The invention relates to a DC-DC converter (1) for a power source (2) generating extremely low voltage, the converter (1) operating in discontinuous mode, wherein the converter (1) comprises a self-oscillating charge pump (3a) having an array of interconnected ring oscillators (RO1-RON) for successively stepping up an input voltage (Vin) so as to result in the accumulated voltage (XN) at the last ring oscillator (RON), an amplifier (3b) and a pulse signal generator (3c) that generates a pulse signal that actuates a switch (11) so that the stepped-up, output voltage may be provided via a diode (12). The invention further relates to a method for actuating the DC-DC converter (1) for a power source (2) generating extremely low voltage.