Main Project File

Variable Power Supply with Digital Control 2011

CHAPTER -1

Introduction:- The most frequently used device in electronic workshops and

laboratories is a universal power supply that Variable Power supply with digital

control .That provides a variable, fluctuation-free output. Here we present a variable

power supply with digital control that is simple and easy to construct. The circuit is

built around an adjustable 3-terminal positive-voltage regulator IC LM317, CMOS

decade counter IC CD4017, timer IC NE555 and 3-terminal .

The fixed negative-voltage regulator LM7912.The AC mains supply is stepped down

by transformer X1 to deliver a secondary output of 12V-0-12V AC, 1A. The output of

the transformer is rectified by a full-wave rectifier comprising diodes D1 through D4.

Capacitors C1 through C4 are connected in parallel to rectifier. The diodes to bypass

undesired spikes and provide smooth and fluctuation-free power. Capacitors C5 and

C13 are used as filters to eliminate ripple. Here both negative and positive half cycles

are used to obtain positive as well as negative DC output. LED1, along with current-

limiting resistor R1, is used for mains ‘on’

Indication.Timer IC NE555 (IC1) is wired as an astable multivibrator. It generates clock

pulses when switch S2 is pressed. The output of IC1 is connected, via an RC network,

to the clock input of counter IC CD4017 (IC2).IC CD4017 is a decade ring counter.

Each of its ten outputs goes high one by one when a clock pulse is received. The

outputs of IC CD4017 are connected to the bases of transistors T1 through T10

respectively, as shown in the figure. LED3 through LED11 are used here to indicate the

voltage levels. The collectors of transistors T2 through T10 are connected to presets

VR1 through VR9, respectively, which are used to set the output voltage.Adjustable

voltage regulator IC LM317 (IC4) develops 1.25V nominal reference voltage (VREF)

between its output and the adjustable terminal. The reference voltage appears across

resistor R16. When the voltage is constant, a constant current flows through one of the

output-setting variable resistors (VRset, VR1 through VR9), giving an output voltage at

pin 2 of IC4 as follows: VOUT=1.25(1+VRset/R16).Presets VR1 through VR9 are

adjusted to get the desired output voltage. The collector of transistor T1 is directly

connected to to ADJ terminal (pin 1) of IC4, so the output voltage of IC4 will be the

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voltage across fixed resistor R16, which is equal to 1.25V. When switch S3 is pressed,

pin 3 of IC2 goes high and the output voltage becomes 1.2V. When switch S2 is

pressed, the output of IC1 goes high. As a result, the outputs of IC2 go high one by one

as a ring counter. Since presets VR1 through VR9 are connected at the collectors of

transistors T2 through T10, respectively, different output resistances appear between

the adjustable and ground terminals of IC4, resulting in different output voltages. By

using a properly calibrated digital multimeter you can easily adjust the presets to obtain

1.5V to 12V.A fixed, negative 12V DC can be obtained by using fixed, negative-volt

age regulator IC LM7912 (IC3). Thus the power supply unit can be used for circuits

requiring both negative and positive DC voltages. When CD4017 is reset by pressing

switch S3, the output voltage becomes 1.2V and all the voltage-indication LEDs turn

off. Assemble the circuit on any general purpose PCB and enclose it in a suitable

cabinet. Use suitable heat-sinks for regulators IC3 and IC4. Since pin con figurations of

the regulators are different, never fix both regulators on the same heat sink. For S2 and

S3, using micro switches will enhance the beauty of the unit. LED2 is used to indicate

the 12V DC voltage.

1.2 PROJECT SURVEY & SELECTION

During the survey time for the Project we have selected the followed of topic for our

project.

Variable power supply with digital control

AC Voltage regulator PWM with rpm counter High current d.c .motor controller Medium power low cost inverter Automatic railway gate controller

From above a topic Variable power supply with digital control was chosen because of following point.

Very useful for over knowledge Simple but unique application Easy available components Useful for low power available place

So we select this topic for our project.

2


1.3 Component Required

Semiconductors:-

IC1 -NE555

IC2 -CD4017

IC3 -LM7912

IC4 -LM317

D1-D4 -1N4007

LED1 -RED

LED2 -YELLOW

LED3-LED11 -GREEN

Resistors:-

R1,R7 ,R15 -1 kilo-ohm

R17 -1 kilo-ohm

R2 -22 Kilo- ohm

R3 - 560 ohm

R4,R5 -8.2Kilo ohm

Capacitor:-

C1-C4 -47nF ceramic

C5,C13 -2200µF electrolytic

C6 -10µF electrolytic

C7 -.01µF ceramic

Miscellaneous:-

S1 -ON OFF switch

S2-S3 - PUSH-TO-ON Switch

Transformer -230v,1 Amp.

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1.4 Tools and Instruments used

Following tools and instruments were used for the preparation of this project:

Soldering Iron

Desoldering wire

Drill machine

File

Screw driver

Brush

Petrol

Soldering wire

PCB Etching Kit

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CHAPTER – 2

2.1 Circuit Description

A variable D.C supply is one of the most useful tool in electronic hobby desk. This

circuit shows a voltage up to 24V and variable current limiting up to 2A. P1 set output

current you want delivered by the Power supply on a output voltage. P2 determine the

output voltage and should be a logarithmic taper type, in order to obtain a more linear

scale voltage indication. You can select a Transformer on the basis of the maximum

output voltage and current required. The following is a schematic drawing:

The best option is: 36, 40 or 48V center-tapped and 50, 75, 80 or 100VA. C1 can be

2200 to 6800?F, 35 to 50V. Q4 must be mounted on a good heat sink to keep the output

short-circuit ongoing. In some cases, the rear panel metal box in which you will attach

the circuit can do the job. The 2N3055 transistor (Q4) can be replaced with a slightly

stronger TIP3055 type.

A Variable DC Power Supply is one of the most useful tools on the electronics

hobbyist's workbench. This circuit is not an absolute novelty, but it is simple, reliable,

"rugged" and short-proof, featuring variable voltage up to 24V and variable current

limiting up to 2A. Well suited to supply the circuits shown in this website. You can

adapt it to your own requirements

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2.2 Circuit Diagram:-

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CHAPTER-3

3.1 Working of circuit:- Divide the whole circuit in two parts as power supply

section and voltage selector section. Power supply section:-Transformer x1 step down

230 ac main to 12 v-0-12v,1A ac current. Diode1 to D4 from a bridge rectifier to

recitifiy step down voltage to DC. While capacitor c1 to c4 by pass undesired spikes.

Further filtering is performed by capacitors c5 and c13.This positive 12v dc output is

use to operate Ic1,Ic2,IC4 and to get variable output. A fixed -ve 12v dc output is

obtained by using Ic7912.Yellow Led to indicate –ve 12v output while red Led1

indicate main ON condition.

3.2 VOLTAGE SELECTOR:-The voltage selector section is use to obtained variable

voltage in nine steps from 1.5 to 12v. The section is centered around variable regulator

IC LM317(IC4). The versatility of this ic alow us to obtained voltage range from 1.2v

to 37v. The voltage of its output pin2 related to input resistance as follow:

Vout=1.25(1+VRset/R16)VOLT

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3.3 APPLICATION:-A regulated power supply is one of the most important and

essential requirement in electronics lab .The avilable power supply must provide

varrible output in step as different appliances required differnent supply voltage varying

in the range 1.5 to 12v .Also output must be easily to select and unit should provde

proper display . The present circuit is designed with keeping above point in mind.It give

varible and fluctuantaion free Dc voltage as output in the range of 1.5 to 12v .Proper

display of output selected –ve supply voltage and main ON condition are provided by

using LED.

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CHAPTER-4

4.1Component Description

NE555:- The 555 Timer IC is an integrated circuit (chip) used in a variety of timer

pulse generation and oscillator applications. The IC was designed by Hans R

Camenzind in 1970 and brought to market in 1971 by Signetics (later acquired by

Philip). The original name was the SE555 (metal can)/NE555 (plastic DIP) and the part

was described as "The IC Time Machine" It has been claimed that the 555 gets its name

from the three 5 kΩ resistors used in typical early implementations, but Hans

Camenzind has stated that the number was arbitrary. The part is still in wide use, thanks

to its ease of use, low price and good stability. As of 2003, it is estimated that 1 billion

units are manufactured every year.

Depending on the manufacturer, the standard 555 package includes over 20 transistors,

2 diodes and 15 resistors on a silicon chip installed in an 8-pin mini dual-in-line

package (DIP-8).Variants available include the 556 (a 14-pin DIP combining two 555s

on one chip), and the 558 (a 16-pin DIP combining four slightly modified 555s with

DIS & THR connected internally, and TR falling edge sensitive instead of level

sensitive).

Ultra-low power versions of the 555 are also available, such as the 7555 and

TLC555The 7555 is designed to cause less supply glitching than the classic 555 and the

manufacturer claims that it usually does not require a "control" capacitor and in many

cases does not require a power supply bypass capacitor.

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Features

Direct replacement for SE555/NE555

Timing from microseconds through hours

Operates in both astable and monostable modes

Adjustable duty cycle

Output can source or sink 200 mA

Output and supply TTL compatible

Temperature stability better than 0.005% per °C

Normally on and normally off output

Available in 8-pin MSOP package

Applications

Precision timing

Pulse generation

Sequential timing

Time delay generation

Pulse width modulation

Pulse position modulation

Linear ramp generator

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4.2. 2ND IC:- LM317:- The LM317 series of adjustable 3-terminal positive voltage

regulators is capable of supplying in excess of 1.5A over a 1.2V to 37V output range.

They are exceptionally easy to use and require only two external resistors to set the

output voltage. Further, both line and load regulation are better than standard fixed

regulators. Also, the LM317 is packaged in standard transistor packages which are

easily mounted and handled.

In addition to higher performance than fixed regulators, the LM117 series offers full

overload protection available only in IC's. Included on the chip are current limit,

thermal overload protection and safe area protection. All overload protection circuitry

remains fully functional even if the adjustment terminal is disconnected.

Normally, no capacitors are needed unless the device is situated more than 6 inches

from the input filter capacitors in which case an input bypass is needed. An optional

output capacitor can be added to improve transient response. The adjustment terminal

can be bypassed to achieve very high ripple rejection ratios which are difficult to

achieve with standard 3-terminal regulators.

Besides replacing fixed regulators, the LM117 is useful in a wide variety of other

applications. Since the regulator is “floating” and sees only the input-to-output

differential voltage, supplies of several hundred volts can be regulated as long as the

maximum input to output differential is not exceeded, i.e., avoid short-circuiting the

output.

Also, it makes an especially simple adjustable switching regulator, a programmable

output regulator, or by connecting a fixed resistor between the adjustment pin and

output, the LM117 can be used as a precision current regulator. Supplies with electronic

shutdown can be achieved by clamping the adjustment terminal to ground which

programs the output to 1.2V where most loads draw little current.

For applications requiring greater output current, see LM150 series (3A) and LM138

series (5A) data sheets. For the negative complement, see LM137 series data sheet.

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Features

Guaranteed 1% output voltage tolerance (LM317A)

Guaranteed max. 0.01%/V line regulation (LM317A)

Guaranteed max. 0.3% load regulation (LM117)

Guaranteed 1.5A output current

Adjustable output down to 1.2V

Current limit constant with temperature

4.3 3rd IC:-LM7912:-The LM7912 three terminal negative voltage regulator IC is

available in TO-220 package and with a fixed output voltage of -12 volt, making it

useful in a wide range of applications. Each type employs internal current limiting,

thermal shut down and safe operating area protection, making it essentially

indestructible

Features

Thermal, short circuit and safe area protection

High ripple rejection

1.5A output current

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4.4 4th IC:-CD4017

Description:-The CD4017BM/CD4017BC is a 5-stage divide-by-10 Johnson counter

with 10 decoded outputs and a carry out bit.The CD4022BM/CD4022BC is a 4-stage

divide-by-8 Johnson counter with 8 decoded outputs and a carry-out bit.These counters

are cleared to their zero count by a logical "1" on their reset line. These counters are

advanced on the positive edge of the clock signal when the clock enable signal is in the

logical "0" state.The configuration of the CD4017BM/CD4017BC and

CD4022BM/CD4022BC permits medium speed operation and assures a hazard free

counting sequence. The 10/8 decoded outputs are normally in the logical "0" state and

go to the logical "1" state only at their respective time slot. Each decoded output

remains high for 1 full clock cycle. The carry-out signal completes a full cycle for every

10/8 clock input cycles and is used as a ripple carry signal to any succeeding stages.

Features

Wide supply voltage range: 3.0V to 15V

High noise immunity: 0.45 VDD (typ.)

Low power: Fan out of 2 driving 74L

TTL compatibility: or 1 driving 74LS

Medium speed operation: 5.0 MHz (typ.): with 10V VDD

Low power: 10 µW (typ.)

Fully static operation

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4.5 Pin configuration:-

Applications

Automotive

Instrumentation

Medical electronics

Alarm systems

Industrial electronics

Remote metering

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4.6. TRANSISTOR:-BC548

Description:-A transistor controls the flow of current or presence of voltage in a

circuit, acting as a switch, gate or amplifier for electronic signals. The transistor may be

driven in a digital manner, so that the "gate" is either on or off, or it may be operated in

an analog manner, allowing variable current flow depending on the needs of the circuit

Related

Application:- The LM3411 is a low power fixed-voltage (3.3V or 5.0V) precision

shunt regulator designed specifically for driving an optoisolator to provide feedback

isolation in a switching regulator. The LM3411 circuitry includes an internally

compensated op amp, a bandgap reference, NPN output transistor, and voltage setting

resistors. A trimmed precision bandgap reference with temperature drift curvature

correction, provides a guaranteed 1% precision over the operating temperature range (A

grade version).

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4.7 DIODE:-

4.1 IN4007

Description:------Design active filter circuits including low pass, high pass, band stop,

and band pass filters using op amps ICs. Bessel, Butterworth, Chebyshev (0.01dB to

1dB), Equiripple with Linear Phase, Transitional Gaussian, and Legendre Papoulis filter

approximations are supported. Filter circuits are composed of 2nd order Sallen-Key,

Multiple Feedback, State Variable, Dual Follower, Fliege, Gyrator, or Voltage-

Controlled Voltage Source stages supported.

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4.8. LED:-

RED LED : Light emitting diodes, commonly called LEDs, are real unsung heroes in

the electronics world. They do dozens of different jobs and are found in all kinds of

devices. Among other things, they form the numbers on digital clocks transmit

information from remote controls, light up watches and tell you when your appliances

are turned on. Collected together, they can form images on a jumbo television screen or

illuminate a traffic light.

Basically, LEDs are just tiny light bulbs that fit easily into an electrical circuit. But

unlike ordinary incandescent bulbs, they don't have a filament that will burn out, and

they don't get especially hot. They are illuminated solely by the movement of electrons

in a semiconductor material, and they last just as long as a standard transistor. In this

article, we'll examine the simple principles behind these ubiquitous blinkers,

illuminating some cool principles of electricity and light in the process.

Description:------ LEDs must be connected the correct way round,

the diagram may be labelled a or + for anode and k or - for cathode

(yes, it really is k, not c, for cathode!). The cathode is the short lead

and there may be a slight flat on the body of round LEDs. If you can see inside the LED

the cathode is the larger electrode (but this is not an official identification method).

LEDs can be damaged by heat when soldering, but the risk is small unless you are very

slow. No special precautions are needed for soldering most LEDs.

Example: Circuit symbol:

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LED SECOND:-YELLOW LED:-

Description: LEDs - those blinky things. A must have for power indication, pin status,

opto-electronic sensors, and fun blinky.

DIAGRAM:-

This is a very standard, yellow LED. The lens is 3mm in diameter and it is diffused.

Features:

2.0-2.4VDC forward drop

Max current: 20mA

Suggested using current: 16-18mA

Luminous Intensity: 40-100mcd

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4.9. RESISTORS:-

DESCRIPTION:- Electrical energy is converted to heat when current flows

through a resistor. Usually the effect is negligible, but if the resistance is low (or the

voltage across the resistor high) a large current may pass making the resistor become

noticeably warm. The resistor must be able to withstand the heating effect and resistors

have power ratings to show this.

Power ratings of resistors are rarely quoted in parts lists because for most circuits the

standard power ratings of 0.25W or 0.5W are suitable. For the rare cases where a higher

power is required it should be clearly specified in the parts list, these will be circuits

using low value resistors (less than about 300 ) or high voltages (more than 15V).

Example: Circuit symbol:

Function

Resistors restrict the flow of electric current, for example a resistor is placed in series

with a light-emitting diode (LED) to limit the current passing through the LED.

Connecting and soldering

Resistors may be connected either way round. They are not damaged by heat when

soldering.

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Resistor values - the resistor colour code

Resistance is measured in ohms, the symbol for ohm is an omega

.

1 is0 quite small so resistor values are often given in k and M .

1 k = 1000 1 M = 1000000 .

Resistor values are normally shown using coloured bands.

Each colour represents a number as shown in the table.

Most resistors have 4 bands:

o The first band gives the first digit.

o The second band gives the second digit.

o The third band indicates the number of zeros.

o The fourth band is used to shows the tolerance (precision) of the resistor, this may

be ignored for almost all circuits but further details are given below.

Table – 5 Resistor colour coding

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The Resistor

Colour Code

Colour Number

Black 0

Brown 1

Red 2

Orange 3

Yellow 4

Green 5

Blue 6

Violet 7

Grey 8

White 9


This resistor has red (2), violet (7), yellow (4 zeros) and gold bands.

So its value is 270000 = 270 k .

On circuit diagrams the is usually omitted and the value is written 270K.

The power, P, developed in a resistor is given by:

P = I² × R

or

P = V² / R

where: P = power developed in the resistor in watts (W)

I = current through the resistor in amps (A)

R = resistance of the resistor in ohms ( )

V = voltage across the resistor in volts (V)

Examples:

A 470 resistor with 10V across it, needs a power rating P = V²/R = 10²/470 =

0.21W.

In this case a standard 0.25W resistor would be suitable.

A 27 resistor with 10V across it, needs a power rating P = V²/R = 10²/27 =

3.7W.

A high power resistor with a rating of 5W would be suitable.

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4.10 CAPACITOR:- Capacitor:-(ceramic capacitor)ceramic capacitor is the

"disc capacitor". This device pre-dates the transistor and was use

Description:- A ceramic capacitor is a two-terminal, non-polar device. The classical

extensively in vacuum-tube equipment (e.g., radio receivers) from about 1930 through

the 1950s, and in discrete transistor equipment from the 1950s through the 1980s. As of

2007, ceramic disc capacitors are in widespread use in electronic equipment, providing

high capacity and small size at low price compared to other low value capacitor types.

Ceramic capacitors come in various shapes and styles

Application of ceramic capacitor:- Ceramic capacitors are suitable for moderately

high-frequency work (into the high hundreds of megahertz range, or, with great care,

into the low gigahertz range), as modern ceramic caps are fairly non-inductive

compared to the other major classes of capacitors (film and electrolytic). Capacitor

technologies with higher self-resonant frequencies tend to be expensive and esoteric

(typically, mica or glass capacitors).

22


Electrolytic capacitor:-

Description:- Electrolytic capacitors are capable of providing the highest capacitance

values of any type of capacitor but they have drawbacks which limit their use. The

standard design requires that the applied voltage must be polarized; one specified

terminal must always have positive potential with respect to the other. Therefore they

cannot be used with AC signals without a DC polarizing bias. However there are

special non-polarized electrolytic capacitors for AC use which do not require a DC bias.

Electrolytic capacitors also have relatively low breakdown voltage, higher leakage

current and inductance, poorer tolerances and temperature range, and shorter

DIAGRAM:-

7.4 Application :- The first major application of DC versions of this type of capacitor

was in large telephone exchanges, to reduce relay hash (noise) on the 48 volt DC power

supply. The development of AC-operated domestic radio receivers in the late 1920s

created a demand for large capacitance (for the time) high voltage capacitors, typically

at least 4 microfarads and rated at around 500 volts DC. Waxed paper and oiled silk

capacitors were available but devices with that order of capacitance and voltage rating

were bulky and prohibitively expensive.

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4.11 TRANSFORMER:-

Description:- A transformer is a static device that transfers electrical energy from

one circuit to another through inductively couple with conductors—the transformer's

coils. A varying current in the first or primary winding creates a varying magnetic

flux in the transformer's core and thus a varying magnetic field through

the secondary winding. This varying magnetic field induces a varying electromotive

force (EMF) or "voltage" in the secondary winding. This effect is called mutual

induction.

If a load is connected to the secondary, an electric current will flow in the secondary

winding and electrical energy will be transferred from the primary circuit through the

transformer to the load. In an ideal transformer, the induced voltage in the secondary

winding (Vs) is in proportion to the primary voltage (Vp), and is given by the ratio of the

number of turns in the secondary (Ns) to the number of turns in the primary (Np) as

follows:

By appropriate selection of the ratio of turns, a transformer thus allows

an alternating current (AC) voltage to be "stepped up" by making Ns greater

than Np, or "stepped down" by making Ns less than Np.

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Circuit diagram:-

APPLICATION:- A major application of transformers is to increase voltage

before transmitting electrical energy over long distances through wires. Wires

have resistance and so dissipate electrical energy at a rate proportional to the square of

the current through the wire. By transforming electrical power to a high-voltage (and

therefore low-current) form for transmission and back again afterward, transformers

enable economical transmission of power over long distances. Consequently,

transformers have shaped the electricity supply industry, permitting generation to be

located remotely from points of demand. All but a tiny fraction of the world's electrical

power has passed through a series of transformers by the time it reaches the con.

Transformers are also used extensively in electronic products to step down the

supply voltage to a level suitable for the low voltage circuits they contain. The

transformer also electrically isolates the end user from contact with the supply voltage.

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4.12 FUSE:-A fuse consists of a metal strip or wire fuse element, of small cross-

section compared to the circuit conductors, mounted between a pair of electrical

terminals, and (usually) enclosed by a non-conducting and non-combustible housing.

The fuse is arranged in series to carry all the current passing through the protected

circuit. The resistance of the element generates heat due to the current flow. The size

and construction of the element is (empirically) determined so that the heat produced

for a normal current does not cause the element to attain a high temperature. If too high

a current flows, the element rises to a higher temperature and either directly melts, or

else melts a soldered joint within the fuse, opening the circuit.

When the metal conductor parts, an electric arc forms between the un-melted ends of

the element. The arc grows in length until the voltage required to sustain the arc is

higher than the available voltage in the circuit, terminating current flow. In alternating

current circuits the current naturally reverses direction on each cycle, greatly enhancing

the speed of fuse interruption. In the case of a current-limiting fuse, the voltage required

to sustain the arc builds up quickly enough to essentially stop the fault current before

the first peak of the AC waveform. This effect significantly limits damage to

downstream protected devices

The fuse element may be surrounded by air, or by materials intended to speed the

quenching of the arc. Silica sand or non-conducting liquids may be used.

DIAGRAM:-

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4.13 HEAT SINK:-

Descption:- A heat sink is an object that transfers thermal energy from a higher

temperature to a lower temperature fluid medium. The fluid medium is frequently air,

but can also be water or in the case of heat exchangers, refrigerants and oil. If the fluid

medium is water, the 'heat sink' is frequently called a cold plate.

To understand the principle of a heat sink, consider Fourier's law of heat

conduction. Joseph Fourier was a French mathematician who made important

contributions to the analytical treatment of heat conduction. Fourier's law of heat

conduction, simplified to a one-dimensional form in the x-direction, shows that when

there is a temperature gradient in a body, heat will be transferred from the higher

temperature region to the lower temperature region. The rate at which heat is transferred

by conduction, qk, is proportional to the product of the temperature gradient and the

cross-sectional area through which heat is transferred.

10.2 Application:- Heat dissipation is an unavoidable by-product of all but

micropower electronic devices and circuits. In general, the temperature of the device or

component will depend on the thermal resistance from the component to the

environment, and the heat dissipated by the component. To ensure that the component

temperature does not overheat, a thermal engineer seeks to find an efficient heat transfer

path from the device to the environment. The heat transfer path may be from the

component to a printed circuit board (PCB), to a heat sink, to air flow provided by a

fan, but in all instances, eventually to the environment.

4.14 Transistors

Transistors amplify current, for example they can be used to amplify the small output

current from a logic IC so that it can operate a lamp, relay or other high current device.

In many circuits a resistor is used to convert the changing current to a changing voltage,

so the transistor is being used to amplify voltage.

A transistor may be used as a switch (either fully on with maximum current, or fully off

with no current) and as an amplifier (always partly on).

27


Types of transistor

NPN

PNP

Fig- 11 Transistors

4.15 Solder

Soldering filler materials are available in many different alloys for differing

applications. In electronics assembly, the eutectic alloy of 63% tin and 37% lead (or

60/40, which is almost identical in performance to the eutectic) has been the alloy of

choice. Other alloys are used for plumbing, mechanical assembly, and other

applications. A eutectic formulation has several advantages for soldering; chief among

these is the coincidence of the liquidus and solidus temperatures, i.e. the absence of a

plastic phase. This allows for quicker wetting out as the solder heats up, and quicker

setup as the solder cools.

Soldering Iron and Soldering Wire

4.16 Flux

In high-temperature metal joining processes (welding, brazing and soldering), the

primary purpose of flux is to prevent oxidation of the base and filler materials. Tin-lead

solder, for example, attaches very well to copper, but poorly to the various oxides of

copper, which form quickly at soldering temperatures. Flux is a substance which is

nearly inert at room temperature, but which becomes strongly reducing at elevated

temperatures, preventing the formation of metal oxides. Secondarily, flux acts as a

28


wetting agent in the soldering process, reducing the surface tension of the molten solder

and causing it to better wet out the parts to be joined. Fluxes currently available include

water-soluble fluxes and 'no-clean' fluxes which are mild enough to not require removal

at all.

CHAPTER-5

29


5.1 Soldering of Components on PCB

For hand soldering of electronic components, the heat source tool should be selected to

provide adequate heat for the size of joint to be completed. A 100 watt soldering iron

may provide too much heat for printed circuit boards, while a 25 watt iron will not

Soldered Components

provide enough heat for large electrical connectors, joining copper roof flashing, or

large stained-glass lead came. Using a tool with too high a temperature can damage

sensitive components, but protected heating by a tool that is too cool or under powered

can also cause extensive heat damage. Hand-soldering techniques require a great deal of

skill to use on the finest pitch chip packages. The soldering iron tip must be clean and

pre-tinned with solder to ensure rapid heat transfer. Components which dissipate large

amounts of heat during operation are sometimes elevated above the PCB to avoid PCB

overheating. After inserting a through-hole mounted component, the excess lead is cut

off, leaving a length of about the radius of the pad. Visually, a good solder joint will

appear smooth and shiny, with the outline of the soldered wire clearly visible. The tip of

the iron is kept wetted with solder ("tinned") when hot to minimize oxidation and

corrosion of the tip itself.

Applications

30


One of the most frequent applications of soldering is assembling electronic components

to printed circuit boards (PCBs). Another common application is making permanent but

reversible connections between copper pipes in plumbing systems. Joints in sheet metal

objects such as food cans, roof flashing, rain gutters and automobile radiators have also

historically been soldered, and occasionally still are. Jewelry components are assembled

Applications of Soldering

and repaired by soldering. Small mechanical parts are often soldered as well. Soldering

is also used to join lead came and copper foil in stained glass work. Soldering can also

be used as a semi-permanent patch for a leak in a container or cooking vessel.

4.2 PCB Fabrication

A printed circuit board, or PCB, is used to mechanically support and electrically

connect electronic components using conductive pathways, tracks, or traces, etched

from copper sheets laminated onto a non-conductive substrate. It is also referred to as

printed wiring board (PWB) or etched wiring board. A PCB populated with electronic

components is a printed circuit assembly (PCA), also known as a printed circuit board

assembly (PCBA).

The PCB fabrication steps are:

• PCB board design

• Printing Artwork

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• Exposure

• Developing

• Etching

• Cutting and Drilling

• Tinning and Masking

PCB Board Design

Material and Equipment

• Electronics Schematic Design Computer

• Protel DXP or PCB design software

PCB design introduction

Before any PCB fabrication can be done, we need to design PCB electrical pads for

component placing and trace for component connectivity. It can be draw by hand but if

your design is very complex, the PCB software will be very helpful. The software have

ready to use components footprint, and modification can be easy done, saving you a lot

of time and effort as compare to manual drawing. Professional PCB software such as

CADSTAR and PROTEL can easy cost above thousands of dollars. Simple and basic

PCB software such as Eagle or Easy-PC is slightly lower in cost, in the range of about

$500 to $1200. They are cheaper in cost, but features can be limited. Limitation can be

in the form of limited board size, number of board layer or the number of component's

pin allowed in the design.

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PCB layout

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5.3 Printing Artwork


• PCB artwork

• Paper

• Printer

• Transparency

• Laser printer or photo copier

Artwork introduction

The PCB layout can be printed from a normal home printer onto a white piece of paper.

The printing will be photocopied to a transparency. The transparency will be use for

photo-resist PCB board exposure in the next stage. A laser printer is preferred for

sharper trace, especially if the traces are very close to each other. The laser printer can

also print directly to transparency. The transparency is cut to PCB size 15x10cm. Five

PCB artwork are squeezed and arranged to maximize board usage. The following step

presents the traditional photo exposure method. The etch resistance layer can be formed

on the photo sensitive board after the exposure.

Fig. 23 A Closer View of a Printed PCB Pad and Traces

Photocopied onto a Transparency

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• Ultra violet lamp

• A box

• Positive Acting Presensitized PCB board

• Transparency with PCB artwork printed

• Scotch tape

Exposure Equipment

Exposure introduction

A typical Ultra Violet UV lamp for exposure on a Positive Acting Presensitized Kinsten

PCB board. Preparing PCB board for exposure. Tear off the white/black protective film

on the board. Place the transparency artwork on top of the PCB board. Secure the

artwork position with scotch tape.

Exposure setup

If you have a piece of glass, place it on top, to make a good contact between the artwork

and the PCB board. Close proximity should be maintained to make sure that traces are

not exposing to the UV light.

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PCB exposure

Turn on and expose the PCB board for 90 seconds for ultra violet lamp, or 6-10 minutes

for normal fluorescent lamp. The above reference is base on the guideline of the lamp

of about 5 cm distances away from the artwork PCB. If the distance is far from the

typical one, the exposure time should increase proportionally.

Peeling off the Protective Film from the PCB Board

5.3 Developing


• Sodium Hydroxide or Developer solution

• Distill or plain water

• Glove

• Glass, plastic, wooden rod or old chopstick

• Container slightly bigger than the PCB board

• Exposed PCB board

• Container with water for washing

36


Developer introduction

Sodium Hydroxide is used as a developer. Correct proportion is necessary as too much

will destroy the photo-resist coating instantly, while too little will have no effect in

developing the PCB. Commercial developer solution (pre-mixed with distill water)

might work better since mixture is in the correct ratio for PCB developing. Silicate

makes a better developer as less likely to be over-developed. Higher concentration will

increase the developing speed.

Developer Equipment

Developer mixture

The solvent composite for making the developer consist ratio of about 1unit of Sodium

Hydroxide is to 20 unit of Water. The solution must be of uniform concentration. Stir

the mixture until NaOH is fully dissolved in the water. If the chemical is not fully

dissolved, the region with concentrated NaOH can destroy the photo-resist coating

instantly. When mixing NaOH to water, heat will be produce. Stir the water solution

constantly while adding in NaOH slowly.

Various Developing Chemicals

- Sodium Metasilicate (msds) - Sodium Hydroxide NaOH (msds)

37


Developing PCB board

The board is fully developed when the PCB traces appear green in color. This green

layer is the photo resist layer which protects the copper surface underneath during the

etching process. The region to be etched away later will be exposing and is brown in

color. The brown color is the actual color of the copper. There is no photo-resist coating

to protect the surface. Rinse the developed PCB board with running water after

developing.

Remove Transparency and do Coating

5.4 Etching


• Ferric Chloride powder

• Distill or plain water

• Glove

• Glass, plastic, wooden rod or old chopstick

• Long container for the etchant

• A boarder container for boiling hot water below

• 3 liters of boiling water

• Drilling machine

38


Etching introduction

Ferric Chloride is use to etch away copper surface on the PCB board. It is a very toxin

chemical and is harmful to the environment. It is dark yellowish in color and can stain

your clothing. Remember to wear protective gloves while handling FeCl3. Chemical is

toxin and will cause skin irritation. Wash skin with running water immediately when in

contact with skin. Stronger FeCl3 solution enables etching process to be faster. When

designing PCB board, it may be a good idea to fill up with regions of copper. This is to

minimize the area of copper surface to be etched away.

Etchant mixture

The solvent composite for making the etchant consist of about 1 unit of Ferric Chloride

FeCl3 is to 3 unit of water or about 1 unit of Ammonium Persulphate is to 5 unit of

water. Stir the mixture until FeCl3 is fully dissolved with the water.

Various Etching chemicals

- Ferric Chloride FeCl3 (msds)

- Ammonium Persulphate (msds)

- Sodium Persulphate (msds)

- Peroxy Sulfuric (recyclable chemical)

- Ammonium Persulphate (msds)

Warming up Etchant

Warm up the FeCl3 solution on a tray (blue) filled with hot water. Temperature range

from about 50°C to 60°C will be suitable to speed up etching process. Drill a small hole

on the PCB board so that a string can be secure to the board. The string is use to

position or pull out the PCB in the toxin solution.

Etching PCB

Immerse the PCB board slowly into the FeCl3 solution. Agitate the PCB by tilting the

container to and fro gently, until the unwanted copper layer is properly etched away,

39


leaving only the required region on the PCB. The process may take 15 - 60 minutes to

complete. Process duration will depends on the concentration, temperature of the

etchant solution. Etching method also plays a part in the etching speed. If you leave the

board without any agitation, the process may take hours.

The etching effectiveness will be reduced if the solution is re-used for a number of

times. Strong FeCl3 concentration and high temperature can increase the etching speed.

Testing various etch resist material

The photos simulate a developed PCB board masked with some scotch tape, masking

tape, and text using oil based marker. The board is over-developed and is used for

testing various etch resist materials. The experiment shows that adhesive tapes and oil

base marker can be implemented to perform as a mask to resist from the etchant.

Fig. 28 Etching Machine

Washing board condemned with FeCl3

Prepare a container of detergent solution to wash the PCB board condemned with

chemical FeCl3. Detergent contains Sodium Carbonate or Sodium Hydroxide, which

can neutralize FeCl3. Photo-resist mask or marking of the traces can be removed using

the NaOH developer. It is the same developer used during the developing process.

Stronger solution can be use this time round as the etching is already completed. The

protective coating is no more in use. A cloth soak with the solution can be use to wipe

40


on the PCB board surface to remove the coating. For the marker stain, it can be

removed using commercial available contact cleaner, alcohol, or thinner solution. Rinse

with water, clean and dry the PCB board.

Disposing toxin chemical

Ferric Chloride FeCl3 is a toxin chemical. Please consult your local authority for

proper dispose of chemical waste product. As recommended, detergent (or other baking

soda) can be mixed to the FeCl3 solution. The mixture solution can easily produce

bubble foam which can grow 10 times in volume. Lay waste paper under the container

to prevent toxin overflowing out of the container onto the floor. Leave it to dry before

disposing the waste. PCB board etching until the unwanted copper is remove

completely by the chemical.

Etching

5.5 Cutting and Drilling

Material and equipment

• Dot punch or sharp tool

• Drilling machine or hand drill

• 1mm, 1.5mm drill bits

• Hand files

• Penknife

• Steel ruler

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Drill Machine

Introduction to cutting and drilling

The etching is completed. The original artwork is arranged to maximize the use of the

PCB board. 5 small PCB can be fabricated on the 15cm x 10cm board. 3 of the PCB

pattern is not formed properly during the developing process, therefore only 2 PCB

board can be extracted. Hole is necessary to mount component (example: resistor,

capacitor, inductor, board mount switch, DIP integrated circuit IC etc). Before drilling,

a dot punch is used to mark the hole position. This serves as a shallow guide for the

drill bit to align easily while drilling. Any other sharp pointed tool can be use to do the

marking. The drill is fitted with a 1mm drill bit. A 1mm drill bit is thin and can break

easily. Hold the drill steady and drill in straight slowly. The hole will be drilled with

little force applied.

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Complete Fabrication of Smaller Individual PCB Board

5.6 Tinning and Masking


• Solder flux

• Soldering iron (flat tip is available)

• Soldering stand with wetted sponge

• Solder sucker

Tinning the copper surface

Copper will oxidize when exposed to oxygen environment. Oxidization should be

avoided as soldering is difficult on oxidization surface. A thin layer of solder is coated

43


on the copper surface to prevent oxidization. Apply solder to the copper surface with

hot soldering iron and spread the liquefied solder across the surface. Covering the

copper surface with solder helps protect the copper from oxidization.

Masking PCB board

Masking can be applied to non-soldering area to protect the board from potential short

circuit, oxidization and overflow of solder during soldering. The soldering would also

be easier and nicer.

Tinned and Finish PCB Product

Take a suitable copper Clad Board and draw the layout on it with the help of a carbon

paper.

Now overdraw the layout by nail polish solution. A syringe can be used for the purpose.

Dry the board.

Prepare the Ferric Chloride Solution for etching copper-clad board.

Now etch the unwanted copper from the board using ferric Chloride Solution. PCB

should be submerged into Solution properly.

With regular stirring, etching will take 20 minutes or longer depending on how many

times the solution has been used before.

While etching proper care should be given to protect your hands and body from the

solution. Latex gloves can be used for the purpose.

Now Dry the PCB

After Drying, drilling is done. You can use a PCB hand drill or a motor driver drill.

Clean the PCB and it is ready for use.

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CHAPTER-6

6.1 Digital Voltmeter:-

A voltmeter is an instrument used for measuring the electrical potential difference

between two points in an electric circuit. Analog voltmeters move a pointer across a

scale in proportion to the voltage of the circuit; digital voltmeters give a numerical

display of voltage by use of an analog to digital converter.

Voltmeters are made in a wide range of styles. Instruments permanently mounted in a

panel are used to monitor generators or other fixed apparatus. Portable instruments,

usually equipped to also measure current and resistance in the form of a multimeter, are

standard test instruments used in electrical and electronics work. Any measurement that

can be converted to a voltage can be displayed on a meter that is suitably calibrated; for

example, pressure, temperature, flow or level in a chemical process plant.

General purpose analog voltmeters may have an accuracy of a few percent of full scale,

and are used with voltages from a fraction of a volt to several thousand volts. Digital

meters can be made with high accuracy, typically better than 1%. Specially calibrated

test instruments have higher accuracies, with laboratory instruments capable of

measuring to accuracies of a few parts per million. Meters using amplifiers can measure

tiny voltages of micro volts or less.

Diagram :-

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Application of voltmeter:- DVMs measure both alternating current (Ac) and direct

current (DC) in electronics. Common laboratory and commercial applications involve

electromechanical machinery with a current flowing through wires and circuits. Often,

a digital voltmeter is used to monitor a unit, such as a generator. Portable or handheld

devices, such as the digital multimeter (DMM), for example, may combine several

functions into one instrument measuring voltage, current, and resistance. This is the

preferred tool of an electrician

6.2 Application

Different units in factory

Bridge street lighting

High loaded device

Electronics Laboratries

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CHAPTER-7

Costing

Parts name Cost

Semiconductors

IC1-NE555 40

IC2-CD4017 40

IC3-LM7912 50

IC4-LM317 50

Transistor 20

PCB 35

7805, 5V regulator 20

Heat Sink 20

Diodes 20

LEDs 30

Resistor

10-kilo-ohm × 2 5

100-kilo-ohm × 2 5

220-ohm 5

1-kilo-ohm × 4 10

Capacitors

1000µF, 35V electrolytic 5

0.1µF ceramic disk 2



Miscellaneous

230V AC primary to 12V,500mA secondary

transformer

100

Push-to-‘on’ switch 15

Fuse 20

Total cost 496

Price LIST

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7.2 Bibliography

[1] www.datasheet.com

[2] www.vishay.com

[3] www.futurlec.com

[4] www.electronics-tutorials.ws/index.html

[5] Electronics for you magazine

48

http://www.futurlec.com/

http://www.vishay.com/

http://www.datasheet.com/

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