# Electronics Engineering

## Electronics Engineering is a branch of engineering that deals with practical applications of electronic components, devices, systems, or equipment. Electronics are devices that operate on low voltage sources, as in electron tubes, transistors, integrated circuits, and printed circuit boards and use electricity as part of its driving force.

###### Asked in Electronics Engineering, Electrical Engineering

### Why in short circuit test iron loss is very less?

In short circuit test very low voltage at primary approx 5 % of
the rated voltage is given and secondary is short circuited by an
ammeter. Due to low voltage very low flux is developed in core of
the transformer and due to that iron losses are very low which can
be neglected.
By Rizwan:
actually it is operated at (10-15)% of the rated voltage and as
you know n case of low voltage low magnetic flux is produced and
then there will be low magnetic field density(B). and we know
hysteresis and eddy current losses depend on (B).as in case of
:
hysteresis depends on B^1.2 and
eddy current depends on B^2
So if B is low then both losses(collectively called constant
losses) will be very very low.

###### Asked in Heating Ventilating and Air Conditioning, Electronics Engineering, Home Appliances

### Which way should you set your ceiling fan to turn - in the summer and in the winter?

These recommendations depend on the height and size of the room,
the season, and the activity taking place in the room.
Keep in mind that warm air rises to the top and cold air settles
on the bottom. Air settles in layers from warm at the top to cold
at the bottom, if left alone at equilibrium.
Ceiling fan recommendations:
In the winter
Set the fan to run counterclockwise (reverse; this looks
clockwise as you are looking up). This will redirect the warm air
from the ceiling and down the walls and into the living space where
the people actually are. In a house, you would run the fan at a low
speed so that you don't actually cool the warm air that you are
moving downward. If you have a high ceiling, or are trying to heat
a hall or a church, you may want to increase the fan speed so that
the warm air will reach the living space as long as the fan speed
does not create an unwanted downdraft at the people below.
In the summer
In a room of normal height (8 - 10 ft), you should operate your
fan so that it turns clockwise (this looks counterclockwise as you
are looking up), causing a more directed downdraft, especially with
the fan running slightly faster. This causes a wind-chill effect
because the skin evaporates slight amounts of water from the sweat
glands and thereby provides cooling through the skin's surface.
However, the air is only moved but not cooled! You may find that
you can turn your thermostat down a degree or two and save more
money on energy costs. The air blowing down won't actually cool the
room though, so you should turn the fan off when there are no
people (or animals) in the room.
In a high hall or church
It may be best NOT to run the fans at all in summer. This lowers
the demand for cooling since the hot layer on top is an excellent
insulation between the cool air near the floor (and the people) and
the hot roof and outside.
A large, tall manufacturing hall would typically have different
goals. There one would have a floor full of heat producing
machinery plus the people operating it, working hard and welcoming
a bit of a breeze. Then it would make sense to run the fans at
fairly high speed to create a certain and directed downdraft. And
with the shifts going throughout the days of the week, the fans
should be running all the time and maybe in all seasons.
Finally, fans typically use 80-100 watts. When used properly,
ceiling fans can really help to optimize the comfort level of the
people and save energy and money.
Another user contributes this:
The important point from the previous answer is that fans are
for cooling people. Advanced Energy (see the Related Link) says:
"The most optimistic estimates I've seen on energy savings from
ceiling fans peg the air conditioning savings at about 15%,
assuming people do raise the thermostat setting and only run the
fans when people are in the room, and taking into account the cost
of energy used by the fan itself."

###### Asked in Electronics Engineering, Electrical Engineering, Circuits

### What is Ohm's law?

Ohm's Law states: "The current flowing through a conductor
is directly proportional to the applied voltage, provided the
temperature of the conductor remains constant."
It specifically refers to conductors and not resistors. And it
takes into consideration the need to maintain a given temperature
as the voltage and current vary. At the time, Georg Ohm already
knew that allowing the temperature to vary would break the constant
ratio.
Keep in mind that this was a historic new understanding that he
had discovered was applicable to various conductors (metals).
Ohm's Law is by no means a universal law, and very few materials
or electrical components actually 'obey' Ohm's Law. Those that do
(some metals) are termed 'linear' or 'ohmic'; those that don't
(most) are termed 'non-linear' or 'non-ohmic'.
Simply put, if the graph of voltage against current, plotted for
variations in voltage, is a straight line, then Ohm's Law applies;
if the graph is not a straight line, then Ohm's Law does not apply.
And very few materials/devices produce a straight line graph. Based
on this, you could say that 'Ohm's Law' is not a 'law' at all, but
simply describes the behaviour of a limited range of materials.
So Ohm's Law doesn't apply to heated metals such as tungsten
filaments, or to circuit components, such as diodes and to
practically all other electronic devices.
The basic unit of electrical resistance was given the name 'The
Ohm' in honor of Georg Ohm. The symbol for the unit is Ω,
pronounced Omega. The ratio of a given voltage to resulting current
will always tell us what the resistance happens to be for that
particular instance. This is because the ratio of voltage to
current is, by definition, resistance - however, this has nothing
whatsoever to do with Ohm's Law, but is simply a definition of
resistance!
E = I R
Voltage = Current times Resistance
As the alternate friendus below clearly indicate, there is a
widespread misunderstanding regarding Ohm's Law. Answer Resistance
defines the relationships between (E) electromotive force in Volts
and (I) current in Amperes. One ohm is defined as the resistance
value through which one volt will maintain a current of one ampere.
In other words, an ohm is a volt per ampere.
(I) Current is what flows on a wire or conductor like water
flowing down a river. Current flows between points of different
voltage. Current is measured in (A) Amperes, abbreviated: amps.
(E) Voltage is the difference in electrical potential between
two points in a circuit. It's the push or pressure behind current
flow through a circuit, and is measured in Volts.
(R) Resistance determines how much current will flow through a
component. Resistors are used to control voltage and current
levels. A very high resistance allows a small amount of current to
flow. A very low resistance allows a large amount of current to
flow. Resistance is measured in Ohms.
Answer The statement taught in electrical training is "Current
is directly proportional to the applied EMF and inversely
proportional to the resistance of the circuit".
Ohm's law: When there is a potential (Voltage-V) different
between two ends of a conductor a follow of charges will be created
(The current-I) through this conductor which is directly
proportional to the voltage difference and inversely proportional
to the resistance of the conductor (Resistance-R ).
I α Vdifference
I α 1/R
I=Vdifference/R : Current increases with increase of voltage,
but decreases with the increase of the resistance
Answer Ohms Law states that the amount of current that passes
through an object is directly proportional to the potential voltage
across that object, and inversely proportional to the resistance,
or electrical impedance, of that object. In other words: * as
voltage goes up, the current goes up by the same proportional
amount * as the impedance goes up, the current is reduced by the
same proportional amount. Ohms Law can be stated mathematically
as:
I = E/R Where: I is the current, E is the voltage, R is the
resistance
As you can see from the above formula, if the voltage were to
double, then so would the current. If the resistance were to
triple, then the current would be one-third of its former value.
You can use Ohms Law to calculate any value if you know the other
two. These are expressed mathematically as: V = I x R (to calculate
Voltage) R = V / I (to calculate Resistance) In the above
calculations, V is measured in 'volts', I is measured in 'amperes'
(or amps), and R is measured in Ohms.
Ohm's Law states Voltage = Current x Resistance. Except in
unusual circumstances the resistance "R" is a constant. When you
increase voltage, current increases.
-----------------------------------------------------------------------------------------------
Ohm's Law states that 'the current flowing through a
conductor at constant temperature is directly proportional to the
potential difference across that conductor'.
Ohm's Law is by no means a universal law, and only
applies to those conductors or devices where the ratio of voltage
to current is constant over a wide range of potential differences.
These materials are termed 'ohmic' or 'linear', whereas those
materials and devices that do not obey Ohm's Law (and there
are a great many!) are termed 'non-ohmic' or 'non-linear'. Examples
of non-ohmic materials and devices include tungsten (lamp
filaments), diodes, electrolytes, etc.
The ratio of voltage to current is termed
resistance (R = E/I), and is derived from the
definition of the ohm, and not (as many people think)
from Ohm's Law. This equation can be applied to both ohmic
and non-ohmic materials and devices, so applies whether or
not Ohm's Law is followed.

###### Asked in Electronics Engineering, Electrical Engineering

### What is dynamic resistance of diode?

The Current-Voltage relationship of a diode is not constant (not
a straight line) and hence the resistance cannot be measured. Due
to this non-linear nature of the the curve, there exists a unique
value of resistance at every point of the curve which is called
dynamic resistance (not static of constant resistance).
The dynamic resistance equals the change in voltage divided by
the change in current, when the voltage is changed by a small
amount. In other words it is the slope of the graph of voltage
against current. The dynamic resistance is different at different
current values.
About 30 years ago, and I do not remeber the brand or maker,
there was a digital multimeter that DID measure dynamic resistance
in diodes. It was a God Send for testing diodes in circuit. Diodes
only conduct in one direction, so the device would show an open in
one direction and a resistance under 1000 ohms on the other or a
short (0 ohms).

###### Asked in Jobs & Education, Electronics Engineering, Electrical Engineering, Pneumatics, How To

### How to calculate power in an inductive load?

Inductive load power is reactive, it is given by the
formula:
pL(t)=VL(t)IL(t),
in time domain (instant power);
PL(s)=VL,RMS(s)IL,RMS(s),
in Laplace transform domain (RMS denotes root mean square
amplitude).
VL is the voltage across the inductor L and IL is its current
(current enters in the "+" voltage reference pin, by applying user
convention in which absorbed power is positive).
Power is reactive since voltage and current are always in
quadrature:
VL(s) = s L IL(s),
in Laplace domain (derived from the time-domain formula vL(t)= L
diL(t)/dt).
A real-life inductor will also show an active power term, which
arises from parasitic resistance non-ideality; it can be modeled as
a resistance DCR in series with the inductor itself:
pACT(t)=DCR IL(t)
<<>>
An inductive load such as an induction motor draws power from
the supply with a power factor of less than 1.
Power = voltage x current x power factor.
This happens because the current reaches its peak in the ac
cycle after the voltage, so that for a small part of the cycle
power flows back into the supply from energy stored in the motor's
internal magnetic field. The time-lag is measured in degrees and
called the phase difference. 360 degrees denotes one complete
cycle.
The power factor is the cosine of the phase difference, so that
(for example) a resistive load has no phase difference so that the
power factor is 1, while for a pure inductor the phase difference
is 90 degrees and the power factor is zero.
If the rms voltage and current are expressed in complex-number
form, also known as vectors or phasors, the real power is the real
part of VI*, where the asterisk denotes the complex conjugate.
Another way to calculate the real power is to calculate the
average value of the instantaneous power V x I. If the voltage is
Vcos(wt) and the current is Icos(wt+phi) then those expressions can
be multiplied together and trigonometry formulas used to show that
the power factor is cos(phi) as stated.
Real power is measured from the average value of volts times
amps with an instrument that contains a voltage coil and a current
coil. The force produced is equal to the instantaneous power, and
the instrument measures its average value muliplied by the
time.

###### Asked in Electronics Engineering, Electrical Engineering, Electrical Wiring, Robotics

### Why hissing noise occur in transformer?

A: Hissing is because is overheating before it destroy itself.
But other noises are caused by loose lamination of the core.
B: Hissing noise is produced due to this reason but here is
another important point is about frequency (e.g for 50 Hz) the core
lamination face attractive and repulsive forces fifty times in
one
cycle because frequency is 50 Hz.
Another Answer
The original answer is unnecessarily melodramatic. Transformers
are fitted with protective devices that will disconnect the
transformer long before a rise in temperature will cause it to
'destroy itself'!
'Hissing', as opposed to 'humming', is usually caused by the
ionisation of air in the immediate vicinity of the transformer's
high-voltage bushings (hollow insulators). This also manifests
itself, after dark, as a blue-coloured luminous discharge.
'Humming', on the other hand, is due to something called
'magnetostriction', a distortion to the core laminations -exactly
as described in the original answer, except that the
attractive/repulsive forces are twice that of the supply frequency
(i.e. 100 times, in the case of 50 Hz), together with harmonics
based on that frequency.

###### Asked in Mobile Phones, Inventions, Electronics Engineering, Wireless Communication

### Who invented the cell phone and when?

Martin Cooper invented the cell (mobile) phone. He was the first
one to make a call and speak on his moble phone.
Mr Cooper, born December 26, 1928, wanted people to be able to
carry their phones with them anywhere. While he was a project
manager at Motorola in 1973, Cooper set up a base station in New
York with the first working prototype of a cellular telephone, the
Motorola Dyna-Tac. After some initial testing in Washington for the
F.C.C., Mr. Cooper and Motorola took the phone technology to New
York to show the public.
The First Cellphone (1973)
Name: Motorola Dyna-Tac
Size: 9 x 5 x 1.75 inches
Weight: 2.5 pounds
Display: None
Number of Circuit Boards: 30
Talk time: 35 minutes
Recharge Time: 10 hours
Features: Talk, listen, dial
See related links for further information on Martin Cooper and
his invention.
The idea of the cell phone began in the 1920's with police radios,
but it wasn't until 1947 that the first one was made by Bell labs.
In 1974 Dr. Martin Cooper is given credit for the cell phone that
is most like the ones we have today. He was working for Motorola at
the time. The phone was only for government use and in 1984 it was
sold to the public for the first time. The early cell phones were
large, heavy, and copied land line phones in style. They were
carried in a zippered bag with the whole bottom as the
battery.
The cell phone was first thought of in the 1920's when the use of
police radios began. In 1947 Bell Labs made the first cell phone,
but it took Dr. Cooper of Motorola to make a cell phone in 1974 for
the government. The public use of cell phones began in 1984.
Your question has two friendus. The phone was invented in 1889 by
Bell. The cell phone idea began in the 1930's, but in 1947 Bell
Labs made a cell type phone. The first cell phone inventor id given
to Dr. Martin Cooper of Motorola in 1974. This phone was sold to
the government. The public did not get it until 1984.
It was made by Bell labs in 1947, but the man given the most credit
for it is Dr. Martin Cooper who made one very much like what we
have today in 1973.
We knew someday everybody would have one. Martin Cooper
created the "DynaTAC," the first commercial cell phone, which hit
the market in 1983. (CNN) -- In 1973, Martin Cooper changed
the world, although he didn't know it yet. With the invention there
was concern regarding brain cancer due to the fact that cell phones
send out high frequency of radio waves.
It was invented by Will Maacmillan in 1969
Doctor Martin Cooper invented the modern cell phone. He invented
the technology responsible for the cell phone when was the Director
of Research and Development at Motorola. Cooper is also known as
the first person to make a call on a cell phone. His groundbreaking
call took place in April of 1973 in New York. He is currently the
CEO of an antenna corporation.

###### Asked in Consumer Electronics, Electronics Engineering, Master of Computer Applications MCA

### What are the uses of logic gates?

Logic gates are in fact the building block of digital
electronics; they are formed by the combination of transistors
(either BJT or MOSFET) to realize some digital operations (like
logical OR, AND, INVERT ). Every digital product, like computers,
mobile, calculators even digital watches, contain logic gates. The
use of logic gates in digital world can be understood better by the
following example: the single bit full adder in digital electronics
is a logic circuit which perform the logical addition of two single
bit binary numbers (a,b,cin) a and b are the the two binary number
of single digit (either 1 or 0) and cin is the carry input . say
for example a,b,cin= 1,1,1 gave an logical sum output of 1 and a
carry of 1 , a,b,cin= 110 gave sum= 0 and carry of 1. Now this
adder can be formed by the combination of many gate like by using
NAND gates only. or by using XOR , AND ,OR gates and so on. So, in
a nutshell, the adder which is of great importance in your computer
processor and also in many more applications is basically built
from the logic gates.

###### Asked in Electronics Engineering

### What is the Need for Doping in Semi conductors?

The Indian electronics system design and manufacturing (ESDM) industry is at a huge inflection point. From being predominantly consumption-driven, the Indian ESDM industry holds potential to become a design-led manufacturing industry. Concerted efforts from both the government and the industry are required to propel the Indian ESDM industry into one of the critical GDP contributors soon.
ndia Electronics and Semiconductor Association (IESA), the trade body, representing the Indian electronic system design and manufacturing space, in collaboration with Markets And Markets, on Tuesday, launched an industry report on Indian semiconductor fabless startup ecosystem at its annual Vision Summit.
The report was launched by Ashwini K Aggarwal, Chairman, IESA; Anilkumar Muniswamy, Director, SLN Technologies Ltd. and Jitendra Chaddah, Chair, Fabless CIG and Senior Director, Strategic Relations and Operations, Intel India on Day 1 of Vision Summit.

###### Asked in Electronics Engineering, Electrical Engineering, The Difference Between

### What is the difference between motors and generators?

A motor converts electrical energy into mechanical energy and a
generator converts mechanical energy into electrical energy.
Longer answer
The primary difference between a motor and a generator is that
one converts electrical energy into mechanical energy (that's the
motor) and the other converts mechanical energy into electrical
energy (that's the generator).
In some cases of direct current (DC) machines, but not
alternating current (AC) machines, there is so little difference
that a single device (it might be called a motor-generator) can be
used as either a motor or a generator.
A superb example of this would be the motor-generator that is
used in electric vehicles: when the vehicle is accelerated, the
batteries supply power to the motor-generator and it acts as a
motor, driving the wheels. When the brake is applied, the
motor-generator shifts function and the vehicle's inertia is used
by the motor-generator to generate electricity and put some energy
back into the batteries. This slows the vehicle down. The one
device (the motor-generator) is being used in either capacity. The
"handle" often applied to electric vehicles with this feature is
dynamic braking.
They alike because they both have stators and rotors they are
different in that the generator is driven by mechanical device that
rotates the rotor, the rotor cuts through magnetic force fields and
electricity is generated. The motor is driven by an input of
electricity into the stator and the rotor is forced to turn by
reaction with magnetic force fields.
Generator will provides current to load ......... but motor will
drawn current............... generator is based on Flemming right
hand rule but motor is based on left hand rule.

###### Asked in Electronics Engineering, Physics, Electrical Engineering

### How many ohm's is a 1M5 resistor?

The plural of 'ohm' is ohms, not ohm's.
The alpha-numeric code for identifying the resistance of a
resistor is quite straightforward.
The letter is used as a multiplier. For example, k
= x1000 and M = x1000 000. In other words, k
represents kilo, and M represents mega.
The position of the letter represents the position of the
decimal marker.
So,
1M5 represents 1.5 x 1000 000, or 1.5 megohms.
15M represents 15 x 1000 000, or 15 megohms.
etc.
Similarly,
1k5 represents 1.5 x 1000, or 1.5 kilohms.
15k represents 15 x 1000, or 15 kilohms.
etc.

###### Asked in Electronics Engineering, Appliance Voltage and Travel Issues

### Is electrical power measured in coulombs?

No.
Coulombs are a measure of charge - literally electrons, although
the whole unit is much larger than a single electron.
In some circuits, such as lithium ion battery chargers,
literally measure the amount of current over time which gives you
the amount of charge - coulombs - that has passed from the battery
into the powered device or vice versa.
All that being said, in this case, the value of the coulombs can
be negative. This simply represents a charge imbalance.
Power is measured in Watts. Power can be generated in Watts or
consumed in Watts.

###### Asked in Home Electricity, Electronics Engineering, Electrical Engineering

### How do I test a capacitor when I cannot remove it out of circuit?

You cannot. It must be taken out of the circuit and then tested
on its own.
That's not 100% true because, if it has wires at its ends, you
can cut through one wire with an appropriate tool and then test the
capacitor "out of circuit". If the capacitor is ok you can then
re-join the two cut wire ends by applying a blob of solder
carefully. (But, to avoid damaging the capacitor, use a suitable
heat sink to shield the body of the capacitor from the heat of the
soldering iron.)
With direct current a capacitor also works like a special type
of resistance. Whilst being charged up, it will show low
resistance. As it slowly (or quickly) charges, the resistance will
grow larger and larger. Whenever I repair circuitry and I have
doubts about a capacitor (in the uF area) I simply use my
multimeter on its Ohms setting. If a capacitor has shorted, then
the result will be 0 Ohm. If the capacitor is working, or partially
working, the resistance will gradually increase until it is out of
range of the multimeter.
Use an ohm-meter first to test the on-board capacitor and then
use it to test a similar capacitor off-board, to see if the results
sort of match up.
Most often they will not match completely as on-board you also
measure the effect of all other components connected into circuit
with the capacitor. It might point you in the right direction
though.
On a separate thought, if you really cannot remove it, or
disconnect one of its connections, then why test it at all? If it
really can't be removed to replace it, then it makes no sense to
test it!
A capacitor can be tested using multimeter without removing it
from circuit. but in order to check it, its polarities should be
noted and then keep the positive terminal of multimeter on positive
of capacitor and negative terminal on negative. It is vital to note
that the readings will be affected by the remainder of the circuit.
To test for capacitor function in circuit demands a good
understanding of the circuit operation.
Of course there are ways to test capacitors, both in circuit and
out. While a truly accurate test involved taking the cap out of
circuit, a basic test can certainly be done in circuit.
Out of circuit, one can either connect to a VM, or better yet,
an oscilloscope, and measure the time for voltage to decay to zero
across the capacitor. This time should equal the time given by the
equation for the time constant, and is dependant on the values
associated with that particular capacitor.
For RC circuits, this equation equals:
τ = R × C. It is the time required to charge the
capacitor, through the resistor, to 63.2 (≈ 63) percent of full
charge; or to discharge it to 36.8 (≈ 37) percent of its initial
voltage. These values are derived from 1 − e − 1 and
e − 1 respectively.
It is important to keep in mind that one must apply a voltage
across the capacitor at its rated value. Thus, if it is a 400V
capacitor driving a tube amp, for instance, it must be driven at
around 400V. Driving it at 12V will lead to useless results.
The only proper way to check for a capacitor value and or
leakage is with a proper test bridge: set it to the capacitor's DC
rating with it removed from the circuit completely. Any other way
is just waste of time.
Additionally, a common in-circuit test for a electrolytic
capacitor is to measure its Equivalent Series Resistance (ESR)
which can be done with an ESR meter. This is a quick and easy way
to locate failing electrolytic capacitors, especially in power
supply circuits.
An effective method of testing any component in-circuit
is with an in-circuit curve tracer. If you have an oscilloscope
with X-Y input mode you can easily build one of these on your own.
They do take some getting used to before you can use it effectively
and are most useful for good board vs. bad board
comparison.

###### Asked in Electronics Engineering

### Working principle of phase control?

A: it must apply to AC since there is no phase in DC. Since AC
is a complete circle 0-360 degrees the principle if to conduct
current at a degree of the circle. And AC has both positive 0 to
180 and negative 180 to 360 polarity it is possible to control
output power by conducting current only at certain angle of the
circle . The phase angle is to differentiate the conducting current
in which quadrant of the circle

###### Asked in Home Electricity, Electronics Engineering, Electrical Engineering

### Can you use ac ammeter to measure dc current?

It depends. If it's an inductive ammeter (the kind that clamps
around a wire), it won't work at all. If it is the type of ammeter
that is actually placed in the circuit, it will work but it won't
be accurate.
Comment
Actually, modern 'clamp on' ammeters WILL measure d.c. currents.
It uses the Hall Effect to measure the current.

###### Asked in Electronics Engineering

### How many watts in computer's 230 volts?

It depends on the current being drawn by the computer's
components. The voltage will remain constant at 230V and should
have a maximum amperage rating labeled on the power supply.
Multiply the volts times the max amp rating to find out the max
wattage that the power supply can handle. The watts actually being
used is probably lower than the rated max (and should be).

###### Asked in Home Electricity, Electronics Engineering, Electrical Engineering

### How do you reduce 9V DC to 3V DC?

Use either DC to Dc converter or voltage regulators for the
required voltages.
Answer
A common method is to use a voltage divider
circuit. This comprises a number of resistors, connected in series,
across the power supply. This creates a series of voltage drops
across each resistor and, by choosing resistors of appropriate
value, the desired load voltage can be achieved.
For example, if three identical resistors are connected in
series across 9 V, then the voltage across each resistor will be 3
V, and the load can be connected across any one of these
resistors.
In practise, selecting the appropriate values of resistance is
more complicated than this simple example, because (1) the
resistors themselves mustn't overload the power supply, and (2) the
load itself, being connected in parallel with one of the voltage
divider resistors, affects the overall resistance of the voltage
divider circuit and must, therefore, be taken into account when
designing the circuit. This is called the 'loading effect' and, to
put it simply, its effect is minimised providing the resistance of
the load is VERY much larger than that of the voltage divider
resistor it is connected across.
Answer
This sounds like you're trying to run a 3-volt device off a
9-volt battery. I would do it in one of three ways.
First way is if there's nothing in the circuit that needs 9
volts. Your best bet here is to replace the 9-volt battery clip
with either a holder for two AAA cells or two A-76 button cells.
Trying to reduce the output of a 9-volt battery to 3 volts will
produce lots of heat. You'll get a fairly short battery life, too.
AAA cells are about the same size as a 9-volt; button cells are way
smaller. There is a 3.3-volt regulator called the 7803SR - Murata
makes it - but they cost $10 each.
Second way is if you need both 3v and 9v...in that case, I would
install a pair of AAA cells alongside the 9v cell and wire the 3v
supply to the circuit that needs it.
And third is if this is a flashlight. In that case it's even
easier: replace the 3v bulb with a 9v bulb (yes, there are 9v
flashlight bulbs) and be happy.

###### Asked in Electronics Engineering

### What is the working principle of uninterrupted power supply?

Typical home use UPS devices for computers are plugged into your
AC power. There is an input circuit that converts AC to DC and
continuously charges the internal batteries in the UPS device. The
DC output from the batteries is then converted to AC to power the
computer or other device connected to the UPS. There is also a
circuit that detects that the house power is no longer functioning
and typically sounds an alarm of some sort.