11 January 2012

App Note 75 part 2

The waveform sampler in Figure 19 is another great circuit. This "track-and-not-hold" topology is basically the core of his settling-time measurement circuit from App Note 74.

Several random instrumentation circuits are included in this app note. Figure 24 is a extremely low-power chopped amplifier. Figure 25 is a thermocouple amplifier for detecting the pilot-light flame in a furnace or hot-water heater (some home improvement during his sabbatical, perhaps?). Figure 26 is a tip detector for shipping containers.

Several oscillator circuits are also included. Figure 27 is the simple 32,768-hertz crystal-oscillator circuit that is used in Figure 10. Figures 29 and 31 are 10-MHz complementary-output oscillators, the former with 50% duty cycle and the latter with nonoverlapping outputs.

A CCFL power-supply circuit returns in Figure 33. I can't believe he isn't completely burned-out on CCFL circuits. Interestingly, this circuit uses the Royer topology, but does not use one of Linear Technology's specialty Royer control chips. Perhaps this circuit is for a low-cost application? A single footnote refers the reader to App Note 65.

The applications section of the app note concludes with more three power supplies. Figures 36 to 39 were contributed by Jeff Witt. Figure 40 is a low-noise off-line power supply using the LT1533 (see App Note 70). The drive on the cascode transistors and the power-limit/current-limit circuits are very interesting.

Best quote (discussing Figure 44): "This data was taken with no input filtering LC components and a nominally nonoptimal layout."

Second-best quote (footnote 12):
Veterans of LTC Application Notes, a weary brigade, may recognize this reference as the object of Application Note 70's (Footnote 14) champagne prize offer. The mystery solved, the messenger was compensated as specified (Veuve Clicquot Ponsardin).
This paper (Reference 24) is the earliest use of the word "cascode" in the literature.

The appendices are updated versions of "Box Sections" A and C from App Note 23. Appendix A discusses low-power techniques and the design evolution of the zoo circuit. Figures A1, A2, and A3 are from App Note 23. Figure A4 is the original Zoo Circuit, and Figure A5 is from App Note 45 Figure 21. Figures 1 and 4, as discussed last time, are the latest circuits in this evolution ("utilizing contemporary components").

Appendix B discusses the effects of test equipment on micropower circuits (in short, avoid loading, or worse, powering, your micropower circuits with your test equipment). Figure B3 is a new addition, borrowed from App Note 47 Appendix E.

The app note concludes with a cartoon that expresses his dog's point of view.


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