I want to add reverse polarity protection on my electronic load which will be capable of sinking 20A and with a max. voltage of 50V (max. power is limited to 250W). Because I want to go with low input voltages for e.g. testing batteries, a typical solution like a PFET at the positive load input terminal is not a solution because of the V_GS_th of the PFET.
Diodes are also not suitable because of the high current and the related power dissipation.
I came across the solution of Spehro Pefhany which is shown in the picture.
I got one question about it: My electronic load input terminals (Vx) are going to be floating (no connection to mains earth because of a transformer). The metal case is going to be connected to mains earth.
Is there a possibility to screw anything up, if some strange connections are made?
E.g. connect the negative load input terminal to the case and attach there the positive terminal of my DUT. Now I connect the negative terminal of my DUT (which is mains earth referenced) to the positive load input terminal. That would short out Q2 and the current would flow through the body diode of Q1. Is this the only case which could cause problems?
What would happen if I connect a mains earth referenced power supply to my load terminals in a normal way (positive to positive and negative to negative)? That would connect the negative floating input terminal to mains earth and would bridge the isolation. Could this be a problem?