Installation Guidelines For Emc - TDK-Lambda CPFE500 Application Note

INSTALLATION GUIDELINES FOR EMC

Mounting
Good EMC performance comes through careful consideration of the power supply installation. All equipment
should be mounted inside an earthed metal box, with joints sealed with EMC gasket material where possible.
If this is not possible then use an earthed metal plane to mount the power supply and load.
Earth Starpoint
The earth connection from the AC supply should be routed to a chassis mounted 'star-point', located as close as
possible to the AC inlet. Note: Compliance with EN60950-1 practice requires the main protective earth
termination to have its own dedicated spring, washer and nut. The PSU earth and all other earth circuits should
be routed directly to the 'star-point', thereby reducing the possibility of creating earth loops in the system.
De-coupling
A significant Radiated and Conducted EMC performance can be achieved through the inclusion of de-coupling
'Y' capacitors, with a minimum value of 470pF, placed immediately adjacent to the AC inlet, as shown in figure
19.
Similar performance improvements can be
achieved through the use of a Schaffner IEC inlet
type FN 9222, which has these capacitors built in,
or the inclusion of a proprietary mains input filter.
TDK Lambda has a wide range of suitable mains
filters available for all circumstances.
Always de-couple the load using approximately 10 – 1000µF of capacitance per Amp of running current. Fit the
capacitance as close as possible to the load.
Cables
All cables and PCB tracks should be regarded as both radiation sources and receivers. The following tips will
assist in maximising EMC performance:
Both AC input and DC power output cables should be run as close as possible to the earthed metal
•
box/plane.
Input and output cables should be routed as far away from each other as possible, kept as short as
•
possible and, ideally, screened from each other.
Tightly twist the AC input cables together. The DC power output cables should also be tightly twisted
•
together.
If Remote Sense is used, also twist these wires tightly together and try to avoid running power and
•
sense cables together in the same loom.
Loops in cables and PCB tracks should be eliminated or kept as small as possible.
•
Connecting between boxes
If cables must be connected between equipment boxes then at the closest possible point to the port where the
cables exit the 1st enclosure connect 100nF decoupling Y caps (between the output and earth). Note that these
capacitors must be rated at the working voltage. Ideally these capacitors should be between all signal cables
which have to connect between boxes although this may not be practical if fast switching [digital] signals are
involved (if this is the case then smaller value Y capacitors should be used).
ESD Protection
Where signal or control ports are connected to a user accessible panel (for example PSU inhibit to a switch,
module good to an indicator circuit, etc), these ports must be protected from electrostatic discharges. This can
be achieved by selecting suitable panel controls or by fitting ESD suppression devices to the connections on the
panel.
CPFE500F Application Note
CPFE500F
Document Number : 61066 iss 2
Figure 19
AC inlet
L
N
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