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Variable Power Supply Lab Report, Lecture notes of Electronics

University of Engineering and Technology Peshawar (UETP)Electronics

This file is a detailed lab report for a variable power supply that will explain each and every component and give some background as well

Typology: Lecture notes

2016/2017

Uploaded on 08/25/2017

cennian
cennian 🇵🇰

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1.1 Introduction:
A variable DC power supply is an integral part of any power supply unit used in the all electronic
equipment’s. It is used as an interface between utility and most of the power
electronic equipment’s. Generally, to convert line frequency ac to dc, a line frequency diode
bridge rectifier is used. To reduce the ripple in the dc output voltage, a large filter capacitors
used at the rectifier output. But due to this large capacitor, the current drawn by this converter
is peaky immature. This input current is rich in low order harmonics. Also, as power
electronics equipment’s are increasingly being used in power conversion, they inject low
order harmonics into the utility. Due to the presence of these harmonics, the total harmonic
distortion is high and the input power factor is poor. Due to problems associated with low
power factor and harmonics, utilities will enforce harmonic standards and guidelines which
will limit the amount of current distortion allowed into the utility and thus the simple diode
rectifiers may not in use. So, there is a need to achieve rectification at close to unity power
factor and low input current distortion.
1.2 Literature Review
The circuit drawn pertains to a regular industrial the project, which shows how the batteries
take control during an outage in electrical supply or variation beyond the normal limits of the
voltage line, without disruption on the operation providing a steady regulated output (5 Volts
by LM7805) and an unregulated supply (12 Volts).The input to the primary winding of the
transformer (TR1) is 220V. The secondary winding can be raised up to 15 Volts if the value
is at least 12 Volts running 3 amp. The fuse (FS1) acts as a mini circuit breaker for protection
against short circuits, or a defective battery cell in fact. The presence of electricity will cause
the LED 1 to light. The light of LED will set off upon power outage and the battery will take
over.
The circuit was designed to offer more flexible pattern wherein it can be customized by using
different regulators and batteries to produce regulated and unregulated voltages. Utilizing 12
Volt batteries in a positive input 7805 five regulator, can control a 5V supply.
1.3 Organization of the Project:
In this report there is eight chapters in total .The first chapter describes a brief idea about
introduction and Preface. The second chapter contains circuit diagram, list of component and
working principle. In third chapter describes voltage regulator and transformer. The fourth
chapter contains theory of diode. Five and six chapters explain the Capacitor and rectifier.
Chapter seven is cost analysis. And finally chapter eight is result.
2. Design and Development
It is a simple variable dc power supply which gives 0 to 12 dc volts as an output. Here we use
a simple full wave rectifier along with a voltage regulator which gives a constant output and
its output can be increased by using a pair of voltage divider resistor in which one resistance
is variable to get variable output.
2.1 Circuit Diagram:
pf3
pf4
pf5

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1.1 Introduction: A variable DC power supply is an integral part of any power supply unit used in the all electronic equipment’s. It is used as an interface between utility and most of the power electronic equipment’s. Generally, to convert line frequency ac to dc, a line frequency diode bridge rectifier is used. To reduce the ripple in the dc output voltage, a large filter capacitors used at the rectifier output. But due to this large capacitor, the current drawn by this converter is peaky immature. This input current is rich in low order harmonics. Also, as power electronics equipment’s are increasingly being used in power conversion, they inject low order harmonics into the utility. Due to the presence of these harmonics, the total harmonic distortion is high and the input power factor is poor. Due to problems associated with low power factor and harmonics, utilities will enforce harmonic standards and guidelines which will limit the amount of current distortion allowed into the utility and thus the simple diode rectifiers may not in use. So, there is a need to achieve rectification at close to unity power factor and low input current distortion. 1.2 Literature Review The circuit drawn pertains to a regular industrial the project, which shows how the batteries take control during an outage in electrical supply or variation beyond the normal limits of the voltage line, without disruption on the operation providing a steady regulated output (5 Volts by LM7805) and an unregulated supply (12 Volts).The input to the primary winding of the transformer (TR1) is 220V. The secondary winding can be raised up to 15 Volts if the value is at least 12 Volts running 3 amp. The fuse (FS1) acts as a mini circuit breaker for protection against short circuits, or a defective battery cell in fact. The presence of electricity will cause the LED 1 to light. The light of LED will set off upon power outage and the battery will take over.

The circuit was designed to offer more flexible pattern wherein it can be customized by using different regulators and batteries to produce regulated and unregulated voltages. Utilizing 12 Volt batteries in a positive input 7805 five regulator, can control a 5V supply. 1.3 Organization of the Project: In this report there is eight chapters in total .The first chapter describes a brief idea about introduction and Preface. The second chapter contains circuit diagram, list of component and working principle. In third chapter describes voltage regulator and transformer. The fourth chapter contains theory of diode. Five and six chapters explain the Capacitor and rectifier. Chapter seven is cost analysis. And finally chapter eight is result.

2. Design and Development

It is a simple variable dc power supply which gives 0 to 12 dc volts as an output. Here we use a simple full wave rectifier along with a voltage regulator which gives a constant output and its output can be increased by using a pair of voltage divider resistor in which one resistance is variable to get variable output.

2.1 Circuit Diagram:

The circuit we use for this project is given below.

2.2 List of Components: These are components that are required for our project •Step down transformer 12V/ 3A •Diode 1N2007 (7) •C1 2700μF (35v). •C2 100μF (25V) •C3-6 100pF (4) •IC 7806 Voltage regulator IC 7808 Voltage regulator IC 7809 Voltage regulator IC 7812 Voltage regulator

  • 500 ohm variable resistor •R1 1K ohm resistor. •R2 220 ohm resistor. •LED •Breadboard •Soldering iron and soldering wire

2.3 Working Principle: The main working principle of this project is full wave rectification which is done by bridge configuration in which we are using 4diodes which rectifies the output of the step-down transformer which step- down the 220 AC v to 12 AC volts .here we are using a voltage regulator which give constant voltage, here we are using 7806 which give 6 volts .these regulators are available in various outputs like 6v, 8v, 9v, 12v.

Now the main task is to get variable output for this we use the pair of voltage divider resistors to increase the output of the regulator and in which of resistance is variable so when we increase or decrease the value of that resistor the output voltage of the regulator will also change and we get a range of 0v to 12v here the given below fig shows the increasing output voltage.

In this circuit we use six capacitor, c^1 to c^5 are used to get constant input to the regulator moreover it also helps to reduce the sharp peaks in the output. Connect the 2700 μF capacitor to close to the input of the regulator and the 100 pF capacitor to the output because these capacitor reduce the noise and also help to reduce the ripples produce by the regulator so that

3.2.3 Pin Diagram:

FIG 3.2: VOLTAGE REGULATOR CIRCUIT DIAGRAM

3.2.4 Pin Description:

Pin No Function Name 1 Input voltage (6V-18V) Input 2 Ground (0V) Ground 3 Regulated output; 6V (4.8V-5.2V) Output

3.3 Transformer [2]

The transformer is a device, or a machine, that transfers electrical energy from one electrical circuit to another electrical circuit through the medium of magnetic field and without a change in the frequency. The electric circuit which receives energy from the supply mains is called primary winding and the other circuit which delivers electric energy to the load is called the secondary winding. Actually, the transformer is an electromagnetic energy conversion device. The energy received by the primary is first converted to magnetic energy and it is then reconverted to useful electrical energy in the other circuits (secondary winding circuit, third winding circuit etc.). Thus primary and secondary windings of a transformer are not connected electrically, but are coupled magnetically. This coupling magnetic field allows the transfer of energy in either direction, from high – voltage to low – voltage circuits or from low – voltage to high – voltage circuits. If the transfer of energy occurs at the same voltage, the purpose of the transformer is merely to isolate the two electric circuits and this use is very rare in power applications. If the secondary winding has more turns than the primary winding, then the secondary voltage is higher than the primary winding and the transformer is called a step – up transformer. In case the secondary winding has less turns than the primary winding, then the secondary voltage is lower than the primary voltage and the transformer is called a step – down transformer. A step – up transformer can be used as a step – down transformer, in which the secondary of step – up transformer becomes the primary of step – down transformer. Actually a transformer can be termed a step – up or step – down transformer only after it has been put into service. Therefore, when referring to the windings of a particular transformer, the terms high – voltage winding and low – voltage winding should be used instead of primary and secondary windings.

3.3.1 The Power Transformer

The transformer is either to step-up or step-down the AC supply voltage to suit the requirement of the solid state electronic devices and circuits fed by the DC power supply. One of the important features of a transformer is the electrical isolation offered between the primary and the secondary. The voltages in the primary and secondary windings are directly proportional to the turn’s ratio of the two windings. If V1 is the voltage applied to the Primary, V2 is voltage induced in the secondary, N1 is the number of turns in the primary and N2 is the number of turns in the secondary, then the relationship between them is given by

the expression

3.3.2 Turns ratio:

3.4 Induction law The transformer is based on two principles: first, that an electric current can produce a magnetic field and second that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction). Changing the current in the Primary coil changes the magnetic flux that is developed. The changing magnetic flux induces a voltage in the secondary coil.

Referring to the two figures here, current passing through the primary coil creates a magnetic field. The primary and secondary coils are wrapped around a core of very high magnetic Permeability, usually iron, so that most of the magnetic flux passes through both the primary and secondary coils. Any secondary winding connected load causes current and voltage induction from primary to secondary circuits in indicated directions. The voltage induced across the secondary coil may be calculated from Faraday's law of induction, which states that: