A power supply unit for a self-powered intelligent electronic device

An apparatus comprising:

• an IED for a LV or MV electric power applications, the IED including a power supply unit having:
• a power transformer stage, which is operatively coupled to a feeding conductor to harvest electric power from said feeding conductor, said power transformer stage being adapted to provide a first voltage (V1);
• a first storage stage, which is electrically connected to said power transformer stage to receive said first voltage, said first storage stage being adapted to store electric energy and provide a first supply voltage (VS1), said power transformer stage being adapted to provide a first charging current (I1) to charge said first storage stage, when a current flows along said feeding conductor;
• a first step-down conversion stage, which is electrically connectable/disconnectable to/from said first storage stage, said first step-down conversion stage being adapted to receive said first supply voltage (VS1) and provide a third voltage (V3) having a lower amplitude than said first supply voltage, when said first step-down conversion stage is electrically connected with said first storage stage;
• a switching stage adapted to electrically connect/disconnect said first step-down conversion stage with/from said first storage stage;
• a second storage stage, which is electrically connected to said first step-down conversion stage, said second storage stage being adapted to store electric energy and provide a second supply voltage (VS2), said first step-down conversion stage being adapted to provide a second charging current (I2) to charge said second storage stage, when said first step-down conversion stage is electrically connected to said first storage stage.