Stacked output driver switching power supply with active clamping and selective bypass of pre-charge circuits

A method of operating a switching power supply circuit, the method comprising:

• providing one or more switching power supply output signals from a plurality of output drivers arranged in a stacked multi-level configuration;
• driving inputs of the output drivers with a corresponding plurality of pre-driver circuits;
• supplying power supply connections of the plurality of pre-driver circuits with operating voltage from a floating rail circuit and with a return to the output terminal of the corresponding output driver;
• selecting between a full-power operating state of the switching power supply circuit and a low-power pulsed operating state;
• and
• responsive to selection of the low-power pulsed operating stage, activating at least one of multiple active clamp circuits that provide corresponding return current paths for current from a corresponding at least one of the pre-driver circuits, whereby an off-state of the plurality of output drivers does not block return currents from the at least one pre-driver circuit.