Power Electronics

Looking Back on the Power Past

Many of the technical news stories we read discuss technology trends and market forecasts that try to give us a glimpse of what's around the corner. However, it doesn't hurt, on occasion, to stop and look back at what was. June — a month filled with graduation ceremonies — seems to encourage this type of reflection. I found myself doing just that recently when I came across a stack of old electronics magazines from the late 1970s and early 1980s.

At first, I scanned the articles, looking for breakthrough components that would represent industry milestones. Finding few such stories, I turned to the ads. Some of these provided indicators of how far the power supply art has advanced, as well as signs that some things have remained the same.

It was fascinating to see the mix of power supply vendors who were plying their wares some 20+ years ago. I encountered some well-known names from the past, such as Boschert and LH Research, which are no longer on the scene. Others, such as Kepco, Sorensen and Acopian, were old-line companies that stuck around, albeit in some cases under new ownership. Then there were relative newcomers who would go on to become major suppliers, as well as familiar names that have recently disappeared.

Naturally, the product descriptions were interesting, too. In August 1978, one ad showed a man dressed in a wide, striped tie and a dark suit vest clutching two 100-W switchers from Deltron. At 9.5 in. × 4 in. × 2.5 in., these U-channel packaged supplies achieved a power density of about 1 W/in3, efficiencies of 75% to 82% at a single 5-V to 28-V output and pricing around $2/W.

To put these specs in perspective, I thumbed through a recent power supply catalog from another vendor. As expected, the newer models offer a few more watts per cubic inch and lower costs. In addition, the newer supplies offer features such as universal input and power factor correction that were absent in those early switchers.

Most of the power supply ads I encountered were for ac-dc switchers with a few linears represented. Nevertheless, some dc-dc converters were in evidence. In June 1977, Reliability Inc. offered their Microprocessor Power Sources, which were regulated dc-dc converters housed in DIPs. Like some modern VRMs, these converters accepted 5-V or 12-V input. However, unlike VRMs, these models were isolated, produced +12-V or -5-V output, and delivered just 1 W.

A new product story from the summer of '78 provided another glimpse of board-mounted power. At that time, Integrated Circuits debuted its µPower line of “miniature” dc/dc converters, which generated up to 9 W of regulated/unregulated single or dual output at 5 V, 12 V and 15 V. Apparently nonisolated, these units accepted an input of 5 V, 12 V, 28 V or 48 V.

In this case, miniature meant a 0.875-in. × 1.75-in. × 0.375-in. fully encapsulated, through-hole package. That translates to about 16 W/in3. In contrast, some comparably sized nonisolated converters now boast more than 200 W/in3. Although there have been other changes as well (open-frame surface-mount design, lower voltages and other new features), some things have remained the same. Then, as now, many versions were required to accommodate all the input/output voltage options — the µPower line consisted of 26 models.

The proliferation of part numbers is still seen in many converter series, exacerbated by the need for more supply voltages and different package types. Only recently have vendors begun to consolidate product lines by widening input voltages ranges and making outputs programmable.

That trend of part number consolidation is expected to continue as the use of digital control in power design spreads. However, power supply designers will always face demands for customization and low cost — factors that may foil attempts at building one-model-fits-all designs. Years from now, readers flipping through the pages of this issue may still be marveling at how, despite all the progress, some aspects of power design never seem to change.

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