PHYSICS COURSE NAME
LAB 07
RECTIFICATION
Lab format: This lab is performed via an internet connection with the Remote Web-based Science
Laboratory (RWSL).
Relationship to theory: This lab is about diodes, rectification, the conversion of alternating current into
direct current.
OBJECTIVES
To examine the effects of rectification of AC signals, from a simple diode circuit to diode bridges used in
AC-to-DC power conversion.
EQUIPMENT LIST
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Half wave rectification circuit for RWSL
Full wave rectification circuit for RWSL
Filtered rectification circuit for RWSL
Rectifier circuit for RWSL
Oscilloscope - ELVIS II
Function generator – ELVIS II
Digital Multimeter – ELVIS II
INTRODUCTION
Electrical power supplied by public utilities comes in the form of alternating current (AC), yet
many pieces of electronic equipment such as radio, television and computers require direct current
(DC). An AC-to-DC converter is often used to address this issue. The process of AC-to-DC conversion is
known as rectification and the “switching” device is known as a rectifier.
This switching can be performed by a mechanical device or an electronic device but there are
many disadvantages associated with the use of a mechanical switch (e.g. a commutator). It is much
slower in comparison and subject to wear and dirt accumulation. In practical applications, the electronic
device of choice is the diode. As a solid-state, semiconductor device, diodes can switch at the rate of
billions of times per second, are silent, and are not subject to wear. Because diodes do not produce
sparks as commutators often do, the emitted RF noise can be significantly quieter. Diodes are extremely
efficient, can switch hundreds of amperes of current and have almost indefinite life.
Solid-state diodes block current flow because of their high resistance in the reverse-bias
connection. They are good conductors in the forward-bias connection. For these reasons, we tend to
regard their resistances to be infinity and zero in their respective directions. This is a generally a good
assumption but we will also observe some real-world departures during this lab.
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I. Rectifier Circuits
The circuit shown in Figure 1 is known as a half-wave rectifier. Since the diode only permits current in
the forward direction (the direction of the diode symbol’s arrow), the current to the resistor is blocked
whenever Vin is negative. If Vin is sinusoidal (see Figure 2), the voltage across the resistor appears as in
Figure 3. V is slightly less than Vin during the positive half-cycle because of the small voltage drop across
a forward-biased diode (~0.7 V for a silicon diode).
Figure 1. Half-wave rectifier circuit
Figure 2. AC input voltage Vin
Figure 3. Half wave rectifier output V
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A full-wave rectifier circuit can be constructed with four diodes in an arrangement known as a bridge
rectifier circuit or a “diode bridge” (Figure 4). When Vin is positive, the current takes the path
D1RD3, and when Vin is negative, the current takes the path D2RD4. In either case, the current
flows through the resistor only from the left of the diagram to the right. The voltage across the resistor,
V, is shown in Figure 5 for a sinusoidal input voltage Vin. Again, V is slightly less than Vin because of the
voltage drops across the two diodes (~1.4 V for a silicon diodes).
Figure 4. Full-wave rectifier circuit
Figure 5. Full-wave rectification output voltage across resistor
II. Filtered Circuits
In each of the rectifier circuits discussed, the rectifier output voltage across the load, V, (shown in Figure
3 and Figure 5) is a pulsating DC. Pulsating DC is adequate for some applications, such as charging
storage batteries, but as power supplies for devices which process signals such as amplifiers, pulsating
DC would interact with the signal and would appear as noise. In fact, it would appear to the amplifier as
though someone were switching the power on and off many times per second.
A practical method of removing pulsations is with a capacitor, as shown in Figure 6. The
pulsations that remain after the “filtering” are known as ripple, as shown in Figure 6. The ripple voltage
is defined as the AC component of V, and will be represented as VAC. Ripple voltage alone is not
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indicative of power supply performance. For example, a 6 V DC power supply with a 0.6 V rms ripple is
not performing as well as a 100 V DC power supply with a 5 V rms ripple.
Figure 6. Filtered rectification
The relative amount of ripple in the output waveform V is characterised by the ripple factor r,
defined as
𝑟≡
𝑉𝐴𝐶𝑟𝑚𝑠
𝑉𝐷𝐶
Equation 1
The ratio r, usually expressed as a percentage, indicates the effectiveness of the filter. (For a review of
various voltage quantities including AC, DC, and rms, see Appendix 5.)
When a capacitor is placed in parallel with the resistor R to achieve filtering, the ripple can be
expressed approximately in terms of R and C as
𝑟≈2
1
3𝑓𝑅𝐶
√
Equation 2
where f is the frequency of the half-wave or the full-wave rectified waveform. This circuit functions as a
RC circuit and Equation 2 is valid as long as the period of the waveform (T=1/f) is much smaller than the
RC time constant of the circuit. Equation 2 can be used to select the appropriate capacitance to
maintain the desired upper limit on the ripple.
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[Note. It is customary in a lab of this type to explore the ripple effects by varying C and/or R. Vin would
be the output from a transformer. For RWSL, it is much more practical to change the frequency f by
taking Vin from a function generator. See the precautionary instructions about ground loops in the
procedures section.]
WARNINGS

There are no special safety warnings associated with this lab.

If connecting your own instruments rather than RWSL, keep in mind that many instruments are
connected to each other through a common ground. Unintentionally creating a ground loop is
a common rookie mistake.
PROCEDURE
Part I: Half wave rectification
 Go to the RWSL pre-set circuit for half wave rectification Figure 7. This circuit is fundamentally
the same as the circuit shown in Figure 1 but one notable difference is that the ground is
explicitly shown. This is a practical consequence of the fact that both channels of the
oscilloscope as well as the function generator are grounded and are thus connected to each
other. [This point becomes more of a concern in Parts II and III.]
Here, we are using R = 1 M (or as specified). Use the function generator to set Vin to a 60 Hz
sine wave with amplitude of about 5 V (see Figure 8).
 The two channels of the oscilloscope will display Vin and V, respectively (Figure 9). Sketch or
capture the two waveforms.
 Compare the traces to expected results.
 For V, measure the peak-to-peak amplitude using the oscilloscope trace. Using this value and
appropriate conversion factors from theory, calculate VDC, Vrms, VACrms. (Vave = VDC)
Figure 7. Half-wave rectification circuit for RWSL using ELVIS II
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Figure 8: Function generator controls.
Figure 9: Oscilloscope traces for Vin (green) and V
(blue). Yours should look very similar.
Part II: Full wave rectification
 Go to the RWSL pre-set circuit for full wave rectification (Figure 10).
 Repeat the measurements and analysis as with Part I.
[Special note: because the input signal is supplied by a function generator, one side is grounded
(see schematic diagram). In this case, the output signal cannot be measured simply by
connecting the two output terminals to the input terminals of one channel of an oscilloscope.
This is because one of these terminals is grounded and the grounded terminals of the function
generator and the oscilloscope are thus connected. Such a connection is not only ineffective in
making the desired measurement but also alters the circuit itself. A quick study of the
schematic diagram shows that this would short circuit one of the diodes – can you tell which
one? In order to display V(t) on the oscilloscope, we connect Ch. 1 to one terminal, Ch. 2 to the
other terminal, and use the “Ch 1 – Ch 2” function of the oscilloscope to display the difference.]
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Figure 10. Full-wave rectification circuit for RWSL using ELVIS II
Although not customary, ground connections are explicitly shown. See text for further explanation.
Part III: Full wave rectification with a capacitor filter
 Go to the RWSL pre-set circuit for filtered rectification (Figure 11). We employ the same
technique as in Part II to avoid a ground loop. Here, we are using R = 5.1 k, C = 0.68 F and f =
100 Hz (or as specified).
 Sketch or capture the input and output waveforms for comparison.
 From the oscilloscope trace, determine Vave and VACmax. Calculate VACrms treating VAC as a
sawtooth wave. Calculate the percent ripple.
 Turn on the DMM and measure Vave and VACrms (How do you do this? i.e. what settings do you
use on the DMM?) Compare the result with those obtained above from the oscilloscope
measurements.
 Calculate the predicted values of r from Equation 1 and Equation 2 and compare with
measurements made above.
 Examine and report the effects varying the input frequency has on the waveform ripple.
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Figure 11. Filtered rectification circuit for RWSL using ELVIS II
Although not customary, ground connections are explicitly shown. See text for further explanation.
REFERENCES
Horowitz, P., and Hill, Winfield., 1989, The Art of Electronics, 2nd Ed., Cambridge University Press,
Cambridge.
Appendix 5 – Averaging Periodic Voltages
Original lab manual by John Wonghen & David Everitt, KPU.
Adapted for remote delivery by T. Sato under the Remote Science Labs for Second Year
Physics Project (2012 – 2013) funded by BCcampus.
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