When Ed Bloom began his engineering career in the 1960s, power-supply design was largely a self-taught subject with no formal instruction available and few reference materials to guide engineers embarking on switchmode power-supply (SMPS) designs. And if power-supply design was obscure, then magnetics design was even more obscure. So, like others working in industry at the time, Bloom mastered the “black art” of magnetics design to complete numerous power-supply projects.
But those early years spent developing power supplies for missile programs, spacecraft, defense projects and computers were just the beginning. Bloom later made his mark as an entrepreneur, instructor and author. In these roles, he labored extensively to demystify the black art of magnetics, enabling countless engineers to learn the principles of magnetics design and even the latest advances, including those he pioneered.
Chief among those advances was Bloom's development of integrated magnetics — the combination of multiple magnetic structures on a single core. For his work in this area, Bloom has been called the “Father of Integrated Magnetics.” Although Bloom has authored multiple patents and conference papers based on his work in this area, his most well-known writing on the magnetics topic may be found in the now-classic textbook Modern DC-to-DC Switchmode Power Converter Circuits, which Bloom co-authored with Rudy Severns.
Bloom was among the first to realize the industry's need for formal but practical power electronics education. He responded in an entrepreneurial spirit, and together with his wife, Joy, expanded his consulting business, e/j Bloom associates, to host some of the first courses on topics such as power-magnetics design, power-supply control methods and stability analysis. Bloom took power electronics education to the engineer, repeating his classes in different cities across the country. Though he enlisted other experts to teach various subjects, Bloom himself taught many advanced classes on magnetics design, introducing numerous engineers to the principles of integrated magnetics design as well as those of planar magnetics.
Through his business, he also provided power electronics engineers with a unique source of specialty books, videos, design software and development tools that helped them to ply their trade. This mail-order segment of the business started in the 1980s, but made an early transition into the Internet age, transforming into a virtual power electronics storefront with the launch of his website in 1994.
Meanwhile, e/j Bloom associates continued to be an outlet for Bloom's consulting services, through which he assisted many well-known but unnameable corporate clients in troubleshooting their power-supply design and manufacturing problems.
Beyond his business activities, Bloom contributed to the industry through his extensive participation in industry conferences in the United States and Europe, where he presented numerous papers and seminars. Between these activities and his business ventures, Bloom has given more than 120 technical courses and presentations on his work experiences.
In addition to sharing his knowledge, Bloom lent his organizational skills to further the advancement of his field. In the late 1970s, Bloom was largely responsible for founding the International Power Conversion Society (IPCS), a nonprofit group based in Southern California that brought together leaders in the emerging power electronics field. Bloom also became a senior member of the IEEE Power Electronics Society.
Bloom's long and varied career in power electronics began shortly after he earned his bachelor's degree in electrical engineering from the University of Kentucky in 1963. Though he didn't know it at the time, his career would be focused on power.
Early on he aspired to become an engineer working in the aerospace industry. As a teenager at Aquinas High School in Columbus, Ohio, Bloom read about the space program and realized it would offer job opportunities for engineers at the time he would be graduating from college. Although he had no mentors in electronics per se, Bloom credits the Dominican monks who taught him chemistry and general science at Aquinas with inspiring him to pursue engineering. That inspiration, together with the bright prospects of the space program, drew him to the study of electrical engineering.
Filling an Educational Vacuum
Bloom had been working in industry for nearly two decades, doing both power-supply design and consulting, when he realized the strong need for power electronics education and decided to take action. Although Bloom had earned both bachelor's and master's degrees in electrical engineering in the 1960s, almost none of his formal training covered power-supply or power-magnetics design. Bloom recalls that his university training on the latter topic consisted of “all of an hour on transmission-line design.”
Like other engineers at that time, he was forced to learn the principles and practical aspects of power-supply and power-magnetics design on the job. That situation persisted through the early 1980s when Bloom decided something needed to be done to train engineers in power electronics.
“I got motivated to teach magnetics design when I began to see there really wasn't a lot of education out there on that topic,” recalls Bloom, who consulted with industry colleagues about what they would like to see offered in the way of power electronics education. In 1981, Bloom and Joy, who had worked in the industry as a programmer, sat down with Col. William McLyman, a magnetics expert from the Jet Propulsion Laboratory, to discuss their ideas for offering a course on magnetics design.
“We all decided we could do this course,” says Bloom, remembering their plan. “We'll put together a course, and we'll do it nationwide. We'll run around the nation for a year and see what kind of response we get.”
The course consisted of three days of instruction by McLyman, whom Bloom selected because of McLyman's extensive experience in designing, building and testing magnetics components. Bloom might have taught the class himself, but he needed to concentrate on promoting the course to ensure it would be well attended. The first class took place on April 20, 1982, in Los Angeles and was then repeated in five other cities over the next five months (see the original brochure to the right).
Both Bloom and Joy were responsible for organizing this first course on “Modern Power Conversion Magnetics Design,” and in launching that course, they were also expanding e/j Bloom associates, which Bloom launched in 1979. Through this business, they later extended their course offerings to several power electronics topics, hiring other experts such as Dan Mitchell and Fred Lee to teach courses on stability analysis and control methods.
Bloom himself went to the blackboard, teaching an advanced course on his specialty, integrated magnetics, which was offered as a followup to McLyman's magnetics course. The company also went on to offer instructional videos, books and design tools, all chosen to aid the power electronics designer.
But as Bloom recalls, with that first course on magnetics design, he, Joy and McLyman were championing the cause of power electronics education. And through that course, many people in industry became acquainted with Bloom and Joy. However, at that time, the Blooms already knew many of the notable figures in the power electronics industry through their work in organizing the IPCS.
The IPCS was created to be a “clearinghouse through which advanced technical information, educational and career improvement opportunities will be made available to technical and professional personnel in the Power Conversion and Power Conditioning industries.” Though it was a small regional organization, the IPCS provided one of the first forums for power electronics specialists to meet and discuss issues of the day in their field.
Busting a Magnetics Myth
Although Bloom did not initially lead the classes on magnetics design that his company offered, he became well known to many engineers as an expert on this topic, for both his teaching and his writing on the subject of integrated magnetics.
“I started teaching when I began to work on integrated magnetics,” Bloom says. “There, in addition to describing a magnetics design, I had to show people how you go about combining a number of magnetic elements together.”
“The basic idea of multifunction magnetics is really old,” says Rudy Severns, who credits professors Slobodan Ćuk and David Middlebrook with reawakening interest in integrated magnetics as it applies to power electronics in the 1970s, when they addressed the topic in their work at Caltech.
However, the work done by Ćuk and Middlebrook on integrated magnetics was narrowly focused on its application to Ćuk's now-famous converter topology. In the mid-1980s, Bloom, together with Severns, published papers explaining how integrated magnetics had a much broader application in power electronics.
“One of the first things Dr. Ćuk talked about in describing his converter was how you go about integrating the transformer and inductor on a single core structure. So, when he started publishing that information, engineers thought that the Ćuk converter was the only one for which the magnetics could be integrated,” says Bloom. “One of the motivations that I had to start writing about the topic was to show people that that's not really the case. You can apply integrated magnetics to almost any converter topology.”
Bloom's earliest writings on this subject include “The Generalized Use of Integrated Magnetics and Zero-Ripple Techniques in Switchmode Power Converters,” which was presented in 1984 at the IEEE PESC conference. As the title suggests, the zero-ripple concept was one of the motivations for combining multiple magnetic elements on the same core. But as Bloom notes, the main benefit of integrated magnetics is to save space and weight, as it allows the number of magnetic components to be reduced from three or four elements to one.
Following the publication of the PESC paper, Bloom proceeded to publish numerous papers on this topic at industry conferences as well as articles in trade journals.* He also authored two patents to discuss his work in this area.[4-5]
Bloom's work on integrated magnetics required the application of theory and real-world design. Ultimately, he built integrated magnetic components in his lab to test and demonstrate the concepts he was presenting in his writings. Perhaps the most familiar of these writings for most readers is his chapter on integrated magnetics in Modern DC-to-DC Switchmode Power Converter Circuits. Commenting on this text, Bloom notes, “It was and still is the only book that has a chapter on the integration of magnetics.”
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.
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.”
As Bloom recalls, there were only a small number of technical books on SMPS design available in the early 1970s, and none on power-converter topology character classification. That was despite the prevalence of SMPSs. Severns and Bloom discussed this issue at various conferences and agreed that the lack of literature need to be addressed. The final push to write the book came when the two were approached by a representative of the book publisher Van Nostrand Reinhold Co., who was looking for a book on this very topic.
After its original printing, the book was later reprinted in Russian (see photo above), which Bloom only learned of after the fact. Though Van Nostrand is no longer in business, Bloom continues to reprint the book.
Early Career in Industry
After receiving a BSEE degree from the University of Kentucky in 1963, Bloom was recruited to work at General Dynamics in San Diego. At that time, General Dynamics was producing the Atlas missile for the Mercury space program. Bloom's main assignment there involved the development of the programmer unit for the autopilot system on the Atlas.
General Dynamics also gave Bloom his first taste of SMPS design. Around 1965, Bloom was tasked with the job of converting a linear power supply to a solid-state switcher. He was then confronted with the scarcity of information on switching power supplies.
“I had no way of finding out about what was done in switch-mode power supplies. There were no references in the public domain and no courses to take. My starting point was talking to people in the company who had worked on similar designs.”
After about five years at General Dynamics, Bloom went on to work at several other military and commercial companies in Southern California, including Cubic Corp., Honeywell's Peripheral division, Teledyne-Ryan and Litton Industries. At these companies, he designed power supplies for displays used in countermeasure radar, data-entry systems, the landing radar on the Viking Mars spacecraft and the B2 bomber. He also worked out techniques for creating radiation-hardened power supplies, and subsequently published one of the first papers on this topic at POWERCON4.
While working for Cubic, Bloom also obtained an MSEE degree from San Diego State in 1969. But, like his undergraduate training, the master's program did not expose him to any power electronics instruction.
While at Litton, Bloom began consulting on the side, which led to the formation of his business, e/j Bloom associates, in 1979. The company later became a full-time venture for Bloom and Joy when they decided to move from Southern California to Northern California. This move essentially forced Bloom to go into business for himself full time, because there were no electronics companies for whom he could work in the immediate area. However, from his contacts in industry, Bloom knew there was demand for his consulting services from companies in the South Bay. By then, he also was busy organizing and teaching power electronics courses, and researching and writing about magnetics.
Though he was still teaching magnetics seminars up until a couple years ago, Bloom now considers himself fully retired. However, he admits he may still take on projects for friends. Given his knowledge of magnetics and the many connections Bloom has made throughout the industry, friends may be knocking on his door for years to come.
Severns, R., and Bloom, G. Modern DC-to-DC Switchmode Power Converter Circuits, Van Nostrand Reinhold Co., 1985.
International Power Conversion Society advertisement for membership, “Solid-State Power Conversion,” November/December 1978, pp. 45-48.
Bloom, G., and Severns R., “The Generalized Use of Integrated Magnetics and Zero-Ripple Techniques in Switchmode Power Converters,” IEEE PESC 1984, pp. 15-33.
Bloom, G., “Integrated Magnetic Power Converter,” U. S. patent 4,864,478, Sept. 5, 1989.
Bloom, G. E., “Integrated Magnetic Apparatus,” U.S. patent 5,726,615, March 10, 1998.
Bloom, G. E., “Planar Integrated-Magnetic Power Components (Phase One Studies),” NASA SBIR Final Report NAS7-1225, Aug. 13, 1993.
Additional Patents by Ed Bloom:
“Tunnel Diode Protective Circuit for Voltage Regulators,” Patent Applied for 1964 (Convair).
“Noise Generator and Conditioner,” Patent Applied for 1965 (Convair).
“An Economical Low-Voltage DC Regulator,” Patent Applied for 1970 (Honeywell).
“AC Voltage Regulator for Multi-Output Power Supplies,” Patent Applied for 1970, (Honeywell).
“An Optimum Topology Push-Pull Power Converter,” Patent Applied for 1979 (Litton).
“Low-Noise DC-DC Converter,” U.S. Patent #4,262,328, 1981 (Litton)
“DC-to-DC Converter,” by G. Bloom and A. Eris, U. S. Patent 4262328, April 14,
Additional Publications by Ed Bloom:
“High Current Pulse Generator,” Electronics Design, 1964.
“Tunnel Diode Protection for a Simple Series Regulator,” EEE, 1964.
“LED Doubles as Overload Indicator,” Electronics Design, 1975.
“Fundamentals of EMP Susceptibility Programs,” Inteference Technology Master Directory, 1975.
“Improved Foldback Current Limiting,” EDN, 1975.
“Using Ferrite Beads as a EMP Reduction Tool,” IEEE Transactions on Nuclear Science, 1975.
“The ABCs of Radiation-Hardening Programs,” IRT Corporation brochure, 1975.
“A Magnetic Approach to Upset Protection of Logic Latches,” IEEE Transactions on Nuclear Science, 1976; Magnetics, 1977.
“Ferrite Beads,” Inteference Technology Master Directory, 1977.
“Saturable Transformers Harden Logic Latches,” Electronics, 1977.
“Designing Power Supplies Against the Effects of Nuclear Radiation,” POWERCON 4, 1977.
“Practical Design Considerations of a Multi-Output Ćuk Converter,” by G. Bloom and A. Eris, IEEE Power Electronics Specialists Conference, 1979.
“Modeling, Analysis, and Design of a Multi-Output Ćuk Converter,” POWERCON 7, 1980.
“Unusual DC-DC Power Conversion Systems,” MIDCON Professional Program, 1980.
“Modeling and Analysis of a Multi-Output Ćuk Converter,” by G.E. Bloom, A.Eris, and R.Ruble, IEEE PESC 1980, pp.33-47.
“New Integrated-Magnetic Power Converter Circuits for Telecommunications Systems,” IEEE INTELEC Conference Record, 1984, pp. 359- 366 (IEEE Publication 84CH2073-5).
“Magnetic Integration Methods for Transformer Isolated Buck and Boost Converters,” by G. E. Bloom and R. Severns, POWERCON 11, April 1984.
“Core Selection For and Design Aspects of An Integrated-Magnetic Forward Converter,” IEEE APEC’86, pp. 141-150.
“New Integrated Magnetic DC-DC Power Converter Circuits & Systems,” IEEE APEC’87, pp.57-66.
“Planar Integrated-Magnetic Power Components (Phase One Studies),” NASA SBIR Final Report NAS7-1225, August 13, 1993.
“New Multi-Chambered Power Magnetics Concepts,” IEEE Trans. Magnetics (MMM-INTERMAG Conference Issue), Fall Issue,1998
“Multi-Chambered Planar Magnetics Design Techniques” IEEE PESC, Vol 1, June 2000, pp.295-301.
“Planar Power Magnetics, New Low Profile Approaches For Low-Cost Magnetics Design” Magnetics Business & Technology, summer issue and August 2002 issue.
“Analysis and Design of a DC-DC SEPIC Converter with Tapped Secondaries,” by Philip Cooke, Analog Devices and Ed Bloom, E/J Associates, Power Electronics Technology Conference 2002.
“Multi-Chambered Planar Magnetics Blends Inductors and Transformers,” Power Electronics Technology, April 2003