To obtain the ripple factor and percentage regulation of a Full-Wave rectifier without and with filters
S.NO
DESCRIPTION OF ITEM
RANGE
QUANTITY
1.
Diodes
1N 4007
2 No.
2.
Milliammeter
0 - 25m Amp.
1 No.
3.
CRO
20 MHz
1 No.
4.
Center taped Transformer
6-0-6 V
1 No.
5.
Patch cords
6.
Voltmeter
0-20 V
1 No.
7.
Decade Resistance Box
1Ω – 10 M Ω
1 No.
In the full-wave rectifier, a small sinusoidal voltage of say, 12V-0-12VAC derived from the mains supply of 230VAC using a center-tapped step-down transformer is applied to two rectifying diodes. The diodes are so connected that conduction takes place through one diode during one half of the power cycle and through the other diode during the other half of the power cycle. During the positive half cycle when the point A is positive with respect to B, the diode D1 conducts and current i1 flows through RL. During the negative half cycle the point C is positive with respect to B and hence the diode D2conducts and current i2 flows through RL.
The output voltage is the sum of the two half cycles of ac voltage and is still a pulsating DC voltage resulting in a frequency of pulsations that is twice the main frequency (Fig. 6). The output voltage waveform across the load resistor contains ripples. However, in contrast to the half-wave rectifier, the ripple content of the full-wave rectifier is considerably less because one of the diodesD1or D2 conducts during either half of the ac power input cycle.
The output voltage waveform across the load resistor RL contains ripples.
The output DC voltage is given by Where Vm is the peak sinusoidal voltage; Rf is the forward static resistance of the diode and Idc=Vm/Rf+RL
To reduce the ripple further, a capacitor “filter”, is connected across the load resistor. The capacitor charges up to the peak voltage of the ac input (minus the diode voltage drop) during the first quarter of the ac input and when the ac input swings below the peak, the diode is cut- off and the capacitor discharges through the load resistor (Fig. 7), thereby minimizing the ripple component of the voltage (measured by VAC across the load) applied to the load. The expression for the dc output voltage Vdc (from graphical analysis) may be approximated as.
The ripple factor can be measured using an AC and a DC voltmeter and the ripple factor computed
from .
1. Connect the circuit according to Fig. 1 and Switch ON the power supply.
2. Set RL to 1 KΩ and note down the load voltage VL.
3. Note down the output AC and DC voltages in the Table-1. (Since a moving coil analog voltmeter will not respond to AC voltages, a digital voltmeter is used to measure AC voltages, and the values recorded are RMS values). Note: Use separate DC and AC (digital) voltmeters.
4. Observe the input and output waveforms on the oscilloscope and plot these on a graph paper and measure the peak voltage Vm from the oscilloscope screen after ensuring that the Volt/div front knob is in the “Cal” position to obtain accurate Vm readings. Calculate and then plot the ripple factor and percentage regulation vs. load current on graph paper.
1. Connect the capacitor according to the diagram in Fig. 2.
2. Repeat the steps in 3) and 4) above, while noting down the readings in Table -1.
3. Plot the ripple factor and percentage regulation vs. load current with capacitor filter on graph paper.
1. Connect the inductor according to the diagram in Fig.3.
2. Repeat the steps in 3) and 4) above, while noting down the readings in Table -1.
3. Plot the ripple factor and percentage regulation vs. load current with capacitor filter on graph paper.
1. Connect the inductor according to the diagram in Fig.4.
2. Repeat the steps in 3) and 4) above, while noting down the readings in Table -1.
3. Plot the ripple factor and percentage regulation vs. load current with capacitor filter on graph paper.
1. Connect the inductor according to the diagram in Fig.5.
2. Repeat the steps in 3) and 4) above, while noting down the readings in Table -1.
3. Plot the ripple factor and percentage regulation vs. load current with capacitor filter on graph paper.
1.5.1.1 TABLE -1 FULL WAVE RECTIFIER [WITHOUT AND WITH FILTER]
RL = 1K Ohm
Circuit
VNL(DC) Volts Open Circuit or with 20 K Ohm
Vm Volts
VAC Volts
VDC Volts
IAC mA
IDC mA
Ripple Factor VAC/VDC
Theoretical values using Expression Below
Ripple Factor
VAC/VDC
Practical
%Regulation
VNL – VFL / VFL x 100
Without Filter
With inductor Filter
With Capacitor Filter
With L-Section Filter
With π -Section Filter
Expressions for Im, Idc, Irms and Ripple factor γ and Efficiency
Ripple factor (independent of current waveshape and applicable to both half-wave and full wave rectifiers)
In the following expressions ω = 2πf and f = 50 c/s
Ripple factor (with capacitor filter)
Ripple factor (with Inductor filter)
Ripple factor (with L-section filter)
Ripple factor (with π-section filter)
%Regulation
1. VNL (without capacitor) = DC output (load) voltage open circuit or with 20 KΩ load resistor ……volts.
2. VFL (without capacitor) = DC output (load) voltage with 1KΩ load resistor = volts.
3. VNL (with capacitor) = DC output (load) voltage without load (open circuit) = volts.
4. VFL (with capacitor) = DC output (load) voltage with 1KΩ load resistor = volts.
5. The Ripple Factor is a Measure of the Fluctuating Components of a Rectifier
6. Ripple Factor = VAC/VDC at the particular Load RL
7. The variation of dc output voltage as a function of dc load current (depends on RL) is called
regulation.
8. %Regulation Where VL
Note:
The full load (FL) values of voltage VFL depend on the current rating of the transformer, which for the experiment is assumed as the load current with a 1KΩ load resistor.
1. The ripple factor and percentage regulation of the Half-wave rectifier without the filter capacitor are determined.
2. The ripple factor and percentage regulation of the Half-wave rectifier without the filter capacitor are determined.
3. The input and output waveform of the Half-wave rectifier without and with filter are plotted.
4. The graphs of the ripple factor vs. load current and percentage regulation vs. load current for the rectifier.
1. Compare the Vdc(output) of a half wave rectifier with that of full wave rectifier without filter and by what ratio do they differ ignoring source resistance.
2. Define regulation and ripple factor. What are the ideal values for these quantities? What are the practical values?
3. What is the Peak Inverse Voltage in the case of half wave rectifier?
4. How are ripples remove from a rectifier output?