Be aware of standards. Standards determine the design of every product, all the way down to the circuit protection. Moreover, the list of standards that designers need to be aware of is seemingly endless. "Standards are a big part of every project," Will Li, global standards manager for Littelfuse's Electronics Business Unit, told us. "The beginning of every product should always be to understand the standards."
Standards pertinent to circuit protection include those from Underwriters Labs, Energy Star, NEMA, ATCA, CSA Group, IEEE, and standards bodies in Canada, South America, Japan, Korea, and Europe, among others.
Li says that designers need to be aware of standards from the outset of every project. "It's not as simple as coming in later and saying, 'I've got this new product, so tell me about the standards," he said. "It doesn't work that way."
Be ready to seek help. Because circuit protection isn't taught in universities, most engineers are more well versed in the complexities of product design than in the issues of over-current and shock immunity. That problem is compounded by the fact that most design engineers are also juggling several projects and have too little time to research the topic.
Some circuit protection manufacturers provide Websites with whitepapers, product specs, and case studies. Littelfuse, for example, offers its speed2design site, which is geared toward helping time-challenged designers find circuit protection solutions. The company also links designers to circuit protection advice by phone.
"This is a subject that's not taught in school, so new designers always struggle with it," said Juan Morales, global product manager, for Littelfuse's Electronics Business Unit. "It's something that definitely needs to be learned through experience."
A fire control panel was not working and I was tasked with fixing it. I discovered that a large mechanical relay was throwing off some energy. In my experiments to discover how much, I ended up routinely disconnecting my mouse and resetting my PC with the relay's discharge.
I added the proper relay suppression system, and the panel work perfectly after.
Unfortunately, I was a victim of the afterthought.
Static discharge has caused a few accidents with missiles. in `84 there was a fatal accident of a Pershing II that burned its 4 tons of propellant. The motor was being removed from the casing at the time of the accident and the discharge ignited the motor from the inside. The unfired igniter was recovered from the scene.
Charles, this is an extremely important article. When I was in the aerospace industry we would frequently visit Titan II silos to affect repairs. As a member of AFLC, I worked on the thrust chamber and the turbopumps for that defense system. Initiation of launch required the firing electrical "squibs". This was accomplished with a 28 volt DC source. With this low voltage, it would not be impossible to ignite the squibs with static discharges. This has happened. Due to this possibility, we were not allowed to bring or wear metal objects into certain levels of the silos. No belt buckles, no wedding rings, no watches, no jewelry of any kind. Even the eyelets in our shoes had to be taped or booties worn. For some areas, special clothing was also a necessity. I can certainly understand the need for proper circuit protection regarding electronic devices such as the ones you mentioned. This will be an ongoing problem unless engineers and engineering managers address the possibilities.
Reading this article brought back a lot of memories. At one place I worked we had an automated ESD tester for our ram chips - you could seat the part in the fixture and program in the voltages and it would both zap and test the part. In product engineering at another company we would do ESD testing on our discrete hall effects with a handheld tester. You would adjust the voltage and then place the tip on the lead and give it a zap - then test it afterwards. While it is important to have protection circuitry - hopefully the problem is also being addressed at the discrete level like we were doing. We always cracked up laughing at our hand held ESD "Zapper" - the instructions specifically directed the user "Do Not Use As A Cattle Prod."
In addition to circuit protection, power supplies are an afterthought as well. Being an engineer, I'm guilty of focusing on the key subcircuits of the products I've design and realized they needed clean efficient power to operate. To eliminate this afterthought mindset, I'll include in my system architecture design a sub-block for power supplies, interconnectors, and circuit protection devices.
Avnet Electronics is hosting its annual virtual Power Forum conference. Circuit Protection, power supplies, interconnectors, batteries, and electromechanical devices lectures will be presented in this virtual event. For additional information the weblink is shown below.
Designs must also take into account suppression of electromagnetic and radio-frequency interference, and compatibility with other devices. Lack of attention to these effects can cause an expensive failure when a product undergoes compliance testing.
I recall an engineer telling me a device would not pass an emissions test because someone had cut ventillation slots in a metal case for the device. Thise openings served as perfect slot antennas for signals generated inside the box. If you don't think about this "stuff" you can get into trouble rather quickly.
It's funny what people think about as an afterthought. Earlier in the mobile era, people said it was always the battery that was an afterthought. Hence, we had more OEM battery shapes and sizes than the battery OEMs would care to remember. Then it was the wireless technology, which designers often thought of (for good reason) as being a black box that they could simply drop into their design. Now it's the circuit protection. What's next?
It typically isn't too complicated to make a device immune static discharge and surges, but it should certainly not be an afterthought. Something as simple as adding a little series resistance to keyboard lines may be all it takes to keep from turning your silicon back into sand. It's worth investing in, or renting a static discharge (simulator) gun.
As a side note, I was performing static discharge tests on a device with a membrane switch panel. The device passed several tests, I turned off the gun and the reached for the device to turn it off. I was greeted by a very hearty jolt, as the front panel was holding a healthy charge and using the switch panel as a capacitor.
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