A self-oscillating DC-DC buck converter with zero hysteresis is described. The converter comprises a comparator with a supply input, a non-inverting input to which a reference voltage is applied, an inverting input to which a feedback signal is applied, and an output to which a filter network is connected. The feedback signal is derived from the filter network and the output voltage of the converter is determined by the reference voltage. Connecting a filter network with an inductor and a capacitor to the output of the comparator and deriving the feedback signal from the filter network, results in an output of the comparator which is a DC output with a superimposed ripple. The level of the DC output is controlled by the reference voltage applied to the non-inverting input of the comparator, and the inductor current develops the ripple in the equivalent series resistance of the load circuit connected to the comparator output. The ripple can be regarded as the ramp signal in a conventional DC-DC converter. Accordingly, the output voltage is regulated to follow the reference voltage, and the proposed topology is equivalent to a DC-DC buck converter.