Ed Bloom: Lifetime Achievement Award Winner

Sep 1, 2007 12:00 PM
By David Morrison, Editor

When asked about the technical challenges he faced in developing integrated magnetics designs, Bloom points to material limitations as the primary issue.

“Today, the core material of choice for integrated magnetics is typically ferrite because of its ability to change shape. Other core materials can be very difficult to manufacture in nonstandard shapes,” says Bloom. “That conflicts with a key requirement: all integrated magnetic assemblies have to be three-legged. In other words, there have to be three paths associated with the material structure itself. Being restricted to ferrite cores limits the type of applications that integrated magnetics can be applied in because of the limitations on frequencies and power levels.”

The impact on integrated magnetics is difficult to assess, because few engineers openly discuss the designs they are implementing for production. Bloom believes the technology has been primarily applied in power converters for the military. Severns describes integrated magnetics as “another tool in the designer's bag of tricks.”

In addition to his work on integrated magnetics, Bloom also got involved in writing and teaching about planar magnetics around 1990. These components, which may first have been developed for the military, became popular in commercial telecom applications in the 1980s and 1990s because of their low profile. Their use of standard core materials together with pc-board traces (in place of conventional windings) allowed for very flat component designs.

Although Bloom credits Alex Estrov with supplying the first planar-magnetic components to the industry, Bloom believes he may have been the first to teach about planar-magnetics design. Bloom wrote an early paper on this topic.[6]

A Classic Text

Beyond the classroom, Bloom has influenced generations of power electronics engineers through his writings on magnetics in a text that is so well known it is sometimes referred to simply as “Severns and Bloom.” First published in 1985, Modern DC-to-DC Switchmode Power Converter Circuits was one of the first texts to present power-converter design information in a comprehensive manner.

The book primarily focused on discussing power-converter topologies and aimed to make designers aware of the broad range of topologies that were available to them. Although some of these topologies had been written about in conference literature, many were new and simple designs that Severns and Bloom had developed.

“At the time, people were just using a few different topologies to do their jobs, whereas there were many others out there that they could use. And that's what we wanted to show them” said Bloom.

In writing the chapter on integrated magnetics, Bloom said he went well beyond the information that had been previously published. “Some of the concepts in that chapter had never been shown before.” Although Ćuk had discussed integrated magnetics as it related to his particular converter, integration is straightforward in that case, because the converter's waveforms are proportional at all times.

“The waveforms have to be in proportion consistently throughout the converter's range of operation,” explains Bloom. “But for forward and boost topologies, it's not obvious how you do that. It turns out, that you have to convert the magnetics design using a three-legged core. People didn't know that at that time.”

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