Reverse Voltage Protection Circuit

is the connection between J1 and J2 need to be solid ie could coulpling ne via a dc block ie capacitor?

if that doesnt help what about a zener of a voltage below the fault voltage in the circuit ?

or tie the link wire with zener to ground to dump dc.

could you use an opto isolator for coulpling purposes then no dc could pass?

what are the connections between J1 Nd J2 what do they do?

J1 connects to power supply and J2 connects to power supply too. The ground of right circuit connects to the ground of the left circuit.

As a result, the ground of J1 connect to the ground J2.

if J1 And J2 have their own power supplies why do they need to be connected ?

what does the circuit do?

i dont understand why they need to have to be connected if they each have their own power supply ????

Please describe the circuit and its function

or why not just connect J1 to power and as the link takes power across to J2 do not connect J2 to external power supply

You need to add two further diodes (and a fuse would/maybe a good idea too.

Here is a very quick sketch that I hope will help you further:-

Notice that the diodes are reversed and will only conduct if a reverse voltage is applied.

Your circuit is o.k. and there should not be any problem. You have two circuits, taking power from different power supplies. And you have connect the "grounds" of the two circuits (i.e. the "-" of the input voltage) in order to have a common reference ground. Everything is just fine. If you apply a reverse voltage on the input of the one circuit, this circuit is protected by the diode. Why such a reverse voltage should affect the operation of the other circuit (to the input voltage or whatever)??? This does not make sense. The other circuit should operate normally.

You don't give any details of the "fault". What do you mean by that??? What kind of circuits are these??? Maybe the problems arise from a "ground loop" (e.g. if you have connection of the circuits' "grounds" through the signal connectors -e.g. coaxials- and through the external power supplies -by the connection of their negative terminals- you may face "ground loop" problems, especially in analog circuits).

How about this:-

GA. Other than increasing the voltage drop, this will not short the reversed supplies.

What sort of signalling/protocol are you using/proposing to use?

RS232
RS485
something else

synchronous
asynchronous
etc.

If you read my original post, you would note that I mentioned that a fuse should be included to blow and remove the "bad" power connection immediately.

Such systems are extensively used on battery chargers to make safe when a battery is wrongly connected.....the circuit is actually quite common in many types of equipment, especially where a normal safety diode cannot be put in the supply line, due to voltage drop problems.

In the case above, the safety diode originally installed could probably be left out.

The "short" diode needs to be dimensioned so that it can easily handle the short circuit current that will blow the fuse.....the fuse can be put in either the ground or + line.....but it must between the supply and the diode.

With RS 485: receivers are guaranteed to work from -7 Volts to +12 Volts (i.e. 7 volts outside the 5 volt rails) so the additional diode offset won't interfere with the transmission.