Simple Reverse-polarity Protection for Automotive DC-DC Converter: FET or Diode?
If your protecting the 5&nbsp;volt 3&nbsp;amp lines from reverse polarity I would insert an in-line 5 amp fuse for each load. Use a fast blow fuse unless your loads have a high start current, then you would use slow-blow fuses. Install a 6A06 or 6A10 6 amp diode across the 5 volt line on the downstream side of the fuse. The diode has a white line at one end. The end with the white line goes to the (+) feed from the fuse, the other end goes to the (-) or ground return. Do the same to all loads that need isolated protection. If each load draws less than 3 amps then use a fuse with about 50% greater capacity than the load draws. The idea here is that if a reverse connection to the 5 volt power is made, the 6 amp diode will clamp the voltage to maybe -.7 volts at most and the high current will blow the fuse. The diode will survive such events as it is rated twice the supply current.