EEVblog #678 - What is a PCB Spark Gap? - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: October 30, 2014, 10:12:10 pm
content: In this tutorial Dave explains what a PCB spark gap is and how it can be a useful zero cost addition to your PCB layout to help prevent ESD damage.He shows how to easily design them into your board and calculate the approximate voltage rating.And of course has some fun applying 5kV to some gaps to show how them at work.Plugpack teardown:Support the EEVblog through Patreon!http://www.patreon.com/eevblog

author: bktemp
author_rank: Super Contributor
timestamp: October 30, 2014, 10:36:21 pm
content: Can somebody explain, why they have put the spark gap under the common mode input filter to bypass it?It makes no sense to me, because the only thing it protects is the common mode filter. Instead all the energy can pass directly into the circuit.

author: Kohanbash
author_rank: Regular Contributor
timestamp: October 30, 2014, 11:45:56 pm
content: It looks like with 1000V (from 8:12 to 8:14) there is a very small change that occurs near the top of the circle.

author: EEVblog
author_rank: Unknown
timestamp: October 31, 2014, 12:29:28 am
content: Quote from: Kohanbash on October 30, 2014, 11:45:56 pmI didn't see a spark, but did see it deform the board material or some such?

author: coppice
author_rank: Super Contributor
timestamp: October 31, 2014, 01:17:38 am
content: Dave uses a strange formula for breakdown. It has no factor for humidity, which is the biggest factor affecting discharges with open air spark gaps.

author: RobertoLG
author_rank: Frequent Contributor
timestamp: October 31, 2014, 01:27:26 am
content: Quote from: coppice on October 31, 2014, 01:17:38 amya, I was thinking about that too

author: EEVblog
author_rank: Unknown
timestamp: October 31, 2014, 01:33:39 am
content: Quote from: coppice on October 31, 2014, 01:17:38 amIt's a ballpark, and as I said a formula that is thrown around in a few places. It's the best one I could fine, and the only one I have seen before. If you have a better formula backed with some research then please share.

author: coppice
author_rank: Super Contributor
timestamp: October 31, 2014, 01:44:59 am
content: Quote from: EEVblog on October 31, 2014, 01:33:39 amThe variation in air pressure, even at the top of Everest, isn't huge. Try the effect of a seaside town in the especially humid season.The 3000 in the formula shown is the usual 3000V/mm breakdown figure for dry air at STP. Damp air could divide that by several. If the board is of any significant age, and has started to accumulate a film of pollutants from the air, moisture absorbed into that film will greatly reduce the breakdown across the board surface itself, which is why slotting the board is such a big help. It really stabilises the breakdown point. It also avoid the carbon track build up when breakdowns are happening, although narrow slots aren't always easy to achieve. If the board assembly process doesn't include a really rigorous surface cleaning step, slotting increases its usefulness further.

author: coppice
author_rank: Super Contributor
timestamp: October 31, 2014, 01:52:58 am
content: Most equipment is sold with a spec that says its for use in humidities up to 70% or maybe 80%. If your equipment won't actually work up to 98% you are effectively saying "not for sale in Delhi, Mumbai, Singapore, Hong Kong, Houston, .............".

author: Smokey
author_rank: Super Contributor
timestamp: October 31, 2014, 02:06:23 am
content: Some environmental specs are such a joke. My favorite ones are the "Max Altitude" spec, which is usually around 2000meters, or 6500 feet.6300 feet.... ok....6400 feet.... ok....6500 feet....??.....Silly.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 31, 2014, 02:11:18 am
content: Quote from: Smokey on October 31, 2014, 02:06:23 amThat's probably more like,6500 feet, 1% chance of breakdown8500 feet = 10%10000 feet = 50%18000 feet = 90%etc.Tim

author: coppice
author_rank: Super Contributor
timestamp: October 31, 2014, 02:15:50 am
content: Quote from: 3roomlab on October 31, 2014, 02:02:55 amI am not sure of all the factors which come into play, but arcs take time to form. If you hit a discharge tube with a high but very narrow pulse it doesn't discharge at all.

author: Wilksey
author_rank: Super Contributor
timestamp: October 31, 2014, 02:26:54 am
content: Interesting video!I found it particularly useful having the PCB demonstration, you should do that more often!I would quite like to see a video on various input protection methods, I tend to use TVS diodes on mine, but it's always good to see what other people are doing and how they are achieving it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 31, 2014, 02:39:38 am
content: Quote from: 3roomlab on October 31, 2014, 02:02:55 amA spark is a very stochastic (= random...because big words are big) process, where the probability of discharge increases with applied voltage and duration.You can think of the mechanism like this:Normally, there's a very small amount of free charge (and thus conductivity) available in the gas. Usually due to radiation: cosmic rays, background radiation, radioactive isotopes in the construction materials, and radioisotopes intentionally added to the electrode coatings.Now, free charges will move about, and be accelerated by electric field. If they gain enough energy to ionize some gas atoms, they'll probably strike one, which frees more charges, and so on. In a weak electric field, not much energy is gained between collisions, so the conductivity doesn't increase much.In a stronger field, more and more cascades will occur, and you get avalanche breakdown. Assuming enough collisions occurred, and there were enough charges around to start the event.So, for an arbitrarily low voltage, you will always get discharge events, they'll just be imperceptible as leakage current. It's only above a certain point that you get enough average current (and big enough charge dumps) that it's a problem (what we call a spark or arc discharge). Conversely, very sudden voltages might pass unimpeded until, after some nanoseconds, enough cascades have occurred to build a spark proper.So, it's constantly a very random thing, and doing some averages you can come up with characteristics. There's no operational guarantee that it should work at all at almost any voltage -- it's just that it's 99.9999% likely to discharge if you put, say, a thousand volts across it. And accordingly, don't expect it to break down at e.g. 75.0V -- you'll only be able to use a 75V device at maybe 50V nominal, and still have to protect your circuit against rapid pulses in the 500V+, couple ns range. Fortunately, that does mean beefy 8/20 or 10/1000 surges are truncated to ESD-level energy, which is a *LOT* easier to deal with!Tim

author: EEVblog
author_rank: Unknown
timestamp: October 31, 2014, 02:44:44 am
content: Quote from: coppice on October 31, 2014, 01:44:59 amI totally agree.There are two points though:a) Where is a researched formula for including such humidity? (that's why I didn't include it)b) In this case of PCB sparkgaps, areductionin the arc voltage is generallybetter, not worse. So you could argue that it's maybe not a good thing to include humidity in the calculation, because it is reducing the worst case figure.

author: coppice
author_rank: Super Contributor
timestamp: October 31, 2014, 02:57:40 am
content: Quote from: EEVblog on October 31, 2014, 02:44:44 amYou need to have a realistic figure for the gap, or it will be discharging at all the wrong times when the humidity is high. Ever tried selling to Delhi or Hong Kong? :-)Your practical minimum breakdown voltage might be quite high. For example, how will your product get through the fast pulse transient tests needed for IEC 61000 compliance? If you allow the 4.5kV pulses to arc across your spark gap it will probably erode quite badly before the tests are complete. You probably only want your spark gap to catch the really extreme conditions, and let something better defined protect you from the IEC test cases.

author: RobertoLG
author_rank: Frequent Contributor
timestamp: October 31, 2014, 03:03:31 am
content: a) Where is a researched formula for including such humidity? (that's why I didn't include it)b) In this case of PCB sparkgaps, areductionin the arc voltage is generallybetter, not worse. So you could argue that it's maybe not a good thing to include humidity in the calculation, because it is reducing the worst case figure.Clear, thanks

author: EEVblog
author_rank: Unknown
timestamp: October 31, 2014, 03:20:03 am
content: Quote from: coppice on October 31, 2014, 02:57:40 amOf course. When did I suggest that this spark gap approach should in any way be used for any sort of defined protection scenario? I said the opposite several times I thought.As I said, this a very poor-mans protection device.

author: coppice
author_rank: Super Contributor
timestamp: October 31, 2014, 03:38:47 am
content: Quote from: EEVblog on October 31, 2014, 03:20:03 amYou make it sound like a technique that would only be used in lousy equipment, which nobody really cares too much about. Its actually a mainstream way of achieving a number of protection goals in equipment of all quality and price levels. Any equipment from a reputable maker needs to pass at least IEC61000 (and frequently something way beyond that in Australia, because of its desert) and needs to apply its protection in an appropriate manner to do that. Spark gaps are a really key part of the overall protection mix.

author: EEVblog
author_rank: Unknown
timestamp: October 31, 2014, 03:42:06 am
content: Quote from: coppice on October 31, 2014, 03:38:47 amThat was (clearly I thought) not my intention.QuoteSure, in which case you use a specified and repeatable GDT.

author: SeanB
author_rank: Super Contributor
timestamp: October 31, 2014, 04:50:25 am
content: Went hunting yesterday for a spark gap on a pcb, but only found a CRT base panel out of a dead monitor. took it apart and opened it up to show the tiny gap and tested it with a little voltage.Then tried the rest of the board. It did not work afterwards. As I was at work I was not going to go and let out too much smoke, there would have been complaints.

author: coppice
author_rank: Super Contributor
timestamp: October 31, 2014, 07:17:39 am
content: The expression 3000pd + 1350 is quoted very often, but does anyone know where the 1350 is derived from? The expression is obviously a rather rough and ready one, as it suggests a zero width gap will not break down until 1350V. I have some evidence which appears to contradict this.

author: StefanHamminga
author_rank: Contributor
timestamp: October 31, 2014, 07:28:34 am
content: Dave, very interesting video! I noticed your example recommending the rounded trace sticking in the ground fill, but isn't the triangular design better, because a sharp edge promotes spark forming? It would erode quicker, sure, but the initial protection would be better.

author: coppice
author_rank: Super Contributor
timestamp: October 31, 2014, 07:48:55 am
content: Quote from: StefanHamminga on October 31, 2014, 07:28:34 amDave covered this. The point works great the first time, but over the life of the product its performance is highly inconsistent as it wears. The rounded end traces with ground fill around them will be far more consistent. If you look around a lot of people show a similar idea, but they do one key thing in a poorer way than Dave. The use a square ended trace surrounded by ground fill. The corners of that squared off end will not give the long term consistent behaviour that Dave's rounded end, with its resulting even spacing and lack of pointy bits, will.I guess if you only need your product to survive once, because its something disposable, a pointy approach might be superior.

author: alter Ratz
author_rank: Contributor
timestamp: October 31, 2014, 08:27:42 am
content: I liked this video very much, since input protection is something which is IMHO very important, yet it is difficult to find good literature about it. Just recently I had to protect an input using a MOV+PTC and it took ages to find information about part selections, and even then I was not 100% sure that I have done it right (but I must have since it passed TÜV).So a video about the basics of input protection (methods, part selection, combination + pros/cons of methods) would be very welcome.best regards,Bernhard

author: alper.y
author_rank: Contributor
timestamp: October 31, 2014, 09:21:44 am
content: I didn't get that why there shouldn't be any soldermask over spark gap? If both sides are exposed to air and there is a soldermask between pads, isn't it sufficient to create a current path? Does carbonized pcb mean that some current passes through board material itself?

author: max666
author_rank: Frequent Contributor
timestamp: October 31, 2014, 09:22:34 am
content: Quote from: coppice on October 31, 2014, 07:17:39 amA zero width gap isn't really a gap, is it? That reminds me of a quote by Apple Inc.: “A tap is a zero-length swipe.”But to be serious for a moment, that formula isn't intended to be used for very small gaps (and probably not for very wide gaps either). The real thing surely is nonlinear and this formula is only an linear approximation.

author: coppice
author_rank: Super Contributor
timestamp: October 31, 2014, 11:31:12 am
content: Quote from: alper.y on October 31, 2014, 09:21:44 amIf you have solder mask between the arc electrodes everything is OK until an arc occurs. Then you get fried solder mask, which is not good. FR4 is far harder for the arc to damage, so its OK to let the arc run across its surface.

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 31, 2014, 12:45:38 pm
content: I use 15-22r resistors at the input. too much stress and the resistors go up in magic smoke (I'd rather smoke a resistor than a high-end opamp or vactrol).It's great news that you've started to use Patreon too, I hope you get plenty of continued support, your videos are more than worth it. I too set up an account there as a content provider, yet when it comes to payments, they are asking for my paypal password (to receive money?)... Hmmm...!

author: JackOfVA
author_rank: Unknown
timestamp: October 31, 2014, 12:56:38 pm
content: Isn't there a significant difference between breakdown voltage as measured between two rounded objects (spheres traditionally, but in this case a smooth rounded PCB trace and a ground plane strip) versus two sharp points?The electric field potential at the sharp point is divergent and will experience breakdown at about one-third the voltage that will be seen between two smooth balls.Hence, instead of roughly 3 million volts/meter breakdown for dry air at STP two points will break down closer to 1 million v/m.And, there are some other non-linearities associated with breakdown e.g., Paschen effect in breakdown voltage versus pressure. There's also a difference in breakdown voltage with polarity for point emitters, but not so much with spherical or smooth emitters.Nice overview of the subject can be found athttp://cas.web.cern.ch/cas/Slovakia-2012/Lectures/FairclothHighVoltage.pdf

author: Circuitous
author_rank: Unknown
timestamp: October 31, 2014, 01:06:12 pm
content: Dave, nice video and explanation.I would really like to see one on input protection... mains input, DC power input, and logic level input/output.

author: sunnyhighway
author_rank: Frequent Contributor
timestamp: October 31, 2014, 01:25:39 pm
content: Quote from: LektroiD on October 31, 2014, 12:45:38 pmThat's just the typical american style of doing business. They always want to know more about you than what's necessary to do business with you. Gotta fill the demographics database you know. Worth a lot of money. Instead of having you answer 12 pages of irrelevant questions to fill that stupid demographic database they can now access all that data themselves without boring you with all those stupid questions by simply using your password. They will call it "making things easier for the customer, but for some weird reason I don't feel inclined to share that opinion.

author: EEVblog
author_rank: Unknown
timestamp: October 31, 2014, 01:28:03 pm
content: Quote from: LektroiD on October 31, 2014, 12:45:38 pmThey shouldn't ask for your PayPal password!

author: EEVblog
author_rank: Unknown
timestamp: October 31, 2014, 01:33:04 pm
content: Quote from: StefanHamminga on October 31, 2014, 07:28:34 amThere is no such thing a a perfectly round edge, especially in etched PCB traces.Macroscopically looking round edges and straight sides actually have many microscopic points. You can see this in the video when the spark makes it's way around the arc.The user gets to weight up the pros and cons. Personally I'd rather go for reliability over some essentially unknown decrease in the arc voltage.

author: Royce
author_rank: Contributor
timestamp: October 31, 2014, 01:43:56 pm
content: Quote from: Circuitous on October 31, 2014, 01:06:12 pmJoining with the couple of others in the thread. I'd really like to see the video as well. The protection, how one would test it, and how one would expect it to be tested by some sort of agency.

author: StefanHamminga
author_rank: Contributor
timestamp: October 31, 2014, 03:08:20 pm
content: Quote from: EEVblog on October 31, 2014, 01:33:04 pmI was thinking more of 'what's maximum protection I can throw in there' for a simple prototype board, rather than reliability in production quality boards. Out of curiosity I took a quick snap of an OSH Park PCB I had laying around (0.5mm pitch, 0.1524mm ground fill clearance at the thermal pad). The rounded edges look pretty clean to me. Not trying to be a smartass, just curious to find out what the opinions are on finding the balance between low breakdown voltage and lifetime of the contact set.What about the solder on an ENIG board? At one hand the plating doesn't have the insulating properties of the solder oxidation, but it doesn't have its (thermal) mass either.My initial gut feeling would have me try something like the included KiCad screenshot (I can post the footprints for anyone interested).

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 31, 2014, 04:41:29 pm
content: Quote from: EEVblog on October 31, 2014, 01:28:03 pmMy mistake, that was for payments, I was in the wrong part of the site. I've sorted it now

author: zapta
author_rank: Super Contributor
timestamp: October 31, 2014, 05:36:45 pm
content: Would be interesting to discharge a 2.5KV capacitor through the spark gap and see what is the end voltage of the capacitor. I presume that once it starts conducting at the breakout voltage it keeps conducting at lower voltages as well.

author: f4eru
author_rank: Super Contributor
timestamp: October 31, 2014, 06:13:40 pm
content: A tip to mention : put this structure on the component side (TOP in this case), so you don't risk to short it or to contaminate it with flux when soldering.

author: 2shy
author_rank: Newbie
timestamp: October 31, 2014, 07:14:31 pm
content: There's a nice app note on designing for ESD and EMC from NXP:http://sa.nxp-lpc.com/docs/an10897.pdfOn the 22nd page they wrote a little bit about spark gaps, including the formula that Dave showed in the video. Unfortunately I couldn't find the formula regarding the air humidity.BTW, it's my first post here, so hello to everyone

author: StefanHamminga
author_rank: Contributor
timestamp: October 31, 2014, 07:53:59 pm
content: I wonder if the reduced static charge buildup due to the higher conductivity of humid air has something to do with not factoring in humidity in this rule of thumb?

author: sebmadgwick
author_rank: Regular Contributor
timestamp: November 01, 2014, 08:47:32 pm
content: Is this also applicable to battery powered devices? If so, then why would the spark arc to battery ground given that this is just a arbitrary voltage level, presumably just as arbitrary as the IC pin?

author: eV1Te
author_rank: Regular Contributor
timestamp: November 02, 2014, 04:08:13 am
content: Someone mentioned the altitude rating for some equipment, the breakdown voltage is directly proportional to the air-pressure at normal conditions, so at 5000 m ASL the breakdown voltage is about half, (since the pressure is about half) which might affect equipment that uses higher voltages. Electronics in weather balloons etc. where highly susceptible to breakdown when people were still using vacuum tubes.Interestingly for very small spark-gaps or at low pressures, the breakdown voltage increases with reduced distances or pressure, because the electrons do not have time to "find" an atom to collide with.Take a look at this Paschen Curve for example, the X-axis is = spark-gap distance times pressure (bar*cm) (half distance requires twice the voltage), at a distance of 10 um at sea-level the breakdown voltage would starts to increase. So if you would increase the altitude of the device, then the breakdown voltage would actually increase instead of decrease. This only works down to ca. 1-5 um, then field-emission starts to happen.

author: alper.y
author_rank: Contributor
timestamp: November 02, 2014, 06:45:16 pm
content: Quote from: coppice on October 31, 2014, 11:31:12 amThanks.So this difference shouldn't affect breakdown voltage, right?

author: SeanB
author_rank: Super Contributor
timestamp: November 02, 2014, 07:03:13 pm
content: It does affect it, as the solder mask is an insulator, so it raises the breakdown voltage of the gap. When it does break down the solder mask decomposes and leaves a carbon film which reduces the insulation resistance, so that it will either break down at a lower voltage or will conduct continuously.

author: alper.y
author_rank: Contributor
timestamp: November 03, 2014, 07:23:00 pm
content: Quote from: SeanB on November 02, 2014, 07:03:13 pmI didn't understand fully. Since both pads are exposed to air, even if there is an extra insulation layer between them on the board, I don't expect rise in breakdown voltage. But almost all sources suggest not putting solder mask between pads. I am not sure that it is suggested considering breakdown voltage or other issues like carbon film traces as you mentioned.Thanks

author: alank2
author_rank: Super Contributor
timestamp: November 14, 2014, 01:07:11 am
content: So the idea that you want to protect certain nets by giving them a way to arc over to board ground, right?Q#1 - Would this mean that you would preferrably have a TVS on the main vcc net and ground that could soak it up? Or does the arc itself lose some of the power? Or both?Q#2 - Is there a benefit to putting a spark gap on a net you want to protect that already had a TVS protecting it? Is there a benefit to having both?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 14, 2014, 07:35:58 am
content: 1. The current from the transient has to go somewhere. If your power supply already has a very low impedance, even at surge frequencies (ESD has a rise time in the nanoseconds) and for large currents (an 8kV ESD spike is some 16A peak), you don't need to worry.There's also the matter of surges, for circuits that are connected to very long wires that may be subject to induced lightning transients, or full blown strikes (which includes telephone and mains lines, but Dave's recent home security module teardown illustrates another example). These surges are much longer duration and lower impedance, and so contain far more energy. Even a very low impedance power supply is unlikely to stomach this much energy (a small 8/20us pulse with a peak of 10A will charge a 100uF capacitor by maybe 2V), so it needs to be dissipated with a TVS instead.2. There could be, but note that a spark gap won't fire unless the voltage across it gets high enough to trigger. If this never happens, the spark gap was wasted time, effort, space and (if using GDTs) money.A very robust system might be constructed thusly:- Pin to the outside world- Spark gap- Series impedance (air cored inductance, resistance: as much of each as is tolerable)- MOV or TVS (the bigger the better, given limits of capacitance)- More series impedance (including ferrite beads if needed for EMC)- TVS or clamp diodes- Filter cap(s) or band limiting parts (for bandwidth reduction (e.g., radio antenna input, scope front end, etc. etc.) or EMC)- Series resistance- device (transistors, ICs, etc.).Very fast and large pulses cause enough voltage drop across all the series impedances to cause breakdown of the spark gap. This occurs for anything from ESD (fast, short) to sufficiently powerful surges (slow, but lots of peak current and voltage).What's left after the spark gap ranges from short blips of manageable amplitude (the absorbed ESD spark might go from 8kV, 16A and 50ns down to 2kV, 16A and 5ns, followed by a "drool" of maybe 100V and 100ns) to nothing at all (a sufficiently small surge will never spark, and goes through the first series impedance unaffected).The second stage is capable of absorbing lots of energy (MOVs are a cheap source of energy capacity, but high in capacitance; avalanche TVSs of comparable ratings are very expensive; thyristor type TVSs have good ratings but can latch on and blow fuses), but at a relatively high voltage drop (plan on a peak voltage up to three times the MOV rating).The third stage reduces the excess voltage of the second stage, bringing it down to manageable levels for the device.The final stage is always the device itself being protected. No practical surge protection system will fully control the transient, and some will always appear at the device. If the device can ride out some voltage, but must carry zero current (example: unprotected MOSFET gates), the transient protection must reduce the transient to no more than that voltage. If it can shunt some current, it also becomes part of the protection system (e.g., input clamp diodes, CMOS outputs). Some circuits don't mind much either way (a discrete audio amplifier built from BJTs and resistors will draw some current when driven beyond normal range, but rarely anything destructive by the time the protection system is doing its job; such circuits, historically speaking, have rarely if ever bothered with ESD protection at all, anyway).Finally, the purpose of properly designed protection is to limit those transients to the device ratings, as sufficient for the equipment specifications (how much a beating it can take, and whether it must remain functional during or after such events).- Consumer junk rarely uses TVSs at all: they can use chips with built-in ESD protection, and the attached power supply handles surges.- Professional stuff usually has adequate protection (one MOV or TVS, some series impedance as applicable).- Two stage protection is occasionally seen in special purposes. Example: CRT monitors, where internal breakdown in the CRT can deliver over 20kV at impedances much lower than an ESD test, and where the protected circuit (video amplifier) must have absolutely minimal loading capacitance.- Three and four stage protection are the gold standard, but rarely if ever used simply because it's not necessary. Some examples might possibly include military gear that has to survive rough handling, machine model ESD, radar bombardment and jamming, and nuclear EMP, where operation must continue without any reaction or interruption during such events. But I haven't seen such equipment up close, so I don't know what they use.Tim

author: mfeinstein
author_rank: Contributor
timestamp: November 16, 2014, 07:48:17 pm
content: Hey Dave,Two things I think are important to comment about this technique:1- This won't be recommended in high-speed lines, since this "stubs" could cause some signal integrity issues like reflections and distortions. (stubs on high-speed traces)2- Be careful with these exposed pads just sitting so close with the exposed ground, your soldering process could short them out, since there won't be a solder mask to avoid the solder bridge. (solder bridges)

author: pugglewuggle
author_rank: Contributor
timestamp: November 24, 2014, 05:46:57 pm
content: Dave,I'd really like to see a video or series of videos on input protection just as you suggested. It'd be great to see this for both analog and digital (high speed and low speed, busses, etc). Maybe some tidbits on protecting against impulse/ESD vs slow ramping overvoltage vs long periods of overvoltage.

author: max666
author_rank: Frequent Contributor
timestamp: November 27, 2014, 08:28:03 pm
content: Quote from: pugglewuggle on November 24, 2014, 05:46:57 pmseconded

author: eneuro
author_rank: Super Contributor
timestamp: January 24, 2015, 05:09:53 pm
content: Quote from: coppice on October 31, 2014, 01:44:59 amJust made such test ESD gap PCB to connect in parallel to transformer primary coil.Thinking how to finish this copper surface and make some kind of sharp edges between two sides to make this breakdown voltage >400V <1000V at 230VAC 50Hz mains between two sides in normal conditions.The best idea for the moment is in my opinion just solder small copper wires about 10mm-15mm long 1mm-1.5mm in diameter, connect those two sides in clossest designed places and then... simply cut them after soldering to leave some small gap.Those copper wires could be easy to replace if after a few sparks events they were damaged somehow...Any better ideas how to make those ESD PCB gap small, but still be able to refresh spark hitting area without replacing whole PCB?

author: max666
author_rank: Frequent Contributor
timestamp: January 24, 2015, 11:25:22 pm
content: Quote from: eneuro on January 24, 2015, 05:09:53 pmNice PCB spark gap.But if you plan on something easily replaceable or able to take multiple strikes, I don't think a PCB spark gap is the right tool for the job. I would use a gas discharge tube if you plan for more than the exceptional strike.

author: eneuro
author_rank: Super Contributor
timestamp: January 31, 2015, 04:08:57 pm
content: Quote from: max666 on January 24, 2015, 11:25:22 pmAnyway thosedatasheet: Gas Discharge Tube (GDT) Productsfom there:http://www.digikey.com/product-detail/en/CG21000L/F2731-ND/950212looks like has limited to 400 operations life span or missed something?Made also slightly different PCB ESD very simple gap like below, just by soldering 2cm long 2.5mm2 copper wire to PCB and cuted in the middle and adjusted at the height to get given gap size:Cut copper wires edges are very sharp and gap width can be corrected when a few sparks events will destroy small amount of copper, so it looks like it can be easy to inspect from time to time and make adjustments when needed.Those sparks shouldn't happen too often.However, probably it will be good idea to put this thing into thermal cover and isolate somehow, else spark could ignite something in the presence of dangerous gases, etcIn the case of gas tube I have no idea how to verify its working condition after a few sparks while nothing visible and closed inside not glass tube

author: SeanB
author_rank: Super Contributor
timestamp: January 31, 2015, 04:35:28 pm
content: It is intended to be used a protective device, so a limit of 400 operations is no problem. You would find that they will last a lot longer with lower energy put in, and in most applications they typically will be run at a reduced energy due to the wiring resistance and inductance. 400 cycles minimum at a defined test pulse is not bad, equates to around 5 years typical in most areas with lightning strikes nearby.If you are in an area with higher storm frequency you will probably have had the phone lines and local power lines buried decades ago by the utility to keep them from being damaged, so the surges will be a lot smaller and easier to clamp. If not then you will have to cascade the devices to provide protection.In most cases you will find that the surge protection provided in the package with a new ADSL modem or cordless phone is typically not used, or not connected correctly. Only after the first warranty claim that is refused ( and they do do that now as they get frequent complaints from areas so will ask for that as well for the warranty, no SPD installed ( they can see if it has operated) and no warranty, buy a new and here is your bill for time) are they installed and used.

author: JuKu
author_rank: Frequent Contributor
timestamp: February 21, 2015, 02:06:55 pm
content: Quote from: alank2 on November 14, 2014, 01:07:11 amKind of, but a spark gap alone is not sufficient.QuoteThe purpose of a spark gap is to protect the real protection circuitry (and sometimes, allow for cheaper protection scheme). A spark gap takes 10's of kilovolts away, sometimes single digit kilovolts, but even a few ten volts can kill sensitive circuits.In a product test we had a spark gap, 100p to gnd and low power schottky diodes to rails. That was cheap and sufficient. 50kV lightning sustained to connector - As the product designer, it was rather scary to look, but the input pin didn't see more than rail voltage. Without the spark gap, the schottkys turned to ash. (And the inside of the IC as well I suppose, even though I didn't see it. But the IC was certainly dead.)

author: max666
author_rank: Frequent Contributor
timestamp: February 23, 2015, 11:56:49 am
content: Quote from: 3roomlab on February 22, 2015, 02:27:49 pmhttp://youtu.be/KXbz2KUr8HQ?t=9m2sBut when you say "rated to trigger at 125v" I hope you don't mean for using them to protect mains 120 V? Because the trigger voltage of neon tubes can vary substantially, even depending on environmental conditions. Quoting from wikipedia here "Most small neon (indicator-sized) lamps, such as the common NE-2, break down at between 90 and 110 volts".Also keep in mind once a neon tube is triggered it won't shut off until the voltage falls below about a third of the striking voltage.

author: max666
author_rank: Frequent Contributor
timestamp: February 24, 2015, 09:48:46 pm
content: Damn it! I did deliberately burn out a NE-2 (or at least very similar) once, but I can't remember the values.The only thing I can say for sure was that my electrophoresis power supply didn't have enough current to destroy it and it goes up to 400 mA. So I paralleled it up with my lab supply (with a reverse protection diode of course) and I further increased current slowly until the electrodes melted.I think the current was more than 1 A and it couldn't have been more than 2 A, because that's the max of the lab supply. What's really interesting is that the electrodes started melting from the top (at the bottom are the leads which allow heat to be better carried away), and forming a little ball at the end of each electrode, which moved down and got bigger as the melting went on until the two balls touched and shorted out the leads. Of course that was a really slow burn out, so surge behaviour might be completely different. That shorting behaviour however would be really great for a protection device, because with a fuse it would separate the circuit if the neon lamp got overloaded, but again I don’t know if it does that for surge overload reliably.If you want me to replicate the burn out or test something similar let me know, I still have some of the old neon lamps lying around.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 25, 2015, 02:03:45 am
content: Oooh, that sounds fun.Once upon a time -- think I was about 10, I had some neon lights laying around; of course, you only power these with a resistor. You use a large resistor for dim, or a small resistor for bright intensity. Well, I figured, how bright can they get? One neon, two little metal leads, two slots in the wall receptacle.... *POP*I recall never finding any of the glass, only a single rod electrode in my lap.Under slightly less strenuous conditions (like discharging larger and larger capacitors into them), the glow discharge turns from a brighter orange glow, to "sparkier" colors like blue -- presumably, all the gas is becoming singly ionized, and higher ionization states are being produced, with corresponding color changes. I forget how many uF (and V) it takes before damage starts happening; I think the blue spark threshold is around 200V and either 1uF or 10uF?

author: eneuro
author_rank: Super Contributor
timestamp: April 18, 2015, 04:48:47 pm
content: Quote from: max666 on February 23, 2015, 11:56:49 amJust wondering if another PCB on top will create enclosure with edges filled with solder, etc, than a few strikes inside this thing can increase temperature and lower air break voltage, I guess?It was a little bit art work, but final esd gap like this could have copper traces cut on laser CNC and put inside two PCBs to (like one bottom here) spot welded using 1000A pulses, to glue everything together and catch air at given humidity insideThis way ESD from sharp edges could hit into 1mm copper plate walls inside between PCB top/bottom wallsIn this prototype, probably will add on top another PCB with 4 holes and screw them together.Now thinking, how to test this thing-probably will use transformer from microoven teardown and add a few stages of a few kV voltage doublers to make something like preconditioning-hit a few HV strikes to ensure this ESD gap copper rings soldered later will enable breakdown at lower voltage laterProbably this is not needed if 1mm CNC copper plates will be used instead of this temporary copper rods and solder art work

author: SeanB
author_rank: Super Contributor
timestamp: April 19, 2015, 10:39:53 am
content: Or you could just use a gas discharge tube that likely will have both higher surge capacity, higher current handling and more importantly a much more predictable breakover voltage that does not change with ambient air pressure, temperature, composition and humidity.

author: sxanthony06
author_rank: Newbie
timestamp: August 21, 2019, 08:47:11 pm
content: I have a few questions about the material of the first PCB showed in this video. I am studying Electrical Engineering and we need to build high voltage circuits that aren't suitable for breadboards. I have seen this type of board in power supplies we have at the university. So my question is: is this a normal FR4 laminate like they sell on DigiKey and other vendors with the top layer coated with a light yellow soldermask with black silkscreen on it or is this entirely another kind of material? If the latter, where can I buy it?

author: EEVblog
author_rank: Unknown
timestamp: August 22, 2019, 01:32:16 am
content: Quote from: sxanthony06 on August 21, 2019, 08:47:11 pmJust standard FR4 type PCB material.For really high voltage stuff you use routed out slots, so you get genuine clearance instead of creepage paths across the board.