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Technicians hand-book
Any equipment connected to the
stabilizer and which draws power from
the stabilizer is load.
This is the voltage coming from the
main to the stabilizer.
This is the voltage available at the
output terminals of the stabilizer.
This is the current drawn from the
mains by the stabilizer.
This is the current drawn by the load
from the stabilizer.
All input voltages (150V-280V) for
which the stabilizer gives output within
the output voltage range.
The voltage (209-231V) which the
stabilizer is designed to deliver when
the input: within the specified input
voltage range.
The stabilizer is designed cut-off the
output voltage when the input voltage
falls below 150V+/- .
The stabilizer is designed to cut-off the
output voltage when input voltage goes
beyond 280V +/- 5V.
The stabilizer is designed to delay the
supply of mains to output terminal
(2min +/-20 secs) before starting in
case of initial starting, mains failure or
high/low voltage cut-off coming into
operation. This is an automatic
The “ON” delay can be avoided (by
passed) by pressing a switch manually
to obtain the output instantaneously.
Transformers are used to step up or step down a-c voltage. Transformers are
constructed of two coils wound on the same iron core as shown in Fig below. The
voltage is the stepped up or down i.e. applied to coil “F” which is called the primary
coil of the transformer.
When an a-c voltage Vp is connected to the primary coil, a current Ip flows through
the coil. This current creates a magnetic field which passes around the iron core and
through the secondary coil “S”. As the field due to the primary cases and falls with
the continual rising and falling of the a-c current, it cut across the winding of the
secondary coil and induces a voltage Vs across the coil.
If the secondary coil has more turns into the primary, then the voltage will have been
stepped up and the output voltage Vs will be greater than input voltage Vp. On the
other hand,if secondary has few turns than primary, then Vs will be less than Vp and
the voltage will be stepped down.
The number of turns in the secondary (Ns) delivered by the number of turns in the
primary (Np) is called the turns ratio “T” of the transformer:
T= Ns/Np
The total ratio tells us how much the voltage is stepped up or down To find the
output voltage multiply the input voltage by turns ratio
Vs = T x Vp
In order towards the output voltage depends on the ratio of the primary winding and
secondary winding turns expressed as:
Vs = Ns
Vp Np
The voltage of a system can be controlled by changing the turns ratio of a
transformer. The transformer windings may be provided different taps and by
selecting the taps turns ration can be changed.
The main transformer used in the voltage stabilizers has a single continues winding
which is used as primary as well as secondary winding. This is called an Autotransformer. Its theory and principle operation is similar to that of a two winding
transformer. The portion AB is used as primary winding and portion BC as secondary
winding Fig (a) shows a step down and (b) a step up arrangement
N8 = Number of turns for secondary winding
NP = Number of turns for primary winding
By changing/selecting suitable tappings for input and output in a auto-transformer
having different tappings, desired output voltage can be obtained. A simple tap
changing device is a selector switch. As shown figure above number of turns of
primary and secondary can changed through switch S1 and S2 respectively. Thus
the output voltage can be kept in a specified range by changing turns-ratio through
tap changing.
Tap changing can also be done automatically and instantly with the help of relays.
Different arrangements of tap changing are made in the stabilizers, with the help of
relays, which are controlled by electronic control circuits to obtain an output within
the range of 209-231 volts from an input range of 150 to 280 volts. This is explained
in detail while discussing the individual stabilizers.
A relay is an electrically operated switch. Instead of operating a switch by hand to
turn it on or off, an electromagnetic devise is used to the same.
A relay has coil of many turns of insulted copper wire wound around a piece of iron
called the core. This coil with its iron core is the electromagnet. The iron core
becomes a magnet when a current flows in the coil – that is when the coil is
emergenced and the relay is said to the operate. When current quits flowing in the
coil – that is, when the coil is de-energized – the iron core looses its magnetism and
the relay has to release.
An iron are called the armature in front of the core is pulled down, when the relay
generate which is turn closes or open the contacts of the relay, which were in just
opposite state when the relay was de-energized (released) construction. Closing or
opening a contact is similar putting switch on or off.
Only a small amount of current is needed through the coil to operate the relay, but
this on control (make/break) a larger current through its contacts.
Double pole, single throw
Double pole, double throw
Relays the switches come in various combinations of poles and throws. The
numbers of poles are determined by the number of sets of contacts it operates at
one time. A relay is called a single throw when its contacts opens/closes when the
relay operated; and it is called double throw when the set of contacts closes circuits
in both energized and nonenergized positions.
While showing in systematic diagrams the status of the contacts are shown when the
relay is nonenergized (released) condition.(NO= Normally Open, NO = Normally
closed contacts)
Resistors are used in just about every electronic circuit. They control the amount of
current in a circuit, keeping it within desired value. If the resistance is high, the
current will be low: if the resistance is low, the current will be high.
Fixed resistor
Variable resistor
A variable resister also called Potentiometer is one, which has a field value between
the two end terminals, and has a third terminal from a slider contacts (which is
marker with an arrangement schematics drawings). Changing the position of the
slider the resistance between the slider terminal and the other two and terminals can
be varied within the minimum resistance value.
The value of resistors is given in ohms(Ω) and the same is indicates by colour bands
or Figures on the body. Their were handling capacity in watts is also important.
Capacitors are among the very widely used electronic component. The a-c signal
passes through a capacitor while the d-c is blocked out. Capacitors are also able to
store electricity and then feed it back to the circuit required.
Capacitors come in a wide variety
of shapes and sizes. However all
capacitors are essentially the
same: two conducting surfaces
separated by a thin insulator called
a dia-electric. There are two basic
kinds of capacitors and those that
are not electrolytic.
Electrolytic capacitor
Disc capacitor
Electrolytic have much larger capacity than the others, and their terminals are
married (+) and (-). Proper polarity must be observed while connecting in circuits.
Capacitors which are not electrolytic don’t have a polarity mains, since make no
difference which way they are connected.
This is the simplest of all semiconductor devices.
Diode conduct in only one direction (neglecting
small reserve current)
Fig shows schematic symbol and for the diodes.
Its forward resistance is quite low while its reserve
resistance is exactly high.
In the schematic to a choose the arrow point in the
conventional direction of current flow (which is
opposite to the direction of
electron flow.)
Connecting an a-c to d-c is called rectification. Two types of rectifier circuits
discussed in the next page.
Positive current half
cycle thru Load.
Negative current
Half cycles does
not appear in output.
Half -wave rectifier
The simplest of all rectifier circuits is the half have rectifier shown in the figure. The
transformer has the proper turns ratio for the desired secondary voltage. During the
half of the a-c cycle when the transformer secondary polarity is as shown in figure,
the diode will conduct and current will flow through the load. The diode is forward
biased in this condition. During the other half of the a-c cycle, the diode cannot
conduct (it is said to be reverse biased) and no current flows through the load. The
result of the above action that a series of positive half-cycle pulses are developed
across the load and no load, current flows during the negative half of each cycle,
giving d-c at the output.
Full-wave Rectifier
Current path:
Positive half-cycle
Negative half-cycle
Full-wave Rectifier
Fig. above illustrates the basic operation of the full-wave rectifier. Note that the
circuit requires the use of a centre-tapped transformer secondary winding. During
positive half cycles when the top end of centre-tapped secondary is positive with
respect to the centre-tap current flows through the circuit indicated by transformed
arrows (conventional). Current flows through D1 and causes the positive half- cycle
to appear across the load. There is no flow of current through during this part of
cycle. During negative half-cycle, the bottom end of the transformer secondary
winding becomes positive, with respect to the centre-tap and now current will low
through D2 as shown by dashed arrows. Current always flows through one diode
only and both the half-cycle flows through the load in the same direction giving a-c
Current path:
Positive half-cycle
Negative half-cycle
A bridge rectifier circuit is shown in fig. above. The solid arrows show the current
path (conventional), when the secondary winding is positive and dashed arrows
show the current path for the other half-cycle, when the top of the secondary winding
is negative. The current always flows through two diodes. Current for both the half
cycles flows through the load in the same direction giving d-c at output.
Zener diodes are most commonly used as
voltage regulators and voltage limiters. They are
specially designed for sudden break down of
resistance when the designed reverse voltage is reached. They are normally used
with reverse biasing. Zener diode keeps the voltage across itself constant with
variations in current flow through it. This property is very useful as a voltage
If the voltage applied across a zener diode is lower than its break down voltage the
zener current remains very small till its break down voltage. When break down
occurs the resistance of zener decreases to leap the voltage across it at constant for
the input voltages of higher value.
The important specification for zener diode are the zener break down voltage (Ez)
the minimum zener current for good regulation (Izm) the maximum safe current that
the zener can handle (Izm) and wattage ratting.
The transistor can be recognized by its three leads. The three leads are called base
(B),emitter(E) and Collector (C) The transistor is called an active device, meaning
that it performs amplification. A small current flowing between the emitter and base
leads will allow a much larger signal current to follow between the emitter and
collector leads. The emitter’s job is simply to emit current into the transistor. The
base controls the amount to curve that flows from the emitter to the collector. The
collector finally collects all the current in the transistor and transfers it to some type
of load, such as a relay coil/ a speaker.
The operational amplifier (called the Op-amps in short) is a high gain amplifier that
will amplify d-c signals as well as a-c signals.
Symbol of an operational amplifier is shown in the fig. Operational amplifiers have
two inputs marked in the figure. A signal V1 applied to input 1 is reversed in phase
(inverted) upon passing through the operational amplifier. A signal V2 applied to
input 2 retains the same phase in going through the amplifier. Minus (-) sign on the
schematic is used to indicate phase reversal (inverting) and plus (+) sign for the non
inverting input.
If two signals V1 and V2 in phase with each other are applied simultaneously to the
two operational amplifiers inputs, the amplifiers signal V0 is the the difference
between V1 and V2. One input signal subtracts from the other because one signal is
inverted in the output and the other is one. The output voltage is equal to V1-V2
multiplied by the amplifier gain.
It is often necessary to have some means of indicating when two voltages in an
electronic circuit are equal. A voltage comparator using an operational amplifier is a
simple circuit that can do the job. There are number of application for such
comparators, one popular use is as voltage regulators, The operational amplifier
comparator can be used in two basic ways as shown in fig below:
In (a) above, the input voltage (Ein) is applied to the non-inverting input while a
reference voltage is applied to the inverting input. With this circuit the output voltage
(Eout) will remain at its maximum negative value as long as the input voltage is less
positive than the reference voltage. Once Ein increases to a value even only slightly
more positive than the reference voltage, however the output will range to its
maximum positive value.
The circuit in (b) operates similarly, except that the polarity of the output voltage is
reversed. Here the output voltage will be positive if Ein is less than reference voltage
and will swing negative once Ein becomes more positive than the voltage on the non
inverting terminal (Reference voltage).
The above two comparators use one input voltage and a stable reference voltage.
However the circuits can operate in the same manner with two separate, changing
input voltages. In that case, one input is applied to the non-inverting input and the
other to the inverting input. Except for the circuits will operate just file the above.
OP amp is frequently operated from identical positive and negative voltages 12V
When supply is provided this way its output voltage will swing between positive and
negative values that are very close to the power supply voltages as explained above.
Often however a comparator is operated with the negative supply terminal grounded
in which case the output voltage can never become more negative than zero i.e. its
output will be either zero (no output) or a positive voltage very close to the
power supply voltage depending upon the input
They consists of various components like transistors, diodes resistors etc. fabricated
on a single chip.
IC LM324
It consists of four independent high gain operational amplifiers, which were designed
to operate from a single power supply over a wide range of voltage Pin configaration
shown in the figure above.
LM 324
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