Electronic Design


The Original Disposable Lighter
I always enjoy looking back to times when engineers were also part mechanic, sheet metal worker, carpenter, and chef. Your photo of the Fairchild IC in "Fairchild's First Silicon Integrated Digital Circuits" \[Nov. 6, 2000, p. 70\] caught my eye because not long ago, I opened up an older piece of equipment and lo and behold, there was a TO-X canned op-amp (741, you bet). While looking at the photo, it struck me that although some of your readers might never have seen the can, many wouldn't recognize the object lying beside it—the original disposable lighter.
John Rohwer
JR & Friends
Sterling, Illinois

Reader Finds Simpler Solution
I was stunned by the IFD "Low-Dropout Current Regulator Improves LED Driver Efficiency" \[Nov. 6, p. 142\]. I can't believe that someone actually wasted time thinking up this circuit and then writing an article about it. The writer complains that when the LED is off in circuit 1, R2 "wastes well over 100 µA." And, he goes on to design an "improved" circuit.

First, if you don't want to waste the 100 µa, connect the grounded lead of R2 to the LED cathode instead. The switch would turn off both the LED and bias currents and result in 0 µA of LED off current. How is that for improved?

Second, if the switch in the picture is actually a microprocessor pin and not a real switch, connect the LED cathode directly to ground, and "switch" the ground terminal of R2. Simply turning ~100 µA of bias current on and off is much easier for a processor to do than to sink the ~10 µA of LED current.

There's a small problem with this approach in that 5 V would forward bias the C-B junction of Q1, and current would flow through R2, C-B, and then R1 back to the battery. This can be solved by using an open-collector driver or using the processor in an open-collector mode. (Setting the pin to an input will turn off the LED.)

Third, "flip" the whole circuit over, connect the LED anode to the battery, and use NPN's connected to ground. This avoids the whole open collector/forward bias problem mentioned previously. Also, if you're looking to decrease the dropout effect of Q1's VBE, add a pair of biasing resistors to increase the voltage seen at Q1 VBE. These are some of the oldest tricks in the book for current-limiting circuits.

All of these approaches use cheaper, more common parts (bipolars instead of MOSFETs, NPNs versus PNPs). This seems to be a case of someone just not thinking after designing a circuit.
Stephen Dubovsky
Design Engineer
Morningstar Corp.

You're correct. You and a surprisingly few alert readers have noticed this simpler solution. We try to publish interesting alternatives to standard approaches. Sometimes we don't catch that they might be overlooking the most efficient solution. Thanks for keeping us on our toes and for reading Ideas for Design.—Jim Boyd, IFD Editor

Energy For The Future Of Civilization
For the past 140 years, the world's people have evolved a civilization heading toward a state of utopia \["Energy Conservation: Do We Have The Resolve To Do It?" Nov. 6, p. 58\]. Technically, the physical energy to operate this system has come mainly from fossil fuels, the present component of primary importance being conventional petroleum.

Now, we are midway in the exploitation of the conventional petroleum capital that was originally available. That generally means that the rate at which this resource can be obtained will not only cease to increase, but will actually fall exponentially. In light of the fact that the requirement for these fuels will continue to increase at least linearly, the delta will cause their price to rise asymptotically to vertical.

This will result in the substitution of more pollution-causing energy, such as coal, shale oil, or tar sands, or massive disruptions to human comfort, quality of life, and economic prosperity. Great wars and the massive killing of human populations could even ensue.

Once this process is in progress and manifest to all, the supercilious attitude of people and their leaders to energy development and to energy conservation will diametrically change.

Once this change has taken place, energy conservation goals/objectives will be factored into the requirements analysis phase in the development of every architecture. Indeed, it will be a constraint that this must be done.

However, energy conservation is only part of the solution. Energy development must be pursued with even greater fervor. Answers such as wind power and solar power must be expanded with great alacrity.

There's only one ultimate solution, however: controlled thermonuclear fusion. This must be the highest priority—equal to the Manhattan Project.

The human being is the universe's manifestation of consciousness. There's nothing that we're incapable of knowing or doing. The things most required are imagination, vision, and boldness. It's manifest destiny that we move forward to build a civilization fit for the gods.
Bob Dobry
Systems Engineer

Creating Hydrogen In Real Time
Just a though on the topic of your article "Energy Independence—Without Pollution—Lies At Our fingertips" \[Nov. 6, p. 165\]: maybe instead of storing the hydrogen, it could be created in real time. As subs generate their own H and O2, maybe a car could in real time (someday) suck the relative humidity out of the air while running, and split the water molecule into H and O2. Of course, in the desert....with almost no humidity....

TAGS: Components
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