Reverse Polarity Protection for Dual Polarity supply power

Thread Starter

enggricha

Joined May 17, 2014
87
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.
 

Dodgydave

Joined Jun 22, 2012
10,088
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.
 

AlbertHall

Joined Jun 4, 2014
11,598
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...
 

Thread Starter

enggricha

Joined May 17, 2014
87
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?
 

AlbertHall

Joined Jun 4, 2014
11,598
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.
 

crutschow

Joined Mar 14, 2008
28,194
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
 

crutschow

Joined Mar 14, 2008
28,194
If the power is mis-connected then does this not also result in 30V across the R+Load?

View attachment 107188
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.
 
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