A sliding-mode switching power supply (24) having N phases (28) and a method of operating the power supply (24) are provided. N switches (30) are 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 monitor circuit (38) is coupled to the inductances (32) and the capacitance (36) and configured to monitor an output voltage (V.sub.Out) of the power supply (24). A first state-variable generator (42) generates a first state variable (first state variable x.sub.1) in response to the output voltage (V.sub.Out), and a second sate variable generator (44) synthesizes a second state variable (second state variable x.sub.2) from the first state variable (x.sub.1). A feedback-signal generator (46) is coupled to the first and second state-variable generators (42, 44) and generates a comprehensive feedback signal (.sigma.) for all phases (28) using only the two state variables (x.sub.1, x.sub.2).