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Audio/Video System Power Management Audio/Video System
Power Management
-Design Techniques CinemaSource Technical Bulletins. Copyright 2002 by CinemaSource, Inc.
All rights reserved. Printed in the United States of America.
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except in brief quotations embodied in critical reviews.
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800-483-9778 Chapter 1: Circuit Level Solutions for Transients
Blocking Transients ---------------------------------------------------------------
Page 4
Diverting Transients ---------------------------------------------------------------
Page 4
A new transient device for telecom --------------------------------------------
Page 7
Chapter 2: Eliminating EMI/RFI Interference
Understanding EMI/RFI ----------------------------------------------------------
Page 8
Chapter 3: Eliminating Voltage Fluctuations
Voltage Regulation Techniques -------------------------------------------------
Page 9
Chapter 4: Eliminating Power Dropouts
Uninterruptable Power Supplies -------------------------------------------------
Page 11
Calculating KVA Load -------------------------------------------------------------
Page 12
Glossary:
Power management terms ------------------------------------------------------
Page 13
ACKNOWLEDGEMENTS: The author wishes to thank the following
people and companies for helping supplying material for this design guide
Leviton Corpor ation (diagrams and text)
TrippLite Corpor ation (diagrams and text)
PC Power Protection, HWSams and company (diagrams and text)
Bob Whitehead, Whitehead Triangle Foundation (research assistance)
Television Engineering Handbook by Blair Benson, McG raw-Hill, Inc .
George Gavutis (research assistance)
Jamen Towle (research assistance)
Audio/Video System Power Management
- Design Techniques 4
Chapter One: Circuit Level Solutions
CHAPTER ONE:
Circuit Level
Solutions For
Transients
T
he first and foremost duty of any good piece of
power management device is to protect the
equipment connected to it from damaging transients.
The object of transient protection is to keep incoming high
voltage impulses away from semiconductors and other
voltage sensitive devices. Electrical engineers typically
use two standard techniques to accomplish this protection.
Blocking
The first is to electrically block the incoming transient.
Because transients are very fast in nature, they can be
described as high frequency phenomena and the standard
method to block high frequencies is to use an inductor.
Inductors are coils of wire wound around permeable cores
that exhibit the curious phenomena of impeding high
frequencies but allowing low frequencies (such as 60 hz
power) to pass straight through. Engineers generally
combine inductors with capacitors to form "low pass
filters". These are even more adept at reducing high
frequency signals because they include a low impedance
path to ground. If you look at our schematic of a
multistage surge (transient) suppressor below, you will see
a typical low pass filter construction.
Diverting
The second technique used to dispose of transients, is to
dump them to directly to ground (or neutral) before they go
any further. Engineers often refer to this category of
techniques as "diverters" and have many components at
their disposal to accomplish the task. Our table on the
next page shows the four most popular devices. What is
interesting is that all four have characteristics that are
useful for diverting transients, but none alone is ideal for
the job. In order to see why, lets take a quick look at each.
The first diverter to consider is the popular Metal Oxide
Multistage T ransient Suppression Circuits Employ Several Varieties Of
Transient Suppressors
120 VAC Wave Form with T ransients 5
Chapter One: Circuit Level Solutions
Varistor (MOV). MOVs find their way into virtually all surge
suppressors because they are effective and inexpensive.
The problem is: many of the inexpensive "strip-type" surge
suppressors use just one or two MOVs and no other
devices. This, of course, is better than no transient
protection at all, but constitutes a pretty minimal level of
protection.
MOVs are voltage sensitive devices that are capable of
dumping lots of current (up to 6500 amps) but suffer from
several drawbacks. First, they are relatively slow to
respond to high voltage transients and require impulses in
excess of 300 volts to trigger. Another thing: they can
degrade over time and use. In fact, with just a few strong
transients, some MOVs can short and then burn
completely open. This will not damage the equipment
connected to the surge suppressor (the MOV has taken
hit, just like it's supposed to), but the protection capability
disappears completely. The result is that you have a surge
suppressor strip that still works fine, but offers NO
protection capability. (Chances are you have one of those
strip-type surge suppressors in you house right now with
an MOV that is non-functional.)
Another component sometimes used in surge suppressors
are gas discharge tubes. These components are small
glass vials filled with inert gas (Helium or Argon) and are
capable of discharging massive amounts of current
(20,000 + amps). These devices would be ideal for
transient voltage suppression except that they turn on 6
Chapter One: Circuit Level Solutions
A New Transient Protection Device
for Telecom Equipment
Historically Metal Oxide Varistors (MOVs) have been
used to protect the tip and ring lines of telephone
equipment. The problem is that MOVs they act
relatively slowly (10-20 Nanoseconds), exhibit high
capacitance and tend to deteriorate with use.
A new transient protection device called Sidactors
have been developed. Sidactors ion implant devices
that use thyristor technology in an ultrafast, crowbar
circuit topology. They are virtually immune to
overvoltage transients and can divert over 500Amps.
They also exhibit ultralow capacitance and provide
years of use wuth no degradation. Sidactors are now
making their way into premium power conditioning
products. Tripplite, for example, uses sidactors in
their Isobar models.
relatively slowly (1usec or so). This means a high
voltage impulse may be fast enough to rip right
by before any diverting action gets taken.
Specially-built semiconductor devices are also
available for transient suppression. Avalanche
Zener Diodes and Thyristors are the two most
popular. These devices offer ultra-fast switching
times (in the Picosecond range, 1000 times
faster than MOVs) and very sensitive to applied
voltages, some can turn on with a transient of
just a few dozen volts). The drawback to these
devices is that they aren't capable of dumping
the massive currents that the MOV and gas-tube
devices are. Electrical designers typically use the
semiconductor devices physically downstream
from the MOV and gas-tube components as an
extra measure of protection.
Take a look again at our multistage surge
suppressor schematic. You will see many of the
components we just discussed employed in a
multilayered design that calls upon the strengths
of each protective device.
Images Courtesy of MacMillan, Inc. 7
Chapter One: Circuit Level Solutions
O
ne important problem that rises when
addressing transient suppression is the point at
which transients occur along the sine
waveform. Because of the random nature of
transients, they can occur at any time and can show
up at any point on the AC power waveform. As you
can see in the top right diagram, surges that occur at
the lowest point on the waveform (270°) have more
room to build up voltage. Although the devices to
suppress transients are working as they should, if the
transient occurs at just the wrong time excessive
voltage can be allowed to build and this can destroy
sensitive components if it is allowed into electronic
equipment.
In order to eliminate this effect, electrical engineers
use a technique called Sine Wave Tracking. Sine
wave tracking effectively means that the surge
suppression devices operate along the AC
waveform.This keeps damaging transient voltages to
much lower levels than simple clamping techniques.
One of the popular methods designers use to track
the sine waveform involves Ferrite Rod-Core
Inductors. This allows standard transient suppression
devices (MOVs, Gas tubes, Zener diodes, etc.) to
operate regardless of where the surge occurs on the
waveform. In effect, the transient protection devices
ride the AC waveform operating as if they we
referenced to ground. The diagram on the bottom right
illustrates this effect. More sophisticated transient
supressors use hybrid circuits. These supressors are
generally much more expensive but are very effective.
Tripplite Isobar series of surge suppressors offer sine
wave tracking technology.
Understanding
Sine Wave
Trackin