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Buck Converter 
When CH is ON ? ? o t DT ?? 
Voltage across inductor ? ?
L S O
V V V ?? 
When CH is OFF (DT < t < T) 
Voltage across inductor 
LO
VV ? 
Applying volt-sec balance across inductor 
? ? ? ? ? ?
S O O
V V DT V T DT 0 ? ? ? ? ? ? 
 ? ? ? ?
S O O
V V D V 1 D 0 ? ? ? ? 
 
OS
V DV ? 
D = duty cycle = 
ON
T
T
 
Where T = switching period = 
1
f
 
 f = switching frequency 
 
Page 2


 
 
 
 
 
 
 
 
 
 
 
 
Buck Converter 
When CH is ON ? ? o t DT ?? 
Voltage across inductor ? ?
L S O
V V V ?? 
When CH is OFF (DT < t < T) 
Voltage across inductor 
LO
VV ? 
Applying volt-sec balance across inductor 
? ? ? ? ? ?
S O O
V V DT V T DT 0 ? ? ? ? ? ? 
 ? ? ? ?
S O O
V V D V 1 D 0 ? ? ? ? 
 
OS
V DV ? 
D = duty cycle = 
ON
T
T
 
Where T = switching period = 
1
f
 
 f = switching frequency 
 
 
 
 
 
 
 
? Average output voltage = 
S
DV 
? rms output voltage = 
S
DV 
? Average source current = 
O
DI 
? Average current of FD = ? ?
O
1 D I ? 
Ripple in output current 
When CH is ON ? ? 0 t DT ?? 
? ?
L S O S
V V V 1 D V ? ? ? ? 
During this period, since voltage is positive current increase from minimum value to maximum 
value. 
 
max min
i I I ? ? ? 
 t DT 0 DT ? ? ? ? 
 
? ?
? ?
?
? ? ?
S
i
L 1 D V
DT
 
 
? ?
S
D 1 D V
i
fL
?
?? 
? This formula gives approximate value of output ripple current for maximum ripple, D = 0.5 
? ?
S
max
V
i
4fL
?? 
? 
L
max O
I
II
2
?
?? 
? 
L
min O
I
II
2
?
?? 
Critical Inductance (L C) 
Value of inductance at which inductor voltage waveform is just discontinuous. 
            
? ?
?
?
c
1 D R
L
2f
 
 
Page 3


 
 
 
 
 
 
 
 
 
 
 
 
Buck Converter 
When CH is ON ? ? o t DT ?? 
Voltage across inductor ? ?
L S O
V V V ?? 
When CH is OFF (DT < t < T) 
Voltage across inductor 
LO
VV ? 
Applying volt-sec balance across inductor 
? ? ? ? ? ?
S O O
V V DT V T DT 0 ? ? ? ? ? ? 
 ? ? ? ?
S O O
V V D V 1 D 0 ? ? ? ? 
 
OS
V DV ? 
D = duty cycle = 
ON
T
T
 
Where T = switching period = 
1
f
 
 f = switching frequency 
 
 
 
 
 
 
 
? Average output voltage = 
S
DV 
? rms output voltage = 
S
DV 
? Average source current = 
O
DI 
? Average current of FD = ? ?
O
1 D I ? 
Ripple in output current 
When CH is ON ? ? 0 t DT ?? 
? ?
L S O S
V V V 1 D V ? ? ? ? 
During this period, since voltage is positive current increase from minimum value to maximum 
value. 
 
max min
i I I ? ? ? 
 t DT 0 DT ? ? ? ? 
 
? ?
? ?
?
? ? ?
S
i
L 1 D V
DT
 
 
? ?
S
D 1 D V
i
fL
?
?? 
? This formula gives approximate value of output ripple current for maximum ripple, D = 0.5 
? ?
S
max
V
i
4fL
?? 
? 
L
max O
I
II
2
?
?? 
? 
L
min O
I
II
2
?
?? 
Critical Inductance (L C) 
Value of inductance at which inductor voltage waveform is just discontinuous. 
            
? ?
?
?
c
1 D R
L
2f
 
 
 
 
 
 
 
Critical Capacitance (C C) 
Value of capacitance at which capacitor voltage waveform is just discontinuous. 
  
C
1
C
8fR
? 
Step-up chopper (Boost converter) 
? ?
? ? ?
LS
when CHis ON 0 t DT ,     V V 
? ? ? ?
? ? ? ?
L S O
when CHis OFF DT t T ,    V V V 
Applying volt-sec balance across inductor 
? ? ? ? ? ?
S S O
V DT V V 1 D T 0 ? ? ? ? 
? ?
S
O
V
V
1D
?
?
 
? Since D < 1, 
OS
VV ? 
? 
? ?
? ? ? ?
CO
when CHis ON 0 t DT ,    I I 
? ?
? ? ? ? ?
C L O
when CHis OFF DT t T ,   I I I 
 
? ? ? ? ? ?
?
? ? ? ? ?
O L O
Applying Ampere sec balance across capacitor
I DT I I 1 D T 0
 
? ?
?
?
O
L
I
I
1D
 
 
Ripple in inductor current 
 
? ?
??
min max
When CHis ON 0 t DT  , current increase from I to I 
? ? ?
? ? ? ? ?
S
S L
SL
V DT
DV i
L V i
DT L fL
 
 
Page 4


 
 
 
 
 
 
 
 
 
 
 
 
Buck Converter 
When CH is ON ? ? o t DT ?? 
Voltage across inductor ? ?
L S O
V V V ?? 
When CH is OFF (DT < t < T) 
Voltage across inductor 
LO
VV ? 
Applying volt-sec balance across inductor 
? ? ? ? ? ?
S O O
V V DT V T DT 0 ? ? ? ? ? ? 
 ? ? ? ?
S O O
V V D V 1 D 0 ? ? ? ? 
 
OS
V DV ? 
D = duty cycle = 
ON
T
T
 
Where T = switching period = 
1
f
 
 f = switching frequency 
 
 
 
 
 
 
 
? Average output voltage = 
S
DV 
? rms output voltage = 
S
DV 
? Average source current = 
O
DI 
? Average current of FD = ? ?
O
1 D I ? 
Ripple in output current 
When CH is ON ? ? 0 t DT ?? 
? ?
L S O S
V V V 1 D V ? ? ? ? 
During this period, since voltage is positive current increase from minimum value to maximum 
value. 
 
max min
i I I ? ? ? 
 t DT 0 DT ? ? ? ? 
 
? ?
? ?
?
? ? ?
S
i
L 1 D V
DT
 
 
? ?
S
D 1 D V
i
fL
?
?? 
? This formula gives approximate value of output ripple current for maximum ripple, D = 0.5 
? ?
S
max
V
i
4fL
?? 
? 
L
max O
I
II
2
?
?? 
? 
L
min O
I
II
2
?
?? 
Critical Inductance (L C) 
Value of inductance at which inductor voltage waveform is just discontinuous. 
            
? ?
?
?
c
1 D R
L
2f
 
 
 
 
 
 
 
Critical Capacitance (C C) 
Value of capacitance at which capacitor voltage waveform is just discontinuous. 
  
C
1
C
8fR
? 
Step-up chopper (Boost converter) 
? ?
? ? ?
LS
when CHis ON 0 t DT ,     V V 
? ? ? ?
? ? ? ?
L S O
when CHis OFF DT t T ,    V V V 
Applying volt-sec balance across inductor 
? ? ? ? ? ?
S S O
V DT V V 1 D T 0 ? ? ? ? 
? ?
S
O
V
V
1D
?
?
 
? Since D < 1, 
OS
VV ? 
? 
? ?
? ? ? ?
CO
when CHis ON 0 t DT ,    I I 
? ?
? ? ? ? ?
C L O
when CHis OFF DT t T ,   I I I 
 
? ? ? ? ? ?
?
? ? ? ? ?
O L O
Applying Ampere sec balance across capacitor
I DT I I 1 D T 0
 
? ?
?
?
O
L
I
I
1D
 
 
Ripple in inductor current 
 
? ?
??
min max
When CHis ON 0 t DT  , current increase from I to I 
? ? ?
? ? ? ? ?
S
S L
SL
V DT
DV i
L V i
DT L fL
 
 
 
 
 
 
 
Ripple in output voltage 
 
??
CO
when CHis ON , I I 
C
O
V
C. I
DT
?
?? 
? ?
O
OC
I DT
VV
C
?
? ? ? ? 
-ve sign indicates voltage decrease 
? ?
O
O
I DT
V
C
? ? ? 
 
Critical Inductance (Lc) 
 
L
L
I
I
2
?
? 
 
? ?
?
?
C
D 1 D R
L
2f
 
 
Critical Capacitance (C c) 
O
O
V
V
2
?
? 
?
C
D
C
2fR
 
If inductor also has an internal resistance, then 
 
? ?
? ?
OS
2
1D
VV
r
1D
R
??
?
??
?
?? ??
??
 
 r = internal resistance of inductor 
 R = load resistance 
 
 
Page 5


 
 
 
 
 
 
 
 
 
 
 
 
Buck Converter 
When CH is ON ? ? o t DT ?? 
Voltage across inductor ? ?
L S O
V V V ?? 
When CH is OFF (DT < t < T) 
Voltage across inductor 
LO
VV ? 
Applying volt-sec balance across inductor 
? ? ? ? ? ?
S O O
V V DT V T DT 0 ? ? ? ? ? ? 
 ? ? ? ?
S O O
V V D V 1 D 0 ? ? ? ? 
 
OS
V DV ? 
D = duty cycle = 
ON
T
T
 
Where T = switching period = 
1
f
 
 f = switching frequency 
 
 
 
 
 
 
 
? Average output voltage = 
S
DV 
? rms output voltage = 
S
DV 
? Average source current = 
O
DI 
? Average current of FD = ? ?
O
1 D I ? 
Ripple in output current 
When CH is ON ? ? 0 t DT ?? 
? ?
L S O S
V V V 1 D V ? ? ? ? 
During this period, since voltage is positive current increase from minimum value to maximum 
value. 
 
max min
i I I ? ? ? 
 t DT 0 DT ? ? ? ? 
 
? ?
? ?
?
? ? ?
S
i
L 1 D V
DT
 
 
? ?
S
D 1 D V
i
fL
?
?? 
? This formula gives approximate value of output ripple current for maximum ripple, D = 0.5 
? ?
S
max
V
i
4fL
?? 
? 
L
max O
I
II
2
?
?? 
? 
L
min O
I
II
2
?
?? 
Critical Inductance (L C) 
Value of inductance at which inductor voltage waveform is just discontinuous. 
            
? ?
?
?
c
1 D R
L
2f
 
 
 
 
 
 
 
Critical Capacitance (C C) 
Value of capacitance at which capacitor voltage waveform is just discontinuous. 
  
C
1
C
8fR
? 
Step-up chopper (Boost converter) 
? ?
? ? ?
LS
when CHis ON 0 t DT ,     V V 
? ? ? ?
? ? ? ?
L S O
when CHis OFF DT t T ,    V V V 
Applying volt-sec balance across inductor 
? ? ? ? ? ?
S S O
V DT V V 1 D T 0 ? ? ? ? 
? ?
S
O
V
V
1D
?
?
 
? Since D < 1, 
OS
VV ? 
? 
? ?
? ? ? ?
CO
when CHis ON 0 t DT ,    I I 
? ?
? ? ? ? ?
C L O
when CHis OFF DT t T ,   I I I 
 
? ? ? ? ? ?
?
? ? ? ? ?
O L O
Applying Ampere sec balance across capacitor
I DT I I 1 D T 0
 
? ?
?
?
O
L
I
I
1D
 
 
Ripple in inductor current 
 
? ?
??
min max
When CHis ON 0 t DT  , current increase from I to I 
? ? ?
? ? ? ? ?
S
S L
SL
V DT
DV i
L V i
DT L fL
 
 
 
 
 
 
 
Ripple in output voltage 
 
??
CO
when CHis ON , I I 
C
O
V
C. I
DT
?
?? 
? ?
O
OC
I DT
VV
C
?
? ? ? ? 
-ve sign indicates voltage decrease 
? ?
O
O
I DT
V
C
? ? ? 
 
Critical Inductance (Lc) 
 
L
L
I
I
2
?
? 
 
? ?
?
?
C
D 1 D R
L
2f
 
 
Critical Capacitance (C c) 
O
O
V
V
2
?
? 
?
C
D
C
2fR
 
If inductor also has an internal resistance, then 
 
? ?
? ?
OS
2
1D
VV
r
1D
R
??
?
??
?
?? ??
??
 
 r = internal resistance of inductor 
 R = load resistance 
 
 
 
 
 
 
 
Buck-Boost Converter  
When CH is ON (O < t < DT) 
 
LS
VV ? 
 
CO
II ?? 
When CH is OFF (DT < t < T) 
LO
VV ? 
? ?
C L O
I I I ? ? ? 
Applying volt-sec balance across inductor 
 
? ? ? ?
? ? ?
SO
V DT V 1 D T 0 
 
? ?
S
O
DV
V
1D
?
?
?
 
Applying Ampere-sec balance across inductor 
 ? ? ? ? ? ?
O L O
I DT I I 1 D T 0 ? ? ? ? ? 
 
? ?
O
L
I
I
1D
?
?
?
 
 
? ?
? ?
?
??
?
?
2
OS
L
V DV
I
R 1 D
R 1 D
 
Ripple in inductor current 
When CH is ON (O < t < DT) 
Inductor current increase from 
min max
I to I 
?
??
L
S
I
LV
DT
 
S
L
DV
I
fL
??
  
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