1 1
sle118

Mistakenly plugged in 12V - What could go wrong?

Recommended Posts

I used the wrong power adapter this morning on one of my OPI PC... what could go wrong?

 

So far, I noticed that the poor U5 - SY8008B regulator overheated and blew. From the schematics, this seems to be connected to "AVCC" (the H3's PLL and the TV out). 

 

U11 isn't outputting anything, but chip select is off. Since this is the USB host, I'm not too surprised.

 

Is it worth trying to reflow a new regulator on ? Wondering...

Share this post


Link to post
Share on other sites

First RPIs had a Poly Fuse which I think could "recover" after a time. It seems it may have been useful in your case - but there don't use that in those boards ?

Share this post


Link to post
Share on other sites

First RPIs had a Poly Fuse which I think could "recover" after a time. It seems it may have been useful in your case - but there don't use that in those boards ?

Polyfuse would save from overcurrent, but I'm not sure it will offer enough protection from overvoltage - for this there are protection diodes (that are designed to absorb enough current to blow the fuse).

 

Is it worth trying to reflow a new regulator on ? Wondering...

You can try to desolder the old one first, then check for any short circuits and maybe soldering any similar voltage regulator with short wires to check if SoC and DRAM are still alive.

Share this post


Link to post
Share on other sites

Polyfuse would save from overcurrent, but I'm not sure it will offer enough protection from overvoltage - for this there are protection diodes (that are designed to absorb enough current to blow the fuse).

 

 

Yes, that is how it is mounted on a RPI : a Polyfuse before the 5V zener diode. So I think a RPI A/B would survice 12V power and take some time to recover. But what about Chinese boards ?

 

But, I also think there is a drawback : if the resistance of the Polyfuse increase after blow/recover, the total resistance in your power supply may become excessive.

Share this post


Link to post
Share on other sites

But what about Chinese boards ?

Opi PC has a protection diode on the schematic (well, a lot of those - for DC IN, USB, OTG, ...), but looking at all my Orange boards - they are not soldered  :angry:

In any case there is no fuse so all would depend on whether power supply had any overcurrent protection

Share this post


Link to post
Share on other sites

Opi PC has a protection diode on the schematic (well, a lot of those - for DC IN, USB, OTG, ...), but looking at all my Orange boards - they are not soldered  :angry:

In any case there is no fuse so all would depend on whether power supply had any overcurrent protection

 

Well if PSU can give 2A and zener needs to a dissipate 10W in a SMD ? Pshittt ?

Share this post


Link to post
Share on other sites

Well if PSU can give 2A and zener needs to a dissipate 10W in a SMD ? Pshittt ?

I'm not calling these things a Zener diodes because they are TVS/protection diodes designed for slightly different use cases. Look at this datasheet for example characteristics: http://www.littelfuse.com/~/media/electronics/datasheets/tvs_diodes/littelfuse_tvs_diode_smbj_datasheet.pdf.pdf

 

Sure, it can't dissipate 10W for a long period of time, but it can either "Pshittt" and short or "Pshittt" and open. First case - power supply won't be happy, second case - the board won't be happy.

Share this post


Link to post
Share on other sites

I'm not calling these things a Zener diodes because they are TVS/protection diodes designed for slightly different use cases. Look at this datasheet for example characteristics: http://www.littelfuse.com/~/media/electronics/datasheets/tvs_diodes/littelfuse_tvs_diode_smbj_datasheet.pdf.pdf

 

Sure, it can't dissipate 10W for a long period of time, but it can either "Pshittt" and short or "Pshittt" and open. First case - power supply won't be happy, second case - the board won't be happy.

 

Yes, if I understand well, this is a protection against transient voltage and not for powering mistakes as it can only dissipate 5W on long periods. So one has to be cautious ...

 

PSU are supposed to have over current and shortcut protections. And I hope it works because I prefer to loose a  board than to loose a house ... So I don't very much like "noname" PSU, even when sold as "certified for your board" ...

Share this post


Link to post
Share on other sites
Guest
This topic is now closed to further replies.
1 1