Power apps, Prony rides, and the usual batch of good links

This batch of Design Ideas deals mostly with power. A friend related an incident at a design review, in which the lead engineer informed a corporate exec that the project was only 3 dB over its budget. The exec went away happy (for the moment), and the engineer muttered, "That's a factor of two, because money equals power."

Our leadoff Design Idea, "Extend low-output-voltage switching regulator's input range," explores extension of a stepdown voltage-regulator's operating range by adding a second IC regulator. The problem arises when the prime regulator's output transistor runs out of base drive at low input voltages, but the second regulator steps in and squeezes another volt out of the circuit's low-end range.

Entitled, "Automatic latch-off circuit saves batteries," the second of our new Design Ideas focuses on preserving battery life and condition. If you've ever left an instrument switched on until it sucked its rechargeable batteries dangerously dry, you'll see the value of this circuit. The author designed the circuit for use in an LED flashlight powered by NiMH (nickel metal hydride) cells, but you can easily apply the principle to your own favorite battery-eater. While we're on the subject, please recycle dead rechargeable batteries—they don't belong in landfills.

We don't often stray into the world of electromechanics, but if you've ever heard of De Prony brake (pun intended), you've a leg up on most of us electron abusers. Electromagnetic clutches and brakes, respectively, act as SPST rotary power switches and short circuits. A solenoid actuates or releases either device, and sometimes it's important to minimize the power dissipated in the solenoid. The easy way out—applying continuous actuation voltage to the solenoid—wastes power. Taking advantage of the fact that a solenoid's holding voltage averages only a fraction of its actuating voltage, the author of "Switching regulator reduces motor brake's power consumption" shows us how to use a switched-mode power-regulator IC to decrease heat and wasted power.

Once upon a time, analog computers saw service in simulation, control and data processing. Now neglected in favor of microprocessors, analog computing circuits still offer advantages in a few selected applications. While an op amp and a few precision resistors can form an adder or subtractor circuit, division takes more effort. If you'd like to experiment, see "Analog divider uses few components"—a low-cost and modestly accurate circuit that can do the job.

Now for dessert. Some classic engineering texts have reached copyright expiration, and Google offers freely downloadable PDF copies. For example, take a look at Joseph Lipka's "Graphical and Mechanical Computation." You'll find De Prony brakes mentioned in volume 2. While you're at the site, rummage around and see what else is available.

Before you toss out your PC's supposedly dead motherboard, take a close look at its electrolytic capacitors. If any show signs of electrolyte leakage, bulging ends or split cases, you're seeing the effects of counterfeit electrolytic capacitors. Learn more at Badcaps.net. You may be able to salvage that mobo after all.

Psst…wanna build your own CRTs? At home? Visit Nyle Steiner's Web site and check out the YouTube links.

And last but most definitely not least, Jim Brown, K9YC, of Audio Systems Group., Inc., has written an excellent guide to using ferrite cores for interference suppression. Read this paper and you'll gain insights into ferrite applications that really work.

73 for now, and best wishes for the New Year,

Brad, AA1IP