Rev. B 04/15

18

TFS7701-7708

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Figure 18. Proper Heat Sink, TFS-2, and PFC Connections to the Bulk Capacitor, are Necessary to Prevent Interference. PFC and HiperTFS-2 both need Dedicated

Return Traces to Bulk Capacitor B-. Bulk Capacitor is PReferably Placed Between the PFC and HiperTFS-2.

Figure 19. The (-) Terminal of the V

AUX Capacitor Should be Connected to B- of the Bulk Capacitor, and not to the Ground Traces. This will Improve Lightning Surge and

ESD Immunity, due to Capacitive Displacement Currents Flowing Through the Primary-to-Secondary Capacitance in the Flyback Transformer.

PI-7014-053013

Bad

Bulk

Capacitor

Standby

Flyback

VAUX

Good

Ok

G

S

HiperTFS-2

Y Capacitor Connections

Y class safety capacitors connected across the isolation barrier,

should be routed directly to the positive of the bulk capacitor,

and preferably to B+ instead of B- to divert surge and ESD

currents away from the HiperTFS-2 small signal components

and PCB traces. See Figure 20.

PI-7029-053013

Bad

Bad

Ok

Best

B-

Bulk

Capacitor

Heat Sink

Foot

Heat Sink

S

HiperTFS-2

S

PFC

This will also improve surge and ESD immunity. The secondary-

side of the Y capacitor should be connected to the main

transformer secondary return pin. This will reduce the height of

thin “spikes” coincident with the main converter switching

edges in the output ripple, which comes from common-mode

switching noise. See Figure 21.