A power supply device having variable output voltage (Vout), the power supply device comprising: a multiphase chopper section including a plurality of step-down chopper circuits (30A,30B,...,30N) forming a plurality of phases connected in parallel; a controller, performing a feedback control, configured to calculate a manipulated value for controlling the multiphase chopper section from a feedback signal (Vout, iL, iC) outputted from the multiphase chopper section and a command signal (Vref) by a voltage control based on a difference between the feedback signal (Vout, iL, iC) and the command signal (Vref); and a gate signal generator configured to generate gate signals (Gate1-A, Gate1-B, Gate1-C, Gate2-A, Gate2-B, Gate2-C) for performing multiphase control of turning on/off of switching elements (S1A, S1B, S2A, S2B) included in the step-down chopper circuits (30A,30B,...,30N) of the respective phases based on the manipulated value in phases displaced from each other, the gate signal generator being configured to generate the gate signals for the respective phases with the same gate signal generation period (Tph) between consecutive gate signals, wherein the number of phases of the gate signals (Gate1-A, Gate1-B, Gate1-C, Gate2-A, Gate2-B, Gate2-C) equals the number of phases of the step-down chopper circuits (30A,30B,...,30N), wherein the points in time at which the gate signals are generated are points in time after a point in time at which the controller is configured to calculate the manipulated value; characterized in that the command signal (Vref) is alternating between high voltage and low voltage and in that the gate signal generator is configured to generate the gate signals at points in time asynchronous to the command signal (Vref). a multiphase chopper section including a plurality of step-down chopper circuits (30A,30B,...,30N) forming a plurality of phases connected in parallel; a controller, performing a feedback control, configured to calculate a manipulated value for controlling the multiphase chopper section from a feedback signal (Vout, iL, iC) outputted from the multiphase chopper section and a command signal (Vref) by a voltage control based on a difference between the feedback signal (Vout, iL, iC) and the command signal (Vref); and a gate signal generator configured to generate gate signals (Gate1-A, Gate1-B, Gate1-C, Gate2-A, Gate2-B, Gate2-C) for performing multiphase control of turning on/off of switching elements (S1A, S1B, S2A, S2B) included in the step-down chopper circuits (30A,30B,...,30N) of the respective phases based on the manipulated value in phases displaced from each other, the gate signal generator being configured to generate the gate signals for the respective phases with the same gate signal generation period (Tph) between consecutive gate signals, wherein the number of phases of the gate signals (Gate1-A, Gate1-B, Gate1-C, Gate2-A, Gate2-B, Gate2-C) equals the number of phases of the step-down chopper circuits (30A,30B,...,30N), wherein the points in time at which the gate signals are generated are points in time after a point in time at which the controller is configured to calculate the manipulated value; characterized in that the command signal (Vref) is alternating between high voltage and low voltage and in that the gate signal generator is configured to generate the gate signals at points in time asynchronous to the command signal (Vref).