Practical E2: Half wave and F
1.
Objectives
a)
To demonstrate the applications of diodes in rectification,
b)
To study the characteristics of half wave, full wave and bridge rectifier with and without
filters,
c)
To calculate the ripple factor, rectification efficiency of half wave, full wave and bridge
rectifiers.
2.
Equipment needed
 Digital oscilloscope
 Sine Wave AC voltage source (VSINE)
 Silicon PN Junction diodes (IN4001)
 Fixed resistor (1k)
 Single phase bridge rectifier (50 V, 2A)
 Electrolytic capacitors (1 F, 10 F)
 Ideal transformer (XFMR)
 Transformer with centre tapped secondary winding (
3. Introduction
A diode is a two-terminal electrical device formed from a junction of n-type and p-type semiconductor
material that allows the transfer of current in only one direction. Basically, a diode is used for rectifying
waveforms, within radio detectors or within power supplies. They can also be used in various electrical and
electronic circuits where ‘one-way’ result of the diode is required. Most of the diodes are made from
semiconductors like silicon (Si), but sometimes germanium (Ge) is also used. This practical session
focuses on understanding how diodes work and are connected in electric rectifier circuits.
4.
Theory
4.1 Rectification
The most common application of the p-n junction diode is in rectification. The rectifier converts an
alternating voltage into a voltage which has only one polarity and is an essential part of power supply
design. The unique property of a diode, permitting the current to flow in one direction, is utilised in
rectifiers. Diode circuits are mostly used; generally either a single diode (half wave rectification) or an
array of diodes (full wave rectification)
4.1.1 Half wave rectifier
Figure 1: Half have rectifier circuit
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Operation of the half wave rectifier
On the positive cycle the diode is forward biased and on the negative cycle the diode is reverse biased. By
using a diode we have converted an AC source into a pulsating DC source. In summary we have ‘rectified’
the AC signal.
The main advantages of half-wave rectifier are:
i) Their simplicity (lower number of components)
ii) Cheaper up front cost (As they do not require as many components, they are simpler and cheaper to
setup and construct. However, there is a higher cost over time due to increased power losses)
The disadvantages of half-wave rectifier are:
i) They only allow a half-cycle through per sine wave, and the other half-cycle is wasted. This leads to
power loss or transformer utilization factor is low.
ii) They produce a low output voltage.
iii) The output current we obtain is not purely DC, and it still contains a lot of ripple (i.e. it has a high
ripple factor
4.1.2 Full wave rectifier
The half-wave rectifier can do the job of converting an a.c. signal to d.c., but that design is a bit inefficient,
as it throws away half of the input. Fortunately, the full-wave bridge rectifier solves this problem. It
conducts current during both the positive and negative input voltage swings. The solution is to use a full
wave rectifier. Fig. 2 shows the circuit of a full wave rectifier with centre tap in the secondary windings of
the transformer
Figure 2: Full wave rectifier circuit
Operation of the full wave rectifier
During the positive half cycle of the transformer secondary voltage, diode D1 is forward biased and D2 is
reverse biased. So a current flows through the diode D1, load resistor RL and upper half of the transformer
winding. During the negative half cycle, diode D2 becomes forward biased and D1 becomes reverse biased.
The current then flows through the diode D2, load resistor RL and lower half of the transformer winding.
Current flows through the load resistor in the same direction during both half cycles. Peak value of the
output voltage is less than the peak value of the input voltage by about 0.6 - 0.7 V because of the voltage
drop across the diode.
The main advantages of the full wave rectifier are:
i) The rectification efficiency of a full-wave rectifier is double of that of a half-wave rectifier.
ii) Higher output voltage, higher output power and higher Transformer Utilization Factor in case of fullwave rectifier.
iii) The ripple voltage is low and of higher frequency in case of full-wave rectifier so simple filtering
circuit is required
The main disadvantage of the full wave rectifier is that the center tap required in the transformer secondary
makes the transformer required more complicated, bulky and costly.
4.1.3
Bridge rectifier
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Fig. 3 shows the circuit of a full wave bridge rectifier.
Figure 3: Bridge rectifier circuit
Operation of the bridge rectifier
During the positive half cycle of the secondary voltage, diodes D1 and D3 are forward biased and diodes
D2 and D4 are reverse biased. Therefore, current flows through the secondary winding, diode D1, load
resistor RL and diode D3. During the negative half cycle, D2 and D4 are forward biased and diodes D1 and
D3 are reverse biased. Therefore, current flows through the secondary winding, diode D2, load resistor RL
and D4. During both the half cycles, the current flows through the load resistor is in the same direction. The
peak value of the output voltage is less than the peak value of the input voltage by 1.4 V due to the voltage
drop across the two silicon diodes. The ripple factor of the bridge rectifier is the same as that of full wave
rectifier.
The main advantages of the bridge rectifier are:
i) The rectification efficiency is double of that of a half-wave rectifier.
ii) Higher output voltage, higher output power and higher Transformer Utilization Factor.
iii) The ripple voltage is low and of higher frequency, so simple filtering circuit is required
iv) No center tap is required in the transformer secondary so the transformer required is simpler. If
stepping up or stepping down of voltage is not required, transformer can be eliminated even.
v) For a given power output, power transformer of smaller size can be used because current in both
primary and secondary windings of the supply transformer flow for the entire ac cycle.
The main disadvantages of bridge rectifier are:
i) It requires four diodes.
ii) The use of two extra diodes cause an additional voltage drop thereby reducing the output voltage.
4.2
Ripple factor
Ripple factor is a measure of the effectiveness of a rectifier circuit. It is defined as the ratio of RMS value
of the AC component (ripple component), Vr,rms, in the output waveform to the DC component, Vdc, in the
output waveform.

 Vr , rms

 Vdc
2

  1

(1)
We can measure the value of the RMS component of overall output waveform from which we can estimate
the value of Vr,rms.
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For half wave rectifier,
V
Vr , rms  m
2
(2)
V
Vdc  m
(3)

where Vr,rms is the rms value ac component of output waveform, Vdc is the average value of output
waveform and Vm is the peak value of the output waveform.
Note that the divisor in eq (2) is 2 rather than √2 because no power is delivered on the negative half-cycle.
This leads to ripple factor  =1.21 for an ideal half wave rectifier.
For a full wave rectifier (including bridge rectifier),
V
Vr , rms  m
2
Vdc 
(4)
2Vm
(5)

where Vrms = rms value of input, Vdc = average value of input and Vm = peak value of output.
This leads to ripple factor  =0.483 for ideal full wave rectifiers.
4.3 Ripple reduction with filter
The rectified waves from each circuit in Figures 1, 2 and 3 are not good for application: they are dc only in
the sense that they do not change polarity, but do not have constant values and have plenty of ripples i.e.
small waves or undulations (wave like forms) (See Fig. 4 and Fig. 5). Everyday devices require a constant
(“smooth”) power supply. The waveforms from rectifiers have to be smoothed out in order to obtain
authentic direct current. This can be done by means of a capacitor, connected in parallel with the load.
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Figure 4: Output waveform for half wave rectifier circuit without filter
Figure 5: Output waveforms for full wave rectifier and bridge rectifier circuits without filters
The ripple of the rectifier circuit with filter can be quantified. Ripple factor is a ratio of the residual ac
component to dc component in the output voltage and is usually computed as the ratio between the r.m.s.
value of the a.c. component to the d.c. component in the rectifier output (see Fig. 6).
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Figure 6: Measurement of ripple voltage and ripple factor
The value of ripple factor can also be estimated from the waveform of the output voltage as:
Vr , pp

2 3
(6)
Vm  0.5Vr , pp
Where Vm is the peak value of the output voltage and Vr,pp is peak to peak value of the ripple
voltage.
4.4 Rectifier Efficiency
Rectifier efficiency is a measure of the percentage of total a.c. power input converted to useful d.c.
power output. Even with ideal rectifiers with no losses, the efficiency is less than 100% because some of
the output power is AC power rather than DC which manifests as ripple superimposed on the DC
waveform. The ratio can be improved with the use of smoothing circuits which reduce the ripple and hence
reduce the AC content of the output.

Pdc
Pac
(7)
It can also be expressed as a percentage by multiplying by 100%.
For a half-wave rectifier:
V I
Pac  m  m
2 2
(8)
V I
Pdc  m  m
(9)


Again note that the divisors in eq (8) are 2 rather than √2 because no power is delivered on the negative
half-cycle.
Thus, the maximum conversion ratio for a half-wave rectifier is,

Pdc 4

 40.5%
Pac  2
Similarly, for a full-wave rectifier,
V I
Pac  m  m
2 2
Pdc 
(10)
2Vm 2 I m


(11)

Thus, the maximum conversion ratio for a full-wave rectifier is,

Pdc 8

 81.0%
Pac  2
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5.
Procedure
5.1 Build the half-wave rectifier circuit in Fig. 1. Use the signal generator to generate a 120Vrms, 60 Hz
sine wave. Display the output of the signal generator on channel A of the scope, the output of the
transformer on channel B and the voltage across the resistor on channel C. This latter voltage is the
output of the rectifier circuit. See the tutorials at the end of this document for help on how to use
Proteus for this experiment.
5.2 Observe the ac input voltage, the transformer secondary voltage waveform and output voltage
waveform across the load resistor, simultaneously on the CRO screen. Note down Vm and calculate
Vr,rms and Vdc.
5.3 Calculate the ripple factor and rectifier efficiency using the equations given above.
5.4 Connect a 1 F capacitor filter and observe the waveforms. Note down Vm and Vr,ppand calculate
ripple factor and rectifier efficiency using the equations given in the theory.
5.5 Repeat for 10 F capacitor.
5.6 Repeat the above steps for full wave and bridge rectifiers.
6.
Results
6.1 Waveforms
Adjust the oscilloscope to display two or three complete cycles of the signals. Carefully observe the input
signal, the output of the transformer and output of each rectifier, and show the typical waveforms with and
without capacitors (sketch, labeling both the voltage and time axes with tick marks obtained from the scale
factors on the oscilloscope or paste from Proteus - use the “prt scr” on your key board)
6.2 Ripple factor and rectifier efficiency
Tabulate your results as shown below
Table 1: Rectifiers without filters
Vm
Vr.rms = Vm/2
Vdc = Vm/
2
 (%)
2
 (%)

 Vr , rms

 Vdc

  1


 Vr , rms

 Vdc

  1

Half
wave
rectifier
Vm
Vr.rms = Vm/√2
Vdc = 2Vm/
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Full
wave
rectifier
Vm
Vr.rms = Vm/√2
Vdc = 2Vm/

 Vr , rms

 Vdc
 (%)
2

  1

Bridge
rectifier
Table 2: Rectifiers with filter capacitors (C = 1 F)
Vm
Vr,pp
Vr.rms = Vr,pp/2√3
Vdc = Vm - Vr,pp/2
 Vr , rms
 Vdc



 Vr , rms
 Vdc



  
Half wave rectifier
Full wave rectifier
Bridge rectifier
Table 3: Rectifiers with filter capacitors (C = 10 F)
Vm
Vr,pp
Vr.rms = Vr,pp/2√3
Half wave rectifier
Full wave rectifier
Bridge rectifier
7.
Discussion and Conclusions
Discuss your findings as expected.
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Vdc = Vm - Vr,pp/2
  
Half wave rectification tutorial
https://www.youtube.com/watch?v=ny-2PtyfAhM
Full wave rectification tutorial
https://www.youtube.com/watch?v=BgaGsU4nfWk
How to use Oscilloscope in Proteus ISIS
Now in order to add the oscilloscope in the circuit, first click on the Virtual Instruments Mode as shown in
the below figure.
In that mode the first option will be the Oscilloscope which I highlighted in the below figure.
Now drag that oscilloscope and place it in the workspace. As you will see this component has total four
legs means you can view total four different types of signals using this oscilloscope. You can also compare
them, if you need to.
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How to Monitor Oscilloscope
Now in order to monitor the oscilloscope, run / play the Proteus circuit and then double click on the
oscilloscope and a new window will open up as shown in the below figure.
As you can see in the below image there are total two curves showing i.e. Channel A & B. You can show
all four curves or you can switch off those that you do not need.
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Now, if you check the right side of the above figure, you can see there are total four channels, each channel
represent each probe.
If you have attached your signals to A & B now you can change settings of A & B channel and the output
curves will be changed.
Play with this tool and you will see how easy it is to use. Change the position of circular knob and the
amplitude unit will be changed, then change the linear knob of each channel and the dc offset will be added
in the curve.
Visit the link below for a video tutorial on how to use a digital oscilloscope in Proteus:
https://www.youtube.com/watch?v=vtAirF65Izo
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