A step-down controller has an input having a first and a second input terminal for applying an input voltage, an output having a first and a second output terminal at which an output voltage can be provided, a series circuit including a switch and an inductance which is coupled between the first input terminal and the first output terminal. The switch has a control input for applying a control signal. A first diode is coupled between a junction point between the switch and the inductance and a reference potential such that, when the inductance is freewheeling, a current flow through the first diode (D.sub.1) is possible. There is a snubber network with a snubber capacitor, a second and third diode and an auxiliary inductance, a series circuit including the snubber capacitor, the third diode and the auxiliary inductance being coupled in parallel with the inductance.