Power Electronics
Remembering Dr. Middlebrook: Part 1

Remembering Dr. Middlebrook: Part 1

Dr. R. D. Middlebrook was an icon of the power electronics industry who passed away in April 2010. In August 1998, one of Dr. Middlebrook’s old friends and a member of the power electronics community, K. Kit Sum, interviewed him. Dr. Middlebrook revealed his history and that of the start of power electronics as we know it today. In doing this interview, Kit Sum’s objective was to learn how a person’s destiny is guided or shaped by events and people surrounding him. Dr. Middlebrook was very cooperative and frank in revealing the events leading to involvement in power electronics. Following are the questions put forth by Kit Sum (Sum) and Dr. Middlebrook’s (RDM) response.

Sum: What events led you to America?

RDM: I left England and Cambridge University came to the U.S. in 1952 for a graduate fellowships and assistantship at Stanford. That was in the very early days of the transistor. I was brought up on vacuum tubes, so were all the professors. Some had studied transistors as something brand new, but solid state was a branch of physics that was studied along with other things, but the transistor of course is how solid state burst upon the engineering scene. That had just happened, and so my professor and I together went to a summer course at the University of Illinois taught by Shockley, Bardeen, and Brattain, the three who got the Nobel Prize for the invention of the transistor.

Back at Stanford, my professor (Joe Pettit, who later became President of Georgia Tech), of course was busy with his regular work and I was kind of left on my own to follow up on that, to find a research topic. And so I did, and the first thing that I did was try to understand Shockley’s book, which was basically solid state physics. It had device stuff in it and at the time I got my Ph.D., having been the first graduate student at Stanford ever to work in transistors, by the time I finished there were three of us.

I had long since decided that I was going to stay in the States and not go back to England, principally because the professional opportunities were vastly greater and the climate didn’t hurt either, so the job hunting I then did was places like GE Schenectady, RCA Princeton, big industrial research labs because I’d already decided I was never going to teach.

When I was trying to make a decision, a Caltech Professor came up recruiting and said “Why don’t you come down to Caltech and look around?” and I said, “I really don’t want to live in L.A.” That was when L.A. was considered a cultural desert compared to San Francisco, so I said “I really don’t want to go to L.A. and I don’t want to be a professor either, but I’ll go and look.” And so I did and they made me an offer for the same reason that I was at Stanford, which was they wanted someone to start a research activity at Caltech, in solid state and transistors and there wasn’t anyone there either. The transistor came out of Bell Labs, and that’s where most of the early work was done. There wasn’t anyone anywhere in academia except for solid state physics, which was part of a physics department, that’s all there was.

I went to Caltech in 1955, and that was the reason they made me an offer, they wanted to start something in that area, and I accepted it saying “Well, this again postpones the decision about which job to take, and it wasn’t a lousy job opportunity this time, but a pretty good one,” but I always said, “Well, I can always go into industry later if I want to.” It was a three-year appointment and I said “Well, that’s OK, I’ll stick it out in L.A. for three years.” And I’ve been there every since, of course.

Sum: So now you are well on your way to teaching, which is something you have never wanted to do, is that so?

RDM: For the first many years, I developed a course in solid state devices and wrote a book, and the book came out in 1957 and the book was really not what I did at Caltech but what I’d done as a student at Stanford in trying to understand Shockley’s book, and I always called it my “translation” of Shockley from physics to engineering. It was called “An Introduction to Junction Transistor Theory” and it was one of the first books, as a matter of fact, written for engineers about how transistors worked, and so that was the course that I also developed at Caltech.

I did some research work in device electronics, and that went on for 10 years or so, but I’d always been interested in circuits because as an undergraduate at Cambridge and at home I’d built amplifiers and things using vacuum tubes, so I was always interested in the circuit applications end, although by accident the research work was sort of inside the device rather than the outside. Anyway, after 10 years or so at Caltech, I’d brought another professor in from Europe who was in the solid state device end of it and so he started teaching the course on devices and I started the circuits course, and it began as a one-term course and then three years later it became a three-term course and that was in 1969, and that’s the course that I do to this day with numerous modifications and evolutions, teaching basically circuits.

I started out teaching circuits in pretty much the conventional sort of way, that is, there’s a text, we cover these chapters, and you get homework problems, you get exams and all that, just in the conventional sort of way.

I also did consulting, and it was usually the “putting out the fire” kind of consulting. Not that that’s the only kind of consulting, but a lot of it was for me, and my first reaction used to be “This is a pretty lousy design, the design engineer didn’t seem to know what he was doing or why he was doing it.” But it didn’t take long before I had to conclude it’s not the design engineer’s fault, it’s my fault, speaking for the academic community.

Sum: So this is what motivated you to do something about the academic curriculum, is that right?

RDM: Something’s wrong somewhere, and the stuff that I am trying to teach is not getting across in the right way if so many of the engineers out there in industry are making designs like this, which really weren’t very good. At least I didn’t think they were, and so I began to think about how to change the way of teaching things to put more emphasis on how these could be used to do real design, and that was the start of what has now culminated in this three day course whose overall approach is Design-Oriented Analysis. But I didn’t use those words then, I didn’t know those words. But that was the original idea.

Sum: What were the drawbacks of the old school approaches?î

RDM: In retrospect, you always have the clarity of hindsight, and you think you understood something very clearly back then but in fact you don’t. It doesn’t come until much later. But that was one of the starting points, but the actual implementation of it was in doing this consulting work, to try to improve the designs, I actually had to put into practice these techniques that I had learned as a student, and that’s where I really discovered their shortcomings. You get buried in algebra. You write down all these equations, you start applying these methods that you’ve been taught trying to find the answer.

The whole point about this is, I found that these methods as taught weren’t much use, and when you are in the industrial environment even as an outside consultant, there’s always the time pressure. It’s got to be done now. There’s no time to find better methods to do things. We need the answer. Of course this was before the days of computers.

Sum: What were some of the steps you have taken to improve these methods?

RDM: So I began to develop shortcut techniques and over the years there grew to be quite a number of those, and they kept getting refined, and I began to adopt them in teaching the course at Caltech. So I would use these shortcuts as I’d go through things on the blackboard and then I’d hand out homework problems, expecting them to use these shortcut techniques that I’d just done in the lecture, and I found that this didn’t work very well.

As soon as they got the homework problem, their minds went into automatic reset. And they tackled it the same long handed way they had before.

Sum: What seems to be the problem?

RDM: That went on for awhile. Then I began to think, in trying to show them ways to save time and do it with less work, why aren’t they lapping it up? And then I began to recognize this tremendous inertia there, because of the way that we get taught. And so not only had I been expecting them to absorb these methods by a sort of osmosis, if you see me do it this way, then they will, and they didn’t, and I realized that a lot of professors teach better ways of doing things, and shortcuts, but from the student’s point of view, it looks like magic, and someone I was talking to the other day mentioned that word first, magic, and I realized this is true. The professors have learned, or many of them have learned better ways of doing things and they go through it and the students say “Yeah, I understood what happened but I don’t know why”.

Sum: What did you do to overcome this inertia?

RDM: So that’s the way it was left most of the time, and I realized that I was doing the same thing. I was showing what I thought were better methods and they weren’t picking it up, and so the final step was, and this is comparatively recently, in fact less than 10 years ago, I realized that the key to overcoming the problem was I had to give names to these techniques, and I had to establish them as conscious choices and ends in themselves for the student to realize this is the important thing to learn, not the answer, it’s the method, and they had to have names, so that’s when I came up with these two basic phrases: Design-Oriented Analysis in terms of Low Entropy expressions. These names I realized were important in order to make them recognizable to students as something of value in themselves, and it was about that time that, well, there is a parallel story to this which is “power electronics”.

Sum: You have made tremendous contributions in the field of power electronics, what is your historical perspective on this?

RDM: I was doing power electronics courses outside because power electronics didn’t exist as a recognized academic discipline. One kind of power electronics was a descendant of heavy current engineering. The other kind of power electronics is an offshoot of electronics. Electronics itself is an offshoot of heavy current engineering after World War II because World War II was really the beginning of modern electronics. Up until that time, it was radio and the development of the vacuum tubes was pretty much asymptotic at the time. It was the only active device. It was developed at the turn of the century and matured and so did the applications and it was almost all to do with radio and communications. But World War II required a major step ahead in the form of radar and, so there was a tremendous effort put into developing new circuits and systems. A lot of it documented in the MIT Radiation Lab series of books, there’s a whole string of them. But that was all vacuum tube based except for solid state detectors, which were germanium crystal detectors, the descendant of the cat whisker radio detector in the early days of radio.

After World War II, there was this tremendous expansion of electronics and in many universities, this became a well-known area of study. Electronics encompasses control devices and with the advent of the transistor and the IC of course, it just blossomed by orders of magnitude, and solid state physics was another kind of offshoot. Solid state physics in some places splintered off from physics and in other places, splintered off from electrical engineering and departments still called themselves electrical engineering departments. You don’t find many of them with the word “electronics” in the name. But that’s why 95% of the effort in electrical engineering these days in universities is in electronics.

Some universities maintained heavy current engineering and it became kind of a separate option. Some universities dropped it altogether and electronics, or light current engineering was all of electrical engineering for many years. In fact, electrical engineering kind of veered away from engineering as a whole, which was the conventional, mechanical, civil, electrical. Electrical moved away from the others and became more like applied physics, except for the heavy current engineering which is still kind of allied with the mechanical and civil.

This was especially true in the United States. Heavy current engineering disappeared totally from many college programs. Not so in other parts of the world. Almost every other place maintained the heavy current engineering also. So power electronics disappeared from electronics for a number of years. That was called the heavy current stuff.

Then, when higher powered solid state devices were developed to the point of usefulness, the power level went up again and so power electronics was kind of reborn out of the light current engineering.

One of the early incentives for that was the space program, because every electronic system has a power supply in it. Many of them regulated, but in space applications, size and weight are at a premium. It’s got to be small and light, and linear regulators which were the standard way to do it were no longer acceptable. Not efficient enough.

Up until that time, power supplies, sometimes under the name of power conditioning, were considered a little backwater of electronics as a whole being especially with the burgeoning of the main stream communications kind of electronics which I call signal processing and of course the digital stuff as well which was fast coming on. Every system, either analog or digital, has a power supply. By convention the people who designed the interesting part (the signal processing part), automatically did the power supply. That was just part of the job and of course anyone could do a power supply. That’s simple. It’s just dc, isn’t it? And that was fine as long as it was a linear regulator. Sure enough, anyone could design one of those.

But then because of the requirements for small size and weight, the linear regulator had to be displaced by the switching regulator, which is a whole new ballgame, but no one knew it, no one recognized that. No one from management, top to bottom, or design engineers, realized how different a ball game it was. And so there was a long period when power supplies remained in the backwater, the black sheep of the whole field and the people responsible for system design automatically had to design the power supply, and as usual it was the last thing that was given any consideration. The product is ready to go to production and it’s all done except the power supply, and there’s this funny-shaped space in the box left, that’s where the power supply has to go. Who’s going to design it? Well, here’s this guy just out of school. He isn’t doing anything important yet, so let him design the power supply because it’s a trivial job, isn’t it?

We’ve seen that this is a recipe for disaster. When it’s a switching power supply, it’s probably the most important part the system, everything else depends on it, but all the strikes were against it. It’s dull and boring and no one wants to do it. It’s considered trivial and so the least competent people were put on it and on top of all of that, there’s nowhere for them to learn anything, nothing’s written, because switching converters and regulators did not come out of academia, they came out of industry, because of the requirements of the space program. Everything was against it. People didn’t know anything, the least experienced people had to do it, and there was nowhere they could learn.


  1. K. Kit Sum, Advances in Power Sources, PCIM, May 1987
  2. K. Kit Sum, Patent 6,141,230, Valley-fill Power Factor Correction Circuit, October 31, 2000.

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