of Power Quality Problems S
ince the advent of electronic
systems, electrical power related
disturbances have had the
ability to destroy components, disrupt
system operation and interfere with
productivity.
Almost everyone has experienced
the affects of power problems at one
time or another and its a common
belief that system failure is due to
voltage sags and swells. However,
electronic technology is continuously
evolving, and it is important to recog-
nize that this evolution has changed
the way systems respond to power
disturbances. Voltage sags and swells
are not the demons they once were,
and voltage regulators no longer
provide any needed protection for
most modern systems.
TECHNOLOGICAL EVOLUTION
When the first computers came on the
electronics scene in the 1940s, they
used vacuum tubes for the fundamental
logic circuitry. These were high volt-
age, low current devices that were
powered by basic linear power
supply technology. From the ENIAC,
EDVAC, and UNIVAC systems that fol-
lowed to the more familiar systems of
the mid-1980s, little change took place
in power supply design.
By the late 1980s, however, engi-
neers began using large numbers of
integrated circuits which themselves
were being built with increasing num-
bers of transistor junctions. The result
was a low voltage computer, which
used substantial amounts of current.
The Real World of
Power Quality Problems
Voltage regulation
By Denny Ver Mulm
OCTOBER 2006 Linear power supply technology of
the time was inefficient and a supply
capable of meeting the current delivery
requirements of the computer circuitry
would be significantly larger than its
predecessors. For designers who were
striving to make systems smaller, larger
power supplies were not desirable.
The result was the introduction of
the switch-mode power supply. This
design eliminated the 60 Hz step-
down transformer and series regulator
section in favor of a pulse width mod-
ulated, high frequency circuit capable
of rectifying line voltages down to
usable, well regulated DC power for
the computers logic circuitry.
FUNDAMENTAL DIFFERENCES
This technological change is responsi-
ble for some fundamental differences
in the way systems respond to power
problems.
The linear power supply rectified
incoming line voltage and supplied
power to the logic circuitry through
a series regulator. The range of this
regulator was limited, however, and
an input voltage that was too high
or too low would quickly result in
problems. Low input voltage would
cause the supply output to fold
back or drop below the operating
tolerance of the logic circuit. Input
voltage that was too high would
activate the power supplys crow-
bar circuit. In the process of
protecting itself, the power supply
output would again fall below the
operating tolerance of the computers
electronic circuitry.
Because line voltage variations
are frequent, sags and surges were com-
monly the culprit in early electronic
system failure. Voltage regulators were
frequently employed to keep voltage
stable and the system running.
Switch-mode supplies, however, are
very different. The series regulator has
been eliminated along with the input
step-down transformer. switch-mode
p o w e r
s u p p l i e s
c o n s u m e
current from the AC power supply in
gulps and for only portions of
each power line cycle. They are
c o n s i d e r a b l y s m a l l e r a n d m o r e
efficient. An important by-product of
their design is that they are largely
immune to voltage sags and swells. An
explanation is found in the way the sys-
tem operates.
CONSTANT POWER DESIGN
Because the switch-mode supply
draws current for only a brief time
period, much can occur to the line
voltage during the time the switcher is
turned off with little effect on its
operation. If line voltage sags or
swells during the time the supply is
turned on, the supply compensates
for the variation by adjusting its duty
cycle or the time period over which it
draws current.
If line voltage increases, current
consumption decreases and vice
versa. switch-mode power supplies
are called constant power devices
since the power they consume from
the AC circuit (volts times amps)
remains constant.
The capabilities of switch-mode
power supplies with regard to voltage
regulation problems are well document-
ed. One switch-mode supply currently
available operates flawlessly at any volt-
age from 70 to 276 volts, making it not
only tolerant of voltage regulation issues
but also satisfactory for use worldwide
in almost any electrical environment.
THE MIGRATION CONTINUES
In spite of the prevalence of switch-
mode power supply technology,
some analog technology with linear
power supplies still exists in the
audio world. In cases where linear
supplies are in use, its likely that
voltage regulation might still be
required. If so, a variety of voltage
regulation technologies are available,
and care should be exercised in their
selection and application.
ONE NEGATIVE ASPECT
There is one negative aspect about
switch-mode supplies that should be
mentioned. One way that engineers
reduced size and cost and improved
efficiency was to eliminate the
input transformer from the switch-
mode supply design. In doing so,
they destroyed the systems natural
im-munity to common mode noise
and high voltage impulses. Todays
power protection solutions recog-
nize that these immunities must be
restored.
An appropriate power protection
solution for modern systems with
switch-mode power supplies will
incorporate a surge diverter, an isola-
tion transformer, and a noise filter as
part of the power protection design.
These three elements work in concert
with the natural voltage regulating
ability of the switch-mode supply
to provide all the power protection
elements necessary for modern
systems to perform reliably.
s
Denny Ver Mulm
has vast experience in the power con-
ditioning field with a decade of in field engineering
management and over 10 years as an audio veteran.
He is currently a VP at power specialists ETA Systems.
Reach him at dennyv@etasys.com or www.etasys.com.
Published in
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