Power Line Disturbances and Their Effect on Computer Design and Performance by

Arthur W. Duell and W. Vincent Roland Proper site wiring, adequate grounding, and use of isolation devices help assure satisfactory performance.

In this Issue:

When we plug something into an electrical outlet we are connecting it to a voltage that alternates between positive and negative values 50 or 60 times per second, depending on the country. This voltage may be subject to random noise and to large, unpredictable, sudden fluctuations as the utility company supplying us with electric power experiences demand variations, electrical storms, equipment problems, and other disturbances. Electronic circuits like those in television sets, computers, stereo systems, and electronic instruments don't like this kind of power They need steady, well regulated, battery-like voltages Large disturbances can disrupt or even destroy them.

The articles in this issue deal with the problems of changing unregulated alternating voltages to regulated battery-like ones, and of dealing with unpredictable power anomalies. The first two articles are about the design of some innovative new power supplies. Power supplies are electronic devices that convert what comes out of an electrical outlet to regulated voltages for other electronic devices to use. For example, there's a power supply inside every piece of electronic equipment. This kind of power supply should be small and as reliable as the wall outlet it's plugged into. The 65000A Series Modular Power Supplies (cover and page 3) are of this type. There are also power supplies that provide regulated voltages to circuits outside their own cabinets. These might be found sitting on a lab engineer s bench or mounted in a rack as part of a computer-controlled test system. These supplies should be extremely well regulated, accurate, and for some applications remotely programmable. Models 6012A and 6024A Autoranging Power Supplies (page 11) are in this category.

Although they are meant for different applications and represent different design approaches, both of these new power supply families take advantage of a new HP switching transistor called a power MOSFET (metal-oxide-semiconductor field-effect transistor) MOSFETs have been around for a while and their superiority over other kinds of transistors for many high-frequency applications is well known. However, until recently there weren't any with the HP device s combination of high voltage rating, fast switching speed, low resistance, high reliability, and small chip size. The cover photograph shows where the HP power MOSFET fits in the schematic diagram of a 65000A Power Supply. On page 18 is an article about the new MOSFET, telling why it's different and how it's made.

The special problems power line disturbances cause computers (in spite of their well regulated power supplies) are discussed in the article on page 25. This article is based on studies of typical power line conditions, wiring codes for buildings, computer installation procedures, and computer designs. The article should be of interest to anyone who owns a computer system or is considering installing one.

Edilor, Richard P Dolan • Associate Editor. Kenneth A Shaw • An Director. Photographer. Arvid A Danieîson Illustrator Nancy S. VanderMoom a Administrative Services. Typography. Anne S LoPresti • European Production Manage; Dick Leeks m a

2 HEWLETT-PACK A FID JOURNAL AUGUST 19B! ©Hev.1 nil-Packard Company 1981 Printed in U.S A


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