31 August 2011

App Note 29 part 3

This app note has several interesting appendices (of course, Jim's appendices are always interesting).

Appendix A discusses a common topology for a 5V-to-plus-and-minus-15V converter. The topology discussed is the Royer topology, and here, Jim thoroughly badmouths it. His main complaints are the noise (the switching residue) at the output and the current consumption (due to the magnetic saturation behavior). He says, "The converter's inherent operation ensures noisy outputs" and he suggests several schemes to minimize or avoid the noise. The "bracket pulse" and strobed-output operation are worthy of Rube Goldberg. He claims, "While useful, none of these arrangements offer the flexibility of the inherently noise free converters shown in the text." That sentence may be a bit of an overstatement. "Noise free" is an exaggeration.

The funny thing about this appendix is that he returns to the Royer topology for LCD backlight lamps, and expends quote a bit of ink extolling their virtues in that application. Of course, his complaints are still valid in that application, but I wonder if he ever wished that he had tempered his language here a little bit.

Appendices B and C we have seen before in previous app notes.

Appendix D discusses inductor selection. He says "Electromagnetic theory, although applicable to these issues, can be confusing, particularly to the non-specialist." He suggests the purchase of an inductor kit (such as shown in Figure D2) and a cut-and-try method for inductor selection. Jim sure loved his kits and decade boxes! (See previous app notes for praise for his General Radio 1432 resistor decade boxes.) This approach is a practical one, particularly if you can avoid the horrors shown in Figure D6. Yikes.

Appendix E covers converter efficiency and sources on inefficiency. There is good discussion and good advice all around here (with a brief mention of using germanium).

I already covered Appendix F last week.

Appendix G discusses magnetics and inductor selection (again!), and contains another great quote about his own inspiration (page AN29-44): "As a purveyor of switching power ICs we incur responsibility towards addressing the magnetics issue (our publically spirited attitude is, admittedly, capitalistically influenced)."


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