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LAB Report: HALF WAVE&FULL WAVE RECTIFIERS
Half Wave and Full Wave Rectifiers
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September 30, 2015
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LAB Report: HALF WAVE&FULL WAVE RECTIFIERS
Half Wave and Full Wave Rectifiers
Objectives
To understand the operation of half wave and full wave rectifiers
To understand the effect of smoothening capacitor and a load on both half wave and full
wave rectifier.
Equipment and Materials Needed
Materials:

One 240/24 Vrms center-tapped transformer

Two diodes 1N4001

Two 2.2 kΩ resistors

One 100 μF, 50 V electrolytic capacitor (any voltage rating is fine since is simulation
only)

One fuse (any rating is fine since is simulation only)
Equipment:

Oscilloscope

Function generator
Theory
The power supply of an electronic system is used to convert an ac line input to a dc
output. The output from a power supply is used to provide the dc voltages that the circuits in
the system require to operate. The line input is applied to a transformer. The output from the
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LAB Report: HALF WAVE&FULL WAVE RECTIFIERS
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transformer is applied to a rectifier. The rectifier is a diode circuit that converts ac to
pulsating dc. The output from the rectifier is applied to a filter, which is used to reduce the
variations in the rectifier output signal. Finally, a voltage regulator is used to maintain a
constant output from the power supply over a limited range of input variations and load
demands.
The half-wave rectifier contains a single diode that is positioned in series between a
transformer and its load. The diode conducts during half the input cycle and blocks
conduction during the other half. As a result, the output from the rectifier consists of either
positive alternations or negative alternations. The polarity of the output is determined by the
physical orientation of the diode. On the other hand, the full-wave rectifier consists of two
diodes that are connected between a transformer and its load. Note that the circuit requires the
use of a centre-tapped transformer. The circuit shown produces two positive half-cycles out
for each cycle of its ac line input. Reversing the direction of the diodes converts the circuit
into a negative full-wave rectifier.
Procedure
The circuit below of half wave rectifier was set up in Multism with 24V ac
transformer connected to a 240V 50Hz ac line and the load resistor set at 5% tolerance. Then
the oscilloscope was connected as shown below and measurements were taken at voltage,
VSEC, and the load voltage, VLOAD, for this circuit and their waveforms observed.
LAB Report: HALF WAVE&FULL WAVE RECTIFIERS
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A 100 μF capacitor (C1) with a tolerance of 10% was connected in parallel with the
load resistor (RL) and the polarity of the capacitor noted. The dc load voltage, VLOAD, and the
peak-to-peak ripple voltage, VRIPPLE, in the output were measured. The ripple frequency was
also taken and screenshots. The data was Tabulated all data and compared the results with
and without the filter capacitor.
The power was disconnected and the circuit changed to the full-wave rectifier circuit
shown below. The oscilloscope ground was connected as shown. The circuit was carefully
checked before power was applied and the VSEC and VLOAD waveforms were captured
Measurements of the VSEC rms and peak output voltage VLOAD without a filter capacitor were
taken and screen shots of the waveforms.
A 100 μF capacitor (C1) with a tolerance of 10% was connected in parallel with the
load resistor (RL) and the polarity of the capacitor noted. The dc load voltage, VLOAD, and the
peak-to-peak ripple voltage, VRIPPLE, in the output were measured. The ripple frequency was
also taken and screenshots. The data was Tabulated all data and compared the results with
and without the filter capacitor.
Finally the effect of the load resistor on the ripple voltage was investigated by
connecting a second 2.2 kΩ, 5% tolerance, load resistor in parallel with RL and C1 in the full-
LAB Report: HALF WAVE&FULL WAVE RECTIFIERS
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wave circuit as shown below Measurements of the ripple voltage was captured and a
screenshot.
Data Presentation
Half wave rectifier without capacitor
Variable
Measurement across
Measurement across load
transformer
Peak –peak voltage(V)
33.9
16.3
Dc voltage(V)
13.7(uV)
5.10
LAB Report: HALF WAVE&FULL WAVE RECTIFIERS
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I(rms)
3.69mA
3.68mA
I(dc)
2.32mA
2.32mA
V(rms)
12.0
8.10
Waveforms
With a capacitor in parallel with the load
Variable
Across transformer
Across the load
V(dc)
5.44uV
15.6V
V(rms)
12.0V
15.6V
LAB Report: HALF WAVE&FULL WAVE RECTIFIERS
V(p-p)
I(rms)
I(dc)
Waveforms
Full wave rectifier
Without a capacitor
33.9V
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1.30V
LAB Report: HALF WAVE&FULL WAVE RECTIFIERS
Variable
Measurement across
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Measurement across load
transformer
Peak –peak voltage(V)
43.4V
18.6mV
Dc voltage(V)
-13.5V
15.3mV
I(rms)
6.10uA
1.74nA
I(dc)
-10.3nA
1.53nA
V(rms)
21.5V
17.4mV
Waveforms
LAB Report: HALF WAVE&FULL WAVE RECTIFIERS
With a capacitor connected parallel to the load
Conclusion
The ac voltage of half wave rectifier across the secondary winding changes polarities
after every half cycle of input wave. During the positive half-cycles of the input ac voltage
i.e. when upper end of the secondary winding is positive w.r.t. its lower end, the diode is
forward biased and therefore conducts current. If the forward resistance of the diode is
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assumed to be zero (in practice, however, a small resistance exists) the input voltage during
the positive half-cycles is directly applied to the load resistance RL, making its upper end
positive w.r.t. its lower end. The waveforms of the output current and output voltage are of
the same shape as that of the input ac voltage.
During the negative half cycles of the input ac voltage i.e. when the lower end of the
secondary winding is positive w.r.t. its upper end, the diode is reverse biased and so does not
conduct. Thus during the negative half cycles of the input ac voltage, the current through and
voltage across the load remains zero. The reverse current, being very small in magnitude, is
neglected. Thus for the negative half cycles no power is delivered to the load.
Thus the output voltage (VL) developed across load resistance RL is a series of
positive half cycles of alternating voltage, with intervening very small constant negative
voltage levels, It is obvious from the figure that the output is not a steady dc, but only a
pulsating dc wave as depicted in the half wave without capacitor. When a capacitor is
introduced it brings out the smoothening effect. In that during the forward bias of the diode it
charges and when the diode is reverse biased the capacitor act as a source thus reducing
discontinuities.
The full wave rectifier circuit consists of two power diodes connected to a single load
resistance (RL) with each diode taking it in turn to supply current to the load. When point
upper arm of the transformer is positive, diode D1 conducts in the forward direction. When
point second arm positive (in the negative half of the cycle) with respect to point upper arm,
diode D2 conducts in the forward direction and the current flowing through resistor R is in the
same direction for both half-cycles.
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As the output voltage across the resistor R is the phasor sum of the two waveforms combined,
this type of full wave rectifier circuit is also known as a “bi-phase” circuit.
This mechanism gets rids of a zero cycle as shown in the half wave rectifier hence the
waveform shown. As for the case of increasing load, the current goes down as load resistance
goes up. Lower current means the filter capacitor will discharge less for each cycle, thus the
voltage across it will be smaller, which is the ripple voltage.
One of the main advantages of full wave to half wave rectifier is that both the positive
and negative peaks are used. This means the cap is charged up twice as often. Since the
maximum time since the last peak is less, the cap can be less to support the same maximum
current draw. The downside of a full wave rectifier is that it takes 4 diodes instead of 1, and
one more diode drop of voltage is lost. Diodes are cheap and small, so most of the time a full
wave rectifier makes more sense. Another way to make a full wave rectifier is with a centre
tapped transformer secondary. The centre is connected to ground and there is one diode from
each end to the raw positive supply. This full wave rectifies with only one diode drop in the
path, but requires a heavier and more expensive transformer.