The invention provides an AC line power converter comprising a regulation control loop to effect said regulation including means for generating a shaping signal, said shaping signal being substantially periodic at line frequency or harmonics thereof and summing means for introducing the shaping signal to the regulation control loop together with an error signal or control of said regulation control loop, whereby said shaping signal shapes the line current drawn by said converter within said period. The shaping waveform provides corrections for errors and unwanted behaviours and can be varied between cycles. Selection of a shaping waveform permits trade-off between parameters to meet performance goals at points in the operating envelope of the converter.