Introduction to Digital Power Conversion
XMC4000/1000 Family
Converter Topologies
Application Guide
19
V1.0, 2015-01
3.3
PFC
Abstract
The
Power Factor
(
PF
) is defined as the transfer ratio of
real
power [Watt] to
apparent
power [VA]:
PF = Real Power / Apparent Power [Watt / VA]
The
Power-Factor-Correction
(
PFC
) purpose is (according to the environmental context) to achieve:
Real Power = Apparent Power
i.e.:
PF = 1
PFC Rectifier
A PFC rectifier accomplishes
“
PF = 1
” by phase correct rectification of the mains AC voltage – so that
the current conduction angle becomes fully 180
o
in both half periods
– phase correct to the mains AC
voltage
– i.e. without any parasitic or
reactive signal components
reflected back into the mains lines:
In principle, the mains is rectified into a sinusoidal half-wave rippling DC voltage. In turn it is converted
to a ripple-free DC output voltage by a Boost PFC
– e.g. by
Fixed-On-Time
inductor current (
I
L
) mode
control. (Each
Off-Time
interval lasts till the current (
I
L
) falls back to
Zero-Crossing-Detection,
ZCD.
)
Since all
t
On
pulses are fixed, the
I
L(PEAK)
and
I
L(AVERAGE)
envelopes will follow the |V
AC
(t)| in proportion.
Figure 7
Boost Power-Factor-Correction (PFC)
– E.g. in Fixed On-Time Current Mode Control
