Power Electronics

Bruce Carsten: Lifetime Achievement Award Winner

For his extensive record of innovation in the field of power electronics and for his contributions to the industry as an author and educator, Power Electronics Technology is proud to present Bruce Carsten with this year's Lifetime Achievement Award.

Power-supply designer, researcher, consultant, instructor and visionary. All of these terms apply when describing Bruce Carsten and the work he has done to advance the state of the art in power electronics over the past 38 years. His accomplishments in switchmode power-supply design provide a roadmap of the progress made by the field as a whole. As he pushed the state of the art in his power-supply designs, Carsten helped lead the migration to higher switching frequencies, applying innovative circuit-design techniques and architectures, and developing novel analysis tools for design.

Among his many achievements, Carsten pioneered the use of constant-frequency peak-current-mode control in the early 1970s; developed the now ubiquitous active-clamp reset technique in single-ended forward converters in 1978 (see the “Exploiting Active Clamp Reset” subhead below); built what may have been the first hot-swappable power modules in 1980; and designed what’s claimed as the first commercially viable switchmode telecom rectifier in 1982, in which he applied multiphase switching in a dc-dc converter years before it became mainstream in voltage regulator modules (VRMs). Carsten is also highly regarded for advancing the design of high-frequency magnetics. One notable accomplishment in this area is his creation of a procedure for calculating winding eddy current losses for nonsinusoidal drive currents.

Many of Carsten’s designs anticipated the trends that have shaped the power-supply industry over the last 25 years. At times, he was a bit too far ahead of the curve, addressing future challenges that others in the industry failed to recognize. Anticipating the eventual migration of CMOS logic from 5 V to lower supply voltages, Carsten demonstrated a 48-V to 2-V dc-dc converter at a power conference in 1984. But as Carsten relates, this development and his related conference paper were met with “resounding apathy.” Ultimately, however, low-voltage logic arrived and created demand for distributed power as Carsten predicted in his paper (see the “Looking Ahead, But Too Far” subhead below).

While explaining some of the factors underlying his work, Carsten describes himself as skeptical, intellectually curious and willing to challenge conventional wisdom. These traits are evidenced in the story of the 2-V power converter and in his accounts of other work experiences. Carsten’s desire to take charge of his designs is another factor. In his early work as an engineer at smaller companies, Carsten found himself responsible for all aspects of design, development and even customer support. He realized that if he rushed a design into production prematurely, it could lead to power-supply failures in the field, which he would be called on to fix. Carsten’s response to this situation was, “If I’m going to have the responsibility for a project, I’m going to have the authority.”

Speaking of his early years as an engineer working in the industry, Carsten relates the difficulty of developing new technologies in a production environment, while trying to get the design right the first time.
“I think I was largely successful,” says Carsten,” but all I got were complaints about how long it took me to design something. When I pointed out that my products passed production test with the least trouble, had the highest profit margin, the longest product lifetime and a warranty return rate about 3% of the company average, the reply was, ‘That’s nice, but can’t you design it faster?’”

The desire to do the job right and have the authority to do so ultimately led Carsten to abandon production design and employment as a staff engineer in the early 1980s for a career as a design consultant. In spite of this change in his employment, he continued to play a role in the industry at large. Through his writings and his extensive participation in various power electronics conferences, Carsten has been an important team member in the effort to educate fellow engineers and support the advancement of power electronics technology. Over the years, Carsten has authored several influential conference papers and magazine articles, led numerous design tutorials in many countries, served on conference advisory boards and chaired conferences.

Beyond Carsten’s activities in the field of power electronics, over the years he has devoted some of his energies to a rather diverse set of interests ranging from space, astrophysics, math and biology, to woodworking, cars and motorcycles. These varied interests reflect a boundless curiosity and a philosophy that underlies much of Carsten’s work in the power electronics field. As Carsten comments, “If you really want to be innovative and creative, you have to cast your awareness broadly, not look at your narrow field.”

Looking over his body of work, it appears that Carsten’s broad awareness of developments in the electronics field helped him to adapt concepts from other areas to the requirements in power electronics. Furthermore, Carsten often conceived of a novel design idea while working on one project, only to apply the technique to full advantage years later in another design.

First Steps in Engineering

Carsten’s entry into engineering had its origins in his childhood where, at a very early age, he discovered his innate interest in all things mechanical. As a teenager, he developed an interest in electronics after reading about Guglielmo Marconi. Just as important was the influence of his father, whose intellectual curiosity and skepticism inspired these same traits in his son (see the “Steam-Powered Inspiration” subhead below for more background on Carsten’s early influences).

Despite his intellectual curiosity, Carsten was not fully at ease in formal academic settings. However, he did attend Sacramento State University, where he earned a BSEE degree in 1966. After graduation, Carsten went to work for Boeing, where he spent the first year and a half in the 737 flight test program designing instrumentation. But as business boom led to bust, Carsten found himself among the thousands of engineers laid off from Boeing in 1969.

Though losing his first job was unpleasant, it eventually led him to opportunities in power electronics. After leaving Boeing, Carsten found work in Vancouver, British Columbia, Canada, at Glenayre Electronics. This presented a great opportunity for him because, as Carsten describes it, his new employer was “a small struggling-to-stay-afloat company that would take on almost any project to help meet the payroll.” That environment gave him a chance to work on a wide variety of projects, such as a Doppler sonar “fish finder” and an inductively coupled transponder analogous to modern RFID tags. In one project (circa 1973), Carsten was initially using CMOS logic, but was forced by management to design it out in favor of LS TTL to reduce cost. Other engineers subsequently designed CMOS back in as its cost dropped and its lower power consumption proved necessary.

When the change back to CMOS occurred, Carsten was asked disparagingly, “Why didn’t you use CMOS in the first place?” This experience taught Carsten to trust his instincts when it came to anticipating trends in technology, and after a few similar experiences, he learned to say, “Let me do it my way or fire me.” Unfortunately, taking that stand put him at odds with management, and thereafter, he says, “I was not considered to be a good team player.”

In spite of such difficulties, Glenayre Electronics gave Carsten his entry into power-supply design. His first power-supply project was bequeathed to Carsten by a departing engineer who was overly optimistic in describing his power-supply design as “90% finished” when he passed it to Carsten.

A 750-W, 120-V to 24-V dc-dc converter, this design consisted of an unregulated silicon-controlled rectifier (SCR)-powered McMurray-Bedford dc-dc converter followed by a switching regulator built using silicon bipolar junction transistors (BJTs). Carsten spent several months solving design problems while the customer screamed for delivery. “This bad experience with SCRs caused me to shun them to this day,” says Carsten.

At Glenayre, Carsten also designed high-power battery charger/battery eliminators using a transformer rectifier with 480-Vac, 3-phase input followed by a transistor-switching regulator. These switchmode-regulated chargers (circa 1972) put out 120 Vdc nominal at 50 A and 75 A, and 24 Vdc nominal at 200 A. Designing these chargers taught Carsten a few lessons that stuck with him. After incorporating cooling fans in some units, he discovered they tended to suck all the dirt out of the environment and deposit it on the circuitry. That experience sold him on the idea of natural convection cooling, which forced Carsten to become fanatical about efficiency.

But even with highly efficient, convection-cooled units, there were still occasional failures in the field. When units failed, Carsten learned that the person expected to maintain and repair his sophisticated equipment was typically an electrician with a multimeter and a leather tool pouch. “That revelation led me to develop hot-swap power modules years later,” says Carsten.

Developing Peak-Current-Mode Control

Working on high-power switching regulators in the early 1970s turned out to be a rather frustrating endeavor for Carsten. And after a time, Carsten opted to work on lower power dc-dc converter design. In making that change, he encountered a problem inherent in circuits using pulse-width modulation (PWM) control as then implemented using BJTs.

“Most of the requirements were for low-voltage inputs, and the variable BJT storage times led to transformer ‘flux walking’ problems in the push-pull converter topology used with PWM control. I can still remember one late night in 1974 disgustedly watching as the resulting current imbalance (from transformer flux walking) caused the slower transistor to heat up and get slower, increasing the current offset until the transformer saturated and blew the transistor. I thought, ‘Wouldn’t it be nice to sense the transistor currents and shut them both off at the same current? That would solve the current imbalance problem!’”

Carsten expected that, as he thought through this approach, he would discover a reason why it wouldn’t work. He did realize it would be necessary to adjust the transistor current at turn-off in response to load current changes. But that was feasible, and when he tested his idea with an actual circuit, he discovered the technique of constant-frequency peak-current-mode control “worked beautifully.” The only caveat was the need for “slope compensation” at conduction duty cycles greater than 50%.

Current-mode control provided several advantages over the conventional voltage-mode-controlled PWM. As Carsten explains, “It’s a faster control methodology (than PWM); you’re controlling the current into your output capacitor. It’s a first-order system rather than a second-order system, so you don’t need phase-lead compensation in the voltage-control loop. You have an automatic current limit built in just by letting the current reference get to a maximum level. Prior to that time, you had to sense current separately, and when it became excessive, ‘OR’ it in as a control function to limit the current—which didn’t always work fast enough.”

Current-mode control also would enable forced current sharing among paralleled converters. That capability would make multiphase or “polyphase” switching feasible—a technique Carsten had contemplated earlier, but which was impractical with PWM control. A few years later, Carsten would apply multiphase switching in his design of a telecom rectifier.

Carsten first applied peak-current-mode control at Glenayre in designing a 24-V to 12-V dc-dc converter, which delivered “a couple hundred watts” of output. But he found its benefits to be so compelling that he used current-mode control on almost all of his subsequent power-supply designs.

Applying Hot Swap to Power Modules

In 1978, Carsten joined Research Industries in Burnaby, British Columbia, where he exploited an idea that he had thought about in the past: hot swap. Although hot swapping had already been used on logic cards, it was not generally being applied in power applications. It was in a project for Alaska Telecom that Carsten was able to exploit this concept to its full advantage.

In 1980, Alaska Telecom was installing microwave relay sites on mountaintops, which required dc power at 24 V, 48 V, ±130 V and +250 V. Power levels ranged from a few hundred watts to multiple kilowatts and were significantly different for each site. Battery backup was to be at one voltage (initially 48 V), with the other voltages produced by redundant converters. Because the range of power levels required varied as much as 3-to-1 on different voltages, the customer essentially asked for 20 different designs.

To satisfy these requirements, Carsten proposed a system with only two modules, a 48-V to 24-V switching regulator and a 48-V to dual 130-V dc-dc converter, where the outputs were connected in series or parallel and either end grounded (at the “card cage” output) to produce the other three voltages. Enough modules were paralleled to provide the power at each site, with two extras for redundancy.

This modular approach would decrease power-supply development time while increasing production volumes. Although the primary reason for modularity was to permit scaling of power levels, it had the added benefit of permitting the hot-swap capability. So, customers could avoid shutting off power when replacing units. Ironically, the power module’s reliability was so high that the hot-swap capability was almost never used.

Making Telecom Rectifiers Switchmode

Prior to 1980, the conventional wisdom was that switchmode converters were too noisy and unreliable for the demands of the telecommunications industry. But Carsten believed he had learned enough to overcome those difficulties. Sensing he soon would be leaving the world of production design, he decided to give this design challenge his “best shot,” as he believed this project might be his “swan song.”

The result was what Carsten describes as “the first successful switchmode telecom rectifier.” This 48-Vdc (nominal) 200-A power converter used bipolar transistors. (The 1000-V FETs available at the time produced unacceptable turn-on losses no matter how many were paralleled.)

The switchmode rectifier provided a great reduction in size and weight from that of the previous rectifier, which used SCR, saturable reactor phase control or controlled ferroresonant transformers. Because that design operated at the 60-Hz line frequency, it required large, heavy filters to achieve the low-noise performance required in the application. At the time, a typical SCR-based rectifier would produce 48-V dc at currents in the 400-A to 1200-A range and might weigh 1000 pounds to 2000 pounds. Carsten’s switchmode design reduced the weight required for 200 A to less than 200 pounds.

With the tremendous reduction in size and weight, the switchmode rectifier gave telecom operators the ability to expand their power levels, particularly in their “neighborhood collector sites.” Previously, the power equipment was so large and heavy it had to be installed during the construction of the building. The prospects for adding power supplies after the fact were severely limited.

Carsten’s switchmode rectifier, model SMR 48/200, was about 93% efficient at one-half to full load. That’s a leap forward from the 80% to 85% efficiency of the 60-Hz power supplies being replaced. However, better efficiency was not an incentive for the customer, because operating cost was not factored into the rectifier’s purchase cost.

One of the innovations employed in this design was polyphase switching.[1] Carsten opted for four phases because they could be easily digitally controlled using two bits with the basic clock plus the shift register giving you turn-on commands for phases.

Carsten’s work on the telecom rectifier also drove him to investigate the impact of high-frequency effects on magnetics design (see the “Advances in Magnetics Design” subhead below to learn more about Carsten’s work in high-frequency magnetics). At that time, the only reference for calculating winding losses as a function of frequency applied to sinusoidal drives. Carsten discovered that when a nonsinusoidal drive signal is applied, winding losses have to be calculated at every frequency component of the drive signal. This required quite lengthy calculations and led Carsten to develop an intuitive method for analyzing winding losses, including a normalization factor (Kr) that made the results easier to apply. Other researchers took Carsten’s work and extended it, creating a formal way of calculating the loss for any wave shape.

In the mid-1980s, Carsten gave a minitutorial on high-frequency magnetics design within a paper session at a power conference in Germany. The material presented in his tutorial was based on his design experience and lessons learned “the hard way.” Over time, this tutorial evolved into a full-day seminar and then a two-day seminar.

Over the years, Carsten has presented more than 120 design seminars in North America, Europe and Hong Kong on a range of power-design topics, including high-frequency magnetics, designing switched-mode power supplies for low EMI, topology selection, and control and feedback methods.

Carsten left Research Industries, which had become Telecom Power, in 1984 when the Burnaby operation was shut down. “I fully expected to look for another job,” says Carsten, “but I had been doing consulting on the side and had enough work to keep me busy for a few months. And it did not make sense to spend time looking for other employment while I still had consulting projects to finish. The projects kept coming in, however, and I have remained self-employed for the last 22 years.”

Reference

Exploiting Active Clamp Reset

In 1977 while “temporarily unemployed” (i.e., consulting), Carsten worked on another design technique that would later become very popular in the industry. In a typical PWM single-ended forward converter, the transformer off-voltage would be equal to the on-voltage. “But what,” Carsten asked at that time, “if we lower the reset voltage to a value just sufficient to reset the core during the OFF period?”

Carsten discovered that this approach, the active-clamp resetting of the transformer flux, would allow the power converter to operate over a much wider (than usual) input range for a given transistor rating. Moreover, it would improve efficiency and reduce output rectifier reverse voltage.

Carsten would need both these advantages when designing a power supply for one of his customers, EPIC Data Industries. That company was developing an inventory control system that demanded a very small power supply with high power density. In addition, the customer wanted the supply to operate over a universal input range (85 Vac to 265 Vac).

The active clamp technique yielded enough efficiency to fit a convection-cooled, 50-W power supply in the space the size of a paperback book. When completed, the power supply had four outputs (±5 V and ±12 V). The converter architecture was a coupled inductor, forward converter where the 5-V output was regulated to ±1%. Efficiency was around 85% despite the use of Schottky rectifiers on the ±5-V outputs.

This power supply, which went into production in 1978, also used a grounded-base BJT on the input, which allowed it to operate up to the 700-V VCBO rating of the transistor. This power-supply design also provides another example where Carsten was able to reuse a technique for driving bipolar transistors he had developed in 1975 while designing a 1-kW sonar amplifier for the Canadian Navy.

The technique involved grounding the base of the transistor and driving the emitter with a transformer-coupled current source. Carsten called this emitter-drive technique “bulletproof” because if anything went wrong, you had a protective feature as collector current could not exceed the emitter current. When applied in power supplies, the emitter-drive technique offered the advantage that a short on the transistor output would trip a “de-saturation” detector and terminate the conduction period. Carsten drew his original inspiration for this technique from the cascode-type of transistor drive used in oscilloscopes in the vertical deflection amplifier.

Looking Ahead, But Too Far

“In the early ‘80s it became self-evident to me that logic voltages were going to drop below the standard 5 Vdc, largely to reduce power consumption in ever larger and higher speed logic chips,” says Carsten. “I had noticed that some 5-V CMOS logic would still function, albeit very slowly, as low as 300 mV, so the lower limit on supply voltage was obviously very low, and the IEEE Journal of Solid State Physics had articles on lab devices operating from 2 V to 1 V and lower.

“I realized that this would have a major impact on power converter and system design; rectifier losses would become extremely problematic —they were already the largest source of power loss at 5 V—and the conventional central power supply was not viable as voltages dropped to 1 V or 2 V and currents increased to hundreds of amps or more,” Carsten explains. “The power source would have to be located close to the point of load, and thus share board space with the logic, placing unprecedented demands on efficiency and power density. Since it would be unwise to bring the noisy, transient prone ac line power onto the logic board, the only solution was a distributed power system with an intermediate voltage dc distribution bus.

“I demonstrated a proof-of-concept 48-V to 2-V, 50-A, 500-kHz prototype dc-dc converter at the PCI ‘84 conference in Paris, and presented a paper on the development and why I thought that this was the future,” says Carsten. “The converter consisted of a two-stage design with a classic buck converter producing a regulated, but nonisolated 30-V output. The buck converter ran at 500 kHz at a time when 50-kHz switching was the norm.

“The high switching frequency necessitated the use of homebrew surface-mount power components (components in which the die had been removed from the package, or the packages had been modified to shorten interconnects and reduce the associated parasitics,” Carsten explaines. “The second stage stepped down the 30-V intermediate voltage to 2 V, while providing isolation, with isolated feedback from the output to the input regulator.

“The second stage consisted of two single-ended forward converters operating out of phase,” Carsten observes. “Note that the converter uses a preregulator stage followed by an unregulated dc-dc converter, which resembles the approach used in Vicor’s ‘factorized power architecture’ concept, which was introduced a few years ago. Also, at the time this prototype was built, surface-mount components were being used in logic circuits, but were highly unusual in power conversion.

“Like many of my papers, it met with resounding apathy,” Carsten recalls. “When the silence died down, [conference attendees] would look at my prototype, with its home-made surface-mount power components, and say, ‘That's interesting, but logic voltage is 5V. What is it good for?’ I wrote several more papers on the subject, but finally gave up in 1991 since no one seemed to be listening. Of course, today ever-lower logic voltages are old hat, and many engineers don’t remember a time when that was not so.”

More recently, Carsten has been working on advanced algorithmic control methods that provide much faster dynamic response to line and load conditions than is currently possible with power converters using classical feedback techniques.

Carsten explains, “I see such control algorithms as a promising ‘super fast’ control methodology, quite distinct from PWM, voltage regulation in current-mode control and digital control. The inner loop in most current-mode control does qualify as a control algorithm, however. I have used several such control algorithms in the last 20 years, but once again, discussion in one of my seminars and a couple of published papers are meeting with evident apathy. Designers are reluctant to give up what they are familiar with as long as it still seems adequate. But then, I didn’t get much interest in current-mode control at first, either.”

Steam-Powered Inspiration

When Bruce Carsten was born in 1943 in Reedly, Calif., his father, Henry, was half a world away, a sergeant in the U.S. Army serving in the Pacific theater. On his return, Carsten’s father moved the family north to Camino, a sawmill town in the Sierra Nevada foothills.

In this town, the sight of steam-powered trains on the railroad or Shay engines moving lumber around at the sawmill could fuel a young boy’s interest in the mechanical world, particularly since Carsten’s father (who later became a lumber grader) worked at the sawmill. But as Carsten relates, a very early childhood experience may have helped put him on course to eventually become an engineer.

“I seem to have been born with a fascination in things mechanical,” says Carsten.

“One of my early and clearest memories (from about age 2) is of a ride on a steam-powered side-wheeler ferry boat in San Francisco Bay with my mother and grandmother,” Carsten recalls. “As we were leaving the dock one of them mentioned to me that the engine could be viewed through some internal windows.

“I climbed up on a wood slat bench to peer in, and beheld a most wondrous sight! There was a double-acting single-cylinder steam engine overhead, driving the crankshaft underneath through a long connecting rod,” says Carsten. “Two pushrods from the crankshaft operated valves in the steam chest on the cylinder, and the whole thing huffed and chuffed along at about 15 or 20 RPM.

“It was great theater, and I was awestruck, even though I did not fully understand what I saw at the time,” Carsten explaines. “Almost instantaneously my mother was pulling on my arm saying, ‘Come on! We want to go outside and see the sights!’ when the most beautiful sight in the world was right here!”

As he grew up, there were plenty of activities at home to encourage Carsten’s interest in the mechanical world. He helped his father work on cars, learning that it was OK to take machines apart, so long as you noted how they came apart, which allowed you to put them back together. And at a young age, Carsten learned to use the tools in his father’s workshop. Learning how to use power tools responsibly provided Carsten with a background that would prove helpful in his professional career when he would be required to work with potentially lethal voltages in industrial power settings.

Carsten relates how his mechanical interests led him to take apart all types of appliances to see how they worked. Family and friends encouraged Carsten’s interests by giving him items such as broken alarm clocks to disassemble.

Then, as an eighth grader, a story about Marconi sparked Carsten’s interest, so to speak, in electronics. Once again, the family members helped Carsten satisfy his curiosity with unusual presents. “The principle gift was old tube-powered radios,” Carsten recalls. “These were carefully disassembled in stages. Ultimately, I had unwound the transformers and speaker electromagnets, unrolled all the capacitors, and broken open the glass envelopes on the tubes, and separated the plate, grids and filaments. I learned how everything was built before fully understanding how it all worked.”

Carsten notes that his father and mother encouraged their children to pursue whatever interests caught their imaginations. They also instilled a love of books and reading in their home, with Carsten’s father, setting an example as a voracious reader. And though life during the Great Depression had discouraged Carsten’s father from going to college, he was, by nature, “intellectually curious” and “skeptical,” says Carsten, and instilled these traits in his son. As an engineer, both of these traits would come to bear in Carsten’s work. When confronted with engineering challenges, Carsten’s intellectual skepticism caused him to question all assumptions, eschewing a false sense of certainty when looking for answers, and when making decisions, keeping his mind open to conflicting evidence.

Advances in Magnetics Design

When Carsten began investigating the high-frequency effects on magnetics, the only work he could find on the subject was an old multigenerational copy of P.L. Dowell’s “Effects of eddy currents in transformer windings.”[2] “Dowell goes through the whole thing, which has a mathematical derivation, but it only applied to sinusoidal current,” explains Carsten. “I’m thinking it through and I realized that the losses at the different frequencies were orthogonal. In other words, the losses at one frequency did not have any impact on the losses produced by a current at a different frequency, whether harmonically related or not. And I further realized that what you’ve got to do is calculate the loss at every frequency independently, which is going to depend on both the magnitude of the current at that frequency—the harmonic amplitude—and the resistance at that frequency, which has to be calculated separately.

“In order to do the calculations for the single-ended converter used in the switchmode telecom rectifier, I had a programmable calculator running for about six weeks to get the information, 24 hours a day by and large, and printing intermediate results and going back and adding in more harmonics and printing it out for fast rise and fall times. And I just sort of assumed that this was already known and I just couldn’t find the reference.
“Then, at Powercon, P.S. Venkatramen[3] published an analysis of this in which you had to combine the effects of three different graphs to get the results, but everybody was absolutely thrilled. Nobody has ever done this before.” Carsten says he had done a smiliar analysis several years ago, but didn’t think it was worth publishing because he believed, wrongly, that it was already known.

“Well it turned out it wasn’t, so in 1986, I published my results[4], which were similar to Venkatramen’s, but I also had a more intuitive method of combining the results, what I call Kr, the loss resistance factor—a normalization that made it very easy to use the information,” says Carsten.

Others then used Carsten’s methods to push the field further. “Dowell’s analysis wasn’t the most general because you couldn’t apply it to noncurrent carrying shields or noncurrent carrying windings, or other merged windings or multiple secondaries, where a winding is not only producing its own field but also immersed in the field produced by another winding, etc,” explains Carsten. “Apparently, a researcher called Perry did a more general analysis. Then J.P. Vandelac and P. Ziogas applied my ‘toolkit’ to adapt Perry’s analysis to nonsinusoidal current, and that’s sort of become the industry norm for the basic one-dimensional analysis[5]. But it was sort of the formal way of calculating what the loss would be for any wave shape, and the loss normalization factor that was applied, that was my contribution.

“It was very much a community effort,” Carsten points out. “I worked with the results of others. Others took what I did and carried them into more fruitful areas.”

References

1.In 1981, Carsten presented a paper titled, “High Power SMPS Require Intrinsic Reliability” at the Power Conversion International Conference (PCI 1981) in Munich, Germany. This paper described a number of the innovations he conceived in the 1970s, such as his “bulletproof” emitter drive, current-limiting technology and hot-swap power modules. Another concept, polyphase switching, was alluded to in the paper, but not described in detail because Carsten’s employer considered it too proprietary.
2. Dowell, P.L. “Effects of Eddy Currents in Transformer Windings,” Proc. Institute Elec Eng., vol. 113, no.8, pp. 1387-1394, August 1966.
3. Venkatramen, P.S. “Winding Eddy Current Losses in Switch Mode Power Transformers Due To Rectangular Wave Currents,” Powercon 11, 1984.
4. Carsten, Bruce. “High Frequency Conductor Losses in Switchmode Magnetics,” High Frequency Power Conversion Conference proceedings, 1986, pp. 155-176.
5. Vandelac, J.P., and Ziogas, P. “A novel approach for minimizing high frequency transformer copper losses,” IEEE Power Electronics Specialists Conference proceedings, 1987, pp.355-367.

Technical Papers

1. "HIGH POWER SMPS REQUIRE INTRINSIC RELIABILITY"
PCI '81 Proc., Munich, West Germany
PCI '82 Proc., San Francisco, CA (Slightly revised)

2. "DETHRONING THE SINE WAVE” (DC-AC inverter output waveforms)
PCI '84 Proc., Atlantic City, NJ

3. "DESIGN TECHNIQUES FOR THE INHERENT REDUCTION OF POWER CONVERTER EMI"
Powercon 11 Proc., 1984, Dallas, TX

4. "A LOW VOLTAGE SCHOTTKY FOR HIGH EFFICIENCY VLSI POWER SUPPLIES"
PCI '84 Proc., Paris, France

5. "RADIO FREQUENCY POWER CONVERSION: FAD OR THE FUTURE?"
PCIM Magazine, January '86

6. "REVERSE RECOVERY CHARACTERISTICS OF HIGH SPEED RECTIFIERS"
PCIM Magazine, February '86

7. "FAST, ACCURATE MEASUREMENT OF CORE LOSS AT HIGH FREQUENCIES"
PCIM Magazine, March '86

8. "CURRENT MODE CONTROL FOR HIGH FREQUENCY SWITCHMODE"
PCIM Magazine, April '86

9. "SWITCHMODE DESIGN TECHNIQUES ABOVE 500 KHz" (tutorial)
1st HFPC Conf. Proc., 1986, Virginia Beach, VA

10. "HIGH FREQUENCY CONDUCTOR LOSSES IN SWITCHMODE MAGNETICS"
1st HFPC Conf. Proc., 1986, Virginia Beach, VA
PCI '86 Proc., Munich, West Germany
PCIM Magazine, November '86 (revised version)

11. "VLSI & VHSIC POWER SYSTEM DESIGN CONSIDERATIONS"
PCI '86 Proc., Boston, MA

12. "DISTRIBUTED POWER SYSTEMS OF THE FUTURE UTILIZING HIGH FREQUENCY CONVERTERS"; 2nd HFPC Conf. Proc., 1987, Washington, DC

13. "A HYBRID SERIES-PARALLEL RESONANT CONVERTER FOR HIGH FREQUENCIES AND POWER LEVELS"; 2nd HFPC Conf. Proc., 1987, Washington, DC

14. "DESIGN TRICKS, TECHNIQUES, AND TRIBULATIONS AT HIGH CONVERSION FREQUENCIES" (Tutorial) 2nd HFPC Conf. Proc., 1987, Washington, DC;
PCI '87 Proc., Munich, West Germany

15. "ON THE FUNDAMENTAL PERFORMANCE SIMILARITIES OF FLYBACK AND FORWARD CONVERTERS AT HIGH FREQUENCIES": PCI '87 Proc., Long Beach, CA

16. "HIGH SPEED CONTROL OF SINUSOIDAL INPUT CURRENT CONVERTERS FOR MINIMAL ENERGY STORAGE REQUIREMENTS"; PCI '87 Proc., Long Beach, CA

17. "THE POTENTIAL OF SUPERCONDUCTORS AND SYNTHETIC METALS IN SWITCHMODE POWER SUPPLIES OF THE FUTURE"; 3rd HFPC Conf. Proc., 1988, San Diego, CA

18. "TOPOLOGIES FOR INCREASING OUTPUT VOLTAGES WITH SCHOTTKY DIODES"
3rd HFPC Conf., 1988, San Diego, CA

19. "TRENDS IN HIGH FREQUENCY POWER CONVERSION"; (Co-Authored With K. Kit Sum)
3rd HFPC Conf. Proc., 1988, San Diego, CA

20. "CONVERTER COMPONENT LOAD FACTORS; A PERFORMANCE LIMITATION OF VARIOUS TOPOLOGIES"; PCI'88 Proc., Munich, West Germany

21. "COMPATIBLE POWER CONVERTERS FOR LITHIUM BATTERY SYSTEMS"
4th International Meeting on Lithium Batteries
May 24-27, 1988, Vancouver, BC

22. "THE PROXIMITY CURRENT PROBE; OBTAINING WIDEBAND CURRENT WAVEFORMS IN THICK FILM AND PRINTED CIRCUIT CONDUCTORS"
4th HFPC Conf. Proc., 1989, Naples, FL.
PCIM'89 Conf. Proc, June 6-8, 1989, Munich, Germany

23. “DESIGN TECHNIQUES FOR TRANSFORMER ACTIVE RESET CIRCUITS AT HIGH FREQUENCIES AND POWER LEVELS";
5th HFPC Conf. Proc., 1990, Santa Clara, CA

24. “AC MAINS COMPATIBILITY BOX";
PCIM/PQ Conf. Proc., 1990, Philadelphia, PA

25. “SLOW WAVE" TRANSMISSION LINE RESONANCE PHENOMENA IN MONOLITHIC CERAMIC AND STACKED FOIL PLASTIC CAPACITORS"
6th HFPC Conf. Proc., 1991, Toronto, ON

26. “ISOLATION OF FAULTED POWER MODULES IN LOW VOLTAGE DC DISTRIBUTED/REDUNDANT POWER SYSTEMS"; PCIM/PQ Conf. Proc., 1991, Universal City, CA.

27. “POWER CONVERTERS FOR LAPTOP COMPUTERS"; (Tutorial)
PCIM/PQ Conf. Proc., 1991, Universal City, CA.

28. “LOW PROFILE MAGNETICS, GEOMETRY SELECTION AND OPTIMIZATION"
Seminar 8, APEC '92 Conference, Boston MA

29. “DESIGN OF MULTI-STAGE FILTERS FOR USE WITHIN WIDEBAND CONTROL LOOPS"
7th HFPC Conf. Proc., 1992, San Diego, CA

30. “SIMPLIFIED CALCULATION OF MAGNETIC AND ELECTRICAL LOSSES IN UNITY POWER FACTOR BOOST PREREGULATORS"
PCIM/PQ Conf. Proc., 1992, Irvine, CA.

31. “ACHIEVING 80-90% EFFICIENCY OVER A 100:1 LOAD RANGE AT 3.3V WITH SYNCHRONOUS RECTIFICATION AND A CYCLE-BY-CYCLE CONTROL ALGORITHM"
8th HFPC Conf. Proc., 1993, Vienna, VA.

32. “CROSS REGULATION EFFECTS IN MULTIPLE "BATCH REGULATED" OUTPUTS"
8th HFPC Conf. Proc., 1993, Vienna, VA.

33. “THE BIPOLAR TRANSISTOR IS DEAD. LONG LIVE THE BIPOLAR TRANSISTOR"
PCIM/PQ'93 Conf. Proc., 1993, Irvine, CA.

34. “DESIGNING HIGH FREQUENCY CURRENT SHUNTS AND CURRENT TRANSFORMERS"
9th HFPC Conf. Proc., 1994, San Jose, CA.

35. “MEASUREMENT OF POWER LOSSES IN SEMICONDUCTOR CASES WITH KOVAR-GLASS HERMETIC SEALS"; Proc. of PCIM'94; June 28-30, 1994; Nurnberg, Germany

36. “DESIGNING FILTER INDUCTORS FOR SIMULTANEOUS MINIMIZATION OF DC AND HIGH FREQUENCY AC CONDUCTOR LOSSES"
Proc. of PCIM/PQ '94; Sept. 18-22, 1994, Dallas, Texas

37. “LOW PROFILE MAGNETICS"; Proceedings of the Soft Ferrite Users Conference '94; October 24-25, 1994, Rosemont, IL.

38. “WHY THE MAGNETICS DESIGNER SHOULD MEASURE CORE LOSS; WITH A SURVEY OF LOSS MEASUREMENT TECHNIQUES AND A LOW COST, HIGH ACCURACY ALTERNATIVE"
Proc. of HFPC'95; May 7-11, 1995, San Jose, CA.
Proc. of PCIM'95; Nurnberg, June 20-22, Germany

39. "OPTIMIZING OUTPUT FILTERS USING MULTILAYER POLYMER CAPACITORS IN HIGH POWER DENSITY LOW VOLTAGE CONVERTERS"
Proc. of HFPC'95; May 7-11, 1995, San Jose, CA.

40. "A 'CLIPPING PRE-AMPLIFIER' FOR ACCURATE SCOPE MEASUREMENT OF HIGH VOLTAGE SWITCHING TRANSISTOR AND DIODE CONDUCTION VOLTAGES"
Proc. of PCIM/PQ'95, September 9-15, 1995, Long Beach, CA.

41. “FET SELECTION AND DRIVING CONSIDERATIONS FOR ZERO SWITCHING LOSS AND LOW EMI IN HF "THYRISTOR DUAL” POWER CONVERTERS"
Proc. of PCIM'96, May 21-23, 1996, Nurnberg, Germany
Proc. of PowerSystems World, Sept. 7-13, '96, Las Vegas, NV

42. "CALCULATING THE HIGH FREQUENCY RESISTANCE OF SINGLE AND DOUBLE LAYER TOROIDAL WINDINGS"; Proc. of PCIM'97, June 10-12, 1997, Nurnberg, Germany

43. "POTENTIAL FUTURE ALTERNATIVES FOR THE GENERATION OF LOGIC VOLTAGES BELOW 3V"; Proc. of HFPC'97, Sept. 6-12, 1997; Baltimore, MA.

44. "SPACED ROUND WIRE TO EQUIVALENT FOIL TRANSFORMATION FOR CALCULATING HF LOSSES IN SOLENOIDAL WINDINGS"
Proc. of HFPC'97, Sept® 6-12, 1997; Baltimore, MD.

45. "THE NORMAL MODE INDUCTANCE OF COMMON MODE INDUCTORS"
Proc. of PWS'98, Nov. 8-13, 1998; Santa Clara, CA.

46. "STACKED FLYBACK CONVERTERS FOR LOW POWER OUTPUTS WITH INPUT VOLTAGES OVER 500V"; (co-authored with Paul Greenland, Allegro Microsystems)
Proc. of HFPC'99, Nov. 9-11, Chicago, IL.

47. "HINTS AND KINKS ON PATENTING YOUR INVENTION"
Proc. of HFPC 2000, Oct. 3-5, 2000, Boston, MA.

48. "THE LOW LEAKAGE INDUCTANCE OF PLANAR TRANSFORMERS; FACT OR MYTH?";
Proc. of APEC'01, March 6, 2001, Anaheim, CA.

49. "THE ADVANTAGES OF BJTs OVER FETs FOR SYNCHRONOUS RECTIFICATION BELOW 3 VOLTS"; Proc. of PCIM 2002, May 14-16, 2002, Nuremberg, Germany.

50. "CURRENT CAPABILITIES OF CONDUCTORS ON INSULATED METAL SUBSTRATES, INCLUDING FREQUENCY EFFECTS"; (co-authored with Herb Fick, Bergquist)
Proc. of PCIM 2002, May 14-16, 2002, Nuremberg, Germany

51. "FINDING AND FIXING SMPS RINGING WAVEFORM EMI"; Proc. of PowerSystems World Conference, October 29-31, 2002, Rosemont, IL

52. "THE APPLICATION OF CURRENT MULTIPLYING RECTIFIERS TO NON-ISOLATED BUCK REGULATORS"; Proc. of PCIM 2003, May 20-22, 2003, Nuremberg, Germany

53. "CURRENT MULTIPLYING RECTIFIERS FOR HIGH CURRENT OUTPUTS"; Proc. of PowerSystems World Conference, November 4-6, 2003, Long Beach, CA

54. "THE CONTROL ALGORITHM AS A HIGH PERFORMANCE ALTERNATIVE OR SUPPLEMENT TO LINEAR/ANALOG FEEDBACK CONTROL"
Proc. of PCIM 2004, May 25-27, 2004 Nuremberg, Germany

55. "A NEW HIGH SATURATION FERRITE INCREASES SWITCHMODE INDUCTOR ENERGY DENSITY"; Proc. of PCIM 2006, May 30 - June 1, 2006, Nuremberg, Germany

Other Articles:
"Surface Mount Technology Aids Portable Equipment Designs"; PCIM magazine, December 1991

"Clipping Preamplifier Provides Accurate Measurement of Transistor Conduction Voltages" PCIM magazine, August 1996

“Finite Element Analysis Software Generates formulas for Calculation of High Frequency toroid Resistance”; PCIM Magazine, April 1997

“Sniffer Probe Locates Sources of EMI”; EDN magazine, June 4, 1998

"Stacked Flyback Converters Allow Lower Voltage MOSFETs for High AC Line Voltage Operation" by Paul Greenland, Allegro Microsystems Inc. and Bruce Carsten, Bruce Carsten Associates. PCIM magazine, March 2000

“H-Field Probes Spot Switchmode Supply EMI”; PCIM magazine, September, 2001

”CURRENT SHUNTS”; Wiley Encyclopedia of Electrical and Electronic Engineering, John Wiley & Sons, Inc., 1999, Vol.4, pp. 452-458.

“CURRENT TRANSFORMERS”: ibid, pp. 459-466

“Carsten’s Corner” Columns in PCIM Magazine
1. “Will the Real R&D Lab Please Stand Up?”; June 1988, p.39

2. “Why Are Breakthroughs So Much Work?”: July 1988, p.77

3. “How About a Conference Paper from You?”, August 1988, p.96

4. “The Engineer’s Lament”; October 1988, P. 59

5. Untitled in the magazine; the intended title was “Will the U.S. Lose its Technological Lead to Japan?”; November 1988, p.12

6. “Can a FET be Damaged by Switching Too Fast?”; December 1988, p. 47

7. “Capital Equipment and Personnel”; January 1989, p.86

8. “Things we’d Like to See: More Application Specific Components for SMPS”; February 1989, p.78

9. “Why is There No “Electrostatic” Dual to the Transformer?” March 1989, p.36

10. “Why do Most Innovations Seem to Come From Smaller Companies?”, April 1989, p.94

11. “More on the Electrostatic Dual to the Transformer” (In response to reader’s comments) May 1989, p. 79

12. “The Role of the Consultant”; June 1989, p.51

13. “STILL More on the “Electrostatic” Transformer”: August 1989, p.67

14. “They Oughta Make a Safe “Yankable” Power Cord”; September 1989, p.109

15. “”Work” vs ‘”Play” as a Learning Experience”; October 1989, p.90

16. “Let’s Define a Few Terms”, November 1989, p.38

17. “Can There be a Simple Solution to Every Problem?”; December 1989, p. 45

18. “You Can’t Solve an Undefined Problem!” February 1990, p.57

19. “Where Are Our Future Innovators to Come From?”; March 1990, P. 124

20. “Distributed Power Systems”; May 1990, p.63

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