Regulation of output full wave rectified voltage with load.

Regulation of output full wave rectified voltage with load.

Objectives:

The main objective of this experiment is to regulate he output voltage produced by full wave rectifier.

Apparatus:

1.      1 Resistor

2.      4 Diode

3.      Power Supply

4.      Power Cable

5.      AC Oscillator

6.      Connecting Wires

7.      Cathode Ray Oscilloscope

8.      Bread Board

9.      Capacitor

Introduction/Literature Background:

Most electrical components require DC voltages to operate properly. Since most equipment is connected to the 120-V AC power line, so this AC source must be converted into the required DC value. A circuit that converts the AC power line voltage to the required DC voltage is called a power supply. The most important components in power supplies are rectifier diodes, which convert AC line voltage to Diodes are able to produce a DC output voltage because they are unidirectional devices allowing current to flow through them in only one direction. Mostly diodes used are of silicon.

Ideally, the output of most power supplies should be a constant voltage. Unfortunately, this is difficult to achieve. There are two factors that can cause the output voltage to change. First, the ac line voltage is not constant. The second factor that can change the dc output voltage is a change in the load resistance. In complex electronic equipment, the load can change as circuits are switched in and out. In a television receiver, the load on a particular power supply may depend on the brightness of the screen, the control settings, or even the channel selected.
These variations in load resistance tend to change the applied dc voltage because the power supply has a fixed internal resistance. If the load resistance decreases, the internal resistance of the power supply drops more voltage. This causes a decrease in the voltage across the load.

Many circuits are designed to operate with a particular supply voltage. When the supply voltage changes, the operation of the circuit may be adversely affected. Consequently, some types of equipment must have power supplies that produce the same output voltage regardless of changes in the load resistance or changes in the ac line voltage. This constant output voltage may be achieved by adding a circuit called the VOLTAGE REGULATOR at the output of the filter.

Rectification is the process in which AC is converted into DC.A direct current flows from the positive to negative terminal of source supply when it is connected by a circuit. The current flows continuously without changing direction. But in case of AC the direction of flow keeps on changing. Because of their ability to conduct current in one direction and block current in the other direction, diodes are used in circuits called rectifiers that convert ac voltage into DC voltage.

Full wave rectifier rectifies the full cycle in the waveform i.e. it rectifies both the positive and negative cycles in the waveform. As the center tapped rectifier is expensive and not easily available hence bridge rectifier is mostly used for full wave rectification. In this type four diodes are arranged in the form of bridge. This actually provides same output polarity with either polarity.  The output of a rectifier consists of a DC component and an AC component (also known as ripple).

The AC component is undesirable and accounts for the pulsations in the rectifier output. The effectiveness of a rectifier depends upon the magnitude of AC component, the smaller this component the more effective is the rectifier. In full wave rectification the DC component exceeds the AC component in the output. This results in greater pulsation, and less effectiveness of the rectifier. To regulate the voltage capacitor is used along with our circuit. Hence charging and discharging of capacitor produces pure DC.

Circuit Diagram Description:

Our circuit contains four diodes, one resistor, one capacitor, bread board and AC supply. Diodes are connected in series with the capacitor. Capacitor is connected in parallel with resistor. Input is given to the opposite terminals of diodes while output is taken across the resistor as shown in the following diagram:

Procedure/Experimentation:

The steps while doing this experiment are given below:

1.      Circuit diagram is drawn.

2.      Diodes are inserted in series with the capacitor on the bread board.

3.      Resistance is connected in parallel with the capacitor.

4.      AC input is given to the circuit through the AC oscillator.

5.      AC input waveform is seen on CRO by directly connecting CRO with oscillator.

6.     Connected the CRO to the output of the rectifier. Output wave is observed.

7.     Output Wave form (pulsating DC) is observed on CRO.

8.     Value for resistance and capacitance is measured by varying the resistor and capacitor on board such that the discharging time elongates.

9.     Output waveform of pure DC is drawn on notebook.

Observation & Calculation:

Pure DC is observed as a straight line on CRO. Value of capacitance and resistance for which the discharging time elongated is:

Suitable value for resistance=4200ohms

Suitable value for capacitance=22 micro farads

Conclusion:

Output voltage by a full wave rectifier is regulated with the help of a capacitor.

Short Question:

1.      In filter circuits why capacitor is always used in parallel with resistor?

Capacitor allows AC and blocks DC signal. In rectifier for conversion of AC into DC, capacitor is placed in parallel with output not in series .If the capacitor is placed in series then there will be no output.

2.      What determines the rate of discharge of capacitor?

Capacitor and load resistance in circuit determines the discharge of capacitor.

3.      Does low ripple output voltage determines good or bad filtering?

Low ripple output voltage determines that we have done good filtering.

4.      Is a full wave rectifier is easy to filter than that of a half wave rectifier?

Yes the filtering of full wave is easier than that of half wave rectifier.

5.      What is the difference between ripple AC value of full and half wave rectification?

Full wave rectifier has a smaller ripple AC value as compared to half wave wave rectifier.

6.      Which value of capacitor is used for more effective filtering, smaller or larger?

Large value of capacitor should be used to increase filtering. Hence C should be large but X_C should be small.