A power inverter is disclosed herein. The power inverter is suitable for driving a transmitter coil in an inductive power transfer system, wherein the inverter is suitable for class 'EF' operation. The inverter is arranged to drive a load resistance, and comprises a switching device arranged between a power source and ground and arranged to switch at a switching frequency. The inverter also comprises a resonant network arranged in parallel with the switching device between the power source and ground, the resonant network having a resonant frequency which is a non-integer multiple of the switching frequency, such that, in operation, a substantially constant current passes through the load resistance.