How do you test for voltage transients? - Page 1
Forum section: electronics / beginners

author: L1L1
author_rank: Regular Contributor
timestamp: January 18, 2019, 05:56:53 pm
content: Hi all,I have designed boards that are supposed to work in noisy environments (e.g. inside a car). Following best practices, I've added input and output protection on my IOs, such as TVS diodes, over-current protection, etc.I was wondering how I can really test in practice my setup for voltage transients?Is there a specific tool to generate voltage spikes? Should I just build a test circuit with a big inductor or something?Thanks,Alain

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 18, 2019, 06:44:00 pm
content: Yes, ISO 7637 automotive transients to be precise. Among others.If you can't afford time at a testing lab (\$$$$), you can look up the standard ($$$, or maybe you'll get lucky finding an unsecured copy online, or you can look up bits and pieces referenced by appnotes) and design around it at least, and maybe design a few tests to approximate or reproduce it.The impulse tests are most relevant to your question, i guess; they are usually modest (100s volts) and so could be easily generated with a capacitor discharge circuit and coupling network.The full standard is quite picky, including some seemingly stupid tests, like cutting power to the EUT and verifying it operates afterwards. Well, the only thing I can think about that is: why is such a stupid test there? Someone, somewhere in history, must've designed a device so idiotically, that it damaged itself when powered down. Who knows...The other thing to keep in mind is: if you're designing for OEM, your product is likely to be made in the millions. A one-in-a-million failure (which is pretty damn good, pushing six sigmas) still means tens or hundreds of failed parts, angry calls from customers / service techs, maybe even recalls. For the most part, OEMs deliver mind boggling quality, with dozens (hundreds?) of systems working together reliably over the life of the vehicle (a decade or so, and often longer).But on the other hand -- if you're only making one-offs, it's probably no big deal to fix or replace it when it fails, and if that gets annoying, consider adding some protection. Or if you're selling thousands, fast transients (including ESD) would be a good idea, but the very rare events (like jump start or load dump), your products might never even see.Tim

author: cdev
author_rank: Super Contributor
timestamp: January 18, 2019, 06:48:39 pm
content: as far as measuring peak transients it depends on what kind of measurement gear you have access to. I have two meters that would give me a peak voltage measurement but neither one is likely to give me any data about the length of the transient. For that a scope set to trigger on the point where the voltage starts to get problematic in the positive direction (assuming your problem is with positive going transients. It also might be possible to have a transient in the opposite direction, thats why a diode for reverse polarity protection is useful in a mobile device).Another low cost tool that might be useful is a data logger that logged voltage at regular instants in time. Thats not necessarily going to capture the peak transient the first time you sample but if you've access to one device to measure peak voltage and another device to see how often/when the peaks occur in time - between all of the above I personally would be satisfied that I had done what I needed to do for a hobby project.As far as generating transients - you likely dont want to have an unpredictable transient, I would personally want my generated transients to be known quantities.. I might try to do it with a transformer secondary in series with the supply to allow the induced voltage to be superimposed over the supply voltage, and I would test the dynamics of the setup with a dummy load (resistance) if possible not my actual device. For reverse transient protection you could use a diode that would shunt any reverse transients to ground and blow an inline fuse rather than let your device receive it.

author: Ian.M
author_rank: Super Contributor
timestamp: January 18, 2019, 07:55:42 pm
content: I made a few suggestions for possible methods to generate load dump transients that could be made fairly close to the ISO 7637 pulse specs, on demand, on the bench in a thread last year:https://www.eevblog.com/forum/beginners/circuit-to-convert-from-12v-automotive-into-a-microcontroller-voltage/msg1611781/#msg1611781I certainly wouldn't suggest the ghetto pulse generator described there as suitable for ISO 7637 compliance testing, but it might be viable for in-house pre-compliance testing.