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Topology Impacts on Component Stress
+ Vo
Vd +
-
-
Parameter
Transistor Vˆ
Transistor Iˆ
-
Buck
Vin
I out
-
Boost
Vin  Vout
I in
Iin  I out
DI in
Transistor I
DI out
DI in
Diode I
1  D  Iout
Pulse
Current
Input
Buck/Boost
Vout
DI out
I out
-
-
Transistor I rms
Inductor I
+ Vo
Vd +
+ Vo
Vd +
1  D Iin
I in
Output
D  I in  I out
D  I in  I out
1  D   I in
Iin  I out
Both


 I out

Single Ended Primary Inductor
SEPIC
+
VIN
+
IL1
VC2
+
-
IL3
IL3
-
VOUT
-
VIN D  VIN  VO  VC 2   1  D   0
VIN
 VO  VC 2
1  D 
VIN
VO
 VO 
 VO
D
1  D 
VC 2 D VO 1  D   0
VC 2  VO
1  D 
D
D
 VO  VIN
1  D 
VO

 VO
D
CUK Converter
+
+
VC2
-
VIN
+
VOUT
-
-
D
VO  VIN
1 D
Worst Case Conditions
If it is desired that a converter operate in CCM at all times,
it must be recognized that DCM occurs for low values of
inductor currents. For regulated output applications, this
condition is associated with large resistance (low current)
loading, and/or high input voltages. Inductor values should
be chosen accordingly, with appropriate safety factors.
Low Voltage Applications
For low output voltage applications (~ 1 v) the voltage drop
associated with a freewheeling diode may be unacceptably
high. In this case, the diode is replace by another active
switching device with very low ON-resistance.
Interleaving Converters
Multiple converters
can be operated in
parallel with their
switching
waveforms delayed
with respect to
each other (phase
shifted). This tends
to smooth out the
residual pulsation
currents.