Specifications

Chapter 4 – Coupling Circuits
134 PL 3120/PL 3150/PL 3170 Power Line Smart Transceiver Data Boo
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to transceivers using non-earth-return coupling. For this reason, when a safety ground connection is known to be
available throughout the wiring system, a line-to-earth coupling scheme is preferred.
In applications where a safety ground connection is not always available, or where line-to-earth coupling is precluded by
local regulations, the coupling circuit must be connected between the line and neutral wires. This style of coupling is
known as either line-to-neutral or neutral-return coupling. Line-to-neutral coupling is recommended for in-home
applications world wide, and is illustrated in Figure 4.16.
Figure 4.16 Line-to-Neutral Coupling Style
In the following section the simple circuits shown in Figures 4.15 and 4.16 are expanded to make them practical in real
applications. The following discussion applies to both line-to-neutral coupling and line-to-earth coupling, as the coupling
circuit topology for each is the same.
Power Line Coupling Details
The coupling circuits shown in Figures 4.15 and 16 require the addition of a small number of components to make them
practical. Figure 4.17 shows the addition of an AC coupling capacitor (C102) to prevent the inductor from shorting the
DC bias voltage of the transmit amplifier.