There is disclosed a parallel loaded series resonant converter 300 suitable for supplying DC to a three axis gradient amplifier in an MRI system. In conventional resonant circuits, output voltage is regulated by controlling the switching frequency of an H-bridge or half bridge switching arrangement and the resonant circuit (334, 335) is under more stress at no load than at full load. The voltage across the resonant capacitor (334) is a function of the switching frequency, the load and the voltage applied across the resonant circuit (V A -V B ). In the present invention, the peak current at no load is reduced to lower than the peak current at full load by controlling the voltage applied to the resonant circuit (V A -V B ) rather than controlling the switching frequency.