Simple load dump protecion, is this enough? - Page 1
Forum section: electronics / beginners

author: kjr18
author_rank: Regular Contributor
timestamp: August 15, 2023, 01:41:03 pm
content: Hi, I'm in the process of designing small esp32 powered display for my car, to display additional information or maybe log some data during drive. All of this is to be connected to obd2 port, and placed in small spot between odometer and rpm meter (enough space to put small 1.7" lcd). Power will be taken from diagnostic port as well (somehow in my car pin 1 of obd2 port is switched 12v - checked it with scope), and my question is:Will P4SMA18A TVS with some polyfuse before it will be enough to protect rest of the circuit? Or should I use bidirectional one? And when I checked power with a scope I noticed negative voltage spike when i turned key to off position, somewhere around -16V.Should i use some Shottky in series with fuse or TVS will take care of that for me? For regulating voltage I plan to use AP63203, should be enough for this purpose. As for fuse - will this fuse be too much? I want to use 0ZCG0050AF2C fuse with 500mA hold and 1A trip current.

author: Terry Bites
author_rank: Super Contributor
timestamp: August 15, 2023, 08:40:42 pm
content: A small TVS will be probably destroyed during a load dump event. Something beefier is needed.Have yourself a read of the attached documents.As shown in the TI paper, you can easily cure reverse polarity issues with a simple bridge recitifer.Over voltages are killed by the TL431 comparator /disconnect circuit.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: August 16, 2023, 02:59:59 am
content: The TI paper posted above is great.And before someone post that load dumps are a myth, all it takes is a bad/broken battery cable clamp.

author: EPAIII
author_rank: Super Contributor
timestamp: August 16, 2023, 07:19:15 am
content: Interesting post. I wonder how much auto diagnostic equipment is protected from these dangers. And what about simple things, like LEDs? Are they just more robust than ones used in places like residential lighting? Or do the light circuits in vehicles incorporate the protection?

author: Terry Bites
author_rank: Super Contributor
timestamp: August 22, 2023, 05:26:38 pm
content: Most modern vehicles have to many electronic systems to risk not fitting dump protection.Ask your auto dealer if it comes as standard or if its an extra..."Load dump sir, of course. Just down the corridor to the left."

author: Siwastaja
author_rank: Super Contributor
timestamp: August 22, 2023, 05:31:49 pm
content: Probably not. Load dumps are rare. It's an event which destroys stuff like headlights anyway. Never seen one personally. For an entertainment gadget, you can decide not to implement it. If you decide you need load dump protection, then pay attention to doing it properly. On the other hand, if you are designing say ECU or ABS controller, then obviously load dumps need to be handled.

author: mk_
author_rank: Regular Contributor
timestamp: August 22, 2023, 05:51:24 pm
content: Quote from: EPAIII on August 16, 2023, 07:19:15 amIt`s must if you want your stuff buildt in legal in a car.Modern cars do have e central LD-protection in the alternator which helps a lot. Anyway, it`s not difficult to design a robust protection, the TI-paper shows how.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 22, 2023, 05:52:54 pm
content: Quote from: mk_ on August 22, 2023, 05:51:24 pmThis is clearly a hobby project made completely out of non-automotive qualified parts. As such, there is no such requirement.

author: Neilm
author_rank: Super Contributor
timestamp: August 22, 2023, 06:13:36 pm
content: Personally, I'd use a beefy TVS and a fuse

author: liaifat85
author_rank: Regular Contributor
timestamp: August 23, 2023, 03:15:10 pm
content: Quote from: Heisen on August 15, 2023, 02:05:34 pmI think this option is satisfactory.

author: kjr18
author_rank: Regular Contributor
timestamp: August 28, 2023, 11:47:57 am
content: Quote from: Siwastaja on August 22, 2023, 05:52:54 pmYes, it's purely hobby project, just to add few things.So after reading both documents, simply beefier TVS and some diode bridge will take care of my problems. As board space is kind of issue, I'll put them on separate board.

author: Psi
author_rank: Super Contributor
timestamp: August 28, 2023, 01:15:56 pm
content: For lower current stuff I would definitely recommend a series diode to block rev voltage instead of trying to use a TVS + polyfuse/fuse to clamp it crowbar style.I had issues with 400W SMB size TVS in automotive, ended up changing to a 3000W SMC size version which clamped to 39V. 39V is nice because there's lots of regulator options that are fine up to 40V eg 7805.But for my application I was protecting a power input that supplied 10A to my circuit, so it limited the options. It's much easier if your circuit only needs 500mA for example.If your circuit doesn't need much current you can add a series resistor that will limit the max input current and that also applies when the TVS is clamping, so you can get away with a smaller TVS with lower max current rating.

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 28, 2023, 02:33:41 pm
content: Use a decent automotive DC/DC converter.Some are meant to work at 14-18V under normal circumstances, but they're designed to turn off themselves when the voltage rise too much, widthstanding quite nasty spikes.Use a decently sized TVS with a series polyfuse shoudl do the job.The SMC3K series can stand 3KW peak, but polyfuses can get damaged with really high currents and voltages, so use a decent sized one.The fuse will add some resistance (0.1-0.2 Ohms or so depending on the fuse) so it'll also limit the peak current.

author: kjr18
author_rank: Regular Contributor
timestamp: August 28, 2023, 05:07:01 pm
content: It's not like I need every mV so I'm fine with diode drop, as for power, I think that around 300mA @ 3.3V will be absolute max for ESP32, display and TF card (optional), so current draw will be small enough for even 1N4007 diode. I think that low power TVS would be enough. And one more question: Should I use uni-directional or bidirectional TVS?

author: Andreas
author_rank: Super Contributor
timestamp: August 29, 2023, 05:22:51 am
content: Hello,designing a TVS for load dump is not an easy task.Especially when you also want to cover jump start (from a 24V truck battery).Formerly some beefy diodes like LDP24A (ST) where used for this.In modern cars there is already a Load dump protection in the alternator.This limits load dump voltage somewhere between 40-50V.So I would use a automotive buck converter with a input voltage of 60V (e.g. LMR36506) to be on the safe side.So all what you need is a reverse polarity protection diode (200V) and some input and bulk capacitors.No TVS diode.By the way: a unidirectional TVS diode will be only useful if you have a mains relais as reverse battery protection. (has to be placed after reverse battery protection).with best regardsAndreas

author: Psi
author_rank: Super Contributor
timestamp: August 29, 2023, 08:39:32 am
content: Quote from: Andreas on August 29, 2023, 05:22:51 amThe difficultly designing for load dump is proportional to how much current your device needs.If your device is a low power MCU that draws 20mA max and you want to add load dump protection to it, this is VERY different compared to trying to add load dump protection to a device that needs to pull 20A from the battery.For low current stuff, a few 100mA or so, you can probably get away with a 1 ohm resistor in series then a small 400W TVS to GND that will clamp to 30-40V, (or whatever your circuit can handle, the higher the better). The likelihood you will blow up a 400W TVS with a 1 ohm resistor in series with it from load dump is practically zero. And if your circuit is taking 12V and regulating that down to 5V or 3.3V then you don't care about losing half a volt or so across the resistor.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 29, 2023, 04:51:49 pm
content: Load dump isn't THAT high in voltage, the problem is it's long-duration event so high-energy, if you try to shunt it.The obvious solution is not to shunt it, but to series regulate, which can be simplified to zero "protection components" by just simply choosing the input regulator (which you usually need to have anyway) so that it handles the maximum voltage. 100V max input switch mode converter ICs are commonplace and not that much more expensive than, say, those rated to 30V. Input capacitor obviously needs to be rated to 100V, too (or maybe 80V). If you do that, design is not any more complex and has the same part count as a max 30V design, but will happily ride through not only load dump, but a longer-lasting "load dump on steroids", while staying operational.

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 29, 2023, 09:59:01 pm
content: Quote from: kjr18 on August 28, 2023, 05:07:01 pmThat's all? You can simply add a OVP switch so it disconnects when the voltage exceeds certain value.You should still add a TVS at the output to remove high frequency spikes that might get through.Rougly, the ovp limit calculation is R2/R1*0.6, so 120/4.7*0.6=15V, but it's a bit higher in the simulation giving around 18V.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 30, 2023, 02:33:31 am
content: Simple: since your load is low current, use an LDO of adequate rating (Vin range and power dissipation). Or equivalent circuit, like a depletion MOS voltage limiter.An overvoltage switch-off is also quite reasonable, and can be more compact as it doesn't need to dissipate much power, or is suitable for higher current loads when that should be relevant.If it's not for permanent installation, you might just as well skip it -- aftermarket junk often does so, which among other things of course contributes to poor reputation, but people still buy it at the price.Tim

author: Psi
author_rank: Super Contributor
timestamp: August 30, 2023, 10:09:57 am
content: You can get many automotive regulators that are tolerated of up to 60V transients.Some can even handle reverse battery voltage.Expect to pay 2-4x more than a normal regulator though.

author: kjr18
author_rank: Regular Contributor
timestamp: August 30, 2023, 10:18:37 am
content: It will be semi permanent, as for load dump on steroids, i think when it happens, I'll have other things to worry about. I think I will go with small 400W TVS and some power limiting resistor, all that on separate board, so I can in case of failure replace it with something bigger, without making whole board again. It will take some time, but I will post update when I manage to find enough time for completing this hobby project.Quote from: Psi on August 30, 2023, 10:09:57 amAs I plan to use spare boards (minimum for PCBWay or JLCPCB is 5) for other uses I don't want to automotive parts where I won't use them. It's not like I make things to sell. There are just for me.