Regulation of output half wave rectified voltage with load.

Regulation of output half wave rectified voltage with load.

Objectives:

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

Apparatus:

1.      1 Resistor

2.      1 Diode

3.      Power Supply

4.      Power Cable

5.      AC Oscillator

6.      Connecting Wires

7.      Cathode Ray Oscilloscope

8.      Bread Board

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.

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.

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.

In half wave rectification type only half of the cycle is rectified. The output is positive and significant during the positive half cycles of input wave. At the same time the output is zero during negative half cycles of input wave. Summarizing as that in half wave rectification the rectifier conducts only during the positive half cycles of input AC supply. The negative half cycle of AC supply are suppressed i.e. during negative half cycle, no current conducted hence no voltage appears across the load. 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 half wave rectification the AC component exceeds the DC 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.

Procedure/Experimentation:

The steps while doing this experiment are given below:

1.      Circuit diagram is drawn.

2.      Diode is 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=4700 ohms

Suitable value for capacitance=50 micro farads

Conclusion:

Output voltage of half wave rectifier is regulated with the help of a capacitor

Short Question:

1.      What is meant by voltage regulation?

The regulation of a supply is an index which shows how the output varies with load, the voltage regulation of the transformer is the percentage change in the output voltage from no-load to full-load.

2.      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.

3.      Is filtering better at higher frequency or lower?

Filtering is better at higher frequency, as X_C decrease hence decreasing the impedance. And Ac can now more easily flow through the capacitor and filtering is more easier now.

4.      Does the filtering circuit increases or decreases the output voltage?

Filtering increases the average output voltage.

5.      How does changing the load resistance affects the ripple voltage?

Ripple voltage, in the presence of a filter capacitor, is inversely proportional to load resistance. 
If the load were zero (resistance infinite), then there would be no ripple voltage. As the load increases (resistance decreases), the ripple voltage increases.