The present invention relates voltage conversion device in which a regulated output voltage is supplied by current pulses generated by the voltage conversion device from a voltage source. In particular, the invention relates to an improved control of an pulse frequency modulation (PFM) operation mode in which the frequency of the generated current pulses is modulated to regulated the desired output voltage, namely how PFM pulses can be generated without the need for a high-frequency clock of a time controlled system. By having pulse phases are current mode controlled and providing a mode detector to generate the right kind of current pulse, the high-frequency clock is no longer needed. Further, the presented solution allows for a higher PWM as well as PFM frequency, the external components of the converter can be made smaller. Eliminating the need for a high-frequency clock makes the device simpler, smaller and more energy-efficient.