Personal AnecdoteFamiliar with the 1971 Yu and Biess papers and Nathan Sokal's 1973 paper, I set out to make a simulation using CSMP software on a PDP 11-40 computer of how adding an EMI filter to a switching-mode power supply caused the combination to go unstable. This was in 1974 at the Naval Ocean Systems Center (NOSC) What I found was the published criteria didn't really work. The criteria predicted oscillations in stable systems and did not predict oscillations in unstable systems. At Powercon I (Beverly Hills, March 20-22, 1975) I brought up the question from the floor to a panel of chief engineers of power supply companies. None of them had heard of the problem and generally did not believe it. However, several others in the audience had experienced it and we met at break time. There was a enough experience in this group to report after the break that it was a real problem and should be considered by designers.
Later, I tried to get Thomas Wilson at Duke University to look at the problem, but Duke was swamped with NASA work. What I wanted were two procedures for MIL-HDBK-241. One procedure would let a designer design an EMI filter and switching-mode power supply combination that would not oscillate. The other procedure would allow a filter to be designed having only "black box" measurements on the power supply. At PESC'75 (Culver City, June 9-11, 1975) I talked to R. David Middlebrook at Caltech, who had just given a paper in which he discussed the problem. He thought he could do what I asked using a new canonical model of switching-mode power supplies developed at Caltech. I funded the work. The result was both a section for MIL-HDBK-241 and Middlebrook's landmark IEEE paper. This was also the first contract I issued with the provision that if the author published the work in a conference likely to be well attended and read by American power supply designers, the government report could simply be a cover letter including a copy of the paper. This concept proved very successful and resulted in government sponsored work being published in the open literature rather than buried in obscure government reports never read by those most needing the information. I had a lot to be proud of during my eight years at NOSC, but this policy, combined with getting funding for needed research, is what I feel best about. I was sorry to see it abandoned when I left NOSC. Almost nothing was published in the open literature on the Navy 100 W per Cubic Inch program. Do not use this information for design without independent verification of the information. Editor: Jerrold Foutz |
