minor project vvr

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  A Minor Project Submitted in partial fulfillment of the requirement for the award of the degree BACHELOR OF ENGINEERING (Electrical & Electronics Engg.) Submitted To RAJIV GANDHI PRODYOGIKI VISHWAVIDYALAYA, BHOPAL (M.P.) Submitted by Ghanshyam Kumar Baghel Roll No. 0133EX091021  Under the supervision of Mr. Vivek Shrivastava Lecturer SAGAR INSTITUTE OF RESEARCH AND TECHNOLOGY (Department of Electrical & Electronics Engineering) BHOPAL (M.P.) June-2012

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Page 1: Minor Project Vvr

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A Minor Project

Submitted in partial fulfillment of the requirement for the award of the degree

BACHELOR OF ENGINEERING

(Electrical & Electronics Engg.)

Submitted To 

RAJIV GANDHI PRODYOGIKI VISHWAVIDYALAYA,

BHOPAL (M.P.)

Submitted by

Ghanshyam Kumar Baghel

Roll No. 0133EX091021 

Under the supervision of 

Mr. Vivek Shrivastava

Lecturer

SAGAR INSTITUTE OF RESEARCH AND TECHNOLOGY

(Department of Electrical & Electronics Engineering)

BHOPAL (M.P.)

June-2012

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SAGAR INSTITUTE OF RESEARCH AND TECHNOLOGY

(Department of Electrical & Electronics Engineering)

BHOPAL (M.P.)

CERTIFICATE

This is to certify that the work embodies in this project entitled  “Variable Voltage Regulator

(VVR)” being Submitted by Ghanshyam Baghel Enrollment No. [0133EX091021] in partial

fulfillment of Minor Project for the award of the degree of “Bachelor Of Engineering” to RAJIV

GANDHI PRODYOGIKI VISHWAVIDYALAYA, BHOPAL (M.P.) during the academic year

2009-13 is a record of bonafide piece of work, carried out by him under my supervision and guidance

in the Department of Electrical & Electronics Engineering, Sagar Institute  of Research &

Technology, Bhopal.

Prof. A. A. Ansari Mr. Vivek Shrivastava

HOD (EX) Guided By

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SAGAR INSTITUTE OF RESEARCH AND TECHNOLOGY

(Department of Electrical & Electrical Engineering)

BHOPAL (M.P.)

DECLARATION

I Ghanshyam Baghel, a student of  “Bachelor Of Engineering  in Sagar Institute of Research &

Technology” , session 2009-13, Bhopal (M.P.)  here by informed that the work presented in this

Minor Project entitled “Variable Voltage Regulator (VVR)” is the outcome of my own work, is

bonafide and correct to the best of my knowledge and this work has been carried out taking care of 

Engineering Ethics. The work presented does not infringe any patented work and has not been

submitted to any other University or anywhere else for the award of any degree or any professional

diploma.

GHANSHYAM BAGHEL

Roll No 0133EX091021 

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 ACKNOWLEDGEMENT

I take an opportunity to acknowledge and extend my heartfelt gratitude to my guide and the pivot

of this enterprise, Lect. Mr. Vivek Shrivastava who is most responsible for helping me to complete

this work. He showed me different ways to approach the problems and the need to be persistent to

accomplish my goal. His discernment in the choice of topic, his confidence in me when I doubted

myself and his admirable guidance are some cogent reasons that make me over that without his

support this thesis would be a chimera.

I am also thankful to Prof. Pratima Singh, TG EX, Prof. A. A. Ansari, Head of Department of

Electrical & Electronics Engineering for cooperation and support to complete this work. I would also

like to express my thanks to Dr. S.C.Bhageria  Group Director, and SIRT Bhopal providing

necessary facilities.Thanks are due to all the staff members and lab staff of Department of Electrical

and Electronics Engineering SIRT for providing all help and support.

GHANSHYAM BAGHEL 

Roll No 0133EX091021

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SAGAR INSTITUTE OF RESEARCH AND TECHNOLOGY

(Department of Electrical & Electrical Engineering)

BHOPAL (M.P.)

CERTIFICATE OF APPROVAL

This foregoing project work is hereby approved as a creditable

engineering study carried out and presented in a manner satisfactory to

warranty of its acceptance as a prerequisite to the degree for which it

has been submitted. It is understood that by this approval the undersigned

do not necessarily endorse or approve any statement made. Opinion

expressed or conclusion drawn therein, but approve the thesis only for

the purpose for which it has been submitted. 

(Internal Examiner) (External Examiner)

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  ABSTRACT 

This DC power supply circuit is adjustable using IC Voltage Regulator LM317. LM317 is a

versatile and highly efficient 1.2-37V voltage regulator that can Provide up to 1.5A of 

current with a large heat sink. It's ideal for just about any application. This was my firstworkbench power supply and I still use it. Since LM317 is protected against short-circuit,

no fuse is necessary.

Thanks to automatic thermal shutdown, it will turn off if heating excessively. All in all,

a very powerful (and affordable!) package, indeed. Although voltage regulator LM317 iscapable of delivering up to 37V, the DC power supply output circuit here is limited to

25V for the sake of safety and simplicity. Any higher output voltage would require

additional components and a larger heat sink. Make sure that the input voltage is

atleast a couple of Volts higher than the desired output. It's OK to use a trim-pot if you're building a fixed-voltage supply.

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  INTRODUCTION 

This is a variable Voltage Regulator which in this circuit IC LM317 be a heart. LM317 is a voltage regulator IC

that is well known among practitioners of the power supply. It is easy in assembling and calculating

when wanting specific output voltage values. To construct this variable DC powersupply using atransformer with a capacity of 2-3A with the output voltage of approximately 28VDC.

The output of this  power supply can be changed from 1.25V to 25 V DC byturning thepotentiometer 5K.Capacitors are used on a variable DC power supply is intended to filter

the DCoutput voltage. Diode bridge rectifier is used to full wave to reduce noise in thedischarge voltage.In the

variable DC power supply schematic we will find a principle of calculation of an LM317 circuit. Itcan handle currents up to 1A. Use proper heat sink for LM317 if it has to dissipate more than 1W.

LM317 is the standard part number for an integrated three-terminal adjustable linear voltageregulator. LM317 is a positive voltage regulator supporting input voltage of 3V to 40V and output

voltage between 1.25V and 37V. A typical current rating is 1.5A although several lower and higher

current models are available. Variable output voltage is achieved by using a potentiometer or avariable voltage from another source to apply a control voltage to the control terminal. LM317 alsohas a built-in current limiter to prevent the output current from exceeding the rated current, and

LM317 will automatically reduce its output current if an overheat condition occurs under load.

LM317 is manufactured by many companies, including National Semiconductor, FairchildSemiconductor, and STMicroelectronics.

Although LM317 is an adjustable regulator, it is sometimes preferred for high-precision fixed voltageapplications instead of the similar LM78xx devices because the LM317 is designed with superior

output tolerances. For a fixed voltage application, the control pin will typically be biased with a fixed

resistor network, a Zener diode network, or a fixed control voltage from another source.

Manufacturer datasheets provide standard configurations for achieving various design applications,including the use of a pass transistor to achieve regulated output currents in excess of what the

LM317 alone can provide.

LM317 is available in a wide range of package forms for different applications including heatsink 

mounting and surface-mount applications. Common form factors for high-current applications

include TO-220 with part number LM317T and TO-3 with part number LM317K. LM317 is capableof dissipating a large amount of heat at medium to high current loads and the use of a heatsink is

recommended to maximize the lifespan and power-handling capability.

The LM317L is an adjustable 3-terminal positive voltage regulator capable of supplying 100mA

over a 1.2V to 37V output range. It is exceptionally easy to use and requires only two externalresistors to set the output voltage. Further, both line and load regulation are better than standard fixed

regulators. Also, the LM317L is available packaged in a standard TO-92 transistor package which is

easy to use.

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DESCRIPTION OF PROJECT

VARIABLE DC POWER SUPPLY

This project is a positive variable power supply that is compact and easy to build. It is ideal for

powering any application requiring a DC supply at current levels upto 1.5A. This power supplyproject should be among the first project that all electronic hobbyist should embark on. With this

power supply, one can use it to power up many electronic kits and projects instead of using batteries.

The featuresof this circuit are:·

  Output reverse polarity and back - voltage  protection·

  LED power on indication·

  Variable output voltage·  AC or DC input voltage·

  Low noise

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  Voltage regulator

A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. A voltage regulator may be a simple "feed-forward" design or may include negative feedback  

control loops. It may use an electromechanical mechanism, or electronic components. Depending on

the design, it may be used to regulate one or more AC or DC voltages.

Electronic voltage regulators are found in devices such as computer power supplies where they

stabilize the DC voltages used by the processor and other elements. In automobile alternators andcentral power station generator plants, voltage regulators control the output of the plant. In an electricpower distribution system, voltage regulators may be installed at a substation or along distribution

lines so that all customers receive steady voltage independent of how much power is drawn from the

line.

What is a Linear Regulator?

IC linear voltage regulators have been around for decades. These simple-to-use devices appear in

nearly every type of electronic equipment, where they produce a clean, accurate output voltage used

by sensitive components. Historically, linear regulators with PNP outputs have been expensive and

limited to low current applications. However, Micrel Semiconductor’s unique “Super beta PNP™”line of low dropout regulators provides up to 7.5 amperes of current with dropout voltages less than

0.6V, guaranteed. A lower cost product line outputs the same currents with only 1V of dropout.These low dropout voltages guarantee the microprocessor gets a clean, well regulated supply thatquickly reacts to processor-induced load changes as well as input supply variations. The low dropout

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linear voltage regulator is a easy-to-use, low cost, yet high performance meansof powering your

systems.

Why Use Regulators?

Their most basic function, voltage regulation, provides clean, constant, accurate voltage to a circuit.Voltage regulators are a fundamental block in the power supplies of most all electronic equipment.

Key regulator benefits and applications include:

  Accurate supply voltage

  Active noise filtering

  Protection from overcurrent faults  Inter-stage isolation (decoupling)

  Generation of multiple output voltages from a single source

  Useful in constant current sources

Measures of regulator quality

The output voltage can only be held roughly constant; the regulation is specified by two

measurements:

  load regulation is the change in output voltage for a given change in load current (for

example: "typically 15mV, maximum 100mV for load currents between 5mA and 1.4A, atsome specified temperature and input voltage").

  line regulation or input regulation is the degree to which output voltage changes with input

(supply) voltage changes - as a ratio of output to input change (for example "typically

13mV/V"), or the output voltage change over the entire specified input voltage range (forexample "plus or minus 2% for input voltages between 90V and 260V, 50-60Hz").

Other important parameters are:

  Temperature coefficient of the output voltage is the change in output voltage with

temperature (perhaps averaged over a given temperature range), while...

  Initial accuracy of a voltage regulator (or simply "the voltage accuracy") reflects the error in

output voltage for a fixed regulator without taking into account temperature or aging effects

on output accuracy.

  Dropout voltage is the minimum difference between input voltage and output voltage for

which the regulator can still supply the specified current. A Low Drop-Out (LDO) regulator

is designed to work well even with an input supply only a Volt or so above the outputvoltage. The input-output differential at which the voltage regulator will no longer maintain

regulation is the dropout voltage. Further reduction in input voltage will result in reduced

output voltage. This value is dependent on load current and junction temperature.

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  Absolute maximum ratings are defined for regulator components, specifying the continuous

and peak output currents that may be used (sometimes internally limited), the maximum inputvoltage, maximum power dissipation at a given temperature, etc.

  Output noise (thermal white noise) and output dynamic impedance may be specified as

graphs versus frequency, while output ripple noise (mains "hum" or switch-mode "hash"noise) may be given as peak-to-peak or RMS voltages, or in terms of their spectra.

  Quiescent current in a regulator circuit is the current drawn internally, not available to theload, normally measured as the input current while no load is connected (and hence a source

of inefficiency; some linear regulators are, surprisingly, more efficient at very low current

loads than switch-mode designs because of this).

  Transient response is the reaction of a regulator when a (sudden) change of the load current

(called the load transient) or input voltage (called the line transient) occurs. Some regulators

will tend to oscillate or have a slow response time which in some cases might lead to

undesired results. This value is different from the regulation parameters, as that is the stablesituation definition. The transient response shows the behaviour of the regulator on a change.

This data is usually provided in the technical documentation of a regulator and is alsodependent on output capacitance.

  Mirror-image Insertion Protection means that regulators are designed for use when there is

a voltage on its output pin and AC power is disconnected. Regulators with "Mirror-imageInsertion Protection" can tolerate the input being grounded and output being at a higher

potential than the input, but not higher than the maximum input voltage of the regulator. Only

some regulators can continuously withstand this situation; others might only manage for aminute [60 seconds](it will be usually be specified in the datasheet). This situation is similar

to the three terminal regulators being mounted as a mirror image. The three terminalregulators when mounted incorrectly on PCB has output terminal connected to unregulated

DC input and input is connected to load. "Mirror-image Insertion Protection" is importantwhen Regulator circuit is used in battery charging circuits. A regulator without "Mirror-image

Insertion Protection" may get damaged if AC power fails or is not turned on. In this situation

DC input to regulator is zero volts, whereas output terminal is at battery terminal voltage.This leads to reverse voltage across I/p and O/P terminals of the three terminal regulators.

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  PCB design process

The PCB Design training covers how to use the PCB Editor to create a PCB from setup, through

component placement, routing, design rule checking and CAM output. We first look at the overall

PCB design process.

The diagram below shows an overview of the PCB design process from schematic entry through to

PCB design completion.

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Once the PCB design is completed and verified, the Create Manufacturing Output process is used

to generate the PCB output files. This process is outlined below in Figure.

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Transferring design information to the PCB

Rather than using an intermediate netlist file to transfer design changes from the schematic to the

PCB, Altium Designer has a powerful design synchronization feature.

Design synchronization

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The core features of the synchroniser are:

  Difference engine  – compares the schematic project to the PCB. The difference engine can

compare the component and connective information between almost all kinds of documents.

It can compare a schematic project to a PCB, one PCB to another PCB, a netlist to a PCB, a

netlist to a netlist, and so on. The differences found by the difference engine are listed in thedifference dialog.

  Difference dialog  – lists all differences detected between the compared documents. You canthen define which document should be updated to synchronize the documents. This approach

allows you to make changes in both directions in a single update process, giving your bi-

directiona synchronization. Right-click in the dialog for direction options. This dialog is

usually only seen when using the process Project » Show Differences.

  Engineering Change Order dialog  – Once the direction of update for the differences has

been defined, a list of engineering change orders is generated. A report of these can be

generated.

There are two approaches to performing an update:

  Select Design » Update to push all changes from schematic to PCB (or PCB to schematic). If 

you choose this option, you have indicated the direction to use, so you go straight to the ECOdialog.

  Select Project » Show Differences if you need selective control of the direction. You also usethis option if you wish to compare any other document kinds, for example, to compare a

netlist to a PCB (also referred to as loading a netlist into a PCB).

Resolving synchronization errors

Most problems with synchronizing a design generally fall into two categories:

  Missing component footprints. This occurs when A footprint is missing from the componentinformation in the schematic.

  You have forgotten to add the required PCB libraries to the currently available libraries.

  The footprint in the schematic does not match any PCB library component.

  Footprint pin numbers not matched to schematic pin numbers. Altium Designer supportsuser-definable pin-to-pad mapping, the default behavior is to expect the same number/letter

on both sides. Pin-to-pad mapping is defined in the PCB Model dialog (edit the schematicsymbol, select the footprint in the Model region of the dialog, and click Edit).

  Components not matching (). By default Altium Designer attempts to match the componenton the schematic with the component on the PCB, using the Unique ID (UID). If there are

any miss-matches the Failed to Match dialog will open, offering to attempt to match bydesignator instead. Generally it is better to resolve the UID mismatches, rather than matching

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by designator. To check and resolve unmatched UIDs, select Project » Component Links

when the PCB is the active document.

  To resolve errors, perform a Show Differences, then in the Differences dialog click theExplore Differences button. The Differences panel will appear – as well as information on

what the problem is. This panel lists the objects in question on both the schematic and PCB.Click on an object to display it.

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Transferring the design

In this exercise, you will transfer the design data from the schematic into the new PCB that you have

created. This means that all required footprints must be present in available libraries. Keep these

points in mind:

  Footprints that are in your project PcbLib are automatically available  For components placed from an integrated library, such as the PIC Microcontroller, the

default state is to only look for the footprint in that integrated library, so it must be available

during design transfer.

To transfer the design:

  In the Libraries panel, click the button to open the Available Libraries dialog. This dialog

shows all libraries that are currently available to you.

  Confirm that the Temperature Sensor.PcbLib is listed in the Projects tab.

  In the Installed tab, confirm that the following libraries are installed:

  The 2 default libraries must also be installed, Miscellaneous Devices.IntLib and

Miscellaneous Connectors.IntLib. If these have been uninstalled, they can be found in the

root of the \Altium Designer Summer 09\Library folder.  Select Design » Import Changes from Temperature Sensor.PrjPCB from the PCB editor

menus. The ECO dialog displays, listing all the changes that must be made to the PCB so that

it matches the schematic. Note that you do not need to open the schematic sheets, this is

handled automatically.  Scroll down through the list of changes, they should include adding 19 components, 22 nets,

4 component classes, 1 net class and 3 design rules. Click on Validate Changes to check the

changes are valid.  Click on Execute Changes to transfer the design data. Close the ECO dialog.  The components will be placed on the new PCB, positioned to the right of the board outline.

  Save the board.

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Using the PCB Panel

This section investigates how to browse through a PCB design. The PCB panel is loaded by going to

the panel control and clicking PCB » PCB.

PCB Panel

The PCB panel provides a powerful method of examining the contents of the PCB workspace.

Clicking on an entry in the panel will filter the workspace to highlight that object  – the highlighting

will depend on the settings of the options at the top of the panel. To begin with, enable all the

options.

Browse mode selection list

The drop down list at the top of the panel allows you to list, locate or edit the following PCB object

types in the active PCB document:  Components (and then Component Classes)

  Nets (and then Net Classes)

  From-Tos

  Split planes

  Differential pairs

  Polygons

  Hole sizes

When you select an object in the panel, it will be highlighted in the workspace, according to theoptions at the top of the panel. Each Browse function is described in the following:

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Browsing nets and net classes

  To browse nets, select Nets from the drop-down list in the PCB panel.

  Click on All Nets in the Net Classes region of the dialog to browse all nets on the PCB. The

nets are listed in the region below and they are also highlighted on the PCB.

  If the design includes Net Classes these are also listed. Net classes such as D[0..7] have beengenerated automatically from busses in the design.

  Click on a net name in the Nets region to choose it – all the objects that belong to that net are

listed in the Net Items region. Also, the net is highlighted on the PCB.

  Click on an item in the Net Items region and note that it is highlighted on the PCB. Also notethat the object that you clicked on is selected.

  Multi-select keys are supported. Hold SHIFT or CTRL as you click on entries in the list.

  Right-click in the Net Items section and note that you can control which net items are

displayed.

  Double-click on a net name to open the Edit Net dialog. Here you can change the net name,

add or remove nodes from the net and define the color of the connection lines for this net.

  The Nets and the Net Items region have multiple columns. Note that you can control the

sorting by clicking the heading on a column.

  Type-ahead is supported. You can type on the keyboard to jump through the lists. Press Escto abort the current type-ahead search and start another pages.

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Browsing components and component classes

  To browse components, select Components from the drop-down list.

  When the panel is being used to filter (highlight) components, you might find it better to have

the Select option at the top of the panel switched off.

  Click on All Components in the Components Class region to browse all components on thePCB. The components are listed in the Components region, as well as being highlighted on

the display.

  If the design includes component classes, these are listed too, when you click on a component

class only the components in that class are listed and highlighted.

  Click on a component name in the Components region to choose it. All the objects that

belong to that component are listed in the Component Primitives region. Also, the component

is highlighted on the PCB.

  Click on an item in the Component Items region, Note that it is highlighted on the PCB. Alsonote that the object that you clicked on is selected.

  Multi-select keys are supported. Hold SHIFT or CTRL as you click on entries in the list.  Right-click in the Component Items section. Note that you can control which component

primitives are displayed.

  Double-click on a component name to open the Component dialog where you can modify anyattribute of the component.

  The Components and the Component Items region have multiple columns. Note that you can

control the sorting by clicking the heading on a column.

  The order of the columns can also be changed; click and drag a column to change the column

order. This is handy when you wish to use the type-ahead feature on a different column.

  Type-ahead is supported. You can type on the keyboard to jump through the lists. Press ESC

to abort the current type-ahead search and start another. The type-ahead is always performedon the left-most column, so drag any column to make it the left-most.

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From-To editor

  Choose From-To Editor from the drop-down field at the top of the PCB panel. The top listsection of the panel will fill with all nets currently defined for the design.

  As you click on a net entry, all of the nodes on that net will be loaded into the middle list

section of the panel. Filtering will be applied and a mask automatically used in order to leave just the nodes (pads) on the net fully visible. All other objects are dimmed.

  Double-click on a net entry to open the Edit Net dialog where you can edit the properties of 

the net.

  To add a new from-to, select the Nodes on Nets to which you want to add the from-to andclick the Add From To button. The new from-to appears in the From-Tos on Net section.

Click on the from-to in the From-Tos on Net section and click on Generate and select a from-

to topology, e.g. Shortest, Daisy varieties or Starburst.

  The From-To editor can only be used to create from-tos. To browse for existing from-tos,create a query in the Filter panel using the IsFromto keyword.

  Note that all connection lines, other than those that have been defined as From-Tos on thecurrently selected net, will remain dimmed. Switch the panel back to Nets to restore the

display of connection lines.

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Split Plane editor

  You can review and edit split planes in the PCB panel by selecting the Split Plane Editorfrom the drop-down list at the top of the panel.

  Select the plane you want to display by clicking on the Plane name. The split planes and their

nets on that power plane are listed.  Click on a split plane name in the Split Planes and Nets section to show the pads and vias on

that split plane.

  Double-click on a split plane name to edit the net associated with the split plane.

  Right-click on a split plane name to select an option from the menu.

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Differential Pairs Editor

  You can review and edit Differential Pairs in the PCB panel by selecting the Differential

Pairs Editor from the drop-down list at the top of the panel.

  Select the Differential Pair Class you want to display by clicking on the Differential PairClass name. The Differential Pair Designators will then be listed.

  Click on a Differential Pair name in the Differential Pair section to show the constituent nets

of the pair, both positive and negative.

  Double-click on a Differential Pair name to edit the nets associated with the Pair and view the

options.

  Right-click on any Differential Pair Class listing (Excepting the default class of All

Differential Pairs) and the Object Class Explorer dialog will open allowing you to modifyyour Classes.

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3D Models

Use the 3D Models mode of the PCB panel to review 3D models used in the board design.

  Click on a component to locate that component on the board and examine the 3D model.

  The panel lists each component individually, click the Footprint heading to sort by footprint

kind and examine multiple components that have the same 3D model.

  Use the upper Highlighted Models dropdown to change the opacity of the currently selected3D model.

  If the footprint includes both STEP and 3D bodies, use the check boxes to control which is

currently displayed, or the lower Highlighted Models dropdown to control the opacity of oneor the other types of 3D models.

  Elements that are not part of the actual board design, such as the product case, can be placed

in the workspace for interference checking (Place » 3D Body). Use the *Free Models option

at the top of the component list to examine and change the opacity of these elements.

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PCB Fabrication

PCB Basics

Basic PCBs comprise a rigid sheet of epoxy-impregnated fiberglass material within copper sheets

affixed to one or both sides. This is known as copper clad. In multilayer boards (thosewith more than two copper layers), a piece of material called prepreg is placed between core layers.

The outer copper surface of the PCB must be processed to form circuit paths, or traces, that make the

connections between components. Analogous to wires, the traces are formed using a

photolithographic process. In that process, the copper layers are treated with chemical etching that

removes unneeded portions of the copper, leaving only the traces and pads required forcomponent soldering. Pads can be fabricated in many shapes and formats. Components are typically

attached to these pads as surface mount, through hole, or both. After photolithography is completed,

the board is drilled and through holes are plated.

PCB Fabrication Process

For multi-layer designs, the first step is to print etch the inner layers. Each inner circuit is transferredto the copper panel using photographic dry film. The film is hot-roll laminated onto the copper panel.

The film tooling is exposed onto the panel typically using a 5 kilo Watt light source. The panels are

put through a series of vertical conveyors containing various wet processing chemicals. First, the

exposed film on the panels is developed, then the exposed copper (no film on it) is etched away andfinally the remaining film is stripped off resulting in bare copper circuits on laminate. This process

usually takes about three hours. The inner layers are then pinned in a stack with thin sheets of epoxy

glass pre-preg which separates the copper layers. The outer layers are made with a foil of copper.The stack is pinned between two heavy metal plates creating a "book." This book is put in a

hydraulic/heated press for about two hours at 350 degrees F.

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The hydraulic pressure is approximately three tons. Once pressed, these panels look just like double

sided laminate and are ready for drilling. For double-sided panels, drilling is the first process. Thepanels are pinned to the table of a CNC drill. The drill program is loaded, and the proper drill bit

sizes are loaded into the auto-tool-change holders. A typical load size is 15 panels up. The panels are

then deburred after drilling. This process usually lasts anywhere from 30 minutes to two hours.

Electroless copper is next. In order to put a thin (0.000025") coat of copper inside the drilled holes,

there is a series of chemicals required to condition, clean, and activate the surface inside the holes.

The panels sit in a blue liquid of suspended copper for about 45 minutes; the entireprocess takes about two hours. Primary image (i.e., the top & bottom layers) is applied using dry film

plating resist, as before with the inner layers. It is developed, and then it goes into a copper plating

procedure. The panels are cleaned and activated chemically, then connected to a rack inside a largevolume of copper solution. At 25 amps/square foot of copper, the panels are electro-plated for about

one hour to achieve one ounce of copper in the holes and on the surface. Next, tin is plated on top of 

the copper. (During the entire time, the dry film (plating resist) is on the panels to prevent plating

where there are no circuits.)

After plating, the dry film plating resist is stripped off the panel leaving exposed copper. This copper

is chemically etched off the panel leaving only the tin over copper circuitry. Next, the tin is strippedfrom the panel leaving bare copper circuits. Solder Mask is applied directly over the bare copper.

Liquid Photo Imagable (LPI) Solder Mask is flooded onto the panel using a screen. It is then tack 

dried in a convection oven. The panel is aligned to the Solder Mask tooling film using registrationpins and then exposed in a 5 kW light source for about 20 seconds. The panel is then developed to

remove LPI Solder Mask from the pads and holes.

Finally, the panel is baked to cure the remaining mask to its permanent state. The total LPI time isabout two hours. Legend ink (silkscreen) is screened onto the panel using a screen stencil, which is

photographically made from the Legend film work. The panel is cured in a convection oven tocomplete the screening process in about an hour. Next, the panel is put through a Hot Air Solder

Leveler (HASL) in order to put solder on the pads and in the holes. It consists of a flux tank, a soldertank at about 360 degrees F, and air knives to blow out the holes.

The CNC routing is the final step to the pcb fabrication process.The panels are pinned to a backupmaterial. The CNC program is loaded into memory, and a router bit is placed in the tool changer.

Normally, an 0.093" size bit is used. The parts are routed out individually. Gold fingers, if present,

are then beveled.

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PCB MANUFACTURING PROCESS

It is an important process in the fabrication of electronic equipment. The design of PCBs (Printed

Circuit Boards) depends on circuit requirements like noise immunity, working frequency and voltage

levels etc. High power PCBs requires a special design strategy.

The fabrication process to the printed circuit board will determine to a large extent the price and

reliability of the equipment. A common target aimed is the fabrication of small series of highly

reliable professional quality PCBs with low investment. The target becomes especially important for

customer tailored equipments in the area of industrial electronics.

The layout of a PCB has to incorporate all the information of the board before one can go on the

artwork preparation. This means that a concept which clearly defines all the details of the circuit and

partly defines the final equipment is prerequisite before the actual layout can start. The detailed

circuit diagram is very important for the layout designer but he must also be familiar with the design

concept and with the philosophy behind the equipment.

BOARD TYPES:

The two most popular PCB types are:

Single Sided Boards

The single sided PCBs are mostly used in entertainment electronics where manufacturing costs have

to be kept at minimum. However in industrial electronics cost factors cannot be neglected and singlesided boards should be used wherever a particular circuit can be accommodated on such boards.

Single sided design can greatly reduce the cost of your board. If you can fit your design on a single

sided board then it is preferable to do so. Look inside many of today’s consumer items like TV’s andDVD players, and you will almost certainly find some single sided boards. They are still usedbecause they are so cheap to manufacture. Single sided design however requires some unique

techniques which are aren’t required once you go to doubled sided and multi-layer design. It is

certainly more challenging than a double sided layout. In fact, a single sided board design will beregarded inversely proportional to the number of jumper links used. No jumper links earns the

admiration of many peers!

It is all about a balance between board size and the number of jumper links required. Almost every

single sided board will require some jumper links, so it is important to minimise these.

Component placement is even more critical on a single sided board, so this is no time to make all

your components nice and neatly aligned. Arrange your components so that they give the shortestand most efficient tracking possible. It is like playing a game Chess, if you don’t think many movesahead then you will get yourself in a corner pretty quickly. Having just one track running from one

side of your board to the other can ruin your whole layout, as it makes routing any other

perpendicular tracks impossible. Many people will route their board as though it is a double sidedboard, but only with straight tracks on the top layer. Then when the board is to be manufactured, the

top layer tracks are replaced with jumper links. This can PCB Design Tutorial be a rather inefficient

way to approach single sided design, and is not recommended. You must be frugal in your

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 placement, and don’t be afraid to rip everything up and try again if you see a better way to route

something. With experience, you will be able to tell before you even start, if a design if worth tryingto route on a single sided board. 

Double sided Boards

Double-sided PCBs can be made with or without plated through holes. The production of boards withplated through holes is fairly expensive. Therefore plated through hole boards are only chosen where

the circuit complexities and density of components does not leave any other choice. Double sided

design gives an extra degree of freedom for designing your board. Things that were next toimpossible on a single sided board become relatively easy when you add an additional layer.

Many (inexperienced) designers tend to become lazy when laying out double sided boards. They

think that component placement doesn’t matter all that much, and hundreds of vias can be used to get

them out of trouble. They will often lay out components like ICs in neat rows, and then proceed toroute everything using a right angle rules. This means that they will route all the tracks on the bottom

layer in one direction, and then all the tracks on the top layer perpendicular to the bottom layer. The

theory is that if you chop and change between layers enough times you can route almost anything

using a “step” type pattern. This technique can be ugly and inefficient, and is a throw back to the old

manual tape days. Many basic auto routers work in this way. Stick to using good component

placement techniques and efficient building block routing.

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STEPS TAKEN WHILE PREPARING CIRCUIT

PCB DESIGNING

The main purpose of printed circuit is in the routing of electric currents and signal through a thin

copper layer that is bounded firmly to an insulating base material sometimes called the substrate.This base is manufactured with integrally bounded layers of thin copper foil which has to be partly

etched or removed to arrive at a predesigned pattern to suit the circuit connections or other

applications as required.

The term PCB is derived from the original method where a printed pattern is used as the mask over

wanted areas of copper. The PCB provides as an ideal baseboard upon which to assemble and hold

firmly most of the small components.

From the constructor’s point of view, the main attraction of using PCB is its role as the mechanical

support for small components. There is less need for complicated and time consuming metal work of 

chassis contraception except perhaps in providing the final enclosure. Most straight forward circuit

designs can be easily converted into printed wiring layer the thought required to carry out the

inversion cab footed high light a possible error that would otherwise be missed in conventional point

to point wiring. The finished project is usually neater and truly a work of art.

Actual size PCB layout for the circuit is drawn on the copper board. The board is then immersed in

FeCl3 solution for 12 hours. In this process only the exposed copper portion is etched out by the

solution.

Now the petrol washes out the paint and the copper layout on PCB is rubbed with a smooth sand

paper slowly and lightly such that only the oxide layers over the Cu are removed. Now the holes aredrilled at the respective places according to component layout.

LAYOUT DESIGN:

When designing the layout one should observe the minimum size (component body length and

weight). Before starting to design the layout we need all required components in hand so that an

accurate assessment of space can be made. Other space considerations might also be included from

the case to case of mounted components over the printed circuit board or to access path of present

components.

It might be necessary to turn some components around to a different angular position so that

terminals are closer to the connections of the components. The scale can be checked by positioning

the components on the squared paper. If any connection crosses, then one can reroute to avoid such

condition.

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All common or earth lines should ideally be connected to a common line routed around the perimeter

of the layout. This will act as the ground plane. If possible try to route the other supply lines around

the opposite edge of the layout through the centre. The first set is tearing the circuit to eliminate the

crossover without altering the circuit detail in any way.

Plan the layout looking at the topside to this board. First this should be translated inversely; later forthe etching pattern large areas are recommended to maintain good copper adhesion. It is important to

bear in mind always that copper track width must be according to the recommended minimum

dimensions and allowance must be made for increased width where termination holes are needed.

From this aspect, it can become little tricky to negotiate the route to connect small transistors.

There are basically two types of copper interconnections patterns under side the board. The first is

the removal of only the amount of copper necessary to isolate the junctions of the components to one

another. The second is to make the interconnection pattern looking more like conventional point

wiring by routing uniform width of copper from component to component.

ETCHING PROCESS:

Etching process requires the use of chemicals, acid resistant dishes and running water supply. Ferric

chloride is mostly used solution but other etching materials such as ammonium per sulphate can be

used. Nitric acid can be used but in general it is not used due to poisonous fumes.

The pattern prepared is glued to the copper surface of the board using a latex type of adhesive that

can be cubed after use. The pattern is laid firmly on the copper using a very sharp knife to cut round

the pattern carefully to remove the paper corresponding to the required copper pattern areas. Then

apply the resistant solution, which can be a kind of ink solution for the purpose of maintaining

smooth clean outlines as far as possible. While the board is drying, test all the components.

Before going to next stage, check the whole pattern and cross check:

With the circuit diagram. Check for any free metal on the copper. The etching bath should be in a

glass or enamel disc. If using crystal of ferric chloride these should be thoroughly dissolved in water

to the proportion suggested. These should be 0.5 lt. of water for 125 gms of crystal.

To prevent particles of copper hindering further etching, agitate the solutions carefully by gently

twisting or rocking the tray.

The board should not be left in the bath a moment longer than is needed to remove just the right

amount of copper. In spite of there being a resistive coating there is no protection against etching

away through exposed copper edges. This leads to over etching. Have running water ready so that

etched board can be removed properly and rinsed. This will halt etching immediately.

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Drilling is one of those operations that call for great care. For most purposes a 0.5mm drill is used.

Drill all holes with this size first those that need to be larger can be easily drilled again with the

appropriate larger size.

Component Assembly:

From the greatest variety of electronic components available, which runs into thousands of different

types it is often a perplexing task to know which is right for a given job.

There could be damage such as hairline crack on PCB. If there are, then they can be repaired by

soldering a short link of bare copper wire over the affected part.

The most popular method of holding all the items is to bring the wires far apart after they have been

inserted in the appropriate holes. This will hold the component in position ready for soldering.

Some components will be considerably larger .So it is best to start mounting the smallest first andprogressing through to the largest. Before starting, be certain that no further drilling is likely to be

necessary because access may be impossible later.

Next will probably be the resistor, small signal diodes or other similar Size components. Some

capacitors are also very small but it would be best to fit these afterwards. When fitting each group of 

components mark off each one on the circuit as it is fitted so that if we have to leave the job we know

where to recommence.

Although transistors and integrated circuits are small items there are good reasons for leaving the

soldering of these until the last step. The main point is that these components are very sensitive to

heat and if subjected to prolonged application of the soldering iron, they could be internally

damaged.

All the components before mounting are rubbed with sand paper so that oxide layer is removed from

the tips. Now they are mounted according to the component layout.

SOLDERING:

This is the operation of joining the components with PCB after this operation the circuit will be ready

to use to avoid any damage or fault during this operation following care must be taken:

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1. Longer duration contact between soldering iron bit & components lead can exceed the temperature

rating of device & cause partial or total damage of the device. Hence before soldering we must

carefully read the maximum soldering temperature & soldering time for device.

2. The wattage of soldering iron should be selected as minimum as permissible for that soldering

place.

3. To protect the devices by leakage current of iron its bits should be earthed properly.

4. We should select the soldering wire with proper ratio of Pb & Tn to provide the suitable material

melting temperature.

5. Proper amount of good quality flux must be applied on the soldering point to avoid dry soldering.

Soldering considerations need to taken into account when laying out your board. There are threebasic soldering techniques - hand, wave, and reflow. Hand soldering is the traditional method

typically used for prototypes and small production runs. Major impacts when laying out your board

include suitable access for the iron, and thermal reflief for pads. Non-plated through double sidedboards should allow for ample room to get the soldering iron onto the top side pads.

Wave soldering is a common process used for surface mount and through hole production soldering.

It involves passing the entire board over a molten bath of solder. Solder masks are absolutelyessential here to prevent bridging. The major thing to watch out for when designing is ensuring that

small components are not in the wave solder “shadow” of larger components. The board travelsthrough the wave solder machine in one direction, so there will be a lack of solder trailing behindlarger components. Surface mount devices are fixed to the board with an adhesive before wave

soldering. Reflow soldering is the latest technique, and is suitable for all surface mount components.

The blank board is first coated with a mask of solder paste over the pads (solder “stencils” are usedfor this). Then each component is placed, and is sometimes held in place by an adhesive. The entire

board is then loaded into an infrared or nitrogen oven and “baked”. The solder paste melts (reflows)

on the pads and component leads to make the joint. A newer reflow method called pin-in-paste orintrusive reflow is available for through hole devices. Combinations of wave and reflow soldering

can be used for mixed through hole and surface mount boards. Wave soldering has the advantage of 

being cheap, but the disadvantage of imposing placement limits on your components. Reflow

soldering is more complex and expensive, but it allows for very dense surface mount packing.

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Fig.- SMD Wave Soldering

Fig- Through-hole Wave Soldering

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Fig-SMD Reflow Soldering

Surface Finishies

You can get your PCB manufactured with several different types of pad and track surface finish.

Very low cost single and double sided boards without solder mask typically have a basic tin coated

finish Beware of potential shorts between tracks with this method.

Your standard professionally manufactured board will typically have solder mask over bare copper

(SMOBC) tracks, and a tin finish on the pads and vias which is Hot Air Leveled (HAL). Hot airleveling helps most surface mount components to sit flat on the board. For large and critical surfacemount components, a gold “flash” finish is used on the pads. This gives an 

extremely flat surface finish for dense fine pitch devices. Peelable solder masks are available, and are

handy for temporary masking of areas on your board during wave soldering or conformal coating.

Electrical Testing

You can have your finished PCB checked for electrical continuity and shorts at the time of manufacture. This is done with a automated “flying probe” or “bed of nails” test machine. It checksthat the continuity of the tracks matches your PCB file. It may cost a fair bit extra, but this is pretty

mandatory for multi-layer boards. If you have a manufacturing error on one of your inner layers, itcan be very difficult to fix.

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Signature

Like any work of art, no board is complete without adding your name or signature to it! The

signature can take any form your like. Some people put their name, initials, or a fancy symbol.

Whatever it is, just make sure you add something.

A signature can be placed on any of the copper layers, or on the component overlay.

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