A gradient coil power supply (100, 812) for a magnetic resonance imaging system (800) comprising: at least two H-bridge circuits (104, 106, 108, 200, 202, 204, 206); wherein the H-bridge circuits are connected in series; wherein each of the H-bridge circuits supplies voltage of a first polarity when in a first switching state (200); wherein the each H-bridge circuit supplies voltage of a second polarity when the H-bridge is in a second switching state (202); wherein each H-bridge circuit supplies no voltage when in a third switching state (204); wherein each H-bridge circuit supplies no voltage when in a fourth switching state (206); and a controller (814) for controlling the switching of the H-bridge circuits, wherein the controller is adapted for: —receiving (600, 700) a gradient pulse sequence (818), —creating (602, 702) a switching plan for controlling the switching of each of the H-bridge circuits, wherein the switching plan comprises controlling the voltage output of the gradient coil power supply by alternating between the first switching state and the second switching state, wherein the switching plan further comprises operating (710) at least one H-bridge circuit selected from the H-bridge circuits in either the third or fourth switching state for part of the switching plan to cool the H-bridge circuit, —executing (604, 704) the switching plan.