the present invention relates to an ac / dc converter of the type having an ac / dc conversion stage and a dc / dc conversion stage , the ac / dc conversion stage comprising an input filter stage , an input rectifier stage and a tracking boost converter stage . the boost converter stage in turn comprises an input choke , a boost diode and a bulk capacitor . the bulk capacitor is arranged to store a range of voltages substantially proportional to the input voltage of the converter . the dc / dc stage is arranged to receive the range of voltages from the bulk capacitor and is controllable to provide a desired dc output regardless of the voltage received from the bulk capacitor . this is achieved through careful combination of components and use of output feedback control to control the voltage applied to an isolated transformer in the dc / dc stage .