Specifications

PL 3120/PL 3150/PL 3170 Power Line Smart Transceiver Data Book 173
Noise at the Power Supply Input
In order to achieve maximum communication performance and to comply with the conducted emissions regulations
such as CENELEC EN 50065-1 and FCC Part 15, a switching power supply input must not conduct excessive noise
onto the power mains. A switching power supply contains an oscillator that operates at a frequency between 10kHz
and several MHz. Depending on the power supply design, significant energy at the switching frequency fundamental
and/or its harmonics can appear at the input (mains side) of the power supply. If the amplitude of the signal is large
enough in sensitive frequency ranges the performance of the PL Smart Transceiver may be degraded.
While the PL Smart Transceiver is designed to operate reliably with a combination of attenuation and significant
switching supply noise, noise from the switching power supply closest to the receiver will have the most deleterious
effect on communication performance. Noise from more distant sources will be attenuated before reaching a
receiver, minimizing its effect on reception. For this reason it is important that noise at the input of a switching
supply of a PL Smart Transceiver-based device be controlled to meet the noise masks provided in the following
section.
Switching Power Supply Input Noise Masks
The noise “masks” presented in Figures 5.12 through 5.15 show the maximum noise allowable at the input of a
switching power supply such that optimum performance of the PL Smart Transceiver is achieved and the appropriate
conducted emissions regulation satisfied. Figure 5.12 defines the noise mask for C-band CENELEC EN 50065-1 [2]
conducted emissions compliance. Figure 5.13 defines the noise mask for C-band FCC [1] conducted emissions
compliance. Likewise Figure 5.14 defines the noise mask for A-band CENELEC EN 50065-1 conducted emissions
compliance and Figure 5.15 defines the noise mask for A-band FCC conducted emissions compliance.
Measurements of a particular power supply should be made by connecting the supply to the artificial mains network
as specified in sub clause 8.2.1 of CISPR Publication 16 [3]. Measurements should be made over the full range of
anticipated loads on the supply because many switching supplies vary their switching frequency with load. Two
different limits are shown for the CENELEC measurements. One limit is measured using a quasi-peak detector, the
other using an average detector. Note that these limits are the same as required for any other CENELEC compliant
product, except in the communication range of 110kHz to 138kHz for C-band devices (70kHz to 90kHz for A-band
devices), where lower noise levels are specified.
For FCC applications, the limits of Figures 5.13 and 5.15 correspond to FCC Class B limits for frequencies above
450kHz. Below 450kHz, the limits are set such that the communication performance of the PL Smart Transceiver is
maintained. A quasi-peak detector should be used when verifying power supply noise against the limit lines of
Figures 5.13 and 5.15.
For both CENELEC and FCC measurements, the measurement bandwidths are 200Hz for frequencies below
150kHz, and 9kHz for frequencies above 150kHz, as described in CISPR 16.