Echelon LonWorks USB Network Interface - Manual (Page 23)

L
ON
W
ORKS
USB Network Interface User’s Guide 17
inductance between the power source and the power line devices. Small EMC
capacitors across the line are acceptable as long as they meet the guidelines in
Chapter 6, EMC Suppression Capacitor Value vs. Application, of the PL 3120 /
PL 3150 Power Line Smart Transceiver Data Book.
Custom AC Isolated Coupling
For high voltage isolated coupling, you will essentially be building your own
custom version of the supplied wall-plug power supply. Refer to this schematic
shown in Figure A.4 for the wall-plug power supply.
AC
INPUT
LINE
NEUTRAL
COUPLING
TRANSFORMER
STEP-DOWN
TRANSFORMER
COMBINED
VA SUPPLY/COUPLING
Figure A.4 High Voltage Isolated Coupling Power Supply Schematic
If you choose to power your U20 interface from the same high voltage AC line,
then you will need a STEP-DOWN TRANSFORMER wired as shown in Figure
A.4 to create a DC voltage in the range of 10.8 to 18VDC.
Optionally, you can choose to power your U20 interface from a battery or DC
power supply and use a coupling transformer to couple the power line
communication to the high voltage network. Batteries and DC power supplies
may lower the input impedance across the COMBINED VA/SUPPLY COUPLING
wires causing an increase in communication signal attenuation. A series
inductor (as shown in Figure A.5) should be added to raise the impedance of the
power source at the communications frequency. The inductor should be rated for
220uH, current >=300mA, and a DC resistance of <=1.0ohms.