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2 Circuit topologies
2.1 Buck (step-down) converters
2 Circuit topologies
2.1 Buck (step-down) converters
The input voltage of the buck converter, also known as step-down converter, is always
higher or very close to the output voltage (Fig. 2.1). There are designs with fixed or
variable output voltage whose minimum or maximum values depend on different
design parameters, e.g. the internal reference.
Fig. 2.1: Schematic relationship between input and output voltage
The buck converter is the simplest converter of all switching regulators and the circuit
topology is very often used to supply power to processors that require a low voltage
and high current. As long as the difference between the input and output voltage is
not too high, a very good efficiency of up to 95% can be achieved. The low number of
components necessary allows for easy design-in, particularly as numerous regulators
and controllers from different manufacturers are already available on the component
market.
An electrical isolation between the input and output is not possible and the buck
converter can only generate one output voltage.
Fig. 2.2: Schematic buck converter
Buck (step-down)
converters
V
in
max
min
0 V
Max
Min
V
out
V
in
≥ V
out
Depending on V
in
L
D
C
in
C
out
R
load
V
in
V
out
I
T
I
L
I
D
I
out
I
in
V
n
TSW
V
D
V
L