Running shoes, hosiery, and nylon shirts can be death for electronic circuits. Taken together, they can generate an electrostatic discharge (ESD) of 30,000V for the briefest of moments, sending handheld devices or laptop computers into a response resembling cardiac arrest. "You walk up to a computer and bam!" Bob Capdevielle, senior applications engineer for Littelfuse Inc., a maker of circuit protection devices, told us. "Suddenly, everything resets."
Still, problems associated with over-voltage and over-current remain an afterthought for most engineers. With their duties expanding and with design cycles compressing, most engineers relegate circuit protection to the end of the to-do list. "These days, engineers have to design the core functionality of their devices as quickly as possible," Jim Colby, manager of technology and business development for Littelfuse, said in an interview. "They have to get the form factor done, get the software done, get the prototype built, and prove out the concept. Then they have time to think about circuit protection."
Polyfuse LoRho SMD Resettable PPTC Resistors provide over-current protection and automatic reset for handhelds. (Source: Littelfuse Inc.)
More than ever, though, that approach is creating problems for product designers. Cellphones, computers, and music players are getting smaller. Moreover, they're running on tiny voltages that are more susceptible to ESD, distant lightning strikes, motor switching, and stray currents from process machinery. "It's usually 10,000 or 15,000 volts," Capdevielle said. "But it can get really high. We're getting calls from people asking about 30,000 volt parts."
The unfortunate result of leaving such matters to the last minute is that design functionality suffers. Engineers can't find room for circuit protection devices on their printed circuit boards. They end up re-spinning the boards and losing valuable development time. Worse, they hurriedly choose the wrong protection device, resulting in functional failures, poor reliability, safety issues, shock, or even fire.
For those who face the gloomy prospect of such problems, however, there's hope. Following are the expert recommendations of engineers whose professional lives revolve around the subjects of over-current protection and shock immunity.
CAD and CAE tools often provide analysis of ESD and other effects. This is very much like security in software. Frankly, when design a program, at any level, the main concern is not security, or any number of other -ilities, but the funtionality of the program. Design tools have been used for a long time to ensure that the software meets these requirements. Hardware design has to take this into account as well.
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.
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?
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.
I remember hearing the same things about batteries, Rich. I suppose most suppliers would just like to see their technology get promoted to a higher spot on the designer's list.
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.
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."
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.
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.
It truly is an important topic, bobjengr. I can't prove this, but I suspect circuit protection often gets overlooked because it never gets mentioned in school.
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.
A new book by Thomas Edison's great-grandniece takes on the notion that he was a lone-wolf inventor and replaces it with an image of a man who ascribed great value to the ideas of colleagues.
In response to rising interest in autonomous vehicles, the federal government has called upon states not to authorize operation of self-driving cars, except for the purpose of testing.
With LEDs dropping in price virtually every year, automakers have begun employing them, not only on luxury vehicles, but on entry-level models, as well.
Using almost 200 light-emitting diodes in the front and back of the new 2014 CTS, Cadillac designers are showing how LEDs can change the character of a vehicle.
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 5
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
For industrial control applications, or even a simple assembly line, that machine can go almost 24/7 without a break. But what happens when the task is a little more complex? That’s where the “smart” machine would come in. The smart machine is one that has some simple (or complex in some cases) processing capability to be able to adapt to changing conditions. Such machines are suited for a host of applications, including automotive, aerospace, defense, medical, computers and electronics, telecommunications, consumer goods, and so on. This radio show will show what’s possible with smart machines, and what tradeoffs need to be made to implement such a solution.
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
23 
