54933021 main project file

7/28/2019 54933021 Main Project File

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Variable Power Supply with Digital Control

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CHAPTER -1 Introduction:- The most frequently used device in electronic workshops andlaboratories is a universal power supply that Variable Power supply with digitalcontrol .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 regulatorIC 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 thetransformer is rectified by a full-wave rectifier comprising diodes D1 throughD4. Capacitors C1 through C4 are connected in parallel to rectif ier. The diodesto 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 outputLED1, 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 transistorsT1 through T10 respectively, as shown in the figure. LED3 through LED11 are usedhere to indicate the voltage levels. The collectors of transistors T2 through T10 are connected to presets VR1 through VR9, respectively, which are used to setthe 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 1


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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 atthe collectors of transistors T2 through T10, respectively, different output resistances appear between the adjustable and ground terminals of IC4, resulting indifferent 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, negativevolt age regulator IC LM7912 (IC3). Thusthe power supply unit can be used for circuits requiring both negative and positive DC voltages. When CD4017 is reset by pressing -indication LEDs turn switch S3, the output voltage becomes 1.2V and all the voltage off. Assemble the circuiton 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 & SELECTIONDuring the survey time for the Project we have selected the followed of topic fo

r 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 becauseof 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.

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1.3 Component Required

Semiconductors:IC1 IC2 IC3 IC4 D1-D4 LED1 LED2 LED3-LED11 -NE555 -CD4017 -LM7912-LM317 -1N4007 -RED -YELLOW -GREEN

Resistors:R1,R7 ,R15 R17 R2 R3 R4,R5 -1 kilo-ohm -1 kilo-ohm -22 Kilo- ohm - 560ohm -8.2Kilo ohm

Capacitor:C1-C4 C5,C13 C6 C7 -47nF ceramic -2200F electrolytic -10F electrolytic -.01F ceramic

Miscellaneous:S1 S2-S3 Transformer -ON OFF switch - PUSH-TO-ON Switch -230v,1 Amp.

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1.4 Tools and Instruments usedFollowing 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 DescriptionA 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 Transformeron the basis of the maximum output voltage and current required. The followingis 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 heatsink 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 VariableDC 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 w ebsite.You can adapt it to your own requirements

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Variable Power Supply with Digital Control 2.2 Circuit Diagram:-

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Variable Power Supply with Digital Control CHAPTER-3

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3.1 Working of circuit:- Divide the whole circuit in two parts as power supplysection and voltage selector section. Power supply section: Transformer x1 stepdown 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 voltageselector section is use to obtained variable voltage in nine steps from 1.5 to12v. 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 voltageof 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 andessential requirement in electronics lab .The avilable power supply must providevarrible 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 timerpulse 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 k resistors used in typical early implementations, butHans

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 20transistors, 2 diodes and 15resistors 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 7555and 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" capa

citor 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

ApplicationsPrecision 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 voltageregulators 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 resistorsto set the output voltage. Further, both line and load regulation are better than standard fixed regulators. Also, the LM317 is packaged in standard transistorpackages 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, ircuitry thermal overload protection and safe area protection. All overload protection c remains fullyfunctional even if the adjustment terminal is disconnected. Normally, no capacitors are needed unless the device is situated more than 6 inches from the inputfilter capacitors in which case an input bypass is needed. An optional output capacitor can be added to improve transient response. The adjustment terminal canbe bypassed to achieve very high ripple rejection ratios which are difficult toachieve 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 ofseveral 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 ma

kes 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 whichprograms 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%/Vline regulation (LM317A) Guaranteed max. 0.3% load regulation (LM117) Guaranteed 1.5A output current Adjustable output down to 1.2V Current limit constant withtemperature

4.3 3rd IC:-LM7912:-The LM7912 three terminal negative voltage regulator IC isavailable in TO-220 package and with a fixed output voltage of -12 volt, makingit 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-10Johnson counterwith 10 decoded outputs and a carry out bit.The CD4022BM/CD4022BC is a 4 -stagedivide-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 clockenable signal is in the logical "0" state.The configuration of the CD4017BM/CD4017BC and CD4022BM/CD4022BC permits medium speed operation and assures a hazardfree 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. Eachdecoded 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 carrysignal to any succeeding stages. Features Wide supply voltage range: 3.0V to 15VHigh 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 10VVDD Low power: 10 W (typ.) Fully static operation

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Variable Power Supply with Digital Control 4.5 Pin configuration:-

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ApplicationsAutomotive 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 orpresence of voltage in acircuit, 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) precisionshunt 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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Variable Power Supply with Digital Control 4.7 DIODE:4.1 IN4007

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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 composedof 2nd order Sallen-Key, Multiple Feedback, State Variable, Dual Follower, Fliege, Gyrator, or VoltageControlled Voltage Source stages supported.

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Variable Power Supply with Digital Control 4.8. LED:-

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RED LED: Light emitting diodes, commonly called LEDs, are real unsung heroes inthe 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 bur out, and n they don't get especially hot. They are illuminated solely bythe movement of electrons in a semiconductor material, and they last just as long as a standard transistor. Inthis article, we'll examine the simple principlesbehind these ubiquitous blinkers, illuminating some cool principles of electricity and light in the process.

Description:------ LEDs must be connected the correct wayround, 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 thecathode is the larger electrode (but this is not an official identification met

hod). 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: 17


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Variable Power Supply with Digital Control LED SECOND:-YELLOW LED:-

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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:y y y y

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 currentflowsthrough 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 theresistor 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 partslist, these will be circuits using low value resistors (less than about 300 ) orhigh voltages (more than 15V).

Example:

Circuit symbol:

Function Resistors restrict the flow of electric current, for example a resistoris 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 d amaged by heat when soldering. 19


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The Resistor values - the resistor colour code Resistance is measured in ohms, the symbol for ohm is an omega . 1 1k is0 quite small so resistor values are often given in k and M . Black = 1000 1M = 1000000 .

Resistor

Colour Code Colour Number 0

Brown 1 2

Resistor values are normally shown using coloured bands. Red 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 Violet resistor, this may be ignored for almost all circuits but further details are given below. White Table 5 Resistor colour Grey

Orange 3 Yellow 4 Green Blue 5 6 7 8 9 coding

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Variable Power Supply with Digital ControlThis resistor has red (2), violet (7), yellow (4 zeros) and gold bands. So its value is 270000 On circuit diagrams the = 270 k .

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is usually omitted and the value is written 270K.

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

P = I R where: P = power developed in the resistor in watts (W) or P = V / R I = current through the resistor in amps (A) R = resistance of the resistor in ohms () V = voltage across the resistor in volts (V)

Examples:y

A 470 0.21W.

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

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

A 27 3.7W.

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

A high power resistor with a rating of 5W would be suitable. 21


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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 classicalextensively in vacuum-tube equipment (e.g., radio receivers) from about 1930 through the 1950s, and in discrete transistor equipment from the 1950s through the1980s. As of 2007, ceramic disc capacitors are in widespread use in electronic equipment, providing high capacity and small size at low price compared to otherlow value capacitor types. Ceramic capacitors come in various shapes and styles

Application of ceramic capacitor:- Ceramic capacitors are suitable for moderatelyhigh-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 capaciors (film and electrolytic). Capacitor t technologies with higher self-resonant frequencies tend to be expensive and esoteric (typically, mica or glass capacitors).

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Electrolytic capacitor:-

Description:- Electrolytic capacitors are capable of providing the highest capacitancevalues 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 breakdownvoltage, 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 capacitorwas in large telephone exchanges, to reduce relay hash (noise) on the 48 volt DCpower supply. The development of AC-operated domestic radio receivers in the late 1920s created a demand for large capacitance (for the time) high voltage capa

citors, typically at least 4 microfarads and rated at around 500 volts DC. Waxedpaper 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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Variable Power Supply with Digital Control 4.11 TRANSFORMER:-

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Description:- A transformer is a static device that transfers electrical energyfromone 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 willflow in the secondary winding and electrical energy will be transferred from theprim circuit through the ary 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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Variable Power Supply with Digital Control Circuit diagram:-

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APPLICATION:- A major application of transformers is to increase voltagebefore transmitting electrical energy over long distances through wires. Wires have resistance and so dissipate electrical energy at a rate proportional to thesquare 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 transformersby 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 enduser 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 crosssection 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) determinedso that the heat p roduced 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 withinthe fuse, opening the circuit. When the metal conductor parts, an electric arcforms between the un -melted ends of the element. The arc grows in length untilthe voltage required to sustain the arc is higher than the available voltage inthe circuit, terminating current flow. In alternatin g 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 fa current before ult 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 highertemperature to a lower temperature fluid medium. The fluid medium is frequentlyair, 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 heatconduction. 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 whenthere is a temperature gradient in a body, heat will be transferre from the higher d temperature region to the lower temperature region. The rate at which heatis 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 butmicropower 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 pat

h may be from the component to a printed circuit board (PCB), to a heat sink, toair flow provided by a fan, but in all instances, eventually to the environment.

4.14 TransistorsTransistors 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 highcurrent 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


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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 mildenough to not require removal at all.

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Variable Power Supply with Digital Control CHAPTER-5

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5.1 Soldering of Components on PCBFor hand soldering of electronic components, the heat source tool should beselected 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, joiningcopper 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 toensure 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.

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Variable Power Supply with Digital Control Applications

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One of the most frequent applications of soldering is assembling ele ctronic 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 automo bile radiators have also historically been soldered, and occasionally still are. Jewelry components are assembled

Applications of Soldering and repaired by soldering. Small mechanical parts areoften soldered as well. Soldering is also used to join lead came and copper foilin stained glass work. Soldering can also be used as a semi-permanent patch fora leak in a container or cooking vessel.

4.2 PCB FabricationA 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 populatedwith electronic components is a printed circuit assembly (PCA), also known as aprinted circuit board assembly (PCBA). The PCB fabrication steps are: PCB boarddesign 31


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Variable Power Supply with Digital Control Printing Artwork Exposure Developing Etching Cutting and Drilling Tinning asking

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PCB Board Design Material and Equipment Electronics Schematic Design Computer Protel DXP or PCB design software

PCB design introductionBefore 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 handbut if your design is very complex, the PCB software will be very helpful. Thesoftware 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 incost, 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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Variable Power Supply with Digital Control 5.3 Printing Artwork

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Material and Equipment PCB artwork Paper Printer Transparency Laser printer or photo copier

Artwork introductionThe 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 willbe use for photo-resist PCB board exposure in the next stage. A laser printer ispreferred for sharper trace, especially if the traces are very close to each other. The laser printer can also print directly to transparency. The transparencyis 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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Variable Power Supply with Digital Control Material and Equipment Ultra violet lamp A box Positive Acting Presensitized PCB board Transparency h PCB artwork printed Scotch tape

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Exposure Equipment

Exposure introductionA 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 setupIf 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 maintain to make sure that traces are ed not exposing to the UV light.

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Variable Power Supply with Digital Control PCB exposure

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Turn on and expose the PCB board for 90 seconds for ultr violet lamp, or 6-10 minutes a 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 distanceis far from the typical one, the exposure time should increase proportio nally.

Peeling off the Protective Film from the PCB Board

5.3 Developing Material and Equipment Sodium Hydroxide or Developer solution Distill or plain water Glove Glassic, wooden rod or old chopstick Container slightly bigger than the PCB board Exposed PCB board Container with water for washing

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Variable Power Supply with Digital Control Developer introduction

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Sodium Hydroxide is used as a developer. Correct proportion is necessary as toomuch will destroy the photo-resist coating instantly, while too little will haveno effect in developing the PCB. Commercial developer solution (pre-mixed withdistill 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 mixtureThe 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


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Developing PCB boardThe 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 underneathduring the etching process. The region to be etched away later will be exposingand is brown in color. The brown color is the actual color of the copper. Thereis no photo-resist coating to protect the surface. Rinse the developed PCB boardwith running water after developing.

Remove Transparency and do Coating

5.4 Etching

Material and Equipment Ferric Chloride powder Distill or plain water Glove Glass, plastic, woor old chopstick Long container for the etchant A boarder container for boiling hot water below 3 liters of boiling water Drilling machine

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Etching introductionFerric 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 handlingFeCl3. Chemical is toxin and will cause skin irritation. Wash skin with runningwater 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 tobe etched away.

Etchant mixtureThe 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 - Ammonium Persulphate - Sodium Persulphate - Peroxy Sulfuric - Ammonium Persulphate (msds) (msds) (msds) (recyclable chemical) (msds)

Warming up EtchantWarm up the FeCl3 solution on a tray (blue) filled with hot water. Temperature range from about 50C to 60C 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

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Immerse the PCB board slowly into the FeCl3 solution. Agitate the PCB by tiltingthe container to and fro gently, until the unwanted copper layer is properly etched away, 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 theetching speed.

Testing various etch resist materialThe photos simulate a developed PCB board masked with some scotch tape, maskingtape, 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. 40


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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 solut on can be use to wipe i on the PCB board surface to remove the coating. For the marker stain, it can be removed using commercial available contact cleaner, alcohol, orthinner solution. Rinse with water, clean and dry the PCB board.

Disposing toxin chemicalFerric Chloride FeCl3 is a toxin chemical. Please consult your local authority for proper dispose of chemical waste product. As recommended, detergent (or otherbaking 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 unwantedcopper 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 bitd files Penknife Steel ruler 41


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Drill Machine

Introduction to cutting and drillingThe etching is completed. The original artwork is arrange to maximize the use ofthe d 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 (exa mple: resistor, capacitor, inductor, board mount switch, DIP integrated circuit IC etc). Before drilling, a dot punch is used to mark the hole position. This servesas a shallow guide for the drill bit to align easily while drilling. Any othersharp pointed tool can be use to do the marking. The drill is fitted with a 1mmdrill 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 Material and Equipment Solder flux Soldering iron (flat tip is available) Soldering stand with wetted ponge Solder sucker

Tinning the copper surfaceCopper 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


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on the copper surface to prevent oxidization. Apply solder to the copper surfacewith 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 boardMasking can be applied to non-soldering area to protect the board from potentialshort 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 acarbon paper. Now overdraw the layout by nail polishsolution. 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 Soluton. PCB i should be submerged into Solution properly. With regular stirring, etching will take 20 minutes or longerdepending on how many times the solution has been used before. While etching proper care should be given to protect your hands and body fromthe solution. Latexgloves 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. 44


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Variable Power Supply with Digital Control CHAPTER-6 6.1 Digital Voltmeter:-

2011

A voltmeter is an instrument used for measuring the electrical potential difference between two points in an electric circuit. Analog voltmeters move a pointeracross 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 apanel are used to monitor generators or other fixed apparatus. Portable instruments , usually equipped to also measure current and resistance in the form of amultimeter, are standard test instruments used in electrical and electronics work. Any measurement that can be converted to a voltage can be displayed on a meterthat is suitably ca librated; for example, pressure, temperature, flow or levelin a chemical process plant.

General purpose analog voltmeters may have an accuracy of a few percent of fullscale, and are used with voltages from a fraction of a volt to several thousandvolts.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 directcurrent (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, andresistance. This is the preferred tool of an electrician

6.2 Application Different units in factory Bridge street lighting High loaded device ElectronicsLaboratries

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Variable Power Supply with Digital Control CHAPTER-7 CostingParts name Semiconductors IC1-NE555 IC2-CD4017 IC3-LM7912 IC4-LM317 40 40 50 50Cost

2011

Transistor PCB 7805, 5V regulator Heat Sink Diodes LEDs Resistor 10-kilo-ohm 2 100-kilo-ohm 2 220-ohm 1-kilo-ohm 4 Capacitors 1000 F, 35V electrolytic 0.1 F ceramic disk 33 F, 16V electrolytic 100 F, 16V electrolytic Miscellaneous

20 35 20 20 20 30

5 5 5 10

5 2 2 2

230V AC primary to 12V,500mA secondary 100 transformer Push-to- on switch FuseTotal cost

15 20496

Price LIST 47


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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

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54933021 main project file

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