Vehicle 12V load dump protection circuit

[kellogs]

https://www.mdpi.com/2624-7402/1/1/2/htm



my questions:

1. What are R1 and C4 for, a low pass filter ?
2. R7 and R9 are a bit low, there is going to be many Watts spent on them; can i make them 10k and 30k instead or will that impact mosfet turn on time too badly ?
3. R8, R6, C3 and  R5. Why are these on the diagram ?
4. Their M3 is a beefy and expensive IGBT module. i would swap it with a PCB TO-220 mosfet and maybe tweak R8 so it limits current through it during the load dump? How far can i push R8 when the load is a 21W light bulb ?

Thanks!

[Seekonk]

I'm wondering more about R6 as they mention inductors. R3 is typical load. R7&9 must be low because of gate capacitance, otherwise turn on would be too slow. I need to spend some time reading this. Most FET would be turning on at this voltage. Even if they didn't the FET could be destroyed by negative and positive spikes certainly over 20V. Zener should be added to gate. They don't show actual design.

[thm_w]

Don't use a paper like this for actual design advice.
Search the forum and read some manufacturer app notes, for more real world recommendations.

https://www.eevblog.com/forum/projects/automotive-(load-dump)-circuit-protection/
https://www.eevblog.com/forum/projects/automotive-dc-protection-(load-dumps-and-such)/
https://www.eevblog.com/forum/projects/load-dump-circuit-reviewimprovements-suggestions/
https://www.ti.com/lit/pdf/snva681

[radiolistener]

R1 probably current limiting resistor

[CaptDon]

That posted schematic is probably the worst 'load dump' spike catch circuit I have ever seen. Looks more like it is designed to kill power mosfets and then burn resistors as an added bonus.

[kellogs]

Ok, I can't get any of the semiconductor designs to work good enough for me. The following setup has nothing to do with the circuit from last year:

How about a MCU + relay based solution ?

- 2 - 10 - [100A (transitory from cold light bulbs)] through relay contacts
- sealed relay, 3ms operate time, unknown bounce time
- relay will operate very close to its 105 deg C limit several weeks per year
- relay will spend most of its life in its normally closed position; perhaps it can get stuck closed over the years ?
- a regular 6.6 kW TVS placed after the relay will take care of the first 10-20 ms of the load dump spike

MCU interrupts as the voltage reaches a certain threshold; afterwards interrupt every 100 us or so and measure voltage until maybe 1ms. Should the voltage be consistently rising in the 15V - 25V range then decide a load dump is going on (and not one of the faster and repetitive transients) and actuate that relay, opening the circuit. Does this sound like it could work ?

Thanks

[Doctorandus_P]

That circuit does look indeed quite horrible.
The murs320 is just a 3A rating, so it will probably act as a fuse when it gets over it's 100A surge current rating.

a relay is also not going to work. As you guessed R1C4 is a low pass filter, and it's probably designed to give the Fet a bit more time to react and short circuit the current. also: IPB144 is a relatively normal FET, and it's IPB147 cousin is in a TO220 package.

https://www.infineon.com/cms/en/product/power/mosfet/n-channel/ipb144n12n3-g/?redirId=120712

https://www.infineon.com/dgdl/Infineon-IPP_I_B147N12N3_G-DS-v02_06-en.pdf?fileId=db3a30432239cccd0122a79a30f57d01

Using a smaller FET or higher series resistor is also a bad Idea. The whole circuit works on the assumption that it is able to short circuit the load dump (which may melt cables instead?)

A combination of a big TVS diode combined with a relay could possibly work, but the relay must be fast enough so the TVS does not overheat and self destruct. The problem with load dump (as I understand it) is that it is a quite fast and high powered transient up to 80V or so.