11 November 2011

App Note 61 part 1

Practical circuitry for measurement and control problems: Circuits designed for a cruel and unyielding world. 40 pages

Another collection of random circuits, like App Note 45 (from June 1991). In fact, the introduction says this circuit collection includes circuits from June 1991 to July 1994. Unfortunately, there is no baby-bottle-rating system, however, there are plenty of great circuits.

Figure 1 shows a switching regulator where the switching frequency is synchronized to the system clock. (Synchronization was also discussed in App Note 55.) This trick is a great one. I once designed a "noise-less" power supply for a sensitive RF receiver with this method... I simply "hid" all of the EMI from the switching regulator underneath the EMI from the digital hardware (I admit that this approach is cheating, but it works).

Some of the circuits were supplied by Steve Pietkiewicz, and many of them were "inspired" by Jim's recent work on CCFL power supplies in App Note 55. Two methods for 1.5V-to-5V conversion are shown in Figure 3 and 6 (high power and low power, respectively). Figure 9 is a low-power CCFL supply (an alternative to App Note 55 Figure 11). Figure 10 is a LCD contrast supply (compare to App Note 55 Figure 14). Figure 11 is a power supply for a HeNe laser (the same as App Note 55 Figure H2), and Figure 12 is an electroluminescent-panel supply.

Jim's interest in instrumentation also appears. Several barometer circuits are shown in Figures 13, 14, 15, and 16, and a quartz-based thermometer appears in Figure 17. A FET-input instrumentation amplifier is shown in Figure 18.

There are also some improvements on circuits from App Note 47. The high-speed adaptive trigger makes another appearance in Figure 21 (compare this circuit to Figure 131 in App Note 47). Another wideband thermally based RMS-to-DC converter is shown in Figure 22 (compare to Figure 137 in App Note 47 and Figure 8 in App Note 22).

The best circuit (so far) is Figure 24, not because it's a great circuit in isolation, but because it is true to his "fixer mentality." Although he doesn't admit it here, I imagine that he was elbow deep into fixing a Tektronix P-6042 current probe when he realized that he couldn't get the replacement parts that he needed (see Figure 25: is M18 still available?). So, he designed his own replacement, and Figure 24 was born.

I'll discuss the rest of the circuits and the appendices next time.

Best quote (page 18, discussing figure 22): "It is worth considering that this circuit performs the same function as instruments costing thousands of dollars."


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