To achieve this, the circuit CTRL is configured to compare the voltage V_T to a threshold Vth and to compare the voltage V_T to a threshold Vth_l when the voltage V_T is, in absolute values, above the threshold Vth, the threshold Vth_l being, in absolute values, higher than the threshold Vth.

The threshold Vth is determined so that when the voltage VT is, in absolute values, above the threshold Vth, the voltage VT is representative of the value of the voltage VP and, thus, of the value of the voltage V_AC.

Indeed, when switch 112 is open and a current flows across winding 1102 and component 116, the voltage VT is equal, in this embodiment, to voltage Vsrc. When switch 112 is open and the current in component 116 ends, the voltage V_T oscillates, in this embodiment, around the potential GND2. When switch 112 is commuted to its closed state, the voltage V_T reaches a steady value representative of the voltage V_P. More precisely, when the voltage V_AC has a value close to its nominal value, the steady value of the voltage V_T is higher, in absolute values, than the value of the voltage Vsrc or than the maximal value of the oscillations of voltage V_T, these two values being both determined by the set point value of the voltage Vsrc.