A controlled power supply (20.sub.1, 22.sub.2) drives a magnetic field gradient coil (16.sub.1) of a magnetic resonance imaging apparatus (10). A gradient amplifier (20.sub.1) includes a plurality of switching power regulators (50, 52, 54, 56) which are electrically connected in series. A bipolar circuit (70) receives power from the series connected switching power regulators (50, 52, 54, 56) and delivers the power at a selected polarity to the gradient coil (16.sub.1). A control circuit (22.sub.1) delivers phase staggered pulse width modulated control signals (A, B, C, D) to the switching power regulators (50, 52, 54, 56).