Tutorial - Power to the people

Protecting equipment from an irregular or poorly conditioned power supply can extend its life as well as solving problems within an AV system. Our tutorial this month focuses on the whys and wherefores of AC power conditioning.

Why is the boardroom’s AV system’s touch screen panel locked up? How did the bulb in our projector go out so quickly? The system was functioning flawlessly a few hours ago! Our A/V contractor promised the finest picture and sound quality available, so why are there faint horizontal lines rolling up our video screen?

These are but a few of the all too common problems that occur when a boardroom’s audio-video system does not have comprehensive, advanced AC power management.

Today’s electronic circuits are more sophisticated than ever, and their susceptibility to AC line problems is far greater. Add to this the fact that today’s AC supply is extremely noisy and plagued with a daily assault of potentially damaging transient voltage spikes, and we have a recipe for component failure, or at the very least, poorly functioning equipment with intermittent, unreliable behavior. In many areas black-outs are known to occur as well.

Western Europe has an AC power supply that is the envy of the world in many regards. Certainly it is true that the voltage stability (or regulation) is superb in most areas. However, the fact that your boardroom’s AC outlets may deliver a relatively unwavering supply of 230 Volts (RMS) does not ensure that the power provided from your local utility is adequate in all regards for today’s ultra-sophisticated audio/video and microprocessing circuits.

Though many confuse voltage stability with clean or “perfect” power, the alternating current (AC) supplied from your service is far from perfect, and in many instances, far from adequate. Transient voltage spikes and surges are ever present and can cripple microprocessing circuitry. The small integrated circuits that store and process your records, critical information and presentations contain thousands of minute circuits that can be permanently damaged by as little as a 3-volt arc across the wrong electrical junction. Fortunately, the regulated direct current (DC) power supplies found in most electronic circuits will not create such a problem, while it is unfortunate that the hundreds of transient voltage spikes produced by your local electric sub-station or your buildings many electrical appliances will.

As the substation’s many transformer banks are regularly switched to adjust for peak load, and as refrigeration or central heating is switched on and off, spikes appear at every neighboring AC outlet. These spikes are small when compared to that of an electrical storm, and many robust appliances (such as a vacuum cleaner or a clock, for example) will not be affected. Today’s microprocessing circuits, however, utilize critical circuits that will steadily degrade as their fragile electrical junctions pit and fissure.

This problem is common knowledge to the world’s leading integrated circuit manufacturers. For this reason, many recommend protection for mission critical clients. Yet, many installers/contractors still do not include power management in their installations, and their clients suffer the consequences of erratic behavior, lost or corrupted data, and the need to constantly re-boot. Others believe a simple surge protected AC strip is adequate, utilizing a surge suppressor at the service panel of the building. Most conventional AC surge strips do not protect as well as they should, and they will sacrifice themselves if the AC conditions are severe enough. This will require service, and create lost time and revenue for your clients’ business. A whole building surge suppressor is good, but it is not capable of eliminating surges from adjacent appliances and electrical circuits. Only a localized (component level) AC power management product can properly protect in this environment. Again, there are many types of AC surge and spike protection, and all are not created equal.

Advanced Transient Voltage Surge Suppression

Most AC surge strips and service panel protectors feature inexpensive surge suppression devices that are designed to “sacrifice” themselves when exposed to sustained over-voltage conditions, or transient voltage spikes.

Professionals can not accept down time or unreliability. It is for that reason that a non-sacrificial transient voltage surge suppression system is the best choice for critical applications. With non-sacrificial protection there’s virtually no down time. Furman’s SMP circuit, for example, has been tested with multiple 6000 volt/3000 amp pulses without sustaining damage. This is far beyond the demands placed on generic surge suppressors, but by constructing a circuit that is capable of this severe test, it ensures that equipment damage or maintenance is unlikely.

The secret to the SMP circuit is its ability to distribute or siphon-off much of the offending transient voltage spike so that the power clamping device does not have the burden of absorbing all of the energy and velocity on its own. While typical surge suppressors are like an outstretched spring with a bullet headed for it, the key to the SMP suppression system is that the velocity of the voltage spike (as well as its overall power level) is reduced to a fraction of what the clamping device can handle. So, like a well tuned shock absorber, the device protects itself as well as the connected equipment. At Furman, the circuit was developed and tested for non-sacrificial surge and spike protection, enjoying a zero percent failure rate, and with hundreds of thousands of units sold since its development.

Sustained Over-Voltage Conditions

Many surge suppression devices are not capable of protecting equipment from sustained over-voltages. This condition is one of the most common and damaging events experienced by today’s electronics, and it can occur for multiple reasons. If equipment is used in remote locations, where AC service is supplied by a custodian or attendant, it may in fact be mislabeled, actually containing high voltage intended for machinery or lighting systems. Or, a power pole may be damaged during a storm or accident, or in some countries, lost or intermittent neutral wiring of a multi-zone system can result in a sudden connection in excess of 400VAC. This will result in destroyed equipment, or at best, a destroyed surge suppression system. In either event, you will not be able to complete the task at hand, and component servicing will be required.

The one way to escape this problem is to insist on a surge suppressor/power conditioner with an extreme voltage shutdown circuit. These circuits monitor the incoming voltage, and once the voltage has risen approximately 15% above nominal, they trigger a power relay to open, thus cutting the supply to all connected components and critical circuits. Once the voltage is corrected, the unit is reset, and operation may continue.

Filtering AC Power

In the past, AC filtering was considered a relatively small concern. As long as pops, crackle, or a local radio station wasn’t picked up by your components power supply, the AC filtering was sufficient. This is no longer true.

AC noise is far greater in both amplitude and bandwidth than ever before. When it couples into critical circuits it will mask and distort low-level information as well as create data corruption, jam-ups, and losses. This is due in part to the widening popularity of switching power supplies and the harmonics that back-feed into our AC power.

Today’s AC power filter must have far greater efficiency, and cover a much broader bandwidth than ever before. The filter should also be linearized. Since traditional AC filter/conditioners have been designed for unrealistic laboratory conditions, they are based solely on filtering or notching out specific radio frequencies at a fixed impedance. Far too often, this can create a noise attenuation curve that resembles a mountain range with multiple peaks and valleys. Outdated filtering schemes assumed impedances were constant, which is far from realistic. Additionally, these designs did not anticipate high resolution audio and video components or computers at the root of their design. If noise reduction is non-linear (uneven) and subject to strong ringing patterns that vary with load and dynamics, the AC filtering actually added noise, making the “cure” worse than the disease.

A linear filter, on the other hand, reduces the AC noise in an even manner across a wide bandwidth  reducing your noise floor in audio and removing noise and artifacts in video.

There are many choices……

Other considerations for advanced power management, such as Uninterruptible Power Supplies (UPS), should be considered as mandatory for projectors and data servers in areas where black-outs are possible. Discrete Symmetrical Isolated AC Power, incorporating a true isolation transformer, may be the only means to eliminate an audio buzz or a video hum-bar rolling up the video display. In some areas, AC voltage regulation (constant voltage output – when voltage at the AC service is erratic or unstable) is necessary. The key point which must be understood is that the sensitivity and sophistication of today’s electronic circuits require serious AC power management. Anything less is too costly to consider.

The author, Garth Powell is a Senior Product Designer for Furman Sound.

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