Rev. D 06/15

17

PFS7323-7329

www.power.com

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.

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 filter or decoupling capacitor should be placed at the output

of the bridge rectifier. This capacitor together with the X capa-

Figure 19. PCB Layout Example for System Power Supply Consisting of a PFC and a Second Stage Converter.

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.

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.

PFC

Output

EMI Filter

Thermistor

Shorting Relay

Bridge

Rectier

PFC

Inductor

HiperPFS

Auxiliary Supply for PFC –

from Standby Power Supply

Input

Capacitor

PFC Output

Capacitor

PI-7010-042313

AC Input