A switching power supply source including an inductance with first and second terminals; an output node; an NMos transistor, the drain of which is connected to the first terminal; a PMos transistor, the drain of which is connected to the first terminal; a control device generating control signals for NMos and PMos transistors assuring that these transistors are not conducting simultaneously; a capacitor with a third terminal connected to the first terminal and a fourth terminal; a resistance with a fifth terminal connected to the fourth terminal and a sixth terminal; and an NMos transistor the drain of which is connected to the grid of the PMos transistor and the gate of which is connected to the fourth terminal.