Electronics Project Power Supply

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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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SKIT Electrical Department 12


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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.

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Electronics Project Power Supply

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