buck converter + v in - + v out - assumptions for first order analysis: all components are ideal,...
TRANSCRIPT
RLoad
Buck Converter
+
Vin
-
+VOUT
-
Assumptions for First Order Analysis:•All components are ideal, including voltage source•Output ripple voltage is negligible (2nd order effect)•Continuous (nonzero) current through inductor
We will examine the case where inductor current goes to zero for part of the cycle at a later time. However, we will identify the condition which causes this to happen.
iL(t) = IOUT + iC(t) IOUT
iC
iL
IL
iL,max
iL,min
IL = IO
TS = t1+t2
t1 =DTS t2 =(1-D)TS
m2m1
Inductor Current > 0
1in outV V
mL
2
0 out outV Vm
L L
1 1
2 2 1 1
in out in outS L
S
out outS L
S
V V V Vm t DT D I
L Lf
V Vm t D T D I
L Lf
1 1
2 2 1 1
in out in outS L
S
out outS L
S
V V V Vm t DT D I
L Lf
V Vm t D T D I
L Lf
1in out out
S S
V V VD D
Lf Lf
in outDV V
1out in out inL
in S S
V V V VI D D
V Lf Lf
IL
iL,max
iL,min
IL = IO
m2m1
Expressions for Inductor Current Variation
iL
IL
iL,max
iL,min
ILB= IOB
IL = IO
TS
DTS
Critical Inductor Current
IO = IL = IL,crit = IL/2
, 2
12
out in outL crit
in S
in
S
V V VI
V Lf
VD D
Lf
, ,
, , ,
O crit L crit
OIn crit L crit L crit
IN
I I
VI I DI
V
iL
IL
iC,max
iC,min
TS = t1+t2
t1 =DTS t2 =(1-D)TS
Capacitor Current
+ Q
TS /2
,
,
1
2 2 2 4
4
L critS Lpp
S
L critpp
S
IT IQ C V
f
IV
Cf
iL
IL
iL,max
iL,min
ISW = ID
TS = t1+t2
t1 =DTS t2 =(1-D)TS
Switch Current = ID
iR
IL
iL,max
iL,min
IR
TS = t1+t2
t1 =DTS t2 =(1-D)TS
Diode Current