In a switching voltage power supply, a series regulator circuit interconnects an input voltage section (44) with an output voltage section (20B) of the switching power supply. The regulator circuit has an n-channel MOSFET transistor (Q1) serving as a regulator element. A gating circuit applies a gating voltage to the gate terminal relative to the drain terminal for establishing states of current conduction and current cut-off in the transistor. A biasing circuit interconnects the gating circuit with the drain terminal for establishing an offset potential of the gate terminal relative to the drain terminal during the state of current conduction, the offset potential counteracting a gate-to-source threshold voltage for reduction of a voltage drop between the drain terminal and the source terminal with a corresponding reduction in power dissipation of the regulator element.