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Back to School & Back to the Drawing Board for Those Who Neglect Circuit Protection

This year, I had an opportunity to talk with members of the IEEE Student Chapter at Stanford University about some of the exciting things we've been doing at Littelfuse, particularly the IndyCar racing and NASA Speed2Design programs we ran over the last two years.

Racing and space exploration are just two examples of how pervasive the need is for circuit protection. Electronics are everywhere in racing, not only on the cars, but in the communications equipment in the pits and garages, as well. Much of that equipment is much more sensitive than in the past, because it involves digital electronics, which requires a higher level of circuit protection. And though static shocks might be little more than a wintertime annoyance to most humans on earth, these discharges can spell real trouble for critical electronics in orbit or on extraterrestrial missions.

Unfortunately for a lot of young engineers today, the intricacies of designing adequate circuit protection often aren't taught in universities. Many graduating engineers are more interested in pursuing careers in product design than in issues like overcurrent and shock immunity. If you have the same product design mindset but realize that your job demands a broader awareness of circuit protection, some highlights of my presentation to the Stanford students may serve as an introduction.

  • Circuit protection components are vital elements in applications from consumer electronics and telecom circuits to automobiles and industrial equipment. They protect devices and business assets against harm caused by short circuits, power surges, electrostatic discharge, lightning, electrical load switching, and other electrically harmful occurrences. Common types of circuit protection devices for electronic products include thyristors, transient voltage suppression diodes and diode arrays, fuses, positive temperature coefficient devices (PTCs), varistors, gas discharge tubes (GDTs), and ESD suppressors.
  • Designing the appropriate circuit protection is critical to preventing dangerous products from reaching the public. For example, lithium ion cells, like the ones in laptops, are subject to thermal runaway. Raising the temperature of a Li-ion battery above 140°F leads to a compromised cell, which can lead to an explosion and fire. Battery packs for laptops and other portable devices contain many levels of protection to assure safety under (almost) all circumstances when in the hands of the public. The safety begins with the battery cell, which includes a built-in temperature switch called a PTC that protects against high current surges, a circuit interrupt device (CID) that opens the electrical path if an overcharge raises the internal cell pressure to 1,000 kPa (145 psi), and a safety vent that releases gas in the event of a rapid increase in cell pressure. In addition to these internal safeguards, an external electronic protection circuit prevents the charge voltage of any cell from exceeding 4.3 V. Furthermore, a fuse cuts the current if the skin temperature of any cell approaches 90°C (194°F). To prevent the battery from overdischarging, a control circuit cuts off the current path at about 2.2 V/cell.
  • All too often, circuit protection is the last thing some engineers think about, because they prioritize designing the core functionality of their devices as quickly as possible. However, treating circuit protection as an afterthought has the potential for serious consequences. Once the PCB is designed, it can be difficult to find room for circuit protection devices, making it necessary to re-layout the boards, which costs more money and wastes valuable development time. Even if they don't have to re-layout the board, time pressure may cause some engineers to choose a less-than-optimal protection device or put a device in a non-optimal location, resulting in functional failures, poor reliability, safety issues, shock, or even fire. The best time to start thinking about circuit protection is after the chip set has been selected and before beginning to lay out circuit boards. At this point, ESD ratings are available, and designers can know how robust or how sensitive the chips are.
  • The beginning of every product should always be to understand the impact of relevant standards. Standards relevant to circuit protection include those from Underwriters Labs, Energy Star, NEMA, JEDEC, CSA Group, IEEE, ANSI/NEMA, and standards bodies in Canada, South America, Japan, Korea, and Europe, among others. Circuit protection manufacturers' websites are good places to look for guidance. For example, the Littlefuse Speed2Design site is geared toward helping time-challenged designers identify circuit protection solutions.

If you're interested in learning more about the next generation of circuit protection users, see the slideshow of my Stanford presentation on the Speed2Design website.

12 comments on “Back to School & Back to the Drawing Board for Those Who Neglect Circuit Protection

  1. Davidled
    June 20, 2014

    It is very crucial that electronic circuit is operated functionally in wide temperature and extreme environment.   Circuit protection includes a lot of meaning including sensor design, component with heat sink, PCB board material and current source related to Op Amp design as current regulator supplying the constant current. Thermal analysis could be executed in the circuit to see which component is getting hot in operation time.

  2. samicksha
    June 23, 2014

    Thank you Daej for mentioning all those points in your comment, one of the important aspect in circuit protection is heat managment, which if not done properly can damage or impact your circuit badly.

  3. geek
    June 25, 2014

    “Many graduating engineers are more interested in pursuing careers in product design than in issues like overcurrent and shock immunity”

    @Bharat: Great post. Thank you for introducing me to an important dimension related to circuits. I certainly agree with you that more students should enter into the area of circuit protection and the technologies that surround it. Do you think Engineering universities have adequate cirriculum and courses as part of their program to address this area and make students specialize in this domain?

  4. geek
    June 25, 2014

    “Thermal analysis could be executed in the circuit to see which component is getting hot in operation time.”

    @DaeJ: I think thermal analysis is just one part of the whole range of sensors that are in-built into the certains which include pressure, humidity, motion etc. All these together wil ensure that the components are protected and no harm is done to the curcuit.

  5. bshenoy
    June 25, 2014

    tzubair – I do not believe that circuit protection is taught in enough detail at the university level. I was never exposed to it when I was in school and don't think that has changed much. Circuit protection design is mostly taught on the job usually sometime in one's career. It is probably other members of the engineering team or even a supplier like Littelfuse that teaches the junior engineer about circuit protection. I do think higher level design classes in universities should at least introduce students to circuit protection but it is probably too narrow of a field to specialize in. The engineers that we hire at Littelfuse are tyoically material scientists as most of our devices have a deeo foundation in material science platforms. I also think suppliers like Littelfuse can help by giving more technical seminars at the university level to build a base of engineers that have been exposed to circuit protection concepts.

     

    Bharat

  6. Netcrawl
    June 26, 2014

    @bshenoy good point, the reality is circuit protection design has advanced a little, making some limited in the ability to meet the requirements demanded in today's fast-evolving world. Yes, it true electronics industry have grown increasingly sophisticated and fast but the design powering them are seriously antiquated or ineffective. 

    Education and training within our industry about circuit protection leaves a lot to be desired and not all of those people have studied the real problems, they missed something important.  

  7. SunitaT
    June 26, 2014

    @Bharat, technical semiars at the universities level is the good idea. Along with seminars , conducting worshops will be an added benefits for the students. Most of the practicals during academics evolve over building circuits on breadboard and watching the result in CROs.

  8. RedDerek
    June 26, 2014

    Nice post. Your comment:

    All too often, circuit protection is the last thing some engineers think about

    is similar to the thought of power supplies in designs. A design is made with all the guts of the circuits – processor, memory, I/O, etc. But the power supply voltage rail generation is the last thought as well.

    It could go that the power supply designer does not think about circuit protection until the end as well.

  9. geek
    June 27, 2014

    “I also think suppliers like Littelfuse can help by giving more technical seminars at the university level to build a base of engineers that have been exposed to circuit protection concepts”

    @Bharat: Seminars would be useful to start with and capture the students' interest towards this subject but I still think a proper majors (as part of a degree) in this domain would be more benefitial in the long run. Perhaps you or someone else in your company can be a faculty member for that course. This would give the students more hands-on exposure to this domain.

  10. yalanand
    June 29, 2014

    When people leave their colleges or universities, they are usually not skilled enough to be able to practice what they have learnt. All the students usually have is just the basic knowledge but they cannot be able to practice it. Students should be able to go back to school; to the drawing board to learn more about the circuit protection. People should learn more about the circuit protection components so that they can be able to design an appropriate circuit protection system.

  11. vasanjk
    July 2, 2014

    tzubair

     

    There is no thumb rule for circuit protection and EMI/EMC reliable design. Though standard guidelines help to a great extent, it is important to know that there are no standard templates to implement just like that. It is important not only to employ right protection components but also to place them in an appropriate manner. A TVS diode placed far from the connector or in a branching track may not be of much use.

     

  12. Victor Lorenzo
    July 3, 2014

    Interesting post, Shenoy.

    I agree with you, “The beginning of every product should always be to understand the impact of relevant standards “. Many times we are so concentrated in defining a fancy and glamourous full featured product specification and almost forget that tiny little task which is listing all aplicable standards.

    Not considering circuit protection and aplicable standards from early design and specification stages often leads to low quality products and massive product redesigns during qualifications and certifications prior to mass production and market release.

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