电源设计培训资料Technical
Training
Adlsong
SMPS Topologies
The Buck Converter
Buck
Buck Converter
Step Down Voltage Regulator
Buck
State 1: S is on, the inductor current rises linearly: (Vin Vo ) D diL = I L = Vin Vo pk Lf S dt Volts Second Balance: Vo = DVin, D = Ton/ T Vin Iin = Vo Io, Iin = IL = Io/D
State 2: S is off, the inductor current decreases linearly: di V (1 D) L L = Vo I pk = o dt Lf S
Buck
Buck
CCM
DCM
Buck
The voltage ripple of output capacitor: iL>Io, Cout is charged
1) Integral during the period
U o = = 1 1 i dt + Ton C C∫2 C ∫Ton (1 D)Vo
Ton 2 Ton + Toff 2
2) The charge during the period
1 I Lpk Ts Q = 2 2 2 (1 D)Vo Q U o = = C out 8L f C out f S 2
iC dt
8 L f C out f S
Take ESR into Account:
U o = ESR I Lpk =
(1 D)Vo ESR Lf fS
Buck
Critical cond……
