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B.Sc Electrical Engineering Project report Full wave bridge rectifier

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Project Edc & work shop project report

Department Of Electrical Engineering Faculty of Engineering Lahore College for Women University, Lahore 2019

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Table of Contents Problem Statement………………………………………………………………..3 Components………………………………………………………………………..3 Objective of Project……………………………………………………………….3 Cicuit diagram…………………………………….3 Project…………………………..4 Working of components…….....4 Working………………………..9 Implementation…………………10 Block diagram……………………11 References………………………………………………………………………11

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Problem statement: To convert 240V AC at 50Hz from main supply to 10-15v DC.

List of components:  Capacitors. 

4 diodes (1N4004)

 Load; a table lamp with an automatic switch relay and a battery Objectives of project: 

To convert AC in to DC.



Make DC smooth by filter in parallel



To make schematic and layout on proteus



Printed circuit board designing

 Circuit diagram:

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Project: A Bridge rectifier is an Alternating Current (AC) to Direct Current (DC) converter that rectifies mains AC input to DC output. Bridge Rectifiers are widely used in power supplies that provide necessary DC voltage for the electronic components or devices. Depending on the load current requirements, a proper bridge rectifier is selected. Components’ ratings and specifications, breakdown voltage, temperature ranges, transient current rating, forward current rating, mounting requirements and other considerations are taken into account while selecting a rectifier power supply for an appropriate electronic circuit’s application. The bridge rectifier circuit diagram consists of various stages of devices like transformer, Diode Bridge, filtering and regulators. Generally all these blocks combination is called as regulated DC power supply that powers various electronic appliances. Transformer: The first stage of the circuit is a transformer which is a step-down type that changes the amplitude of the input voltage. Most of the electronic projects uses 230/12V transformer to step-down the AC mains 230V to 12V AC supply.

Next stage is a diode-bridge rectifier which uses four or more diodes depending on the type of bridge rectifier. Choosing a particular diode or any other switching device for a corresponding rectifier needs some considerations of the device like Peak Inverse Voltage (PIV), forward current If, voltage ratings, etc. It is responsible for producing unidirectional or DC current at the load by conducting a set of diodes for every half cycle of the input signal. Since the output after the diode bridge rectifiers is of pulsating nature, and for producing it as a pure DC, filtering is necessary. Filtering is normally performed with one or more capacitors attached across the load, as you can observe in the below figure wherein smoothing of wave is performed. This capacitor rating also depends on the output voltage. The last stage of this regulated DC supply is a voltage regulator that maintains the output voltage to a constant level. Suppose the microcontroller works at 5V DC, but 4

the output after the bridge rectifier is around 16V, so to reduce this voltage, and to maintain a constant level – no matter voltage changes in input side – a voltage regulator is necessary. Advantage: The main advantage of this bridge circuit is that it does not require a special centre tapped transformer, thereby reducing its size and cost. The single secondary winding is connected to one side of the diode bridge network and the load to the other side as shown below.

The Diode Bridge Rectifier

The four diodes labelled D1 to D4 are arranged in “series pairs” with only two diodes conducting current during each half cycle. During the positive half cycle of the supply, diodes D1 and D2 conduct in series while diodes D3 and D4 are reverse biased and the current flows through the load as shown below. The Positive Half-cycle

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During the negative half cycle of the supply, diodes D3 and D4 conduct in series, but diodes D1 and D2 switch “OFF” as they are now reverse biased. The current flowing through the load is the same direction as before. The Negative Half-cycle

As the current flowing through the load is unidirectional, so the voltage developed across the load is also unidirectional the same as for the previous two diode full-wave rectifier, therefore the average DC voltage across the load is 0.637Vmax.

Typical Bridge Rectifier However in reality, during each half cycle the current flows through two diodes instead of just one so the amplitude of the output voltage is two voltage drops ( 2*0.7 = 1.4V ) less than the input VMAX amplitude. The ripple frequency is now twice the supply frequency (e.g. 100Hz for a 50Hz supply or 120Hz for a 60Hz supply.) Although we can use four individual power diodes to make a full wave bridge rectifier, pre-made bridge rectifier components are available “off-the-shelf” in a range of different voltage and current sizes that can be soldered directly into a PCB circuit board or be connected by spade connectors. The image to the right shows a typical single phase bridge rectifier with one corner cut off. This cut-off corner indicates that the terminal nearest to the corner is the positive or +veoutput terminal or lead with the opposite (diagonal) lead being the negative or ve output lead. The other two connecting leads are for the input alternating voltage from a transformer secondary winding. 6

The Smoothing Capacitor: We saw in the previous section that the single phase half-wave rectifier produces an output wave every half cycle and that it was not practical to use this type of circuit to produce a steady DC supply. The full-wave bridge rectifier however, gives us a greater mean DC value (0.637 Vmax) with less superimposed ripple while the output waveform is twice that of the frequency of the input supply frequency. We can improve the average DC output of the rectifier while at the same time reducing the AC variation of the rectified output by using smoothing capacitors to filter the output waveform. Smoothing or reservoir capacitors connected in parallel with the load across the output of the full wave bridge rectifier circuit increases the average DC output level even higher as the capacitor acts like a storage device as shown below.

The smoothing capacitor converts the full-wave rippled output of the rectifier into a more smooth DC output voltage. 100uF Smoothing Capacitor

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However, there are two important parameters to consider when choosing a suitable smoothing capacitor and these are its Working Voltage, which must be higher than the no-load output value of the rectifier and its Capacitance Value, which determines the amount of ripple that will appear superimposed on top of the DC voltage. Too low a capacitance value and the capacitor has little effect on the output waveform. But if the smoothing capacitor is sufficiently large enough (parallel capacitors can be used) and the load current is not too large, the output voltage will be almost as smooth as pure DC. As a general rule of thumb, we are looking to have a ripple voltage of less than 100mV peak to peak. Regulator: A voltage regulator is used to regulate voltage level. When a steady, reliable voltage is needed, then voltage regulator is the preferred device. It generates a fixed output voltage that remains constant for any changes in an input voltage or load conditions. It acts as a buffer for protecting components from damages. A voltage regulator is a device with a simple feed- forward design and it uses negative feedback control loops. There are mainly two types of voltage regulators: Linear voltage regulators and switching voltage regulators; these are used in wider applications. Linear voltage regulator is the easiest type of voltage regulators. It is available in two types, which are compact and used in low power, low voltage systems. Let us discuss about different types of voltage regulators.

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Voltage Regulator Relay: The basics for all the relays are the same. A relay is an electromagnetic switch operated by a relatively small electric current that can turn on or off a much larger electric current. The heart of a relay is an electromagnet (a coil of wire that becomes a temporary magnet when electricity flows through it) when a relay contact is normally open (NO), there is an open contact when the relay is not energized. When a relay contact is Normally Closed (NC), there is a closed contact when the relay is not energized. In either case, applying electrical current to the contacts will change their state.

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Here in above diagram, we supply power by bridge rectifier. Relay is used as an automatic switch. When supply is cut off then relay is automatically switched to the battery and lights up our lamp even when electricity is off. Working : In this project, the input mains supply is stepped down from 230 V AC to a desired level (depending upon the rating of the load connected). Peak voltage across the load is matched to the peak value of AC voltage from output of a transformer. This is achieved here by using a step down transformer 12-0-12V of 500mA rating. The reduced voltage level (12V) appears on the secondary winding of the transformer. This AC signal has alternating positive and negative waveform cycle while the desired output should always be positive. Therefore the signal is rectified using a bridge rectifier to block the negative portion of the waveform. Almost all rectifiers comprise a number of diodes in a certain arrangement for converting AC to DC than is possible with only one diode. Here, four diodes have been used as shown in the circuit diagram. The bridge rectifier rectifies the stepped down AC to pulsating DC which contains ripples. So a filter capacitor is connected across the output of the rectifier so as to bypass the AC component present in it. The output obtained can now be used to power electronic devices/circuits

Implementation: We draw sematic diagram of our circuit on proteus and run it. Then take layout of our circuit. Print our layout on butter paper. Then convert our circuit on Bakelite sheet. Make chemical reactions on our Bakelite sheet and then wash it with water. We remove ink from sheet by spirit. Then make holes through drilling process on desired places. Insert our components on our circuit and now it’s ready for use.

Block diagram:

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Start

Step down Transformer

AC to DC converter With bridge rectifier

Filter with Capacitor

Load Resistor table lamp with a battery

End

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