PRECONDITIONER
The present invention relates to a preconditioner having a rectifier, arranged to receive an AC voltage from a voltage supply and to deliver a DC voltage (Vo) to a load, a switch mode power supply, arranged to control the current in the rectifier, and a control loop for feedback of the preconditioner output voltage (Vo) to the switch mode power supply, said control loop having a bandwidth greater than the voltage supply frequency. The feedback loop comprises a bandpass filter with a band pass center frequency equal to twice the source frequency, which is connected to said output voltage, and means for generating a feedback signal based on the output voltage and an output signal from said bandpass filter, which feedback signal has reduced ripple around the passband. By eliminating the ripple in the voltage feedback loop, the preconditioner does not waste energy in an attempt to control this ripple, which is inherently present from the AC source.