Author Topic: Never Trust Other People's Equipment!  (Read 2531 times)

0 Members and 1 Guest are viewing this topic.

Offline uski

  • Regular Contributor
  • *
  • Posts: 237
  • Country: us
Re: Never Trust Other People's Equipment!
« Reply #50 on: October 20, 2020, 04:51:32 am »
Last automotive device I designed could handle ~100V sustained at its input for any period of time. In both polarities. And higher for pulses (TVS).
Shipped hundreds of thousands, no noticeable failure rate in the power supply. But it did cost a few extra parts.

Check out IEC 7637-2 for some scary overload voltage waveforms ("load dump") especially for 24V systems (I designed for 12V)
 

Offline uski

  • Regular Contributor
  • *
  • Posts: 237
  • Country: us
Re: Never Trust Other People's Equipment!
« Reply #51 on: October 20, 2020, 04:54:15 am »
I would like to add that you should really add a fuse in your power supply. You decide if you want to put it before or after the TVS (I would put it before, but yes it will blow up if there is a big spike that could otherwise be absorbed by the TVS).

There are failure modes which can lead to a high current consumption and many, many, many people installing devices in cars add high gauge wires like 24AWG, with no additional fuse, on a 10A or 20A line, which can be a fire hazard.
An internal fuse will at least protect the wiring if there is an internal fault such as a MLCC cap shorting or similar. Just my opinion.

Cheapest and simplest is a 0805 or similar non replacable fuse which is what I would install. You could also go with a polyfuse, but I don't really like them since they get really hot in case of failure and also do not turn off the current completely. Or go with a replaceable fuse but most of the time it is not appropriate, you don't want people to start replacing fuses in an automotive PCB.
« Last Edit: October 20, 2020, 04:55:49 am by uski »
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf