A method of controlling a resonant power converter comprising first and second series connected switches (905a, 905b) connected between a supply voltage line and a ground line and a resonance circuit comprising a capacitor and an inductor (Ls, Lm), the resonance circuit connected to a node connecting the first and second switches (905a, 905b), the method comprising the repeated sequential steps of: closing the first switch to start a first conduction interval; sampling a voltage (Vcr) across the capacitor to obtain a first sampled voltage level; and opening (2704, 2705) the first switch to end the first conduction interval when a voltage (Vcr) across the capacitor crosses a voltage level determined by addition of the first sampled voltage level with a first predetermined voltage difference (deltaVcrh); closing the second switch to start a second conduction interval; sampling a voltage across the capacitor to obtain a second sampled voltage level; and opening (2708, 2709) the second switch to end the second conduction interval when a voltage across the capacitor crosses a voltage level determined by addition of the second sampled voltage level to a second predetermined voltage difference (deltaVcrl), wherein the first and second conduction intervals alternate over time, wherein controlling the first predetermined voltage difference (deltaVcrh) determines a power output of the resonant power converter, wherein during the first conduction interval the node connecting the switches (905a, 905b) is connected to the supply voltage line and during the second conduction interval the node is connected to the ground line, characterised in that the first and second predetermined voltage differences (deltaVcrh, deltaVcrl) are unequal in magnitude, resulting in a changing power output of the resonant power converter. closing the first switch to start a first conduction interval; sampling a voltage (Vcr) across the capacitor to obtain a first sampled voltage level; and opening (2704, 2705) the first switch to end the first conduction interval when a voltage (Vcr) across the capacitor crosses a voltage level determined by addition of the first sampled voltage level with a first predetermined voltage difference (deltaVcrh); closing the second switch to start a second conduction interval; sampling a voltage across the capacitor to obtain a second sampled voltage level; and opening (2708, 2709) the second switch to end the second conduction interval when a voltage across the capacitor crosses a voltage level determined by addition of the second sampled voltage level to a second predetermined voltage difference (deltaVcrl), wherein the first and second conduction intervals alternate over time, wherein controlling the first predetermined voltage difference (deltaVcrh) determines a power output of the resonant power converter, wherein during the first conduction interval the node connecting the switches (905a, 905b) is connected to the supply voltage line and during the second conduction interval the node is connected to the ground line, characterised in that the first and second predetermined voltage differences (deltaVcrh, deltaVcrl) are unequal in magnitude, resulting in a changing power output of the resonant power converter.