2. RIPPLE FUNDAMENTALS
The most common meaning of ripple
in electrical science is the small unwanted
residual periodic variation of the direct current
(dc) output of a power supply which has been
derived from an alternating current (ac)
source. This ripple is due to incomplete
suppression of the alternating waveform within
the power supply.
3. As well as this time-varying
phenomenon, there is a frequency domain
ripple that arises in some classes of filter and
other signal processing networks. In this case
the periodic variation is a variation in the
insertion loss of the network against increasing
frequency. The variation may not be strictly
linearly periodic.
4. In this meaning also, ripple is
usually to be considered an unwanted effect,
its existence being a compromise between the
amount of ripple and other design parameters.
5. TIME DOMAIN RIPPLE
Ripple factor (γ) may be defined as the
ratio of the root mean square (rms) value of
the ripple voltage to the absolute value of the
dc component of the output voltage, usually
expressed as a percentage. However, ripple
voltage is also commonly expressed as the
peak-to-peak value. This is largely because
peak-to-peak is both easier to measure on an
oscilloscope and is simpler to calculate
theoretically.
6. Filter circuits intended for the reduction of ripple are usually called smoothing circuits.
Full-wave rectifier circuit with a reservoir capacitor on the output for the purpose of
smoothing ripple is shown above.
7. The simplest scenario
in ac to dc conversion is a rectifier without any
smoothing circuitry at all. The ripple voltage is
very large in this situation; the peak-to-peak
ripple voltage is equal to the peak ac voltage.
A more common arrangement is to allow the
rectifier to work into a large smoothing
capacitor which acts as a reservoir.
8. After a peak in output voltage the
capacitor (C) supplies the current to the load
(R) and continues to do so until the capacitor
voltage has fallen to the value of the now
rising next half-cycle of rectified voltage. At
that point the rectifiers turn on again and
deliver current to the reservoir until peak
voltage is again reached.
9. If the time constant, CR, is large
in comparison to the period of the ac
waveform, then a reasonably accurate
approximation can be made by assuming that
the capacitor voltage falls linearly. A further
useful assumption can be made if the ripple is
small compared to the dc voltage. In this case
the phase angle through which the rectifiers
conduct will be small and it can be assumed
that the capacitor is discharging all the way
from one peak to the next with little loss of
accuracy.
10. Ripple voltage from a full-wave rectifier,
before and after the application of a smoothing
capacitor is shown below
11. For a full-wave rectifier:
For a half-wave rectification:
Where,
Vpp is the peak-to-peak ripple voltage
I is the current in the circuit
f is the frequency of the ac power
C is the capacitance
12. For the rms value of the ripple voltage, the
calculation is more involved as the shape of
the ripple waveform has a bearing on the
result. Assuming a sawtooth waveform is a
similar assumption to the ones above and
yields the result:
Where,
γ is the ripple factor
R is the resistance of the load
13. EFFECTS OF RIPPLE
Ripple is undesirable in many electronic applications
for a variety of reasons:
(1)The ripple frequency and its harmonics are within
the audio band and will therefore be audible on
equipment such as radio receivers, equipment for
playing recordings and professional studio
equipment.
(2)The ripple frequency is within television video
bandwidth. Analogue TV receivers will exhibit a
pattern of moving wavy lines if too much ripple is
present.
14. (3) The presence of ripple can reduce the
resolution of electronic test and measurement
instruments. On an oscilloscope it will manifest
itself as a visible pattern on screen.
(4) Within digital circuits, it reduces the
threshold, as does any form of supply rail
noise, at which logic circuits give incorrect
outputs and data is corrupted.
(5) High-amplitude ripple currents shorten the
life of electrolytic capacitors.
15. HARMONIC FUNDAMENTALS
A distortion is the alteration of the original
shape (or other characteristic) of an object,
image, sound, waveform or other form of
information or representation. Distortion is
usually unwanted, and often many methods
are employed to minimize it in practice. In
some fields, however, distortion may be
desirable; such is the case with electric guitar
distortion.
16. The transfer function of an ideal amplifier, with
perfect gain and delay, is only an
approximation. The true behavior of the
system is usually different. Nonlinearities in the
transfer function of an active device (such as
vacuum tubes, transistor, and op-amp) are a
common source of non-linear distortion; in
passive components (such as a coaxial cable
or optical fiber), linear distortion can be caused
by inhomogeneities, reflections, and so on in
the propagation path.
18. Amplitude Distortion
Amplitude distortion is distortion
occurring in a system, subsystem, or device
when the output amplitude is not a linear
function of the input amplitude under specified
conditions.
19. Harmonic Distortion
Harmonic distortion adds overtones that
are whole number multiples of a sound wave's
frequencies.Nonlinearities that give rise to
amplitude distortion in audio systems are most
often measured in terms of the harmonics
(overtones) added to a pure sinewave fed to
the system. Harmonic distortion may be
expressed in terms of the relative strength of
individual components, in decibels, or the Root
Mean Square of all harmonic components:
Total harmonic distortion (THD), as a
percentage.
20. Frequecy response Distortion
Non-flat frequency response is a
form of distortion that occurs when different
frequencies are amplified by different amounts,
caused by filters. For example, the non-
uniform frequency response curve of AC-
coupled cascade amplifier is an example of
frequency distortion. In the audio case, this is
mainly caused by room acoustics, poor
loudspeakers and microphones, long
loudspeaker cables in combination with
frequency dependent loudspeaker impedance,
etc.
21. Phase Distortion
This form of distortion mostly
occurs due to the reactive component, such as
capacitive reactance or inductive reactance.
Here, all the components of the input signal
are not amplified with the same phase shift,
hence causing some parts of the output signal
to be out of phase with the rest of the output.
22. Group delay Distortion
It can be found only in dispersive media.
In a waveguide, propagation velocity varies
with frequency. In a filter, group delay tends to
peak near the cut-off frequency, resulting in
pulse distortion. When analog long distance
trunks were commonplace, for example in 12
channel carrier, group delay distortion had to
be corrected in repeaters.
23. Audio Distortion
In this context, distortion refers to
any kind of deformation of a waveform,
compared to an input, usually Clipping,
harmonic distortion and intermodulation
distortion (mixing phenomena) caused by non-
linear behavior of electronic components and
power supply limitations. Terms for specific
types of nonlinear audio distortion include:
crossover distortion, slew-Induced Distortion
(SID) and transient intermodulation (TIM).
24. HARMONIC FUNDAMENTALS
Harmonics are electric voltages and
currents that appear on the electric power
system as a result of certain kinds of electric
loads. Harmonic frequencies in the power grid
are a frequent cause of power quality
problems.
25. Causes of Harmonics
When a non-linear load, such as a rectifier,
is connected to the system, it draws a current that
is not necessarily sinusoidal. The current
waveform can become quite complex, depending
on the type of load and its interaction with other
components of the system. Regardless of how
complex the current waveform becomes, as
described through Fourier series analysis, it is
possible to decompose it into a series of simple
sinusoids, which start at the power system
fundamental frequency and occur at integer
multiples of the fundamental frequency.
26. Effects of Harmonics
One of the major effects of power
system harmonics is to increase the current in
the system. This is particularly the case for the
third harmonic, which causes a sharp increase
in the zero sequence current, and therefore
increases the current in the neutral conductor.
This effect can require special consideration in
the design of an electric system to serve non-
linear loads.
27. Effects of Harmonics on electric
motor
Electric motors experience
hysteresis loss caused by eddy currents set up in
the iron core of the motor. These are proportional
to the frequency of the current. Since the
harmonics are at higher frequencies, they produce
more core loss in a motor than the power
frequency would. This results in increased heating
of the motor core, which (if excessive) can shorten
the life of the motor. The 5th harmonic causes a
CEMF (counter electromotive force) in large
motors which acts in the opposite direction of
rotation. The CEMF is not large enough to
counteract the rotation, however it does play a
small role in the resulting rotating speed of the
motor.
28. Effects of Harmonics on Telephone
lines
In the U.S., common telephone lines
are designed to transmit frequencies between
180 and 3200 Hz. Since electric power in U.S.
is distributed at 60 Hz, it normally does not
interfere with telephone communications
because its frequency is too low. However,
since the third harmonic of the power has a
frequency of 180 Hz, its higher-order
harmonics are high enough to interfere with
telephone service if they became induced in
the line.
