Foundation Year 2012/13
Laboratory 5: Half- and Full-wave Rectifier Circuits
Laboratory 4
Laboratory 5
Laboratory 6
Aims and Objectives
The aim of this laboratory is to investigate the effect of a non-linear device on ac signals.
By the end this laboratory you will:
-know how half and full-wave rectifier circuits work;
-know how to extract relevant information from a diode datasheet and use them to select
suitable rectifier diodes;
-be familiar with the ‘MATHS’ function of the oscilloscope.
Guide to progress
You have two half-day sessions to complete this laboratory. Theory related to this laboratory
will be covered in lecture in week 4. You should attempt to reach the end of section 1 during
the first half-day session. If you are stuck on a problem for more than a few minutes or if you
feel you are falling behind, then seek guidance from a demonstrator or a member of
academic staff member.
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Foundation Year 2012/13
1. Half-wave rectifier circuit
In this section you will investigate the effect of a single diode on a sinusoidal voltage
waveform.
Figure 1 shows a circuit diagram of a half-wave rectifier circuit. This circuit can be realised
on the PCB provided to you.
Secondary
coil
D1
1N4001
RL1
10 k
Figure 1. Half-wave rectifier circuit connected to the secondary coil of the
transformer.
(a) Briefly explain the operation of the circuit shown in Figure 1. Sketch the voltage
waveform you would expect at the output (across RL1) for a sinusoidal input to the
rectifier circuit.
(b) Remove all components and links placed on the PSU Design Exercise PCB from
the previous laboratory session before you start this laboratory.
(c) Connect the step-down transformer to the PCB and switch on the transformer.
(d) Use both channels of the oscilloscope to observe the waveforms at two outer-taps of
the transformer making the centre-tap as the reference voltage level (ground). i.e.
connect CH1 probe to TP1 and CH2 probe to TP3 and one of the grounds (croc clip)
of oscilloscope probes to TP2. Note down your observation(s) of the two waveforms.
TIPs: use x10 probes, select the same scales for the vertical axis for both channels,
and adjust the vertical position of both waveforms to observe the two waveforms
clearly.
(e) Measure the following quantities of one of the waveforms (e.g. CH1)
i.
peak-to-peak voltage
ii.
mean voltage
iii.
rms voltage
iv.
frequency
(f) By placing components on the component holder posts in the PCB set up the halfwave rectifier circuit shown in figure 1 across one of the outer-taps (first yellow block
connector) and the centre-tap (black) of the transformer. Always use the centre-tap
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Foundation Year 2012/13
(g)
(h)
(i)
(j)
as the reference terminal (Ground). Place the links on headers J1, J4 and J5
appropriately to complete the circuit.
Use CH2 of the oscilloscope to observe the voltage waveform at the output of the
rectifier circuit while observing the input to the rectifier circuit with CH1. Test points
TP4 or TP9 can be used to observe the output of the rectifier.
Comment whether any part of the output signal is actually of sinusoidal form.
Sketch both waveforms on a graph paper and mark all important quantities on the
sketch.
Measure the following quantities of the waveform at the output
i.
Peak-to-peak voltage
ii.
Mean voltage
iii.
rms voltage
iv.
frequency
v.
peak reverse voltage across the diode
TIPs:
You may need to use MATHS function in the oscilloscope to find this.
Select the same vertical scale for both channels
To switch off the MATHS menu press and hold the MATHS button for a few
seconds.
(k) Briefly explain the reason for the reduction in rms value in the rectified output signal
compared to input signal.
(l) As an engineer it is important to interpret information given in datasheets of
electronic components. The datasheet for the diode is being used in this exercise,
1N4001, is given in the appendix at the end of this script. From the datasheet find the
peak reverse voltage that the diode can withstand and thus comment on the
suitability of the diode for the rectifier circuit you have just built.
(m) Search for a suitable replacement diode for the above application with the price.
Briefly explain reason(s) for your choice supported by relevant parts of its datasheet.
To complete this part you may need to know some component suppliers in the UK
and web addresses of two such companies are given here for you to make a start.
But you are welcome to search the component from any supplier known to you.
RS components - http://uk.rs-online.com/web/
Farnell - http://uk.farnell.com/
DO NOT dismantle the circuit as you will build upon what you have competed so far in
Section 2. If time permits you could start section 2.
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Foundation Year 2012/13
2. Full-wave rectifier circuit
In the previous part you have observed that when an ac signal is applied to a diode a
considerable portion of the signal is ‘lost’. Therefore the half-wave rectifier circuit does not
appear to be an effective way of delivering maximum possible power to a load. In this
section you will build a full-wave rectifier circuit that produce a signal with a greater rms
value.
(a) Add another identical half-wave rectifier to the PCB as shown in Figure 2. Use CH1 and
CH2 of the oscilloscope to monitor the outputs of the two rectifier circuits. Note: You may
need to place links on headers J2 and J3 to complete the circuit.
Secondary
coil
D1
RL1
10 k
RL2
10 k
D2
Figure 2. Two half-wave rectifier circuits.
(b) Sketch the two waveforms and note down the following quantities of the output waveform
of the second rectifier.
i.
peak-to-peak voltage
ii.
mean voltage
iii.
rms voltage
iv.
frequency
The above values should be close to the measurements you obtained in Section 1
part (i).
(c) Based on your observations of the two waveforms suggest a suitable modification(s) to
your circuit to form a full-wave rectifier circuit with a single load resistor (Take RL1 as the
load resistor). Draw the circuit diagram of suggested full-wave rectifier circuit and briefly
explain the operation of your circuit.
(d) Implement your design on the PCB.
(e) Use CH1 and CH2 of the oscilloscope to observe the input and out of the full-wave
rectifier circuit. Sketch both waveforms.
(f) Measure the following quantities of the waveform at the output
i.
peak-to-peak voltage
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Foundation Year 2012/13
ii.
iii.
iv.
v.
mean voltage
rms voltage
frequency
peak reverse voltage across a diode (TIP: you may need to use MATHS function
in the oscilloscope to find this)
(g) Comment whether the selected diode is still suitable for the application based on
measurements you took in (f) and datasheet of the component.
Now you can tabulate the following quantities from sections 1 and 2:
i.
ii.
iii.
iv.
Peak-to-peak voltage
Mean voltage
rms voltage
Frequency
for the input sinusoidal signal (between Yellow and Black), and outputs of the half- and fullwave rectifier circuits. See whether the values are sensible.
Store the circuit to use in the next laboratory exercise.
RNG/JKAE 01/13
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