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SMPS Trainer
NV7002
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Learning Material
Ver 1.1
Designed & Manufactured by:
141-B, Electronic Complex, Pardesipura, Indore- 452 010 India, Tel.: 91-731- 4211500,
Telefax: 91-731-4202959, Toll free: 1800-103-5050, E-mail: [email protected]
Website: www.nvistech.com
NV7002
SMPS Trainer
NV7002
Table of Contents
1.
Introduction
3
2.
Features
4
3.
Technical Specifications
5
4.
Theory
6
5.
EMI (Electromagnetic Interference Filter)
11
 Experiment 1
Study of Primary rectifier and Filter section
16
 Experiment 2
Study of Switching Transformer
19
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7.
Switching Transformer
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6.
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 Experiment 3
Study of PWM switching device
27
MOSFET Switching Device
Optocoupler
Regulation Section
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 Experiment 5
Study of Regulation
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 Experiment 4
Study of Optocoupler
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 Experiment 7
Study of various faults and Procedure of their trouble shooting
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 Experiment 6
Study of SMPS with Variac input (Variable AC)-Regulation Test
10.
Warranty
37
11.
List of Accessories
37
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Introduction
NV7002 SMPS trainer is a very adaptable kit has been designed to explain a very
remarkable and frequently used switching based power supply-The SMPS (Switched
Mode Power Supply).
The kit is designed keeping in mind that a student can comprehend each block of
SMPS in a very easy way. Different test points have been provided so that one can
observe the inputs and outputs of each block contained. Being different from a
conventional block diagram internal structures of different blocks are also shown.
Switching Transformer and Chopper (The Heart of SMPS) are presented in such a
way that a student can readily understand their functioning and pin configuration.
Since SMPS is different from a traditional power supplies because it can be used for
different voltage inputs (from 80V to 300V AC).
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Figure 1
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Features

A Low cost trainer kit demonstrating all basic concepts of SMPS

In Depth elucidation of Switching Transformer, that is one of the most
important components of SMPS

Variac can be connected with the kit

Fault identification feature enabled

Easy illustration of each block

Designed with considering all safety standards

Learning Material
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Technical Specifications
Mains
:
80 to 230V AC, 50/60Hz.
Input of Transformer
:
320V switching DC at 132 kHz.
Output of Transformer
:
30V AC
:
+12V DC regulated
Switching Transformer specifications
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DC Outputs of kit
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-12V DC regulated
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+5V DC regulated.
:
:
355×260×125mm
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Dimensions
Current rating 500mA
500mA
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Theory
SMPS compared with linear “Power Supply Unit”.
There are two main types of regulated power supplies available: SMPS and Linear.
The reasons for choosing one type or the other can be summarized as follows.
Size and weight : Linear power supplies use a transformer operating at the
Mains frequency of 50/60Hz. This component is larger and heavier by several
times than the corresponding smaller transformer in an SMPS, which runs at a
higher frequency (usually above the highest audible frequency, around 50kHz to
400kHz)

Efficiency : Linear power supplies regulate their output by using a higher
voltage in the initial stages and then expending some of it as heat to improve the
power quality. This power loss is necessary to the circuit, and can be reduced
but never eliminated by improving the design, even in theory. SMPSs draw
current at full voltage based on a variable duty cycle, and can increase or
decrease their power consumption to regulate the load as required.
Consequently, a well designed SMPS will be more efficient.

Heat output or power dissipation : A linear supply will regulate the voltage or
current by wasting excess voltage or current as heat, which is very inefficient. A
regulated SMPS will regulate using Pulse Width Modulation or, at power ratings
below 30W, ‘On/Off’ control. In all SMPS topologies, the transistors are always
fully on or fully off. Thus, an "ideal" SMPS will be 100% efficient. The only
heat generated is because ideal components do not exist. Switching losses in the
main switching transistors, non-zero resistance in the "on" state, and rectifier
voltage drop will produce a fair amount of heat. However, by optimizing SMPS
design, the amount of heat produced can be minimized. A good design can have
an efficiency of more than 95%.

Complexity : A linear regulator ultimately consists of a power transistor,
voltage regulating IC and a noise filtering capacitor. An SMPS typically
contains PWM controller, one or several power transistors and diodes as well as
power transformer, inductor and filter capacitors. Multiple voltages can be
generated by one transformer core. For this an SMPS has to use pulse width
modulation on the primary winding and "post-regulating" such as phase control
on the secondary windings, while the linear PSU normally uses independent
voltage regulators for the auxiliary outputs. Both need a careful design for their
transformers, which therefore are often produced in series and available in stock.
Due to the high frequencies in SMPS the inductances and capacitances of the
traces become important.

Radio frequency interference : The currents in a SMPS are switched at a high
frequency. This high-frequency currents can generate undesirable
electromagnetic interference. EMI filters and RF shielding are needed to reduce
the disruptive interference. Linear PSUs, however, generally do not produce
interference.
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
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Electronic noise at the output terminals : Inexpensive linear PSUs with poor
regulation may experience a small AC voltage "riding on" the DC output at
twice Mains frequency (100/120Hz). These "ripples" are usually on the order of
millivolts, and can be suppressed with larger filter capacitors or better voltage
regulators. This small AC voltage can cause problems in some circuits. Quality
linear PSUs will suppress ripples much better. SMPS usually do not exhibit
ripple at the power-line frequency, but do have generally noisier outputs than
linear PSUs; the noise may be correlated with the SMPS switching frequency or
it may also be more broad-band.

Acoustic noise : Linear PSUs typically give off a faint, low frequency hum at
Mains frequency, but this is seldom audible. (The transformer is responsible.)
SMPSs, with their much higher operating frequencies, are not usually audible to
humans (unless they have a fan, in the case of most computer SMPSs). A
malfunctioning SMPS may generate high-pitched sounds, since they do in fact
generate acoustic noise at the oscillator frequency.

Power factor : The current drawn by simple SMPS is non-sinusoidal and do not
follow the supply's input voltage waveform, so the early SMPS designs have a
mediocre power factor of about 0.6, and their use in personal computers and
compact fluorescent lamps presented a growing problem for power distribution.
Power factor correction (PFC) circuits can reduce this problem, and are required
in some countries (European in particular) by regulation. Linear PSUs also do
not have unity power factors, but are not as problematic as SMPSs.

Electronic noise at the input terminals : In a similar fashion, very low cost
SMPS may couple electrical noise back onto the Mains power line; Linear PSUs
rarely do this.
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How an SMPS works?
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
Figure 2
Block diagram of a Mains operated AC-DC SMPS with output voltage
regulation.
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Input rectifier stage :
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Figure 3
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AC, half-wave and full wave rectified signals :
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If the SMPS has an AC input, then its first job is to convert the input to DC. This is
called rectification. The rectifier circuit can be configured as a voltage doubler by the
addition of a switch operated either manually or automatically. This is a feature of
larger supplies to permit operation from nominally 120volt or 240volt supplies. The
rectifier produces an unregulated DC voltage which is then sent to a large filter
capacitor. The current drawn from the Mains supply by this rectifier circuit occurs in
short pulses around the AC voltage peaks. These pulses have significant high
frequency energy which reduces the power factor. Special control techniques can be
employed by the following SMPS to force the average input current to follow the
sinusoidal shape of the AC input voltage thus the designer should try correcting the
power factor. A SMPS with a DC input does not require this stage. A SMPS designed
for AC input can often be run from a DC supply, as the DC passes through the
rectifier stage unchanged. (The user should check the manual before trying this,
though most supplies are quite capable of such operation even though no clue is
provided in the manual!)
If an input range switch is used, the rectifier stage is usually configured to operate as a
voltage doubler when operating on the low voltage (~120VAC) range and as a straight
rectifier when operating on the high voltage (~240VAC) range. If an input range
switch is not used, then a full-wave rectifier is usually used and the downstream
inverter stage is simply designed to be flexible enough to accept the wide range of dc
voltages that will be produced by the rectifier stage. In higher-power SMPSs, some
form of automatic range switching may be used.
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Inverter stage :
The inverter stage converts DC, whether directly from the input or from the rectifier
stage described above, to AC by running it through a power oscillator, whose output
transformer is very small with few windings at a frequency of tens or hundreds of
kilohertz (kHz). The frequency is usually chosen to be above 20kHz, to make it
inaudible to humans. The output voltage is optically coupled to the input and thus
very tightly controlled. The switching is implemented as a multistage (to achieve high
gain) MOSFET amplifier. MOSFETs are a type of transistor with a low on-resistance
and a high current-handling capacity. This section refers to the block marked
"Chopper" in the block diagram.
Voltage converter and output rectifier :
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If the output is required to be isolated from the input, as is usually the case in Mains
power supplies, the inverted AC is used to drive the primary winding of a highfrequency transformer. This converts the voltage up or down to the required output
level on its secondary winding. The output transformer in the block diagram serves
this purpose.
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If a DC output is required, the AC output from the transformer is rectified. For output
voltages above ten volts or so, ordinary silicon diodes are commonly used. For lower
voltages, Schottky diodes are commonly used as the rectifier elements; they have the
advantages of faster recovery times than silicon diodes (allowing low-loss operation
at higher frequencies) and a lower voltage drop when conducting. For even lower
output voltages, MOSFET transistors may be used as synchronous rectifiers;
compared to Schottky diodes, these have even lower "on"-state voltage drops.
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The rectified output is then smoothed by a filter consisting of inductors and
capacitors. For higher switching frequencies, components with lower capacitance and
inductance are needed.
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Simpler, non-isolated power supplies contain an inductor instead of a transformer.
This type includes boost converters, buck converters, and the so called buck-boost
converters. These belong to the simplest class of single input, single output converters
which utilise one inductor and one active switch (MOSFET). The buck converter
reduces the input voltage, in direct proportion, to the ratio of the active switch "on"
time to the total switching period, called the Duty Ratio. For example an ideal buck
converter with a 10V input operating at a duty ratio of 50% will produce an average
output voltage of 5V. A feedback control loop is employed to maintain (regulate) the
output voltage by varying the duty ratio to compensate for variations in input voltage.
The output voltage of a boost converter is always greater than the input voltage and
the buck-boost output voltage is inverted but can be greater than, equal to, or less than
the magnitude of its input voltage. There are many variations and extensions to this
class of converters but these three form the basis of almost all isolated and nonisolated DC to DC converters. By adding a second inductor the Ćuk and SEPIC
converters can be implemented or by adding additional active switches various bridge
converters can be realized.
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Other types of SMPS use a capacitor-diode voltage multiplier instead of inductors and
transformers. These are mostly used for generating high voltages at low currents. The
low voltage variant is called charge pump.
Regulation :
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A feedback circuit monitors the output voltage and compares it with a reference
voltage, which is set manually or electronically to the desired output. If there is an
error in the output voltage, the feedback circuit compensates by adjusting the timing
with which the MOSFETs are switched on and off. This part of the power supply is
called the switching regulator. The "Chopper controller" shown in the block diagram
serves this purpose. Depending on design/safety requirements, the controller may or
may not contain an isolation mechanism (such as opto-couplers) to isolate it from the
DC output. Switching supplies in computers, TVs and VCRs have these opto-couplers
to tightly control the output voltage.
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Open-loop regulators do not have a feedback circuit. Instead, they rely on feeding a
constant voltage to the input of the transformer or inductor, and assume that the
output will be correct. Regulated designs work against the parasitic capacity of the
transformer or coil, monopolar designs also against the magnetic hysteresis of the
core.
Power factor :
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The feedback circuit needs power to run before it can generate power, so an additional
non-switching power-supply for stand-by is added.
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Early switched mode power supplies incorporated a simple full wave rectifier
connected to a large energy storing capacitor. Such SMPS draws current from the AC
line in short pulses when the Mains instantaneous voltage exceeds the voltage across
this capacitor. During the remaining portion of the AC cycle the capacitor provides
energy to the power supply. As the result, input current of such basic switched mode
power supplies has high harmonics content and relatively low power factor. This
creates extra load on utility lines, increases heating of the utility transformers, and
may cause stability problems in some applications such as in emergency generator
systems or aircraft generators. In 2001 the European Union put into effect the
standard IEC/EN61000-3-2 to set limits on the harmonics of the AC input current up
to the 40th harmonic for equipment above 75W. The standard defines four classes of
equipment depending on its type and current waveform. The most rigorous limits
(class D) are established for personal computers, computer monitors, and TV
receivers. In order to comply with these requirements modern switched-mode power
supplies normally include an additional power factor correction (PFC) stage.
Applications :
Switched-mode PSUs in domestic products such as personal computers often have
universal inputs, meaning that they can accept power from most Mains supplies
throughout the world, with rated frequencies from 50Hz to 60Hz and voltages from
100V to 240V (although a manual voltage "range" switch may be required). In
practice they will operate from a much wider frequency range and often from a DC
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supply as well. In 2006, Intel proposed the use of a single 12V supply inside PCs, due
to the high efficiency of switch mode supplies directly on the PCB. Most modern
desktop and laptop computers already have a DC-DC converter on the motherboard,
to step down the voltage from the PSU or the battery to the CPU core voltage -typically 1.8V as of 1998. Most laptop computers also have a DC-AC inverter to step
up the voltage from the battery to drive the backlight, typically around 1000 Vrms.
Cars, trucks, telecom lines, and production plants, but not planes, supply DC to avoid
hum and ease the integration of capacitors and batteries used to buffer the voltage.
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In the case of TV sets, for example, one can test the excellent regulation of the power
supply by using a variac. For example, in some models made by Philips, the power
supply starts when the voltage reaches around 90volts. From there, one can change
the voltage with the variac, and go as low as 40volts and as high as 260, and the
image will show absolutely no alterations.
Electromagnetic Interference
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What is EMI?
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Electromagnetic interference (also called EMI, radio frequency interference, or RFI)
is an unwanted disturbance caused in a radio receiver or other electrical circuit by
electromagnetic radiation emitted from an external source. The disturbance may
interrupt, obstruct, or otherwise degrade or limit the effective performance of the
circuit. The source may be any Objective, artificial or natural, that carries rapidly
changing electrical currents, such as an electrical circuit, the Sun or the Northern
Lights. EMI can be induced intentionally, as in some forms of electronic warfare, or
unintentionally, as a result of spurious emissions and responses, intermodulation
products, and the like. It frequently affects the reception of AM radio in urban areas.
It can also affect FM radio and television reception, although to a lesser extent.
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The most important means of reducing EMI are the use of bypass or "decoupling"
capacitors on each active device (connected across the power supply, as close to the
device as possible), rise time control of high-speed signals using series resistors, and
VCC filtering. Shielding is usually a last resort after other techniques have failed
because of the added expense of RF gaskets and the like.
The efficiency of the radiation depends on the height above the ground or power plane
(at RF one is as good as the other) and the length of the conductor in relation to the
wavelength of the signal component (fundamental, harmonic or transient (overshoot,
undershoot or ringing)). At lower frequencies, such as 133MHz, radiation is almost
exclusively via I/O cables; RF noise gets onto the power planes and is coupled to the
line drivers via the VCC and ground pins. The RF is then coupled to the cable through
the line driver as common-mode noise. Since the noise is common-mode, shielding
has very little effect, even with differential pairs. The RF energy is capacitive coupled
from the signal pair to the shield and the shield itself does the radiating. One cure for
this is to use a braid-breaker to reduce the common-mode signal.
At higher frequencies, usually above 500MHz, traces get electrically longer and
higher above the plane. Two techniques are used at these frequencies: wave shaping
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with series resistors and embedding the traces between the two planes. If all these
measures still leave too much EMI, shielding such as RF gaskets and copper tape can
be used. Most digital equipment is designed with metal, or coated plastic, cases.
Switching power supplies can be a source of EMI, but have become less of a problem
as design techniques have improved.
Most countries have legal requirements that electronic and electrical hardware must
still work correctly when subjected to certain amounts of EMI, and should not emit
EMI which could interfere with other equipment (such as radios).
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EMI filters are used to keep stray signals from polluting your design. Commonly
known as "feed through", the basic EMI filter is a low-pass filter, and uses a
combination of shunt capacitance and series inductance to prevent EM signals from
entering your housing our enclosure. EMI is electromagnetic interference and is called
conducted emissions or radiated emissions or radiated emissions. Conducted
emissions mean any unwanted signal or noise on the wiring or copper. The reason for
the reference to power cabling is that EMI filters are the part of the power wiring and
are designed to remove these unwanted properties from the copper wiring when any
current flow creates an associated magnetic field. You cannot have one without the
other. Therefore, this high frequency unwanted signal creates a magnetic field that can
interfere with surrounding equipment. It is the filter’s function to remove this current
so that its associated magnetic field will not interfere. This noise can originate either
from the line or from the associated equipment that the filter is built into. From the
equipment side, the noise could be coming from computer clock frequencies, parasitic
oscillations in the switcher power supply inductors or transformers, power supply
diode noise, harmonics of the line frequencies due to the high peak current charging
the power supply storage capacitor, and many other sources. From the line, the noise
could be due to flattening of the sine wave voltage caused by the high peak currents
slightly ahead of 90 and 270 degrees due to the total of the power supplies fed from
the line without power factor correction circuitry. This generates odd harmonics that
feed the EMI filter. Other sources of noise from the line are other equipment without
any filtering and heavy surges of equipment being turned on and off. Lighting and
EMPs (Electromagnetic pulses, possibly from nuclear explosions) create other line
problems for the filter.
To review, EMI is any unwanted signal from either the power line or the equipment
and must be removed to prevent a magnetic field from interfering with closely
associated equipment or to stop a malfunction of the equipment containing the filter.
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EMI waveforms
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Figure 4
All electronic devices give off electromagnetic emissions. This is radiation that is a
byproduct of electrical or magnetic activity. Unfortunately, the emissions from one
device can interfere with other devices, causing potential problems. Interference can
lead to data loss, picture quality degradation on monitors, and other problems with
your PC, or problems with other devices such as television sets and radios. These are
generally categorized as electromagnetic interference or EMI problems.
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There are actually two different issues here: EMI emissions by the PC and EMI
emissions received by the PC. PCs generally do not cause very much interference
with other devices; they are required by the Federal Communications Commission
(FCC) to be certified as Class B devices. This certification is used to show that the PC
conforms to standards that limit the amount of EMI that a PC can produce. The only
catch to this is that you have to keep the cover on the PC. This is one reason why the
cover is always made from metal. (Keeping the cover on is also an important part of
ensuring proper ventilation).
PCs can be affected by electromagnetic interference from other devices, in two major
ways. One is direct effects through proximity with other devices; another is electrical
interference over the power lines. Most PCs generally do not have many problems
with EMI, but those that do can cause incredible frustrating to their owners. There are
several things that you can do to avoid or at least reduce EMI if you think it is
affecting your PCs :
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Physical Isolation : Devices that emit electromagnetic radiation should be kept
a reasonable distance from your PC, peripherals and media. This includes
television sets, radios, lights, kitchen appliances, and stereo speakers (the ones
designed for use with PCs are generally shielded and are much less of an issue).

Use Dedicated Circuits : Many office buildings especially, have separate
power circuits that are intended for use by PCs. Keeping your PC on a circuit
that is separate from the circuit running your refrigerator and air conditioning
unit means that there will be much less interference passing to the computer
from the other devices (and this will also improve the quality of the power being
sent to your machine in general).

Power Conditioning : The use of a line conditioner or uninterruptible power
supply can filter out interference caused by other devices that share a line with
your PC.
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
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Experiment 1
Objective :
Study of Primary Rectifier and Filter section.
Equipments Needed :
1.
Oscilloscope
2.
DMM (Digital Multimeter)
3.
Attenuator Probe (1:10)
Procedure:
Before performing experiment first select ‘AC Mains/From Variac’ switch of
the Trainer kit at ‘AC Mains’ position and all Fault switches at ‘Off’ position.
2.
Now connect the Mains cord into the Trainer kit and switch ‘On’ the power
supply.
3.
Connect Oscilloscope at TP1 with (1:10) attenuator probe at ×10 position, which
is nothing but a sine wave; record its frequency and amplitude in Observation
table.
4.
Now connect a DMM (at higher DC voltmeter range) across TP4 and Ground
(TP21) and check the voltage. It will be a pulsating DC high voltage.
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1.
From this experiment you can observe following parameters :
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Voltage at TP1
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Parameter
---------------Vpp
--------------Vrms
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Frequency at TP1
---------------Hz
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Switching Transformer
How it works?
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Unlike Mains transformers and audio transformers, a Switching Transformer is
designed not just to transfer energy, but also to store it for a significant fraction of the
switching period. This is achieved by winding the coils on a ferrite core with an air
gap. The air gap increases the reluctance of the magnetic circuit and therefore its
capacity to store energy.
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The primary winding of the Switching Transformer is driven by a relatively low
voltage saw tooth wave, which is ramped up (and sweeping the beam across the
screen to draw a line) and then abruptly switched off (and causing the beam to quickly
fly back from the right to the left of the display) by the horizontal output stage. This is
a ramped and pulsed waveform that repeats at the horizontal (line) frequency of the
display. The fly back (vertical portion of the saw tooth wave) is extremely useful to
the fly back transformer: the faster a magnetic field collapses, the greater the induced
voltage. Furthermore, the high frequency reduces the size of the transformer. In
television sets, this high frequency is about 15 kilohertz (15,750Hz for NTSC), and
vibrations from the related circuitry can often be heard as a high-pitched whine. In
modern computer displays the frequency can vary over a wide range, from about
30kHz to 150kHz.
The alternating current coming from the fly back transformer is converted to direct
current by a high-voltage rectifier. If the output voltage of the Switching Transformer
is not high enough by itself, the rectifier is replaced by a voltage multiplier.
Conversely, early color television sets used a regulator to control the high voltage.
The rectified voltage is then used to charge the anode of the cathode ray tube. There
are often auxiliary secondary windings that produce lower voltages for driving other
parts of the display's circuitry — often the CRT's filament will be driven from the fly
back. In tube sets, a two-turn filament winding is located on the opposite side of the
core as the HV secondary, used to drive the rectifier tube.
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Practical considerations :
In modern displays, the Switching Transformer, voltage multiplier and rectifier are
often integrated into a single package on the main circuit board. There is usually a
thick wire from the Switching Transformer to the anode terminal (covered by a rubber
cap) on the side of the picture tube. The thickness of this wire is mostly due to the
thickness of the plastic insulation, the copper conductor inside being much thinner as
it carries only a small current.
Construction :
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One advantage of operating the transformer at the fly back frequency is that it can be
much smaller and lighter than a comparable transformer operating at Mains (line)
frequency. Another advantage is that it provides a failsafe mechanism — should the
horizontal deflection circuitry fails; the fly back transformer will cease operating and
shut down the rest of the display, preventing the screen burn that would otherwise
result from a stationary electron beam.
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Failure :
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Around a ferrite rod the primary is wound first and around this the secondary. This is
to reduce the leakage inductance of the primary. And around this a ferrite frame
closes the magnetic field lines. The gap between the rod and the frame is air gap with
reduces the remanence. The secondary is wound layer by layer with enameled wire
with Mylar foil between the layers. In this way parts of the wire with higher voltage
between them have more dielectric material between them. The outside of the
winding is on the highest voltage so insulation and screening may be needed to
protect the surrounding. In a variant, to avoid some stray capacity, every layer of the
windings is connected by a rectifying diode to the next layer. Windings go up the rod
and the diodes go down. In this way the AC voltage increases along the rod (axial)
and the DC voltage increases radial from inside to outside. When applied to tape
wound coils this would mean each coil goes from inside to outside and the diode goes
back to the inside.
Fly back transformers are a frequent source of failure for television sets; the high
voltage present in the many turns of wire with the somewhat thin insulation required
for the transformer to be of reasonable size is likely to eventually result in leakage at
one point or another; as the leakage heats the insulation it carbonizes and conducts
more, which leads to even more heat and carbonization, until the leaked current is
high enough for the high voltage to cease to function. As a result, replacement fly
back transformers for almost every set on the market are available through dealers in
electronic parts, typically for a few tens of dollars. The problem is exacerbated by the
tendency of the fly back to accumulate a coating of dust due to electrostatic attraction,
which serves as a path to ground for leaks which might otherwise not be of sufficient
magnitude to initiate the chain of events leading to destructive failure, as described.
As a result, occasional cleaning of the accumulated dust from the high voltage
circuitry inside a television can be beneficial, provided the proper precautions are
taken, as below.
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A fly back transformer and its associated circuitry operate at very high voltages at low
currents (4-15ma), far beyond Mains voltage. While most fly backs do not supply
enough power to kill directly, the voltage they employ can cause violent muscle
spasms if touched; and such spasms usually cause injury. Therefore, only trained
persons should touch or modify these devices, after first ensuring that the transformer
is switched off and any stored energy has been safely discharged. The CRT has an
inherent capacitance which can hold a high voltage charge for a period up to several
days after the power is switched off. Often, a high-resistance bleeder resistor is
connected in parallel to ensure the charge is safely grounded when not in use, but it is
not wise to assume that this is the case.
In many recent televisions, after replacing the fly back transformer, the control
firmware must be recalibrated to account for slight differences in performance
between transformers in order to maintain accurate color reproduction.
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Experiment 2
Objective :
Study of Switching Transformer and its working.
Equipments Needed :
1.
Oscilloscope
2.
DMM (Digital Multimeter)
3.
Attenuator Probe (1:10)
Procedure :
Before performing experiment first select ‘AC Mains/From Variac’ switch of
the Trainer kit at ‘AC Mains’ position and all Fault switches at ‘Off’ position.
2.
Now connect the Mains cord into the Trainer kit and switch ‘On’ the power
supply.
3.
Connect Oscilloscope with (1:10) attenuator probe at ×10 position, at TP4 and
observe the waveform with respect to Ground (TP21), which is nothing but a
PWM waveform, this signal is generated by Tiny switch IC TNY268P which
generates the PWM signal.
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Note : To observe this waveform triggered on Oscilloscope, use Normal
triggering with Level adjustment at Time base position of 5-10 μs and vertical
sensitivity of 10 V/div.
Figure 6
4.
Observe the average frequency of this waveform on Oscilloscope which is
approximately 132kHz.
5.
Now to measure the output of transformer, for this connect DMM (at DC
voltmeter range) at TP7 with respect to TP6, which is approximately 30V DC.
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6.
Similarly you can measure the voltages at other points of transformer like TP8,
TP9, TP10 with respect to TP6.
From this experiment you can observe following parameters :
Value
Frequency of this PWM signal
---------------- kHz
Output voltages of transformer at
TP7 with respect to TP6
TP8 with respect to TP6
TP9 with respect to TP6
TP10 with respect to TP6
------------------V DC
------------------V DC
------------------V DC
------------------V DC
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Parameter
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MOSFET Switching Device
This IC has been used to switch the input waveform of transformer since it is in DC
form. This switching is done at very high frequency (about 132kHz), which behaves
like approximate AC.
Tiny Switch’s Features :
Fully integrated auto-restart for short circuit and open loop fault protection–
saves external component costs.

Built-in circuitry practically eliminates audible noise with ordinary varnished
transformer.

Programmable line under-voltage detect feature prevents power on/off glitches–
saves external components.

Frequency jittering dramatically reduces EMI (~10dB) –minimizes EMI filter
component costs.

132 kHz operation reduces transformer size–allows use of EF12.6 or EE13 cores
for low cost and small size.

Very tight tolerances and negligible temperature variation on key parameters
eases design and lowers cost.

Lowest component count switcher solution.
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Description:
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Tiny Switch-II maintains the simplicity of the Tiny Switch topology, while providing
a number of new enhancements to further reduce system cost and component count,
and to practically eliminate audible noise. Like Tiny Switch, a 700V power MOSFET,
oscillator, high voltage switched current source, current limit and thermal shutdown
circuitry are integrated onto a monolithic device. The start-up and operating power are
derived directly from the voltage on the DRAIN pin, eliminating the need for a bias
winding and associated circuitry. In addition, the PI-2684-101700 Wide-Range HV
DC Input D, S EN/UV, BP, +, - , +, -, DC Output.
Pin Functional Description:
Figure 7
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DRAIN (D) Pin:
Power MOSFET drain connection. Provides internal operating current for both startup and steady-state operation.
BYPASS (BP) Pin:
Connection point for a 0.1μF external bypass capacitor for the internally generated
5.8V supply.
Enable/Under-Voltage (EN/UV) Pin:
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Source (S) Pin:
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This pin has dual functions: enable input and line under-voltage sense. During normal
operation, switching of the power MOSFET is controlled by this pin. MOSFET
switching is terminated when a current greater than 240μA is drawn from this pin.
This pin also senses line under-voltage conditions through an external resistor
connected to the DC line voltage. If there is no external resistor connected to this pin,
Tiny Switch-II detects its absence and disables the line under voltage function.
Control circuit common, internally connected to output MOSFET source.
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Source (HV RTN) Pin:
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Functional Description :
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Output MOSFET source connection for high voltage return.
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Tiny Switch-II combines a high voltage power MOSFET switch with a power supply
controller in one device. Unlike conventional PWM (Pulse Width Modulator)
controllers, Tiny Switch-II uses a simple ‘On/Off’ control to regulate the output
voltage.
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The Tiny Switch-II controller consists of an Oscillator, Enable Circuit (Sense and
Logic), Current Limit State Machine, 5.8V Regulator, Bypass pin Under-Voltage
Circuit, over
Temperature Protection, Current Limit Circuit, Leading Edge Blanking and a 700V
power MOSFET. Tiny Switch-II incorporates additional circuitry for Line UnderVoltage Sense, Auto-Restart and Frequency Jitter. Figure 2 shows the functional
block diagram with the most important features.
Oscillator:
The typical oscillator frequency is internally set to an average of 132 kHz. Two
signals are generated from the oscillator: the Maximum Duty Cycle signal (DCMAX)
and the Clock signal that indicates the beginning of each cycle. The Tiny Switch-II
oscillator incorporates circuitry that introduces a small amount of frequency jitter,
typically 8 kHz peak-to-peak, to minimize EMI emission. The modulation rate of the
frequency jitter is set to 1 kHz to optimize EMI reduction for both average and quasipeak emissions. The frequency jitter should be measured with the oscilloscope
triggered at the falling edge of the DRAIN waveform. The waveform in Figure4
illustrates the frequency jitter of the Tiny Switch-II.
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Enable Input and Current Limit State Machine:
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The enable input circuit at the EN/UV pin consists of a low impedance source
follower output set at 1.0V. The current through the source follower is limited to
240μA. When the current out of this pin exceeds 240μA, a low logic level (disable) is
generated at the output of the enable circuit. This enable circuit output is sampled at
the beginning of each cycle on the rising edge of the clock signal. If high, the power
MOSFET is turned on for that cycle (enabled). If low, the power MOSFET remains
off (disabled). Since the sampling is done only at the beginning of each cycle,
subsequent changes in the EN/UV pin voltage or current during the remainder of the
cycle are ignored. The Current Limit State Machine reduces the current limit by
discrete amounts at light loads when Tiny Switch-II is likely to switch in the audible
frequency range. The lower current limit raises the effective switching frequency
above the audio range and reduces the transformer flux density including the
associated audible noise. The state machine monitors the sequence of EN/UV pin
voltage levels to determine the load condition and adjusts the current limit level
accordingly in discrete amounts. Under most operating conditions (except when close
to no load), the low impedance of the source follower keeps the voltage on the
EN/UV pin from going much below 1.0V in the disabled state. This improves the
response time of the optocoupler that is usually connected to this pin.
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5.8V Regulator and 6.3V Shunt Voltage Clamp :
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The 5.8V regulator charges the bypass capacitor connected to the BYPASS pin to
5.8V by drawing a current from the voltage on the DRAIN pin, whenever the
MOSFET is off. The BYPASS pin is the internal supply voltage node for the Tiny
Switch-II. When the MOSFET is on, the Tiny Switch-II operates from the energy
stored in the bypass capacitor. Extremely low power consumption of the internal
circuitry allows Tiny Switch-II to operate continuously from current it takes from the
DRAIN pin. A bypass capacitor value of 0.1μF is sufficient for both high frequency
decoupling and energy storage.
In addition, there is a 6.3V shunt regulator clamping the BYPASS pin at 6.3V when
current is provided to the BYPASS pin through an external resistor. This facilitates
powering of Tiny Switch-II externally through a bias winding to decrease the no load
consumption to about 50mW.
BYPASS Pin Under-Voltage:
The BYPASS pin under-voltage circuitry disables the power MOSFET when the
BYPASS pin voltage drops below 4.8V. Once the BYPASS pin voltage drops below
4.8V, it must rise back to 5.8V to enable (turn-on) the power MOSFET.
IC operation:
Tiny Switch-II devices operate in the current limit mode. When enabled, the oscillator
turns the power MOSFET on at the beginning of each cycle. The MOSFET is turned
off when the current ramps up to the current limit or when the DCMAX limit is
reached. As the highest current limit level and frequency of a Tiny Switch-II design
are constant, the power delivered to the load is proportional to the primary inductance
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of the transformer and peak primary current squared. Hence, designing the supply
involves calculating the primary inductance of the transformer for the maximum
output power required. If the Tiny Switch-II is appropriately chosen for the power
level, the current in the calculated inductance will ramp up to current limit before the
DCMAX limit is reached.
Enable Function:
Tiny Switch-II senses the EN/UV pin to determine whether or not to proceed with the
next switch cycle as described earlier. The sequence of cycles is used to determine the
current limit. Once a cycle is started, it always completes the cycle (even when the
EN/UV pin changes state half way through the cycle). This operation results in a
power supply in which the output voltage ripple is determined by the output capacitor,
amount of energy per switch cycle and the delay of the feedback.
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The EN/UV pin signal is generated on the secondary by comparing the power supply
output voltage with a reference voltage. The EN/UV pin signal is high when the
power supply output voltage is less than the reference voltage.
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In a typical implementation, the EN/UV pin is driven by an optocoupler. The collector
of the optocoupler transistor is connected to the EN/UV pin and the emitter is
connected to the Source pin. The optocoupler LED is connected in series with a Zener
diode across the DC output voltage to be regulated. When the output voltage exceeds
the target regulation voltage level (optocoupler LED voltage drop plus Zener voltage),
the optocoupler LED will start to conduct, pulling the EN/UV pin low. The Zener
diode can be replaced by a TL431 reference circuit for improved accuracy.
‘On/Off’ Operation with Current Limit State Machine:
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The internal clock of the Tiny Switch-II runs all the time. At the beginning of each
clock cycle, it samples the EN/UV pin to decide whether or not to implement a switch
cycle, and based on the sequence of samples over multiple cycles, it determines the
appropriate current limit. At high loads, when the EN/UV pin is high (less than
240µA out of the pin), a switching cycle with the full current limit occurs. At lighter
loads, when EN/UV is high, a switching cycle with a reduced current limit occurs.
At near maximum load, Tiny Switch-II will conduct during nearly all of its clock
cycles at slightly lower load, it will “skip” additional cycles in order to maintain
voltage regulation at the power supply output. At medium loads, cycles will be
skipped and the current limit will be reduced. At very light loads, the current limit
will be reduced even further. Only a small percentage of cycles will occur to satisfy
the power consumption of the power supply.
The response time of the Tiny Switch-II ‘On/Off’ control scheme is very fast
compared to normal PWM control. This provides tight regulation and excellent
transient response.
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Power Up/Down :
Figure 8
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The Tiny Switch-II requires only a 0.1µF capacitor on the BYPASS pin. Because of
its small size, the time to charge this capacitor is kept to an absolute minimum,
typically 0.6ms. Due to the fast nature of the ‘On/Off’ feedback, there is no overshoot
at the power supply output. When an external resistor (2MΩ) is connected from the
positive DC input to the EN/UV pin, the power MOSFET switching will be delayed
during power-up until the DC line voltage
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Exceeds the threshold (100V), in applications with and without an external resistor
(2MΩ) connected to the EN/UV pin.
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During power-down, when an external resistor is used, the power MOSFET will
switch for 50ms after the output loses regulation. The power MOSFET will then
remain off without any glitches since the under-voltage function prohibits restart
when the line voltage is low.
Figures illustrates a very slow power-down timing waveform of Tiny Switch-II as in
Figure 9
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Stand by applications. The external resistor (2MΩ) is connected to the EN/UV pin in
this case to prevent unwanted restarts.
Applications of PWM switching IC :
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The Tiny Switch-II is ideal for low cost, high efficiency power supplies in a wide
range of applications such as cellular phone chargers, PC standby, TV standby, AC
adapters, motor control, appliance control and ISDN or a DSL network termination.
The 132 kHz operation allows the use of a low cost EE13 or EF12.6 core transformer
while still providing good efficiency. The frequency jitter in Tiny Switch-II makes it
possible to use a single inductor (or two small resistors for under 3W applications if
lower efficiency is acceptable) in conjunction with two input capacitors for input EMI
filtering. The auto-restart function removes the need to oversize the output diode for
short circuit conditions allowing the design to be optimized for low cost and
maximum efficiency. In charger applications, it eliminates the need for a second
optocoupler and Zener diode for open loop fault protection. Auto-restart also saves
the cost of adding a fuse or increasing the power rating of the current sense resistors
to survive reverse battery conditions. For applications requiring under-voltage lock
out (UVLO), such as PC standby, the Tiny Switch-II eliminates several components
and saves cost. Tiny Switch-II is well suited for applications that require constant
voltage and constant current output. As Tiny Switch-II is always powered from the
input high voltage, it therefore does not rely on bias winding voltage. Consequently
this greatly simplifies designing chargers that must work down to zero volts on the
output.
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Experiment 3
Objective :
Study of MOSFET switching device ICTNY268P.
Equipments Needed :
1.
Oscilloscope
2.
Attenuator Probe (1:10)
Procedure:
Before performing experiment first select ‘AC Mains/From Variac’ switch of
the Trainer kit at ‘AC Mains’ position and all Fault switches at ‘Off’ position.
2.
Now connect the Mains cord into the Trainer kit and switch ‘On’ the power
supply.
3.
Connect Oscilloscope with (1:10) attenuator probeat ×10 position, at TP4 and
observe the waveform with respect to Ground (TP21), which is nothing but a
PWM waveform, this signal is generated by Tiny switch IC TNY268P which
generates the PWM signal.
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Note : To observe this waveform triggered on Oscilloscope, use Normal
triggering with Level adjustment at Time base position of 0.1 ms.
Figure 10
4.
Now calculate the time period of this waveform which is the switching time
(this will be of ms order) of this IC record this in Observation table.
From this experiment you can observe following parameter :
Parameter
Value
Switching time of TNY IC268P
------------------ ms
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Optocoupler
An opto-isolator internal circuit
Figure 11
Schematic diagram :
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In electronics, an opto-isolator (or optical isolator, optocoupler or photo coupler) is a
device that uses a short optical transmission path to transfer a signal between elements
of a circuit, typically a transmitter and a receiver, while keeping them electrically
isolated — since the signal goes from an electrical signal to an optical signal back to
an electrical signal, electrical contact along the path is broken.
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A common implementation involves an LED and a light sensor, separated so that light
may travel across a barrier but electrical current may not. When an electrical signal is
applied to the input of the opto-isolator, its LED lights, its light sensor then activates,
and a corresponding electrical signal is generated at the output. Unlike a transformer,
the opto-isolator allows for DC coupling and generally provides significant protection
from serious over voltage conditions in one circuit affecting the other.
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With a photodiode as the detector, the output current is proportional to the amount of
incident light supplied by the emitter. The diode can be used in a photovoltaic mode
or a photoconductive mode.
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In photovoltaic mode, the diode acts like a current source in parallel with a forwardbiased diode. The output current and voltage are dependent on the load impedance
and light intensity.
In photoconductive mode, the diode is connected to a supply voltage, and the
magnitude of the current conducted is directly proportional to the intensity of light.
An opto-isolator can also be constructed using a small incandescent lamp in place of
the LED; such a device, because the lamp has a much slower response time than an
LED, will filter out noise or half-wave power in the input signal. In so doing, it will
also filter out any audio- or higher-frequency signals in the input. It has the further
disadvantage, of course, (an overwhelming disadvantage in most applications) that
incandescent lamps have finite life spans. Thus, such an unconventional device is of
extremely limited usefulness, suitable only for applications such as science projects.
The optical path may be air or a dielectric waveguide. The transmitting and receiving
elements of an optical isolator may be contained within a single compact module, for
mounting, for example, on a circuit board; in this case, the module is often called an
optoisolator or opto-isolator. The photosensor may be a photocell, phototransistor, or
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an optically triggered SCR or Triac. Occasionally, this device will in turn operate a
power relay or contactor.
Applications :
Several types of opto-couplers. The top left and far right detect the presence of an
Objective in between them. They are interruptible. The middle one detects reflections
from Objectives in front of it. The two on the bottom left are both opto-isolators.
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Figure 12
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A simple circuit with an opto-isolator. When switch S1 is closed, LED D1 lights,
which triggers phototransistor Q1, which pulls the output pin low. This circuit, thus,
acts as a NOT gate.
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Among other applications, opto-isolators can help cut down on ground loops and
block voltage spikes.
One of the requirements of the MIDI (Musical Instrument Digital Interface)
standard is that input connections be opto-isolated.

They are used to isolate low-current control or signal circuitry from transients
generated or transmitted by power supply and high-current control circuits. The
latter are used within motor and machine control function blocks.

The classical ball computer mouse is a common application, using infrared
emitter LEDs and phototransistors to form optocouplers. The ball of the mouse
turns a pair of optical encoder wheels. These wheels periodically block the
optocouplers and thereby translate the motion of the mouse into a sequence of
pulses. These pulses are then used to record the motion. The principle of
operation does not require infrared light, but the infrared sensor is less sensitive
to interference from common flickering visible light sources such as fluorescent
lamps and CRT displays.
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Experiment 4
Objective :
Study Optocoupler and its application in SMPS.
Equipments Needed :
1.
DMM (Digital Multimeter).
Procedure :
Before performing experiment first select ‘AC Mains/From Variac’ switch of
the Trainer kit at ‘AC Mains’ position and all Fault switches at ‘Off’ position.
2.
Now connect the Mains cord into the Trainer kit and switch ‘On’ the power
supply.
3.
Observe the input voltage of Optocoupler using DMM (at DC voltmeter range)
at TP2 and TP3, which is around 1volt DC. This is the switching voltage
required for its operation; record this voltage in Observation table.
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From this experiment you can observe following parameter:
Input voltage to optocoupler at
TP2 and TP3
Value
--------------------- V
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Parameter
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Regulation Section
After the output of transformer the switched Stepped down DC (approximate AC) is
fed into rectifiers for DC conversion but these rectifiers don’t give smooth regulated
DC hence some sort of regulation is provided using zener diode and different
regulation ICs.
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Zener diode regulator : When forward-biased, zener diodes behave much the same
as standard rectifying diodes: they have a forward voltage drop which follows the
"diode equation" and is about 0.7volts. In reverse-bias mode, they do not conduct
until the applied voltage reaches or exceeds the so-called zener voltage, at which point
the diode is able to conduct substantial current, and in doing so will try to limit the
voltage dropped across it to that zener voltage point. So long as the power dissipated
by this reverse current does not exceed the diode's thermal limits, the diode will not be
harmed.
5V
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Zener diodes are manufactured with zener voltages ranging anywhere from a few
volts to hundreds of volts. This zener voltage changes slightly with temperature, and
like common carbon-composition resistor values, may be anywhere from 5 percent to
10 percent in error from the manufacturer's specifications. However, this stability and
accuracy is generally good enough for the zener diode to be used as a voltage
regulator device in common power supply circuit:
5V
Figure 13
The image shows a simple zener voltage regulator. It is a shunt regulator and operates
by way of the zener diode's action of maintaining a constant voltage across itself when
the current through it is sufficient to take it into the zener breakdown region. The
resistor R1 supplies the zener current IZ as well as the load current IR2 (R2 is the
load). R1 can be calculated as -
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where, VZ is the zener voltage, and IR2 is the required load current.
This regulator is used for very simple low power applications where the currents
involved are very small and the load is permanently connected across the zener diode
(such as voltage reference or voltage source circuits). Once R1 has been calculated,
removing R2 will cause the full load current (plus the zener current) to flow through
the diode and may exceed the diode's maximum current rating thereby damaging it.
The regulation of this circuit is also not very good due to the fact that the zener
current (and hence the zener voltage) will vary depending on VS and inversely
depending on the load current.
The LM78XX series positive regulator :
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Figure 14
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The LM78XX series of three terminal regulators is available with several fixed output
voltages making them useful in a wide range of applications. One of these is local on
card regulation, eliminating the distribution problems associated with single point
regulation. The voltages available allow these regulators to be used in logic systems,
instrumentation, HiFi, and other solid state electronic equipment. Although designed
primarily as fixed voltage regulators these devices can be used with external
components to obtain adjustable voltages and currents.
The LM78XX series is available in an aluminum TO-3 package which will allow over
1.0A load current if adequate heat sinking is provided. Current limiting is included to
limit the peak output current to a safe value. Safe area protection for the output
transistor is provided to limit internal power dissipation.
If internal power dissipation becomes too high for the heat sinking provided, the
thermal shutdown circuit takes over preventing the IC from overheating.
Considerable effort was expanded to make the LM78XX series of regulators easy to
use and mininize the number of external components. It is not necessary to bypass the
output, although this does improve transient response. Input bypassing is needed only
if the regulator is located far from the filter capacitor of the power supply.
For output voltage other than 5V, 12V and 15V the LM117 series provides an output
voltage range from 1.2V to 57V.
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Features:

Output current in excess of 1A

Internal thermal overload protection

No external components required

Output transistor safe area protection

Internal short circuit current limit

Available in the aluminum TO-3 package
Voltage Range:
LM7805C 5V
LM7815C 15V
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LM7812C 12V
The 79XX series negative regulator :
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Figure 15
The LM7900 series of fixed output negative voltage regulators are intended as
complements to the popular MC7800 series devices. These negative regulators are
available in the same seven–voltage options as the MC7800 devices. In addition, one
extra voltage option commonly employed in MECL systems is also available in the
negative MC7900 series. Available in fixed output voltage options from –5.0V to –
24V, these regulators employ current limiting, thermal shutdown, and safe–area
compensation – making them remarkably rugged under most operating conditions.
With adequate heat sinking they can deliver output currents in excess of 1.0A.
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Experiment 5
Objective :
Study of the regulation section
Equipments Needed :
1.
DMM (Digital Multimeter).
Procedure :
Before performing experiment first select ‘AC Mains/From Variac’ switch of
the Trainer kit at ‘AC Mains’ position and all Fault switches at ‘Off’ position.
2.
Now connect the Mains cord into the Trainer kit and switch ‘On’ the power
supply.
3.
Connect the DMM (at DC voltmeter range) at TP11 and TP13, which is the
input of IC7812 and output of the rectifier circuit.
4.
Connect the DMM (at DC voltmeter range) at TP16 and TP17. It will be +12V
DC, output of IC7812.
5.
Connect the DMM (at DC voltmeter range) at TP12 and TP13, which is the
input of IC7912.
6.
Connect the DMM (at DC voltmeter range) at TP18 and TP19. It will be -12V
DC, output of IC7912.
7.
Connect the DMM (at DC voltmeter range) at TP20 and TP21. It will be +5V
DC due to 5V zener diode.
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Experiment 6
Objective :
Study of SMPS with Variac input (Variable AC) – Regulation Test.
Equipments Needed :
1.
DMM (Digital Multimeter)
2.
Variac
Procedure :
First of all make sure that power supply of Variac and Trainer kit is ‘Off’.
2.
Now select ‘AC Mains/From Variac’ switch of the Trainer kit at ‘From Variac’
position and all Fault switches at ‘Off’ position.
3.
Adjust the Variac at zero output position.
4.
Now connect Variac across the terminals P, N and E provided on the kit.
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Note : Make sure that you are connecting earth to the kit and there is no loose
connection otherwise it may cause hazards.
Connect DMM (at voltmeter range) at output of the kit TP16 and TP17.
6.
Now switch ‘On’ the Variac supply and Trainer.
7.
Adjust the Variac input slowly from 0V to onwards and continuously observe
the DMM. Note the point where SMPS gives the desired output i.e., +12V.
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At this point measure the output of Variac at AC voltage position i.e.,-----V AC.
This is the minimum voltage required for SMPS to work properly.
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Continuously increase the voltage and observe maximum voltage of Variac,
where SMPS stops to give response, record this voltage as --------------V AC.
From this experiment you can observe the regulation voltage from -------- V AC to -------- V AC.
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Experiment 7
Objective :
Study of the different faults in SMPS circuit and the systematic procedure of
troubleshooting.
Equipments Needed :
1.
DMM (Digital Multimeter)
2.
Oscilloscope
3.
Attenuator Probe (1:10)
Procedure :
Before performing experiment first select ‘AC Mains/From Variac’ switch of
the Trainer kit at ‘AC Mains’ position and all Fault switches at ‘Off’ position
i.e., no fault is inserted.
2.
Now connect the Mains cord into the kit and switch ‘On’ the power supply.
3.
Test the outputs with DMM (at DC voltmeter range) at TP1-TP21, TP16-TP17,
TP18- TP19and TP20- TP21which are desired outputs i.e., 230V, +12V, - 12V
and +5V respectively.
4.
Now switch ‘On’ the fault switch 1, and observe voltage on Oscilloscope at TP1
with (1:10) attenuator probe at ×10 position. Since the input of the SMPS is cut
therefore no output will be displayed hence the fault occured.
5.
Now switch ‘Off’ the fault switch 1 and switch ‘On’ the fault switch 2, and
observe voltages using DMM (at DC voltmeter range) at various test points
from TP1 to TP21 and find the fault created by the switch. Since the output of
the rectifier is cut from the filter hence the problem occurs.
6.
Now switch ‘Off’ the fault switch 2 and switch ‘On’ the fault switch 3 and try to
identify fault using same testing procedure. This switch will affect the
transformer outputs (Due to feedback, the input of transformer will also be
affected).
7.
Now switch ‘Off’ the fault switch 3 and switch ‘On’ the fault switch 4.
Applying the same testing procedure you will find that this time input of IC7812
is not as desired. Hence there is no putput at TP16.
8.
Now switch ‘Off’ fault switch 4.
9.
In this way you can study step by step fault finding procedure.
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1.
Nvis Technologies Pvt. Ltd.
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NV7002
Warranty
1) We guarantee the product against all manufacturing defects for 24 months from
the date of sale by us or through our dealers. Consumables like dry cell etc. are not
covered under warranty.
2) The guarantee will become void, if
a) The product is not operated as per the instruction given in the operating manual.
b) The agreed payment terms and other conditions of sale are not followed.
c) The customer resells the instrument to another party.
d) Any attempt is made to service and modify the instrument.
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5) The non-working of the product is to be communicated to us immediately giving
full details of the complaints and defects noticed specifically mentioning the type,
serial number of the product and date of purchase etc.
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4) The repair work will be carried out, provided the product is dispatched securely
packed and insured. The transportation charges shall be borne by the customer.
List of Accessories
1.
Attenuator Probe (1:10) .................................................................................1 No.
2.
Learning Material .........................................................................................1 No.
3.
Mains Cord ....................................................................................................1 No.
Nvis Technologies Pvt. Ltd.
37
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