Isolated switched mode power supply

An isolated switched mode power supply, comprising:

• a transformer comprising a primary winding and a secondary winding, said secondary winding having a centre-tap provided between a first portion and a second portion thereof;
• a primary side circuit arranged to generate voltage pulses and thereby to drive the primary winding of the transformer;
• and
• secondary side circuit comprising:
• a rectification network connected to the secondary winding, the rectification network and the transformer being arranged such that, during a free-wheeling period of operation of the switched mode power supply in which the primary winding is not driven by the primary side circuit, a magnetic flux from the first portion of the secondary winding substantially cancels a magnetic flux from the second portion of the secondary winding between the first and second portions of the secondary winding;
• and
• a switching device connected to the centre-tap and an output of the rectification network so as to conduct at least a part of a free-wheeling current flowing in the secondary side circuit during said free-wheeling period.