Full Wave Bridge Rectifier Class12 4z6w52

National Academy Class – Xll Physics Project Topic- Full Wave Bridge Rectifier

Submitted to: Submitted By: Mr. S.k. Sharma Lavish Yadav Roll.No.21-A

Acknowledg ement From the depth of my heart I express my deep sincere gratitude to the Almighty for the Blessings that had bestowed upon me to do this work. Having a successful project is really a great pleasure to us. Yet all these will not have been possible if not for hard work, persistence and cooperation among the researchers. I would like to extend our sincerest appreciation to the following people who helped accomplish the project. They are the people who contributed much for the success of this endeavor. First of all, I would like to thank our parents and benefactors who have shown their unending and provided us with necessary materials I needed. Second, I would like to thank our Physics teacher, Mr. S.K.Sharma for teaching us the fundamental research and investigatory writing and for showing a great deal of patience through the time.

Above all, I would like to thank God for giving us the gift of wisdom and understanding and for answering our prayers.

CONTENTS: THEORY  CIRCUIT DIAGRAM  CONSTRUCTION  FULL WAVE BRIDGE RECTIFIER • HALF WAVE RECTIFICATION • FULL WAVE RECTIFICATION • RECTIFIER OUTPUT SMOOTHING  WORKING OF BRIDGE RECTIFIER]  GRAPH 

BRIDGE RECTIFIER,RC FILTER

 HOW RECTIFIER CIRCUIT WORKS IN ELECTRONICS  FULL WAVE BRIDGE RECTIFIER MERITS AND DEMERITS OF FULL WAVE RECTIFIER OVER HALF WAVE RECTIFIER

THEORY:-

A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The process is known as rectification. Rectifiers have many uses, but are often found serving as components of DC power supplies and high-voltage direct current power transmission systems. Rectification may serve in roles other than to generate direct current for use as a source of power. As noted, detectors of radio signals serve as rectifiers. In gas heating systems flame rectification is used to detect presence of flame. The simple process of rectification produces a type of DC characterized by pulsating voltages and currents (although still unidirectional). Depending upon the type of end-use, this type of DC current may then be further modified into the type of relatively constant voltage DC characteristically produced by such sources as batteries and solar cells. A diode bridge is an arrangement of four (or more) diodes in a bridge circuit configuration that provides the same polarity of output for either polarity of input. When used in its most common application, for conversion of an alternating current (AC) input into a direct current (DC) output, it is known as a bridge rectifier. A bridge rectifier provides full-wave rectification from a two-wire AC input, resulting in lower cost and weight as compared to a rectifier with a 3-wire input from a transformer with a center-tapped secondary winding.

Circuit Diagram:-

Construction:The diodes labelled D1 to D2 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 D4 conduct in series while diodes D2 and D3 are reverse biased and the current flows through the load as shown below.

Full Wave Bridge Rectifier:Half-wave rectification:In half wave rectification of a single-phase supply, either the positive or negative half of the AC wave is ed, while the other half is blocked. Because only one half of the input waveform reaches the output, mean voltage is lower. Half-wave rectification requires a single diode in a single-phase supply, or three in a three-phase supply. Rectifiers yield a unidirectional but pulsating direct current; half-wave rectifiers produce far more ripple than full-wave rectifiers, and much more filtering is needed to eliminate harmonics of the AC frequency from the output.

Full-wave rectification:A full-wave rectifier converts the whole of the input waveform to one of constant polarity (positive or negative) at its output. Full-wave rectification converts both polarities of the input waveform to DC (direct current), and yields a higher mean output voltage. Two diodes and a center tapped transformer, or four diodes in a bridge configuration and any AC source (including a transformer without center tap), are needed. Single semiconductor diodes, double diodes with common cathode or common anode, and four-diode bridges, are manufactured as single components.

Bridge rectifier: A full-wave rectifier using 4 diodes. For single-phase AC, if the transformer is center-tapped, then two diodes back-to-back (cathode-to-cathode or anode-to-anode, depending upon output polarity required) can form a full-wave rectifier. Twice as many turns are required on the transformer secondary to obtain the same output voltage than for a bridge rectifier, but the power rating is unchanged.

Rectifier output smoothing:While half-wave and full-wave rectification can deliver unidirectional current, neither produces a constant voltage. In order to produce steady DC from a rectified AC supply, a smoothing circuit or filter is required. In its simplest form this can be just a reservoir capacitor or smoothing capacitor, placed at the DC output of the rectifier. There will still be an AC ripple voltage component at the power supply frequency for a half-wave rectifier, twice that for full-wave, where the voltage is not completely smoothed.

Sizing of the capacitor represents a tradeoff. For a given load, a larger capacitor will reduce ripple but will cost more and will create higher peak currents in the transformer secondary and in the supply feeding it. The peak current is set in principle by the rate of rise of the supply voltage on the rising edge of the incoming sinewave, but in practice it is reduced by the resistance of the transformer windings. In extreme cases where many rectifiers are loaded onto a power distribution circuit, peak currents may cause difficulty in maintaining a correctly shaped sinusoidal voltage on the ac supply. To limit ripple to a specified value the required capacitor size is proportional to the load current and inversely proportional to the supply frequency and the number of output peaks of the rectifier per input cycle. The load current and the supply frequency are generally outside the control of the designer of the rectifier system but the number of peaks per input cycle can be affected by the choice of rectifier design. A half-wave rectifier will only give one peak per cycle and for this and other reasons is only used in very small power supplies. A full wave rectifier achieves two peaks per cycle, the best possible with a single-phase input. For three-phase inputs a three-phase bridge will give six peaks per cycle; higher numbers of peaks can be achieved by using transformer networks placed before the rectifier to convert to a higher phase order. To further reduce ripple, a capacitor-input filter can be used. This complements the reservoir capacitor with a choke (inductor) and a second filter capacitor, so that a steadier DC output can be obtained across the terminals of the filter capacitor. The choke presents a high

impedance to the ripple current. For use at power-line frequencies inductors require cores of iron or other magnetic materials, and add weight and size. Their use in power supplies for electronic equipment has therefore dwindled in favour of semiconductor circuits such as voltage regulators. A more usual alternative to a filter, and essential if the DC load requires very low ripple voltage, is to follow the reservoir capacitor with an active voltage regulator circuit. The reservoir capacitor needs to be large enough to prevent the troughs of the ripple dropping below

the minimum voltage required by the regulator to produce the required output voltage. The regulator serves both to significantly reduce the ripple and to deal with variations in supply and load characteristics. It would be possible to use a smaller reservoir capacitor (these can be large on high-current power supplies) and then apply some filtering as well as the regulator, but this is not a common strategy. The extreme of this approach is to dispense with the reservoir capacitor altogether and put the rectified waveform straight into a choke-input filter. The advantage of this circuit is that the current waveform is smoother and consequently the rectifier no longer has to deal with the current as a large current pulse, but instead the current delivery is spread over the entire cycle. The disadvantage, apart from extra size and weight, is that the voltage output is much lower – approximately the average of an AC half-cycle rather than the peak.

Working of Bridge Rectifier:-

During the positive input half cycle terminal M of the secondary is positive and N is negative. Diode D1 and D3 becomes forward bias where as D2 and D4 are reversed bias. Hence the current flows along point M, E, A, B, C, F and N producing a drop across RL.

During the negative input half cycle secondary terminal N becomes positive and M is negative. Now D2 and D4 are forward bias and D1 and D3 are reversed bias. Now the current flows along points N, E, A, B, C, F and M. Hence we find that current keeps flowing through load resistance RL in the same direction (A, B). during both half cycles of the AC input the point A of the bridge rectifier always acts as an anode and point C as cathod. It frequency is twice that of supply frequency.

Graph:-

Bridge Rectifier, RC Filter:A bridge rectifier makes use of four diodes in a bridge arrangement to achieve full-wave rectification. This is a widely used configuration, both with individual diodes wired as shown and with single component bridges where the diode bridge is wired internally.

How Rectifier Circuit Works in Electronics:One of the most common uses for rectifier diodes in electronics is to convert household alternating current into direct current that can be used as an alternative to batteries. The rectifier circuit, which is typically made from a set of cleverly interlocked diodes, converts alternating current to direct current. In household current, the voltage swings from positive to negative in cycles that repeat 60 times per second. If you place a diode in series with an alternating current voltage, you eliminate the negative side of the voltage cycle, so you end up with just positive voltage.

If you look at the waveform of the voltage coming out of this rectifier diode, you'll see that it consists of intervals that alternate between a short increase of voltage and periods of no voltage at all. This is a form of direct current because it consists entirely

of positive voltage. However, it pulsates: first it's on, then it's off, then it's on again, and so on. Overall, voltage rectified by a single diode is off half of the time. So although the positive voltage reaches the same peak level as the input voltage, the average level of the rectified voltage is only half the level of the input voltage. This type of rectifier circuit is sometimes called a half-wave rectifier because it es along only half of the incoming alternating current waveform. A better type of rectifier circuit uses four rectifier diodes, in a special circuit called a bridge rectifier.

Look at how this rectifier works on both sides of the alternating current input signal:•

•

In the first half of the AC cycle, D2 and D4 conduct because they're forward biased. Positive voltage is on the anode of D2 and negative voltage is on the cathode of D4. Thus, these two diodes work together to the first half of the signal through. In the second half of the AC cycle, D1 and D3 conduct because they're forward biased:

Positive voltage is on the anode of D1, and negative voltage is on the cathode of D3. The net effect of the bridge rectifier is that both halves of the AC sine wave are allowed to through, but the negative half of the wave is inverted so that it becomes positive. In the bridge circuit four diodes are connected in the form of a Wheatstone bridge, two diametrically opposite junctions of the bridge are connected to the secondary of a transformer and the other two are connected to the load.

Full-wave-bridge-rectifier:As shown in the given diagram of full wave bridge rectifier it consists of four diodes under the condition in which four diodes are connected the called bridge circuit. So due to this type of circuit is named bridge rectifier. A resistor is connected in the circuit where rectified output voltage appears called load resistor RL. When the upper end of the transformer secondary winding is positive, say during first half-cycles of the input supply, diodes D1 and D3 are forward biased and current flows through arm AB, enters the load at positive terminal, leaves the load at negative terminal, and returns back flowing through arm DC. During this half of each input cycle, the diodes D2 and D4 are reverse biased and so the current is not allowed to flow in arms AD and BC. The flow of current is

indicated by solid arrows in the figure. In the second half of the input cycle the lower end of ac supply becomes positive, diodes D2 and D4 become forward biased and current flows through arm CB, enters the load at the positive terminal, leaves the load at negative terminal and returns back flowing through arm DA. Flow of current has been shown by dotted arrows in the figure. Thus the direction of flow of current through the load resistance RL remains the same during both half cycles of the input supply voltage.

Merits and Demerits of Fullwave Rectifier over Half-Wave Rectifier:• Merits:-

.

The rectification efficiency of full-wave rectifier is

double of that of a half-wave rectifier.

.

The ripple voltage is low and of higher frequency

in case of a full-wave rectifier so simple filtering circuit is required.

. .

Higher output voltage higher output power and

higher TUF in case of a full-wave rectifier.

In a full-wave rectifier, there is no problem due

to dc saturation of the core because the dc currents in the two halves of the transformer secondary flow in opposite directions.

• Demerits:Full-wave rectifier needs more circuit elements and is costlier.

TEACHER’S REMARK:-

CERTIFICATE:This is hereby to certify that the original and genuine investigation work has been carried out to investigate about the subject matter and the related data collection and investigation has been completely solely, sincerely and satisfactorily by LAVISH YADAV of class-XII(A), NATIONAL ACADEMY, regarding his project titled “FULL-WAVE BRIDGE RECTIFIER”.