BBQ electronic igniter: it generates DC or AC sparks? - Page 1
Forum section: electronics / projects

author: mcinque
author_rank: Unknown
timestamp: September 09, 2014, 12:02:50 pm
content: I'm stuck in some experiments to understand if I'm doing well for making my device tolerant to ESD.But I can't afford an ESD gun(I know: this is a major problem) so I'm tring with a cheap BBQ electronic igniter but I think I'm missing something...Before applying the ESD protection to my circuit, I've setup a simple spice simulation using a pulse generator that drives a 4KV 4nS pulse into an entry point to see if the ESD protection is ok.As expected the pulse is properly clamped by the components (I've tried RC filters and TVS).But in real life, it's a total fail: no clamping at all and the device resets or hangs.Suddenly I've start to realize that maybe this damn BBQ electronic igniter IT IS NOT generating high DC voltage, but possibly only AC...What do you think? (except that I'm using the wrong hardware?)Can I trust a BBQ igniter as a SIMPLE, BASIC electrostatic gen?

author: mzzj
author_rank: Super Contributor
timestamp: September 09, 2014, 12:24:50 pm
content: Battery powered or piezo ingniter?I would guess that it is ac. Ingniter output is probably more harsh test than esd gun, voltage is more like 20 to 40 kv and i guess available energy levels are also considerably higher. But Good esd and emi shieldind should handle it anyways.

author: ignator
author_rank: Regular Contributor
timestamp: September 09, 2014, 01:56:26 pm
content: The igniter produces AC damped oscillating. No DC. Understand the device has an over center hammer, that hits the piezo crystal. So it oscillates as it recoils from the 'hit'.We used one to pretest avionics, as the official lab test had to use the "feudaldom" engineering support organization and their equipment for ESD, HIRF, and Lightning equipments, and was billed over $1K per hour. If you can pass the the igniter test pulse, you will pass any official ESD required test, as it's an over test (at least for RTCA DO160G Section 25 ESD).Sorry it's been too many years since we measured this with an oscilloscope with a high voltage probe, so I can't give any specifics of the waveform.The biggest problem in avionics was the keyboard area of any cockpit mounted panel. So if your testing for ESD generated by an user/operator, that's where you want to do your injection.

author: Andreas
author_rank: Super Contributor
timestamp: September 09, 2014, 03:15:42 pm
content: Quote from: mcinque on September 09, 2014, 12:02:50 pmNo,thats what I already tried to say here:https://www.eevblog.com/forum/projects/how-to-safely-observe-vcc-behaviour-of-a-dut-with-a-dso-during-an-esd-event/msg494912/#msg494912To verify you should measure the current of your ignitor with a coaxial discharge resistor.(mounted in the wall of a screened cabin).The oscilloscope (>350 MHz) has to be outside the screened cabin. Discharge inside.Measure peak current, rise time, half pulse width and compare that to a normative ESD gun.With best regardsAndreas

author: mcinque
author_rank: Unknown
timestamp: September 09, 2014, 05:09:43 pm
content: Quote from: mzzj on September 09, 2014, 12:24:50 pm1x AAA battery powered.Quote from: mzzj on September 09, 2014, 12:24:50 pmWell, that's what I guess. In spice the components are clamping (as expected) the pulse while in real world they're not doing their work at all. Maybe I'm experiencing EMI issues? If so, even a simple in-air discharge should produce that effect, don't you?Quote from: ignator on September 09, 2014, 01:56:26 pmThis model is an electronic igniter, it doesn't have the piezo crystal. It produces sparks every 1/250s simply powering it with a AAA battery. I guess it's a basic transistor oscillator that drives a 1:1000 transformer and a capacitor.Quote from: ignator on September 09, 2014, 01:56:26 pmOf course I'm testing only the "entry points": keypad, buttons etc, thank you for the advice.Quote from: Andreas on September 09, 2014, 03:15:42 pmAndreas, I apologize for not reading properly that post.Unfortunately I don't have a >350MHz oscilloscope, nor a proper shielded chamber. I know I'm lacking of equipment... Maybe there is some cheap, rude method to produce a proper electrostatic discharge (Van Der Graaf generator?)

author: Zero999
author_rank: Super Contributor
timestamp: September 09, 2014, 07:25:02 pm
content: An electronic ignition will probably produce a damped AC pulse.The ignition probably has two stages: a blocking oscillator, similar to that used in xenon flash unit and a high voltage ignition, consisting spark gap, neon or thyristor connected to the ignition coil When the button is pressed, the blocking oscillator boosts the voltage to a couple of hundred voltages and charges a capacitor. When the voltage on the capacitor exceeds a certain voltage, the spark gap or thyristor fires, discharging it through the ignition coil. You'll probably find the spark rate decreases, as the battery voltage drops, rather than the sparks getting weaker.Unless there's something to prevent the reverse current flow, the output voltage will oscillate a bit, after each spark. Try connecting a neon lamp to the output of the ignition. If both electrodes glow, it's certainly AC but if only one electrode glows, it's definitely DC. Of course it's just as likely both electrodes will glow, just one brighter than the other which indicates an asymmetrical AC waveform.

author: mzzj
author_rank: Super Contributor
timestamp: September 09, 2014, 08:12:05 pm
content: Quote from: mcinque on September 09, 2014, 05:09:43 pmMaybe you can post your spice schematic so that we can take a look if it looks sensible.Yeah, i think you should be able to tell EMI issues with a in-air discharge at similar distance from the UUT.

author: Zero999
author_rank: Super Contributor
timestamp: September 09, 2014, 08:38:19 pm
content: See this link for a schematic of a typical 1.5V powered ignition I was taling about before.http://ridders.nu/Webpaginas/pagina_blokker_vonkcircuit/blokker_circuit_frametekst_engels.htm

author: amyk
author_rank: Super Contributor
timestamp: September 10, 2014, 03:05:00 am
content: Quote from: mcinque on September 09, 2014, 05:09:43 pmDepending on the type of oscillator and whether the transformer's output is followed by a voltage multiplier, it could be either pulsed DC or AC.

author: calexanian
author_rank: Super Contributor
timestamp: September 10, 2014, 04:09:42 am
content: Now that i am thinking about it. Its actually a really deep question with perhaps not a simple answer. How do you model it. Many things at play. Inductive reluctance/reactance, leakage currents, hysteresis of the core, permeability of an magnetic material, non linear load. negative resistance (When the arc happens) flyback emf. All of a sudden a little electric spark is not so simple. A piezo one is actually quite complicated on a physics level.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 10, 2014, 05:16:46 am
content: Yes, a real world example (piezo or inductive) will have many interesting bits in the signal path.My mind fills with vapor as I read:Quote from: mcinque on September 09, 2014, 12:02:50 pmWell what did you expect it to do? You're the engineer who built the model; you should already know what it was going to tell you.The real question is (and which SPICE cannot help you with, aside from showing you something that's different from what you measured, if you measured at all), did you construct your simulation model to be sufficiently representative of the real world? And I'm betting not (because to be fair, doing a thorough job of it for just a small range of the full operating space, is HARD).Examples that come to mind:- Are your TVS models realistic? If junction diodes, do they incorporate forward recovery effects? (No -- at least, no SPICE model of a diode I've ever seen includes this!)- If you used latching type TVSs (GDTs, thyristors), do you have adequate models of those too? (Dunno -- possibly not; they're hard devices to model, period!)- Have you modeled ESL, parasitic C, or even transmission line effects, of your real circuit layout? (Hint: you can't place a TVS just anywhere: if it's hanging off an inch of trace going nowhere else, it's going to do hardly anything!)- Do you have a realistic model of the power distribution network (relevant to clamp diodes)? Do you have bypass caps nearby or not, and have you correctly modeled the ESL, ESR and so on?- Did you model the source adequately? An ESD gun is NOT simply a PULSE voltage source, nor is it as simple as the capacitor-and-resistor cartoon given in the standards (there's no possible way a pure RC network would produce the transient waveform also specified, and there's no way a pure RC network would be representative of a real event, or a real test device, anyway!)- If you have series resistors on input pins, have you modeled their breakdown (if applicable)? Chip resistors are normally rated for around 100V (varies with size), but might arc over closer to 1000V. Likewise, if you have series inductors or ferrite beads, have you modeled their saturation? (Ferrite beads suck if they're carrying any DC or peak AC current at all, and definitely will saturate in the face of a monster ESD wavefront!)- Just one of many possible nonlinearities that SPICE may forget: BJTs won't draw infinite current, there's a current-crowding phenomenon which causes hFE to fall off at high currents. You can use a zener into a BJT as a clamp (or submit ESD to a BJT structure, say a discrete amplifier input pin), but it won't necessarily behave the way you think it will under such strenuous conditions, even if the simulation says it will be okay.- Obviously enough, there's no way for SPICE to know when a device has been stressed to failure. If your definition is "parameters (voltage, current, power, etc.) beyond datasheet ratings", then everything is failed immediately, because that is the nature of an ESD or surge event. The failure mode is generally progressive, where microscopic portions of the stressed components have been damaged in some way (if measurable, usually manifest as increased leakage current). Manufacturers' reliability data, inferring from controlled test conditions, is usually the only good way to estimate this sort of damage (which isn't saying much).The list goes on and on. There are many things that SPICE can and cannot do; it's up to the engineer to figure it out. Often, back-of-the-envelope calculations are much more informative (to-the-point and relevant, without wasting time on excessively complex models, that are poorly defined to begin with!).Tim

author: Andreas
author_rank: Super Contributor
timestamp: September 10, 2014, 07:37:32 am
content: Quote from: mcinque on September 09, 2014, 05:09:43 pmHello,most probably in your modeling the components are used in differential mode.(your pulse source is connected between input and ground of the cirquit).ESD is also a problem of common mode:The erratic pulse is created by a (large) current along the ground ( and VCC) inductivity of your cirquit.1 cm of ground line gives 10nH inductivity. dI/dt may be up to around 1Amps/1ns (within cirquit from 8000V/330 Ohms from the generator) creating a voltage difference of 10V along 10 mm of ground line.If you want to understand how EMC works you will have to understand how the RF-current flows.(along ground inductivity and through parasitic capacities eg. at the crystal housing of the processor).With best regardsAndreas

author: mcinque
author_rank: Unknown
timestamp: September 10, 2014, 10:47:40 pm
content: Quote from: T3sl4co1l on September 10, 2014, 05:16:46 amYeah, that's the point. Like you said, probably not.Quote from: T3sl4co1l on September 10, 2014, 05:16:46 amDamn, all your thoughts are so damn appropriate. They makes me realize that there is many factors to take in consideration. Probably more than I can handle.However, attached is the ESD protection I've choosen for the MCU pins that can be affected by ESD (entering from the keypad for example).Keep in mind it's a basic design only to show the idea.The TVS clamps positive peaks while the zener the negative ones, and the filter capacitor act as a current/rf limiter.In real life, this doesn't work, (but remember I'm using a cheap BBQ electronic igniter -the manufacturer specify >12.000V output): the board act like if the power supply goes to zero for a uS resetting the MCU.One important thing that probably I forgot to mention is that my design is battery powered circuit, housed in a non conductive shielding, so there is no discharge path to the ground.I've properly bypassed the MCU and the IC used on the board, so I can't really understand why with a clampling circuit like the one attached, the discharge isn't clamped by the TVS or the zener and filtered by the 0.01 cap.I really like to observe with my DSO what happens during the discharge, but I've not the equipment to do it (shielded chamber and high voltage probe). I'm not an engineer, so I lack in knowledge, but If I could see what's happening during the discharge event I'm confident I could understand where I should work in my design.In the next days I will attach my circuit (even if it's so simple that probably it doesn't make any difference) to make you see better and maybe allow to give me some advices.

author: mcinque
author_rank: Unknown
timestamp: September 10, 2014, 10:51:44 pm
content: Quote from: Andreas on September 10, 2014, 07:37:32 amThank you Andreas, do you have some advice on readings to download/purchase about the argument?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 10, 2014, 11:48:46 pm
content: Quote from: Andreas on September 10, 2014, 07:37:32 amYes, you can induce ESD type upsets in a circuit without any contact at all. Holding the ground wire from the "ignitor" near the tip (so it sparks to itself, but not to the circuit, and has no electrical connection to the circuit), and holding that loop near the circuit, is often enough to do all sorts of things.Tim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 11, 2014, 12:24:24 am
content: Give this a look:Exact values for the "pulse forming network" are of course impossible to determine for sure; IEC 61000-4-2 usually has a double-hump sort of wave, which might mean a small inductor towards the tip (lead inductance only?), a little capacitance up front (maybe 10-30% of the total 150pF?), then some more inductance (~1uH??) before the rest.I emphasize the diode inductance, because manufacturer models rarely attempt to describe it (they're usually either a simple .MODEL only -- the ideal SPICE diode component, no parasitics -- or a .SUBCKT containing several components, to better emulate breakdown or reverse or leakage characteristics), and the exact value is subject to your layout anyway. So it's usually a good idea to express that inductance in your circuit, manually (rather than relying on a model, even if you were so adventurous as to build your own .SUBCKT with ESL included).More hints,http://www.littelfuse.com/~/media/electronics/application_notes/esd/littelfuse_tips_for_enhancing_esd_protection_application_note.pdf.pdf

author: Andreas
author_rank: Super Contributor
timestamp: September 11, 2014, 09:35:05 am
content: Quote from: mcinque on September 10, 2014, 10:47:40 pmHello,With plastic housings the best strategy is not to let ESD pulses to come into the cirquit. (Use a foil in front of the keypad with enough isolation around the edges). For the magnetic fields of ESD you have to route your sensitive signal lines in pair with ground to minimize loop (antenna) area.your measures work only against destruction of the pins not against secondary (common mode) effects like resets.The EMC effects have much to do with construction of the board so a circuit diagram is by far not enough to judge EMC stability. You have for e.g. look after your star-points of your ground paths from ESD entry point with respect to large parasitic capacitances (battery, X-TAL, electrolytics, heat sinks etc.)If you have reset pulses I would first put a 1-10nF capacitor from reset pin to gnd pin of the processor (on the shortest possible path). If you have a X-TAL this might also be a source of problems. (stray capacitance).Measures agains ESD can sometimes also be done in software:It is often not necessary that there is no malfunction during ESD pulse (if there is no risk/hazard for the user).But after ESD-pulse the device should work in the same operation mode (and perhaps without data loss) as before.And no I do not know a good book. All I have are experiences from the "valley of tears" = EMC-lab.If you have a good lab they should be able to give some advice individually for your circuit / construction.With best regardsAndreas

author: mcinque
author_rank: Unknown
timestamp: September 11, 2014, 11:36:44 am
content: T3sl4co1l and Andreas, I really appreciate the time you spent writing your replies.T3sl4co1l, thanks a lot for your notes on the JPG, I will try to modify the circtit ASAP and make you know the results.Thank you also for the specifics you posted and for the link.Andreas, thanks for your advices and for pointing that "your measures work only against destruction of the pins not against secondary (common mode) effects like resets."Quote from: Andreas on September 11, 2014, 09:35:05 amIndeed, but I'm using a (metal) key switch to turn on the device, and I've noticed that a simple discharge over the key brings to reset of the MCU (clearly the spark jumps to the circuit thru the key switch), so I must do something to avoid it.Quote from: Andreas on September 11, 2014, 09:35:05 amI guess this foilshouldn'tbe floating, right?Thank you all again, i really appreciate the time you're spending writing the replies!

author: Andreas
author_rank: Super Contributor
timestamp: September 11, 2014, 02:12:31 pm
content: Hello,I thought of a plastic (isolation) foil for the keyboard.But with your metal key switch you are set.One possiblilty is a metal foil (may be floating) connected to the switch housing surrounding all the remaing electronics (faraday cage).So no voltage difference within the cirquit is possible. All parasitic capacities go to the faraday cage.If the remainig cirquit is not sensible to the magnetic field then this would be the solution.With best regardsAndreas

author: Zero999
author_rank: Super Contributor
timestamp: September 11, 2014, 08:43:10 pm
content: Quote from: mcinque on September 11, 2014, 11:36:44 amTry connecting the metal part of the key switch to either supply rail.

author: jlmoon
author_rank: Unknown
timestamp: September 11, 2014, 09:35:29 pm
content: Quote from: ignator on September 09, 2014, 01:56:26 pmI would venture to say the BBQ 'piezo' igniter generates a pulse similar to a bell that has been struck.. High energy with very fast decay rate.

author: mcinque
author_rank: Unknown
timestamp: September 16, 2014, 11:47:29 am
content: Well, using your advices I've apparently (I'm on PCB/breadboad testing) solved. I'm gonna try with a PCB only version (without breadboard and jumper wires that adds a lot of capacitance).By now, thank you all!