electronics project power supply
TRANSCRIPT
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Chapter 1
POWER SUPPLY
Power supply can be defined as electronic equipment, which is a stable
source of D.C. power for electronic circuits.
Power supply can be classified into two major categories: -
1.1 Unregulated power supply
1.2 Regulated power supply
1.1 UNREGULATED POWER SUPPLY: -
These power supplies, supply power to the load but do not take into variation
of power supply output voltage or current with respect to the change in A.C.
mains voltage, load current or temperature variations. In other words, we can
say that the output voltage or current of an unregulated power supply changes
with the change in A.C.mains voltage, load current and temperature.
A block diagram as shown below can represent unregulated power
supply:
A .C. INPUTRECTIFIER FILTER LOAD
BLOCK DIAGRAM OF UNREGULATED POWER SUPPLY
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1.2 REGULATED POWER SUPPLY: -
These power supplies are regulated over the change in source voltage or load
current i.e. its output remain stable.
Regulated power supplies are of two types: -
CURRENT REGULATED POWER SUPPLIES
These are constant current supplies in spite of change in load or input
voltage.
VOLTAGE REGULATED POWER SUPPLIES
These supplies supply constant output voltage with respect to the variation in
load or source input voltage.
Block diagram of a regulated power supply can be given as below:
RECTIFIER FILTER REGULATORA.C.
INPUTVac Vdc VL LOAD
UNREGULATED POWER SUPPLY
OCK DIAGRAM OF REGULATED POWER SUPPLY
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CIRCUIT OF REGULATED POWER SUPPLY WITH HALF
WAVE RECTIFIER AND IC-7809 AS A REGULATOR
Here diode D1, D2, D3 and D4 forms half wave rectifier. Capacitor C1 is
filtering capacitor. IC-7809 is used for voltage regulation. Capacitor C2 is used
for bypassing, if any ripples are present then it eliminates those ripples.
As IC-7809 is used so it gives 9v dc regulated voltage ideally. If we
take 16 volts transformer then we will get 8.97v at output. Thus voltage is
regulated.
C2
0.1uF
IN
COM
OUT
C1
1000uFD4D3D2D1
T1
10TO1 OUTPU
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Chapter 2
Resistors are components that have a predetermined resistance. Resistance
determines how much current will flow through a component. Resistors are
used to control voltages and currents. A very high resistance allows very little
current to flow. Air has very high resistance. Current almost never flows
through air. (Sparks and lightning are brief displays of current flow through air.
The light is created as the current burns parts of the air.) A low resistance
allows a large amount of current to flow. Metals have very low resistance.
That is why wires are made of metal. They allow current to flow from one point
to another point without any resistance. Wires are usually covered with rubber
or plastic. This keeps the wires from coming in contact with other wires and
creating short circuits. High voltage power lines are covered with thick layers
of plastic to make them safe, but they become very dangerous when the line
breaks and the wire is exposed and is no longer separated from other things
by insulation.
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Resistance is given in units of ohms. (Ohms are named after Mho Ohms who
played with electricity as a young boy in Germany.) Common resistor values
are from 100 ohms to 100,000 ohms. Each resistor is marked with colored
stripes to indicate its resistance.
2.2 Variable Resistors
Variable resistors are also common components. They have a dial or a knob
that allows you to change the resistance. This is very useful for many
situations. Volume controls are variable resistors. When you change the
volume you are changing the resistance which changes the current. Making
the resistance higher will let less current flow so the volume goes down.
Making the resistance lower will let more current flow so the volume goes up.
The value of a variable resistor is given as its highest resistance value. For
example, a 500 ohm variable resistor can have a resistance of anywhere
between 0 ohms and 500 ohms. A variable resistor may also be called a
potentiometer (pot for short).
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2.3 Capacitors
Now suppose you want to control how the current in your circuit changes (or
not changes) over time. Now why would you? Well radio signals require very
fast current changes. Robot motors cause current fluctuations in your circuit
which you need to control. What do you do when batteries cannot supply
current as fast as you circuit drains them? How do you prevent sudden
current spikes that could fry your robot circuitry? The solution to this is
capacitors.
Capacitors are like electron storage banks. If your circuit is running low, it will
deliver electrons to your circuit.
In our water analogy, think of this as a water tank with water always flowing in,
but with drainage valves opening and closing. Since capacitors take time to
charge, and time to discharge, they can also be used for timing circuits.
Timing circuits can be used to generate signals such as PWM or be used to
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turn on/off motors in solar powered BEAM robots.
Quick note, some capacitors are polarized, meaning current can only flow one
direction through them. If a capacitor has a lead that is longer than the other,
assume the longer lead must always connect to positive.
Power surge /drainage management
The problem with using robot components that drain a large amount of power
is sometimes your battery cannot handle the high drain rate, Motors and
servos being perfect examples. This would cause a system wide voltage drop,
often resetting your microcontroller, or at least causing it to not work properly.
Just a side note, it is bad to use the same power source for both your circuit
and your motors. So don't do it.
Or suppose your robot motors are not operating at its full potential because
the battery cannot supply enough current, the capacitor will make up for it.
The solution is to place a large electrolytic capacitor between the source and
ground of your power source. Get a capacitor that is rated at least twice the
voltage you expect to go through it. Have it rated at 1mF-10mF for every amp
required. For example, if your 20V motors will use 3 amps, use a 3mF-30mF
50V rated capacitor. Exactly how much will depend on how often you expect
your motor to change speed and direction, as well as momentum of what you
are actuating. Just note that if your capacitor is too large, it may take a long
time to charge up when you first turn your robot on. If it is too small, it will
drain of electrons and your circuit will be left with a deficit. It is also bad to
allow a large capacitor to remain fully charged when you turn off your robot.
Some things could accidentally short and fry. So use a simple power on LED
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in your motor circuit to drain the capacitor after your robot is turned off. If your
capacitor is not rated properly for voltage, then can explode with smoke.
Fortunately they do not overheat if given excessive amounts of current. So
just make sure your capacitor is rated higher than your highest expected.
Capacitors can also be used to prevent power spikes that could potentially fry
circuitry. Next to any on/off switch or anything that that could affect power
suddenly should have a capacitor across it?
Capacitors can eliminate switch bouncing. When you flip a mechanical switch,
the switch actually bounces several times within a microsecond range.
Normally this is too small of a time for anyone to care (or even notice), but
note that a microcontroller can take hundreds of readings in a single
microsecond. So if your robot was counting the number of times a switch is
flipped, a single flip can count as dozens. So how do you stop this? Use a
small ceramic capacitor! Just experiment until you find the power capacitance
value.
2.4 Diodes
Diodes are components that allow current to flow in only one direction. They
have a positive side (leg) and a negative side. When the voltage on the
positive leg is higher than on the negative leg then current flows through the
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diode (the resistance is very low). When the voltage is lower on the positive
leg than on the negative leg then the current does not flow (the resistance is
very high). The negative leg of a diode is the one with the line closest to it. It is
called the cathode. The positive end is called the anode.
Usually when current is flowing through a diode, the voltage on the positive
leg is 0.65 volts higher than on the negative leg.
2.5 Switches
Switches are devices that create a short circuit or an open circuit depending
on the position of the switch. For a light switch, ON means short circuit
(current flows through the switch, and lights light up.) When the switch is OFF,
that means there is an open circuit (no current flows, lights go out.
When the switch is ON it looks and acts like a wire. When the switch is OFF
there is no connection.
2.6 The LED
An LED is the device shown above. Besides red, they can also be yellow,
green and blue. The letters LED stand for Light Emitting Diode. The important
thing to remember about diodes (including LEDs) is that current can only flow
in one direction.
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2.7 The Transistor
Transistors are basic components in all of today's electronics. They are just
simple switches that we can use to turn things on and off. Even though they
are simple, they are the most important electrical component. For example,
transistors are almost the only components used to build a Pentium
processor. A single Pentium chip has about 3.5 million transistors. The ones
in the Pentium are smaller than the ones we will use but they work the same
way.
Transistors that we will use in projects look like this:
The transistor has three legs, the Collector (C), Base (B), and Emitter (E).
Sometimes they are labeled on the flat side of the transistor. Transistors
always have one round side and one flat side. If the round side is facing you,
the Collector leg is on the left, the Base leg is in the middle, and the Emitter
leg is on the right.
Transistor Symbol
The following symbol is used in circuit drawings (schematics) to represent a
transistor.
Basic Circuit
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The Base (B) is the On/Off switch for the transistor. If a current is flowing to
the Base, there will be a path from the Collector (C) to the Emitter (E) where
current can flow (The Switch is On.) If there is no current flowing to the Base,
then no current can flow from the Collector to the Emitter. (The Switch is off.)
Below is the basic circuit we will use for all of our transistors.
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Chapter - 3
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Chapter 4
Relays
A relay is usually an electromechanical device that is actuated by an electrical
current. The current flowing in one circuit causes the opening or closing of another
circuit. Relays are like remote control switches and are used in many applications
because of their relative simplicity, long life, and proven high reliability. They are
used in a wide variety of applications throughout industry, such as in telephone
exchanges, digital computers and automation systems.
4.1 How do relays work?
All relays contain a sensing unit, the electric coil, which is powered by AC or DC
current. When the applied current or voltage exceeds a threshold value, the coil
activates the armature, which operates either to close the open contacts or to open
the closed contacts. When a power is supplied to the coil, it generates a magnetic
force that actuates the switch mechanism. The magnetic force is, in effect, relaying
the action from one circuit to another. The first circuit is called the control circuit; the
second is called the load circuit. A relay is usually an electromechanical device that
is actuated by an electrical current.
The current flowing in one circuit causes the opening or closing of another ckt.
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4.2 Types of Relays
There are two basic classifications of relays:
1. Electromechanical Relay
2. Solid State Relay.
Electromechanical relays have moving parts, whereas solid state relays have no
moving parts. Advantages of Electromechanical relays include lower cost, no heat
sink is required, multiple poles are available, and they can switch AC or DC with
equal ease.
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1. Electromechanical Relays
General Purpose Relay: The general-purpose relay is rated by the amount of
current its switch contacts can handle. Most versions of the general-purpose relay
have one to eight poles and can be single or double throw. These are found in
computers, copy machines, and other consumer electronic equipment and
appliances.
Power Relay: The power relay is capable of handling larger power loads 10-50
amperes or more.
They are usually single-pole or double-pole units.
Contactor: A special type of high power relay, its used mainly to control high
voltages and currents in industrial electrical applications. Because of these high
power requirements, contactors always have double-make contacts.
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Time-Delay Relay: The contacts might not open or close until some time interval
after the coil has been energized. This is called delay-on-operate. Delay-on-release
means that the contacts will remain in their actuated position until some interval after
the power has been removed from the coil.
A third delay is called interval timing. Contacts revert to their alternate position at a
specific interval of time after the coil has been energized.
The timing of these actions may be a fixed parameter of the relay, or adjusted by a
knob on the relay itself, or remotely adjusted through an external circuit.
2. Solid State Relays
These active semiconductor devices use light instead of magnetism to actuate a
switch. The light comes from an LED, or light emitting diode. When control power is
applied to the devices output, the light is turned on and shines across an open
space.
On the load side of this space, a part of the devicesenses the presence of the light,
and triggers a solid state switch that either opens or closes the circuitunder control.
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Often, solid state relays are used where the circuit under control must be protected
from the introduction of electrical noises.
Advantages of Solid State Relays include low EMI/RFI, long life, no moving parts, no
contact bounce, and fast response.
The drawback to usinga solid state relay is that it can only accomplish single pole
switching.
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Chapter - 5
BASIC CIRCUIT DIAGRAM
SOLID STATE SINGLE PHASE PREVENTER
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REGULATED POWER SUPPLY
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Chapter 6
Result And Conclusion
Solid state single phase preventer is a unique device which helps us in
preventing phase. This device detach the supply when any phase from
the three phases R Y B cut or due to any kind of fault in the three
phases .
Solid state single phase preventer prevents the electricity . it only works
when all the three phases delivers power so it also serve as a safty
device for heavy electrical machinery as it detach the supply from the
system when there is any type of fault(low voltage,etc) in any phase in
three phases system.