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Top 3 Reasons You Should Care About Over-Voltage Conditions

This live chat session will discuss circuit protection solutions for ESD. This is the second of three tech briefs before the Ask the Experts session.

  1. Over-voltage conditions are very common. They are usually caused by lightning strikes, ESD, a sudden load reduction, switching of transient loads, or a failure of the control equipment. ESD is especially common in consumer electronics applications — the everyday technologies we depend on to function. Many of the chipsets used in modern consumer electronics are developed in state-of-the-art technologies well below 130nm. Typical applications include USB 2.0, USB 3.0, and HDMI ports on set-top boxes, Blu-ray players, LCD TVs, digital cameras, desktop PCs, smartphones, tablets, and ultrabooks/notebooks.
  2. Over-voltage conditions are dangerous. Over-voltages can damage the sensitive chipsets on high-speed data lines. Because today’s consumer electronics are becoming smaller and smaller, the sensitivity of the electronics and chipsets within these devices is increasing. The more sensitive the chipset, the easier it is to become damaged by ESD. Since these technologies have a minimal tolerance to DC voltages that are over 3.3V, an ESD pulse can be catastrophic for such a device. If the ESD device does not provide enough protection, the chipset could experience premature failure.
  3. Over-voltage conditions are easy to protect against. Why? Because their effects are well-known. Also, because it’s more convenient and cheaper to incorporate over-voltage protection devices during the design phase — before the product has been developed and tested, and before any damage has been caused by ESD. Which circuit protection (CP) products are ideal for over-voltage protection, especially ESD? Choose semiconductor products that offer the second or third line of defense against ESD. Although these are also board-level components, they are designed to protect the microprocessor chipsets on the board by suppressing ESD and other transients at the point of entry.

Two examples of components that protect highly sensitive chipsets are:

TVS Diode Arrays provide low capacitance ESD protection in a number of form factors for electronic circuit designers.

TVS Diode Arrays provide low capacitance ESD protection in a number of form factors for electronic circuit designers.

  1. TVS diodes: These devices protect electronic circuits against transients and overvoltage threats such as ESD. They are silicon avalanche devices selected for their fast response time (low clamping voltage), range of breakdown voltages, and low leakage current.
  2. TVS diode arrays: These devices protect electronics from very fast and often damaging voltage transients, including lightning and ESD. TVS diode arrays offer a high level of protection (up to 30kV per IEC 61000-4-2) with very low capacitance, leakage current, and clamping voltage. They offer an ideal protection solution for I/O interfaces and digital/analog signal lines in the computer and portable consumer electronics markets.

Ready to learn more about the importance of circuit protection? Have a question or two about choosing the right over-voltage protection solutions for your next design?

Join us for the Planet Analog Chat Session on Circuit Protection, September 24, 20014, 1:00 p.m. ET (10:00 a.m. PT).

Sign up now by clicking here to join or to leave an early message! Just click Reply or Post Message when you get to the site.

22 comments on “Top 3 Reasons You Should Care About Over-Voltage Conditions

  1. Tony.Mowbray
    September 20, 2014

    Yes, TVS diodes are a good start, but sometimes more is needed. It depends on the voltages and the energy contained within the overvoltage event.

    I often have to protect TTL electronics against overvoltages approaching 8MV (yes you read it right). The first approach is to delay any excursion – the best way is a combination of gas filled spark arrestors, even air arrestors, this gets rid of the initial surge – these device start at around 90V.

    Follow this with PI filters (capacitive input filters) to continue shunting off rising surges as the frequency rises. Consider some extra in-line chokes to further delay the transients, or at least the leading edge. Designing these as low pass filters is another discussion.

    The third level is TVS diodes. TVS diodes, like all protective components, have a time to react to any event – hopefully this event will not kill them – so these devices (while quite hefty in their capabilities) need to be protected to an extent until they start working correctly and without risk of letting smoke out, and toasting the electronics they are protecting.

    I have tried many different devices over the years, and this combo works for the events I have to protect against.

    Success is when you enjoy a spark of great magnitude, the sytem shuts down (safer this way), but is able to be restarted and still work to specification, after the transient event.

    The electronics, I have to protect, take the best part of a day to access as they are inside a particle accelerator – down-time is frowned upon…

  2. eafpres
    September 20, 2014

    Hi Tim–great way to tee-up the chat.  Thanks for setting the stage.

    I started to wonder what the absolute most common device for over-voltage (and/or, over-current) protection was. If I guess on a volume basis, I would guess that fuses still have the lion's share of the market.

    For low-cost electronics, I've seen the trace on a PCB designed to fail to prevent something worse from happening.  That, of course, leaves the device inoperative.

  3. eafpres
    September 20, 2014

    @Tim–I'm also interested in fuse devices that return to normal after a time.  I'm frankly not well versed in the technologies used for that.

  4. samicksha
    September 21, 2014

    I agree to to Tony here, TVS will fail if they are subjected to voltages. Can you also help to explore more on I often have to protect TTL electronics against overvoltages approaching 8MV

  5. Tony.Mowbray
    September 21, 2014

    Referring to a “Polyfuse” here, I think. These are resettable due to over-temperature tripping and resetting when they cool down – I think also known as thermal fuses. They will probably still blow on a short circuit but if your circuit is designed right, could provide the protection you are after.

    The voltage across these Polyfuses is generally in the region of 30-60 Volts, so they can only be used when the supply voltage is quite low. I would imagine a 24V circuit would be served well by a 60V polyfuse – 30V being too close for comfort, in my opinion.

    I am experimenting with polyfuses right now, but have not tested any in a real situation.

  6. TimLittelfuse
    September 22, 2014

    samicksha,

    Thanks for your reply, my primary product experience has been with TVS within consumer applications, and have found them to be extremely well suited for protecting circuits against overvoltage durign fast transient events, such as an ESD attack.

     

  7. TimLittelfuse
    September 22, 2014

    I can not agree that anything circuit protection related can be overused.  Fuses have thier place, as do overcurrent and overvoltage TVS.  

    To answer you question directly, in the consumer market, the most popular components for circuit protection is the TVS array, which protects the user interfaces agasint damage caused by the human operating in the environment, creating Electrostatic Discharge.

     

  8. eafpres
    September 22, 2014

    Thanks, Tim.  I need to do some reading on TVS and TVS arrays.  

    I used to work in RF materials including passive EMI devices like ferrites for signal lines and absorbers for radiated EMI.  The rule there was that the designer would leave them out if they could, so the target price was often zero.  Of course, that is false economy.

    I think similar rules might apply on over-voltage protection, thankfully we have regulatory and certification bodies to prevent low-cost builders from leaving out needed protection. 

  9. Tim Patel
    September 23, 2014

    Tony,

    Yes, resettable fuses are commonly refferred to as polymeric positive temperature coefficient (PPTC) devices.  They are normally very conductive until an overcurrent condition trips the PPTC into a high-resistance state.  Once the overcurrent condition has passed, the PPTC returns back to its conductive state, thus acting like a resettable fuse.

    Polyfuses/PPTCs are typically only rated for 30-60 V, so they are ideal for use in low voltage circuits.

     

  10. etnapowers
    September 24, 2014

    “They are normally very conductive until an overcurrent condition trips the PPTC into a high-resistance state”

     

    @Tim: what is the typical peak value of the overcurrent that puts the PPTC into the high impedance state?

  11. Tim Patel
    September 24, 2014

    @etnapowers — Much like traditional fuses, PPTCs are available in a wide range of trip current ratings.  They are available with trip currents in the hundreds of mA range all the way up to the tens of Amperes range.  The rated trip current is the minimum overcurrent value at which the PPTC switches into a high-resistance state.  Additionally, most PPTCs have a maximum current rating, which is the absolute maximum fault current the component can withstand at its rated voltage without damage.

  12. vasanjk
    September 26, 2014

    Tim,

    Are resettable fuses available in slo-blow and fast-blow versions like glass fuses?

    Can Resettable fuses replace glass fuses in all applications or are there any limitations? How does one make the distinction?

  13. samicksha
    September 26, 2014

    I guess one of the most common cause of esd is friction created by two different material.

  14. Tim Patel
    September 26, 2014

    @vasanjk — Resettable fuses do not come in slow-blow and fast-blow versions like glass cartridge fuses, but they do come in a wide range of trip times.

    Resettable fuses won't be able to completely replace glass cartridge fuses in all applications.  Glass cartridge fuses are typically rated for higher operating voltages and higher short-circuit currents than resettable fuses are.  Use of a resettable fuse vs. a glass cartridge fuse really depends on the end application.  Factors such as expected inrush current, peak fault voltages, available short-circuit current, reaction times, etc. need to be considered to make the right decision.

  15. geek
    September 27, 2014

    @Tim: What about the cost differences between glass cartridge fuses and resettable fuses? Doesn't the cost difference also determines which of these to use? Of course the application matters as well but cost should also be a factor in my view.

  16. Tim Patel
    September 27, 2014

    @tzubair — Yes, cost is always a factor in any design, but many times the required functionality of the protective component is the main driving factor.  Glass cartridge fuses may be a lower-cost option, but the performance of a resettable fuse may offset the cost difference.

  17. geek
    September 28, 2014

    “Glass cartridge fuses may be a lower-cost option, but the performance of a resettable fuse may offset the cost difference”

    @Tim: When you refer to performance, do you mean that resettable fuses ensure higher protection for the circuits and ensure that the fuse breaks every time there's an issue? Or, does the performance has to do with the fact that it's easy to reset the circuit and bring the application back to normal without a significant waste in time?

  18. Tim Patel
    September 29, 2014

    @tzubair — Regarding “performance,” I mean that the trip time for a resettable fuse may often be faster than the opening time of a fuse under certain overload conditions.  By “overload” conditions, we are talking about over-currents that are, say, 135% to 210% of the nominal current rating of a fuse.  Under these overload conditions, fuses tend to remain conductive up to a certain timeframe where the heat build-up can no longer be dissipated by the fuse and the fuse element opens.  For applications where power needs to be disconnected (or reduced) quickly, a resettable fuse may be desired.  For other applications where these conditions are expected repeatedly, but no down time is desired, a fuse may be a better solution.

  19. etnapowers
    October 7, 2014

    @Tim, thank you for the useful informations you provided, just another question for you: what is usually the difference between the  absolute maximum rating of current and the rating current? An order of magnitude , more or less?

  20. Tim Patel
    October 7, 2014

    @etnapowers — Typically, the maximum current rating is an order of magntitude larger than the trip current rating.  Some radial leaded products have trip currents in the 10 A range with max. current ratings up to 100 A.  Some surface mount products have trip currents in the 1 A or less range with max. current ratings up to 40 A.

  21. etnapowers
    October 10, 2014

    @Tim: thank you for the informations. I find very valuable the SMD products, it's very difficult to manage a current of 40 A for a surface mounted device, because there is no room for heat dissipation.

  22. Davidled
    October 11, 2014

    Re-settable fuses might have warranty police including the number of resetting cycle that could be measured by the circuit. Module could store the number of current resetting cycles in the memory. Designer might monitor it.

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