A power supply device comprising: a step-down LC chopper circuit configured to combine current values of multiple interleaved phases of said LC chopper circuit, each phase comprising an LC circuit including an inductance, and a switching circuit configured to provide the LC circuit with inductance current (iL) by performing multi-phase switching control, an output capacitance of said LC circuit is connected to said inductance of said LC circuit of each phase; the LC chopper circuit being configured to receive an input voltage (Vin) and to deliver an output voltage (Vo) and a load current (iR), and a controller configured to perform a step response control to allow the output voltage (v O) to follow a command voltage (V REF) based on per-phase switching control of the LC circuit according to constant current control using as control current i L (t), a combined current of respective phase current values in the LC chopper circuit, wherein the combined current is the sum of the currents flowing in each of the inductances of said LC chopper circuit, and the control system is provided with a factor A V related to the control current, as an adjustment parameter for a response characteristics to the command voltage (VREF); characterized in that the control current is expressed by i L (t)= A V V REF − v o t + β 3 i c t + i R t, wherein V REF is the command voltage, v O (t) is the output voltage, i c (t) is the capacitance current flowing through the output capacitor and i R (t) is the current delivered by the LC chopper circuit to a load connectable to the output of the LC chopper circuit, the factor Av is expressed by Av = 3T/L, where T is the sampling cycle and L is the inductance of the LC circuit; wherein the factor β 3 by which the capacitance current in the LC circuit is multiplied, satisfies 2 ω n 2 T 2 π < 1 − β 3 < ω n T 2 + ω n T 4 2 − ω n T 4 and ωn is expressed by: ω n = 3 LC. a controller configured to perform a step response control to allow the output voltage (v O) to follow a command voltage (V REF) based on per-phase switching control of the LC circuit according to constant current control using as control current i L (t), a combined current of respective phase current values in the LC chopper circuit, wherein the combined current is the sum of the currents flowing in each of the inductances of said LC chopper circuit, and the control system is provided with a factor A V related to the control current, as an adjustment parameter for a response characteristics to the command voltage (VREF); characterized in that the control current is expressed by i L (t)= A V V REF − v o t + β 3 i c t + i R t, wherein V REF is the command voltage, v O (t) is the output voltage, i c (t) is the capacitance current flowing through the output capacitor and i R (t) is the current delivered by the LC chopper circuit to a load connectable to the output of the LC chopper circuit, the factor Av is expressed by Av = 3T/L, where T is the sampling cycle and L is the inductance of the LC circuit; wherein the factor β 3 by which the capacitance current in the LC circuit is multiplied, satisfies 2 ω n 2 T 2 π < 1 − β 3 < ω n T 2 + ω n T 4 2 − ω n T 4 and ωn is expressed by: ω n = 3 LC.