting industry changes in
intensity are called “fades” and can be “fade up” or “fade down”. Dimmers with direct manual
control had a limit on the speed they could be varied at but this issue has been largely
eliminated with modern digital units (although very fast changes in brightness may still be
avoided for other reasons like lamp life).

FIG:DIMMER USING DIAC AND TRIAC.

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A triac may be considered as two SCR's (Silicon Controlled Rectifiers)connected in opposite

directions. A diac is a gate trigger device. Triacs, diacs & SCR's are different types of
Thyristors .A triac is a 3 terminal ac semiconductor switch which is triggered ON when a low
energy signal is applied to its Gate. Switching is fast. The low energy of switching means
that a wide range of low cost control circuits can be used, for example, optically coupled
switches. Since the triac is bilateral (2 SCR's connected in opposite directions) the terms
anode and cathode have no meaning. So the terms Main Terminal 1 and 2 (MT1, MT2) are
used. It is standard to use MT1 as a reference point. The circuit here controls the average
power to a load through the triac by phase control. The ac supply is applied to the load for
only a controlled fraction of each cycle. The triac is held in an OFF condition for a portion of
its cycle then is triggered ON at a time determined by the circuit. The main problem with this
circuit is radiofrequency interference (RFI.)RFI. Each time the triac is turned on the load
current changes very quickly - a few micro seconds - from zero to a value determined by
the lamp resistance and the value of the mains voltage at that instant in time. This transition
generates RFI. It is greatest when the triac is triggered at90o and least when it is triggered
at close to zero or 180oof the mains AC waveform. Since there may be long lengths of
mains wire between the triac and the lamp load which will radiate this RFI an L-C RFI
suppression network is usually built into these types of circuits. You may detect this RFI by
bringing an FM radio close to the dimmer circuit.

PROCEDURE:-

1. Connect the circuit as per shown in the diagram.

2. Now vary the pot 500K, intensity of LED will vary.

CIRCUIT DIAGRAM:-

OBSERVATION:-

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• Put pot 500K at minimum position, LED gives maximum intensity.

• As we increasing pot 500K,then intensity of LED will goes on decreasing and LED
will OFF at maximum position.
• Keep CRO probe at 10X position.

Pot minimum → LED drops the current of 15 mA = MAX intensity.

Pot at 100K → LED drops the current of 5 mA = MIN intensity.

CAPTURED WAVEFORM:-

• Input AC waveform (across supply) probe at 10X.

• Output across LED (POT at minimum position).

• Output across LED (POT at 40K).

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• Output across LED (POT at 100K).

• Output across LED (POT at 120K).

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EXPERIMENT
NO. 6

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EXPERIMENT NO:6

NAME:-

Half Wave Control Rectifier

OBJECTIVE:-

Study of half wave control rectifier

THEORY:-

While half-wave and suffice to deliver a form of DC output, neither produces constant-
voltage DC. In order to produce steady DC from a rectified AC supply, a smoothing circuit
or filter is required In its simplest form this can be just a reservoir capacitor or smoothing
capacitor, placed at the DC output of the rectifier. There will still remain an amount of AC
ripple voltage where the voltage is not completely smoothed. RC-Filter Rectifier: This circuit
was designed and simulated using Multisim 8 software. Sizing of the capacitor represents
a tradeoff. For a given load, a larger capacitor will reduce ripple but will cost more and will
create higher peak currents in the transformer secondary and in the supply feeding it. In
extreme cases where many rectifiers are loaded onto a power distribution circuit, it may
prove difficult for the power distribution authority to maintain a correctly shaped sinusoidal
voltage curve .For a given tolerable ripple the required capacitor size is proportional to the
load current and inversely proportional to the supply frequency and the number of output
peaks of the rectifier per input cycle. The load current and the supply frequency are
generally outside the control of the designer of the rectifier system but the number of peaks
per input cycle can be affected by the choice of rectifier design. A half-wave rectifier will only
give one peak per cycle and for this and other reasons is only used in very small power
supplies. A full wave rectifier achieves two peaks per cycle and this is the best that can be
done with single-phase input. For three-phase inputs a three-phase bridge will give six
peaks per cycle and even higher numbers of peaks can be achieved by using transformer
networks placed before the rectifier to convert to a higher phase order.

PROCEDURE:-

1. Refer the circuit diagram carry out the following connections.

2. Connect power supply in proper polarity to the kit BEL-PET

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CIRCUIT DIAGRAM:-

OBSERVATION:-
CAPTURED WAVEFORM
• Input AC waveform(Across supply) probe 10X.

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• Half wave rectified output probe 10X.

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EXPERIMENT
NO. 7

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EXPERIMENT NO:7

NAME:-

Full Wave Control Rectifier

OBJECTIVE:-
Study of full wave control rectifier

THEORY:-

Single phase uncontrolled Full wave rectifiers suffer from poor output voltage and/or input
current ripple factor. In addition, the input current contains a dc component which may cause
problem (e.g. Transformer saturation etc) in the power supply system. The output dc voltage
is also relatively less. Some of these problems can be addressed using a full wave rectifier.
They use more number of diodes but provide higher average and rms output voltage.
There are two types of full wave uncontrolled rectifiers commonly in use. If a split power
supply is available (e.g. output from a split secondary transformer) only two diode will be
required to produce a full wave rectifier. These are called split secondary rectifiers and are
commonly used as the input stage of a linear dc voltage regulator. However, if no split supply
is available the bridge configuration of the full wave rectifier is used. This is the more
commonly used full wave uncontrolled rectifier configuration.

PROCEDURE:-
1. Refer the circuit diagram carry out the following connections.
2. Connect power supply in proper polarity to the kit BEL-PET

CIRCUIT DIAGRAM:-

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OBSERVATION:-

CAPTURED WAVEFORM
• AC input waveform

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• Full wave rectified output

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EXPERIMENT
NO. 8

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EXPERIMENT NO:8

NAME:-

AC Power Flasher Using SCR

OBJECTIVE:-

Study of AC power flasher using SCR

THEORY:-

A flash is a device used in photography producing a flash of artificial light (typically 1/1000
to 1/200 of a second) at a color temperature of about 5500 K to help illuminate a scene. A
major purpose of a flash is to illuminate a dark scene. Other uses are capturing quickly
moving objects or changing the quality of light. Flash refers either to the flash of light itself
or to the electronic flash unit discharging the light. Most current flash units are electronic,
having evolved from single-use flashbulbs and flammable powders. Modern cameras often
activate flash units automatically. Flash units are commonly built directly into a camera.
Some cameras allow separate flash units to be mounted via a standardized "accessory
mount" bracket (hot shoe). In professional studio equipment, flashes may be large,
standalone units, or studio strobes, powered by special battery packs or connected to mains
power. They are either synchronized with the camera using a flash synchronization cable
or radio signal, or are light-triggered, meaning that only one flash unit needs to be
synchronized with the camera, and in turn triggers the other units

FIG:LINE POWER FLASHER

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Here is an unusual flasher circuit for 120VAC loads. The circuit is similar to the two-transistor
flasher seen in several circuits in techlib.com except that an SCR is used. A

little circuit trick is hiding in the selection of the 0.1uF capacitor in series with the 1k
resistor. When the SCR is off, this capacitor smoothes the ripple from the bridge sufficiently
for the transistor flasher circuitry to work properly but when the SCR turns on, the capacitor
immediately discharges and will not provide enough current to keep the SCR on. Also, the
capacity is low enough to leave quite a bit of ripple voltage causing the circuit to trigger near
zero volts - a desirable feature

PROCEDURE:-
1. Refer the circuit diagram carry out the following connections.
2. Connect power supply in proper polarity to the kit BEL-PET

CIRCUIT DIAGRAM:-

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OBSERVATION:-
CAPTURED WAVEFORM
• Input AC waveform(Across supply) probe 10X

• Output across LED

• Waveform across SCR (A-K)

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EXPERIMENT
NO. 9

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EXPERIMENT NO:9

NAME:-

SCR Triggering Using 555

OBJECTIVE:-
To study SCR triggering using 555

THEORY:-

SCR triggering in the normal "off" state, the device restricts current to the leakage current.
When the gate-to-cathode voltage exceeds a certain threshold, the device turns "on" and
conducts current. The device will remain in the "on" state even after gate current is removed
so long as current through the device remains above the holding current. Once current falls
below the holding current for an appropriate period of time, the device will switch "off". If the
gate is pulsed and the current through the device is below the holding current, the device
will remain in the "off" state. If the applied voltage increases rapidly enough, capacitive
coupling may induce enough charge into the gate to trigger the device into the "on" state;
this is referred to as "dv/dt triggering." This is usually prevented by limiting the rate of voltage
rise across the device, perhaps by using a snubber. "dv/dt triggering" may not switch the
SCR into full conduction rapidly and the partially-triggered SCR may dissipate more power
than is usual, possibly harming the device. SCRs can also be triggered by increasing the
forward voltage beyond their rated breakdown voltage (also called as break over voltage),
but again, this does not rapidly switch the entire device into conduction and so may be
harmful so this mode of operation is also usually avoided. Also, the actual breakdown
voltage may be substantially higher than the rated breakdown voltage, so the exact trigger
point will vary from device to device. This device is generally used in switching applications.

PROCEDURE:-

1. Make the Connection as per circuit diagram.

2. Keep frequency pot of 555 at MAX (1.7 HZ) position.

OBSERVATION:-
• Observe LED flashing at O/P.
• Similarly by Varying Frequency pot of timer 555. Observe its effect on LED O/P, it will
increase frequency.
• We can observe LED flashing from 0 HZ to 35 HZ Freq.

CIRCUIT DIAGRAM:-

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OBSERVATION:-

CAPTURED WAVEFORM
• 555 o/p pulses (POT 5 maximum i.e. Frequency =1.45HZ) waveform across SCR.

• Waveform at F=2HZ

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• Waveform at F=3HZ.

• Waveform at F=5HZ.

• Waveform at F=9HZ.

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EXPERIMENT
NO. 10

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EXPERIMENT NO:10

NAME:-

SCR Time Delay Relay

OBJECTIVE:-

To study SCR time delay relay

THEORY:-

Time delay relays are built in these four basic modes of contact operation:
• Normally-open, timed-closed. Abbreviated "NOTC", these relays open immediately
upon coil de-energization and close only if the coil is continuously energized for the
time duration period. Also called normally-open, on-delay relays.
• Normally-open, timed-open. Abbreviated "NOTO", these relays close immediately
upon coil energization and open after the coil has been de-energized for the time
duration period. Also called normally-open, off delay relays
• Normally-closed, timed-open. Abbreviated "NCTO", these relays close immediately
upon coil de-energization and open only if the coil is continuously energized for the
time duration period. Also called normally-closed, on-delay relays.
• Normally-closed, timed-closed. Abbreviated "NCTC", these relays open immediately
upon coil energization and close after the coil has been de-energized for the time
duration period. Also called normally-closed, off delay relays. One-shot timers provide
a single contact pulse of specified duration for each coil energization (transition from
coil off to coil on). Recycle timers provide a repeating sequence of on-off contact pulses
as long as the coil is maintained in an energized state. Watchdog timers actuate their
contacts only if the coil fails to be continuously sequenced on and off (energized and
de-energized) at a minimum frequency.

PROCEDURE:-
1. Connect the circuit as per circuit diagram.

OBSERVATIONS:-

• At Min position of pot R1 we get 9.65V at output.(Relay ON)

• At Max position of pot R1 we get 0.4V at output.(Relay OFF)

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CIRCUIT DIAGRAM:-

OBSERVATION:-

CAPTURED WAVEFORM
• Waveform at emitter of UJT &Wave at gate of SCR POT at maximum position.

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• At POT-MID position.

• At POT-MINIMUM position.

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EXPERIMENT
NO. 11

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EXPERIMENT NO:11

NAME:-

DC Chopper

OBJECTIVE:-

To study DC chopper

THEORY:-

In electronics, a chopper circuit is used to refer to numerous types of electronic switching

devices and circuits used in power control and signal applications. A chopper is a switching
device that converts fixed DC input to a variable DC output voltage directly. Essentially, a
chopper is an electronic switch that is used to interrupt one signal under the control of
another.
In power electronics applications, since the switching element is either fully on or fully
off, its losses are low, and the circuit can provide high efficiency. However, the current
supplied to the load is discontinuous and may require smoothing or a high switching
frequency to avoid undesirable effects. In signal processing circuits, use of a chopper
stabilizes a system against drift of electronic components; the original signal can be
recovered after amplification or other processing by a synchronous demodulator that
essentially un-does the "chopping" process.
For all the chopper configurations operating from a fixed DC input voltage, the average
value of the output voltage is controlled by periodic opening and closing of the switches
used in the chopper circuit. The average output voltage can be controlled by different
techniques namely:

• Pulse width modulation technique

• Frequency modulation
• Variable frequency, variable pulse width
• CLC control

PROCEDURE:-
• Connect the circuit as per circuit diagram.
• First create +9V by using 500K POT and 12V supply.
• Then connect 9V to circuit as shown in fig.
• Change the ON time of PWM wave then observed output.

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OBSERVATIONS:-

• Observe the waveform of PWM and note down the frequency.

• Observe the waveform across load resistor 560 /2W.

CIRCUIT DIAGRAM:-

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EXPERIMENT
NO. 12

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EXPERIMENT NO:12

NAME:-

Switched Mode Converter / Rectifier.

OBJECTIVE:-

To study Switched Mode Converter / Rectifier

THEORY:-

The Switched Converter is used in SMPS circuits where the DC output voltage needs to
be lower than the DC input voltage. The DC input can be derived from rectified AC or
from any DC supply. It is useful where electrical isolation is not needed between the
switching circuit and the output, but where the input is from a rectified AC source,
isolation between the AC source and the rectifier could be provided by a mains isolating
transformer.

The Switching Converter also known as Buck Converter. The switching transistor between
the input and output of the Buck Converter continually switches on and off at high
frequency. To maintain a continuous output, the circuit uses the energy stored in the
inductor L, during the on periods of the switching transistor, to continue supplying the load
during the off periods. The circuit operation depends on what is sometimes also called a
Flywheel Circuit. This is because the circuit acts rather like a mechanical flywheel that,
given regularly spaced pulses of energy keeps spinning smoothly (outputting energy) at a
steady rate.

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For negative supplies the circuit shown in above fig. can be used. This involves a
change around in the positions of L1 and D1, and reversing the polarity of C compared
to the circuit in Fig 3.1.2. This variation of the basic buck converter now inverts the
positive DC input to produce a negative supply in the range of 0V to −V IN.

PROCEDURE:-
• Connect the circuit as per circuit diagram.
• Do the proper setting of DSO to observe o/p waveform.
• Use HPWM/LPWM as oscillated signal.

OBSERVATIONS:-

• Observe the waveform of PWM and note down the frequency.

• Observe the waveform across Capacitor 47 F/63V.

CIRCUIT DIAGRAM:-

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WAVEFORM:-

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EXPERIMENT
NO. 13

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EXPERIMENT NO: 13

NAME:-

SCR Turn ON Methods.

OBJECTIVE:-

To study SCR Turn ON Methods.

THEORY:-

The various SCR triggering methods are

• Forward Voltage Triggering

• Thermal or Temperature Triggering
• Radiation or Light triggering.
• dv/dt Triggering
• Gate Triggering

(a) Forward Voltage Triggering:-

• In this mode, an additional forward voltage is applied between anode and

cathode.
• When the anode terminal is positive with respect to cathode(VAK) , Junction J1
and J3 is forward biased and junction J2 is reverse biased.
• No current flows due to depletion region in J2 is reverse biased (except leakage
current).
• As VAK is further increased, at a voltage VBO (Forward Break Over Voltage) the
junction J2 undergoes avalanche breakdown and so a current flows and the
device tends to turn ON(even when gate is open)

(b) Thermal (or) Temperature Triggering:-

• The width of depletion layer of SCR decreases with increase in junction

temperature.
• Therefore in SCR when VAR is very near its breakdown voltage, the device is
triggered by increasing the junction temperature.
• By increasing the junction temperature the reverse biased junction collapses
thus the device starts to conduct.

(c) Radiation Triggering (or) Light Triggering:-

• For light triggered SCRs a special terminal niche is made inside the inner P
layer instead of gate terminal.

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• When light is allowed to strike this terminal, free charge carriers are generated.
• When intensity of light becomes more than a normal value, the thyristor starts
conducting.
• This type of SCRs are called as LASCR

(d) dv/dt Triggering:-

• When the device is forward biased, J1 and J3 are forward biased, J2 is reverse
biased.
• Junction J2 behaves as a capacitor, due to the charges existing across the
junction.
• If voltage across the device is V, the charge by Q and capacitance by C then,
ic = dQ/dt
Q = CV
ic = d(CV) / dt
=C. dV/dt + V. dC/dt
as dC/dt = 0
ic = C.dV/dt
• Therefore when the rate of change of voltage across the device becomes large,
the device may turn ON, even if the voltage across the device is small.

(e) Gate Triggering:-

• This is most widely used SCR triggering method.

• Applying a positive voltage between gate and cathode can Turn ON a forward
biased thyristor.
• When a positive voltage is applied at the gate terminal, charge carriers are
injected in the inner P-layer, thereby reducing the depletion layer thickness.

As the applied voltage increases, the carrier injection increases, therefore the voltage
at which forward break-over occurs decreases.

PROCEDURE:-
• We will perform Gate triggering of SCR using UJT.
• Connect the circuit as per circuit diagram.

OBSERVATION:-
• When pot R1 is at minimum position, LED will remain ON.
• As we increasing pot R1, OFF time of LED will increase and ON time of LED is
for ½ second.

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CIRCUIT DIAGRAM:-
Gate Triggering Method Using UJT

CAPTURED WAVEFORM:-
Waveform at point E of UJT (2N2646) at R1=13K waveform across LED.

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A waveform at R1=50K.

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EXPERIMENT
NO. 14

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EXPERIMENT NO:14

NAME:-

SCR Firing circuits.

OBJECTIVE:-

To study SCR Firing circuits.

THEORY:-

(i) Resistance triggering:

The following circuit shows the resistance triggering.

• In this method, the variable resistance R is used to control the gate current.
• Depending upon the value of R, when the magnitude of the gate current reaches
the sufficient value (latching current of the device) the SCR starts to conduct.
• The diode D is called as blocking diode. It prevents the gate cathode junction from
getting damaged in the negative half cycle.
• By considering that the gate circuit is purely resistive, the gate current is in phase
with the applied voltage.
• By using this method we can achieve maximum firing angle up to 90°

(ii) RC Triggering
The following circuit shows the resistance-capacitance triggering.

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• By using this method we can achieve firing angle more than 90°.
• In the positive half cycle, the capacitor is charged through the variable resistance R
up to the peak value of the applied voltage.
• The variable resistor R controls the charging time of the capacitor.
• Depends upon the voltage across the capacitor, when sufficient amount of gate
current will flow in the circuit, the SCR starts to conduct.
• In the negative half cycle, the capacitor C is charged up to the negative peak value
through the diode D2.
• Diode D1 is used to prevent the reverse break down of the gate cathode junction in
the negative half cycle.

R FIRING CIRCUIT:

PROCEDURE:-
• Connect the circuit as per circuit diagram.
• Keep the PWM knob at minimum position.
• Keep the knob of 500K POT at minimum position.
• Power ON the kit.
• Slowly increase the resistance of POT. Observe the o/p.

OBSERVATION:-
• Observe the waveform at 20T.
• Observe the waveform across LED.
• Observe the waveform across different terminals of SCR at a different position of
potentiometer.

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Waveform of R firing circuit of SCR:

When POT. Resistor at minimum position

When POT Resistor at maximum position

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Waveform of RC firing circuit of SCR

When POT Resistor at minimum position

When POT Resistor at maximum position

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EXPERIMENT
NO. 15

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EXPERIMENT NO:15

NAME:-

Time delay Circuit.

OBJECTIVE:-

To study Time delay Circuit.

THEORY:-

In many electronic circuit applications a delay of a few seconds or minutes becomes a

crucial requirement for ensuring correct operation of the circuit. Without the specified delay
the circuit could malfunction or even get damaged. The first circuit diagram shows how
transistors and a few other passive components may be connected for acquiring the
intended delay timing outputs. The transistor has been provided with the usual base
resistor for the current limiting functions. A LED which is used here just indication purposes
behaves like the collector load of the circuit. A capacitor, which is the crucial part of the
circuit gets the specific position in the circuit, we can see that it's been placed at the other
end of the base resistor and not directly to the base of the transistor.

A push button is used to initiate the circuit. On depressing the button momentarily, a
positive voltage from the supply line enters the base resistor and switches ON the transistor
and subsequently the LED. However in the course of the above action, the capacitor also
gets charged fully. On releasing the push button, though the power to the base gets
disconnected, the transistor continues to conduct with the aid of the stored energy in the
capacitor which now starts discharging its stored charge via the transistor. The LED also
stays switched ON until the capacitor gets fully discharged.

The value of the capacitor determines the time delay or for how long the transistor stays
in the conducting mode. Along with the capacitor, the value of the base resistor also plays
an important role in determining the timing for which the transistor remains switched ON
after the push button is released. However the circuit using just one transistor will be able
to produce time delays which may range only for a few seconds. By adding one more
transistor stage (next figure) the above time delay range can be increased significantly.
The addition of another transistor stage increases the sensitivity of the circuit, which
enables the use of larger values of the timing resistor thereby enhancing the time delay
range of the circuit.

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CIRCUIT DIAGRAM:-

Circuit 1

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Circuit 2

PROCEDURE:-
• Connect the circuit as per circuit diagram.
• Then close the switch, LED will glow immediately.
• Open the switch, LED will remain in ON condition for particular time period & then
OFF the LED slowly.

OBSERVATION:-
• Observe the LED when switched ON & OFF position.
• Observe the delay time required to OFF the LED.
• Calculate the delay Time.

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EXPERIMENT
NO. 16

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EXPERIMENT NO: 15

NAME:-

AC Voltage Controller

OBJECTIVE:-

To study AC Voltage Controller by using TRAIC.

THEORY:-

A voltage controller, also called an AC voltage controller or AC regulator is an electronic

module based on either thyristors, TRIACs ,SCRs or IGBTs, which converts a fixed voltage,
fixed frequency alternating current (AC) electrical input supply to obtain variable voltage in
output delivered to a resistive load. This varied voltage output is used for dimming street
lights, varying heating temperatures in homes or industry, speed control of fans and winding
machines and many other applications, in a similar fashion to an autotransformer. Voltage
controller modules come under the purview of power electronics. Because they are low-
maintenance and very efficient, voltage controllers have largely replaced such modules as
magnetic amplifiers and saturable reactors in industrial use.

Modes of Operation
Voltage controllers work in two different ways; either through "on-and-off control" or
through "phase control".

ON-and-OFF control
In an on-and-off controller, thyristors are used to switch on the circuits for a few cycles
of voltage and off for certain cycles, thus altering the total RMS voltage value of the output
and acting as a high speed AC switch. The rapid switching results in high frequency
distortion artifacts which can cause a rise in temperature, and may lead to interference in
nearby electronics. Such designs are not practical except in low power applications.

Phase angle control

In phase angle control, thyristors are used to halve the voltage cycle during input. By
controlling the phase angle or trigger angle, the output RMS voltage of the load can be
varied. The thyristor is turned on for every half-cycle and switched off for each remaining
half-cycle. The phase angle is the position at which the thyristor is switched on. TRIACs
are often used instead of thyristors to perform the same function for better efficiency. If the
load is a combination of resistance and inductance, the current cycle lags the voltage cycle,
decreasing overall power output.

CIRCUIT DIAGRAM:-

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PROCEDURE:-

• Connect the circuit as per circuit diagram.

• Keep PWM knob at minimum position so observed sine wave at 20T.
• Initially keep POT Resistance at maximum position. Switch ON the kit.
• LED will not glow, then decrease resistance of POT.
• At particular point LED start glowing.

OBSERVATION:-
• Observe the LED when POT Resistance at maximum & minimum position.
• Observe the waveform across LED.
• Observed the waveforms across different terminals of TRAIC.

WAVEFORMS:-

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When POT resistance at maximum position

When POT resistance at minimum position

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