Oh, No! We Forgot the Bozo Protection (and other Persistent Design Errors)
We’ve contributed to hundreds of electronics design projects wherein the circuitry was subjected to rigorous WCA+ (WCA+ is our advanced version of Worst Case Analysis; see “Four Costly Myths About WCA“). Our analyses invariably detected various design deficiencies, both stress and functional. Unfortunately, like an annoying relative who can’t get the hint to please not visit again, some common problems that we were finding decades ago are still regularly popping up in today’s new designs. These include:
- Lack of protection from Bozo the Clown: inadequate ESD protection; connectors without reverse-polarity keying; identical connectors for all ports (you don’t expect Bozo to pay any attention to cable labels or connector colors, do you?); no spills/immersion protection (e.g., coffee, slurpees, beer, or even juice from a steak being thawed on top of a warm electronics unit (no kidding)).
- Transient protection devices (TPDs) not present at circuit interfaces. Not just the AC power and load interfaces, but all the internal interfaces that are exposed to ESD or potentially unruly test equipment during testing, particularly for costly subassemblies. We’ve seen a hugely expensive and schedule-critical board blown up by a test instrument failure; a disaster that could have been prevented by a few bucks’ worth of TPDs.
- Failure to account for dissimilar power supply voltages, causing interface overdrive and/or latchup. (Sometimes this only occurs during transient conditions, making the deficiency hard to catch during testing. You will typically learn about it after you’ve shipped a few thousand units and your boss is frantically paging you to get back to work after you’ve had too many beers and the last thing you want is to work through the night and the weekend on warranty repairs while angry customers are screaming at you on the phone…but I digress…)
- Inadequate ratings for AC mains rectifiers and other power components, particularly in switchmode supplies. Hint: Don’t completely rely on SPICE or other simulations to identify realistic worst case performance boundaries for these components. Or do, but then be sure to not provide a warranty with your product.
For some more tips, see page 210 of The Design Analysis Handbook; still very relevant after all of these years. (Note: We’re out of copies of the Revised Edition, but it’s still available from Amazon and Elsevier.)
P.S. We’re considering creating some low-cost mini-modules of our Design Master WCA+ software, configured for common design tasks such as proper TPD selection, op amp gain stage analysis, etc. (If you care to comment, your feedback will be appreciated and will help us make a decision. You can add a comment to this post, or email us at firstname.lastname@example.org.)