Capacitors in series

I needed a capacitor that can withstand over 400V. But what I had were 250V capacitors. So I put two identical capacitors in series. I monitored the voltages applied across each of the capacitors. There was surprisingly amount of imbalance, and progressively getting worse. One of the capacitors took up the larger share of the voltage. I placed 150K resistors across each of the capacitors, about 1mA and 0.5W dissipation. That was enough to restore the balance.

EE books for a practicing EE

This list also appears here.

1. Troubleshooting Analog Circuits (EDN Series for Design Engineers) by Robert A. Pease "To learn about subtleties of basic components."

2. Analysis and Design of Analog Integrated Circuits by Robert G. Meyer "For analog IC design. It is still unsurpassed as a standard introduction of analog IC design."

3. The Art of Electronics by Paul Horowitz "Very comprehensive coverage. It is a good reference to start and does not exhaust even as you gain experience."

4. Noise Reduction Techniques in Electronic Systems, 2nd Edition by Henry W. Ott "For thorny noise problems. It's done much to demystify noise mitigation methods."

5. Analog Circuit Design: Art, Science and Personalities (EDN Series for Design Engineers) by Jim Williams "To learn about the temperament of an analog circuit designer."

6. CMOS Circuit Design, Layout, and Simulation by R. Jacob Baker "For CMOS IC design."

7. The Design of CMOS Radio-Frequency Integrated Circuits by Thomas H. Lee "For CMOS RF IC design. If it can be done in CMOS, it will be done in CMOS."

8. High Speed Digital Design: A Handbook of Black Magic by Howard W. Johnson "For high speed digital design. It deals with the unpleasant non-ideal aspects of digital signals."

9. The Feynman Lectures on Physics, The Definitive Edition Volume 2 (2nd Edition) by Richard P. Feynman "For physical foundation of electromagnetism. Even though you do not intend to be a physicist, a solid background of classical EM serves you well for years to come."

10. Semiconductor Devices: Physics and Technology by S. M. Sze "For device physics. Unless you are involved in device fabrications, it is a sufficient introduction for circuit designers."

11. Operational Amplifiers: Theory and Practice by James K. Roberge "For feedback theory. It is slightly dated, but still useful. To be an effective circuit designer, you have to know feedback theory."

12. Solid State Radio Engineering by Herbert L. Krauss "For RF design. You are an incomplete EE if you cannot build a radio."

13. Principles of CMOS VLSI Design by Neil H. E. Weste "For CMOS digital ASIC design."

14. Electric Motors and Drives: Fundamentals, Types and Applications (3rd Edition) by Austin Hughes "For operating principles of various motor types."

15. RF Circuit Design by John E. Blyler "A very good starter book on RF design."

16. Oliver Heaviside: The Life, Work, and Times of an Electrical Genius of the Victorian Age by Paul J. Nahin "To see how our profession begins."

17. Designing Analog Chips by Hans Camenzind "A good introductory account from an experienced designer."

18. The Soul of A New Machine by Tracy Kidder "The human aspect of computer design."

19. Switching Power Supply Design, 3rd Ed. by Abraham I. Pressman "An insightful book on switching regulators."

Enlightenment

In the course of one's life, there are a few moments of enlightenment that significantly alter one's conception. Here are the some of the technical nature.

Origin of Scientific Theory

Studying sciences up to high school gives the impression that a scientific theory is a summary of all the scientific facts and observations which are so painstakingly collected. Then there are modern physics with theory of relativity and quantum theory, which are much hard to deduce from just experimental observations. There was relatively little experimental data to suggest the theory of general relativity. Einstein claimed that scientific theory is the free creation of human mind. Kant already pointed out that the condition of human mind shapes the perception of external world. Science does not simply proceed from experiments to theory.

Evolution of Humans

From my early science classes, it seemed natural that the human species evolved from local apes. So the Peking man might be the ancestor of the Asian people. It was astonishing to learn that all humans evolved from a single group from Africa which migrated to the rest of the world.

Pseudo code

When I first learned about computer programming in high school, the teacher drew the flow diagrams. I never quite got it and programming was very hard for me. Then in the college, the professor showed the pseudo code and stepwise refinement. You start with very high level human language description and refine it to the degree that can be coded in the computer programming language. Suddenly programming became a lot easier. Later I learned that the technique was described in an article "Program Development by Stepwise Refinement" by Niklaus Wirth in 1971.

Circuit Theory

In the high school physics class, I encountered some circuit analysis problems. At that time, no systematic approach was presented. Each problem seemed to require some trick. Finally, in the first course of electrical engineering, the Kirchhoff's circuit laws were introduced, then there was a mechanical way for all linear circuits. But later in the real world engineering, it became clear the loop method and the nodal method were unwieldy for anything but the simplest circuits.

Computer architecture

The first introduction to central processing unit (CPU) was ugly. The accumulator architecture of the early days just did not appeal to me. Then the x86 assembly class was even worse; it is hard to like x86 architecture. Only after I read Hennessy and Patterson's book on RISC architecture, the whole computer design started to make sense to me. But it was a little too late.

Next in the computing world

Over the short span of computer history, we saw the main frame computers gave way to the minicomputers, the minicomputers succumbed to the workstations, and the workstations overtaken by the personal computers. The clear trend of large yields to small and expensive yields to low-cost. Computers companies, such as DEC and Sun flourish and perish in the process. Computers reach ever more to the population. If we extrapolate, the PC's will be replaced by something even smaller and more ubiquitous. And it is already happening. The smartphones will supplant the PC's. So what will happen to the tech giants of today? Who will flourish, who will perish?

PC Power Supply

I have a number of PC power supplies that have failed. They are easy enough to replace, but the reasons for failure are unclear. So I decided to tear one down to investigate.

Enermax Noisetaker 420W power supply (designed and manufactured in 2004-2005) looks nice on the outside, but it failed shortly and generated no output. I opened it up before and found the fuse blown. So I replaced the fuse (250V 10A), it was blown violently as soon as I plugged in the AC. So there is a short somewhere. Despite of the massive heatsinks, the one-layer power supply PCB is surprisingly easy to desolder. I find inside the familiar forward converter topology. There are two separately transformers, one for main power and the other for standby power (5V). Two FET's in parallel drive the primary, controlled by UC3842 with opto feedback. Schottky diode pairs are on the secondary. A magnetic amplifier is there to improve regulation. A 7912 is used for -12V. One IC monitors the outputs. There is one custom IC with Enermax logo; it appears to be one to throttle the fans depending the temperature.

Not long I found the culprit, a diode (HER208) connected to the reset coil of the primary failed short, effectively shorted the rectified DC bus. A nice power supply is brought down by a lowly diode. Then how did the diode fail? HER208 is rated 1000V 30A peak. There is no obvious damage on the outside.

Now I have in hand a nice collection of capacitors, inductors, transformers, FETs and diodes.

Smart AC Adapter

I'm sure the designers thought it was a good idea to build smarts into a lowly notebook AC adapter. My HP notebook AC adapter comes with a 3-pin power plug. As an electrical engineer, I had guessed that the center pin was a sensing pin to compensate for the IR drop of the wires. I measured the voltages: the inner ring is 20.0V and the center pin is 15.4V. I did not think too much of it why HP thought was necessary to have a center pin until a few months ago. My computer ran slow and took a long time to boot. Of course, I suspected software problems, maybe virus. I reinstalled the OS and the problem seemed to go away, but only reappeared later. It was very frustrating. One day I noticed that the computer would run fine when I unplugged the power adapter. It was very repeatable; I could see the CPU loading changing as I plugged and unplugged the AC adapter. I could not believe that the running on AC adapter could cause the computer to slow down. A quick search on the web showed other people had the similar problems. HP called the power adapter smart AC adapter. Apparently information is communicated between the AC adapter and the notebook PC and the PC throttles the CPU accordingly. When there is a connection problem on this center pin, the notebook gets stuck in the slow mode. I could juggle the wire to make the problem go away. The technical support at HP seemed unaware of this particular problem. (In general, HP tech support just isn't very good.)

Power supply failures seem very common on the computers. Now the smart AC adapter adds a new way for the power to fail.

Power factor

The power factor is defined as the ratio of real power and apparent power. Real power is consumed to do work (useful or not); apparent power is what is delivered by the generator. The concept is only relevant when we are looking at AC power. If power is delivered to an inductive load, there is no real power consumed and power is stored then returned back to the generator. There appears no power is lost, so why do we care about power factor? What does the generator see when it is driving an inductive load? If a person is to crank the generator, how does he feel? During one half of the cycle, he consumes energy to crank the generator; in the other half of the cycle, he gets pushed by the generator. Since a person cannot real absorb this returned energy, in a sense this energy is lost. Similarly in a power plant, a free spinning turbine cannot really put energy back. Then not to mention power is lost to wiring resistance. We need to maximize the power factor to get the most out of the generator.