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I am building a Pi into some equipment just to drive a display. Now this is normally powered by a USB lead with the usual 5VDC. So I will have to cut the USB cable and put ferrules on the leads (omitting the data lines) to connect to the 5VDC supply on the DIN rail.

The question being, if someone gets the polarity wrong in production, will it destroy the Pi, or is there internal protection? Is there typically internal polarity protection on other devices that take power from USB eg phones? Is putting in such protection feasible given (say) the voltage drop produced by a simple diode? What other protection circuits exist that do not drop voltage (if this is even possible)?

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closed as off-topic by Elliot Alderson, Chris Stratton, Ale..chenski, RoyC, Oleg Mazurov Aug 19 at 16:13

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." – Chris Stratton, Ale..chenski, RoyC, Oleg Mazurov
If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ Why don't you check the schematic? \$\endgroup\$ – Leon Heller Aug 18 at 14:45
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    \$\begingroup\$ I don't think there is a general answer. There is no body that would be able to enforce such a requirement, so you can't assume anything. \$\endgroup\$ – Elliot Alderson Aug 18 at 15:01
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    \$\begingroup\$ Actually, it depends on the model. Some seem to have a polarity protection MOSFET, newer models only have a diode which would simply blow up. \$\endgroup\$ – Turbo J Aug 18 at 15:03
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    \$\begingroup\$ @DirkBruere If this is likely to be a problem, then it looks like an additional step in production to confirm the polarity is correct is would be a good idea. \$\endgroup\$ – Andrew Morton Aug 18 at 16:51
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    \$\begingroup\$ Why not insert a polarity diode yourself when you "have to cut the USB cable and put ferrules on the leads"? \$\endgroup\$ – Huisman Aug 18 at 18:14
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The 3B+ is not intentionally reverse polarity protected. However, D7 could clamp it to somewhere around -1.5V, the forward voltage of suppression diodes is quite high.

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