A multiphase sliding-mode switching power supply (24) and a method of operating the power supply (24) are provided. A switch (30) for each phase (28) is coupled to a bipolar power source (22), with each switch (30) effecting one phase (28). An inductance (32) is coupled to each switch (30), and a capacitance (36) is coupled to the inductances (32). A load (26) is coupled across the capacitance (36). A sliding-surface generator (78) is coupled to the monitor circuit (38) and generates a single sliding surface (.sigma.) for all phases (28). A translation circuit (102) is coupled to the sliding-surface generator (78) and configured to translate the sliding surface (.sigma.) into a stream of switching pulses (86). A transient control (52) is coupled to the translation circuit (102) and configured to adjust said stream of switching pulses upon detection of an out-of-range transient. A switching circuit (138) is coupled to the switches (30) and the transient control (52), and switches the switches (30) in response to the stream of switching pulses (86).