Method and circuit for protecting an on-board charging device

A circuit for protecting an on-board charging device, wherein said charging device comprises a socket for connection to a grid and a converter assembly configured to convert an alternating current coming from the grid into a direct current usable for charging a battery pack and a compensation circuit configured to generate a compensation current equal and opposite to one or more leakage currents flowing towards earth;

• said device comprising:
• a summing network configured to receive as input signals representing the phase and neutral voltages of the grid and to generate as output a homopolar voltage signal;
• an element for detecting a current signal representing the compensation current;
• a conversion stage configured to receive as input said homopolar voltage signal and said current signal and to generate a first square wave representative of said homopolar voltage signal and a second square wave representative of said current signal;
• a combining stage configured for combining the first and second square waves to generate an output signal having a first logic level when said first and second square waves are in phase and a second logic level when said first and second square waves are out of phase;
• a charging module operationally arranged downstream of the combining stage (6) and configured to generate a first voltage increasing in proportion to a duration of each section of the output signal having said first value;
• a comparator element configured to compare the value of said first voltage with a limit value and to generate an alarm signal if the value of said first voltage exceeds said limit value.