Reverse Polarity Protection for Dual Polarity supply power

Discussion in 'The Projects Forum' started by enggricha, Jun 3, 2016.

  1. enggricha

    Thread Starter Member

    May 17, 2014
    62
    1
    I have a -15V - 0V(Gnd) - +15V power source that I have to connect to a PCB while ensuring that if any two of these, or all three are connected wrong still there is no damage to the PCB. Is there practically viable way to do this. I know implementing a reverse polarity protection of a +15V - 0V (Gnd) is straight forward and I have done that many times, with diodes and P-channel FETs.

    Have spend a couple of days on this and haven't been able to come up with any way to do this.

    TIA,
    Richa.
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    5,000
    745
    Yes, you can use inputting diodes in series with each pos and neg legs this will however drop a small voltage, OR use diodes in reverse across the supply, the latter will blow the fuses on the psu and wont drop any forward voltage.
     
    #12 likes this.
  3. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    That protects against reverse voltages but if the -15V and 0V are swapped then 30V will be applied between +15V and 0V, so some overvoltage protection would be required as well - VDR, crowbar...
     
  4. enggricha

    Thread Starter Member

    May 17, 2014
    62
    1
    I agree with albert here. Infact this is the problem area that I got stuck at. RVP_1.gif
    I saw this schematic elsewhere. As albert mentioned if we swap GND and -15V we will have a 30V across the intended +15V and GND.

    What am not understanding here?
     
  5. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    If your power supply has a reliable current limit then two shunt schottky diodes should do the job. In the case where the -15V and 0V connections are swapped then the -15V supply will be shorted to 0V by the diode thus restricting the +15V (which would otherwise have been +30V) to 15V + one diode drop. The series diodes shown in your diagram would stop that happening though.
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    You can use an N-MOSFET (no diodes) to provide minus voltage reverse protection, the same as you use a P-MOSFET for positive voltage reverse protection, as shown below.
    Here's an explanation.
    upload_2016-6-3_13-47-12.png
     
  7. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    If the power is mis-connected then does this not also result in 30V across the R+Load?

    upload_2016-6-3_21-10-28.png
     
  8. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    Yes, but that's an unusual mis-connection.
    Normally it's just interchanging the plus and minus connection that is the problem since the power supply grounds are usually connected together internally in the supply.
    The only way to prevent the problem you show is to add an OVP circuit.
     
    Last edited: Jun 3, 2016
  9. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    The shunt diodes do work for all mis-connections .
    upload_2016-6-4_9-36-4.png
     
  10. #12

    Expert

    Nov 30, 2010
    16,343
    6,828
    You might use a 3 pin connector that can only be plugged in one way.
     
    Last edited: Jun 4, 2016
  11. crutschow

    Expert

    Mar 14, 2008
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    3,244
    Until the diode opens from the short circuit current.
    You likely need to add a fuse to the shunt scheme (and I hate fuses).
     
  12. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    Most regulated supplies include a current limit - sorted.
     
  13. tom_s

    Member

    Jun 27, 2014
    285
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    aka polarised/polarized connectors (depending on which side of the planet you on)
     
  14. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    The OP said "power source" not power supply so don't know if it's current limited.
     
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