I get a lot of press releases, mostly for ICs (of course) as well as for passives, connectors, modules, and power supplies, to cite just a few categories. It's easy to get glazed over and even a little jaded as they come in the email in-box each day.
But I look at them all, every once in awhile, I get an unexpected one which makes me stop and think, like one that came recently. It was for a carbon composition resistor, a venerable product technology that has been around (it seems) forever and apparently still has a role. The release I got was from Stackpole Electronics, highlighting a new carbon-composition resistor in values from 1 Ω to 22 MΩ, and dissipation to 1 W.
Why carbon composition? I'll quote from the press release: “. . . an outstanding choice for high-speed or high-energy pulse-handling requirements due to the large mass of the carbon resistive element and extremely low inductance. It remains a favorite choice for switch-mode power supplies as well as many other snubber and energy-dumping applications . . . [It is] also a popular resistor for surge withstanding in meters and data collection devices as well as a variety of lighting products.”
Way back in the day of vacuum-tube products and even the early days of transistor and IC-based design, “carbon comp” was pretty much the only resistor in use; there were also “wire-wound” units but they were only for specialized, costly applications. Carbon comps were cheap, and usually came in small cylindrical packages with axial leads (you could get radial lead versions, on special order), with dissipation ratings of ¼ W and ½ W as the most common sizes. They had colored bands which indicated their resistance value, and every engineer was expected to know that color code; it was actually pretty convenient. You could even remove and replace them, and re-use removed resistors, except it wasn't considered recycling or “green” in those days. And oh, that distinctive smell when you cooked one by exceeding its dissipation ratings, that was something never to forget (nor hide from co-workers!).
Flash forward to the present. We have many resistor technologies, too numerous to mention here, and surface-mount package in “ground-pepper”, nearly invisible package sizes (0201, for example) are the norm. Today's PCBs could not be practical or possible using those old carbon comp units, that's the reality.
But it is also nice to know that some of the older technologies still play a critical role in our latest, greatest applications, due to some unique or specialized characteristics they have. Maybe there is a little technological justice out there, somewhere. ♦