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 (L), and a switching circuit configured to provide the LC circuit with inductance current (iL) by performing multi-phase switching control, an output capacitance (C) of said LC circuit is connected to said inductance (L) 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 (L) 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 (C) and i R (t) is the current delivered by the LC chopper circuit to a load (R) 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 (L) 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 (C) and i R (t) is the current delivered by the LC chopper circuit to a load (R) 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 . <EOS>