Introduction to Digital Power Conversion
XMC4000/1000 Family
Converter Topologies
Application Guide 22 V1.0, 2015-01
3.5 LLC (Inductor-Inductor-Capacitor)
The LLC converter is a series resonant converter. Power is transferred in a sinusoidal manner, so the
switching devices are softly commutated by ZVS (Zero-Voltage-Switching) and without capacitive
loss. A transformer takes part in the process, making the LLC an isolating converter.
Figure 10 LLC Principle – Using Half-Bridge Control
Performance
A resonant converter enables high voltage and faster switching, which allows for smaller components
thanks to the reduced switching losses.
An LLC converter, with two inductors (L
r
,L
m
) and a capacitor (C
r
), is superior to all other types of
resonant converters, especially with respect to a wide load range.
Properties
The LLC inductor L
m
shunts the transformer primary coil when the impedance becomes infinite:
If there is no diode current, the resonant tank will become “(L
r
+L
m
)C
r
“
If there is diode current, the tank is “L
r
C
r
“. Therefore open load can be handled. The power
transfer is tuned by frequency or PWM.
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