PFS7323-7329
PCB Design Guidelines and Design Example
The line-sense network and the feedback circuit use large
resistance values in order to minimize power dissipation in the
feedback network and the line-sense network. Care should be
taken to place the feedback circuit and the line-sense network
components away from the high-voltage and high current
nodes to minimize any interference. Any noise injected in the
feedback network or the line-sense network will typically
manifest as degradation of power factor. Excessive noise
injection can lead to waveform instability or dissymmetry.
citance in the EMI filter and the differential inductance of the
EMI filter section and the source impedance, works as a filter to
reduce the switching frequency current ripple in the input
current. This capacitor also helps to minimize the loop area of
the switching frequency current loop thereby reducing EMI.
The connection between the HiperPFS-2 drain node, output
diode drain terminal and the PFC inductor should be kept as
small as possible.
The EMI filter components should be clustered together to improve
filter effectiveness. The placement of the EMI filter components
on the circuit board should be such that the input circuit is
located away from the drain node of the, or the PFC inductor.
A low-loss ceramic dielectric capacitor should be connected
between the cathode of the PFC output diode and the source
terminal of the HiperPFS-2. This ensures that the loop area of
the loop carrying high frequency currents at the transition of
switch-off of the MOSFET is small and helps to reduce radiated
EMI due to high frequency pulsating nature of the diode current
traversing through the loop.
A filter or decoupling capacitor should be placed at the output
of the bridge rectifier. This capacitor together with the X capa-
PFC Output
Capacitor
PFC
Output
HiperPFS
PFC
Inductor
Auxiliary Supply for PFC –
from Standby Power Supply
Input
Capacitor
Bridge
Rectiꢀer
EMI Filter
AC Input
Thermistor
Shorting Relay
PI-7010-042313
Figure 19. PCB Layout Example for System Power Supply Consisting of a PFC and a Second Stage Converter.
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Rev. B 06/13
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