DC Power Supply Design for Broadband PLC Modem with Low Common-Mode EMI Coupling

A power line communications (PLC) test bed is designed to understand the mechanism of common-mode (CM) coupling from the PLC modem circuitry to the power lines. It is found that the step-down power transformer that provides the DC power supply to the modem circuitry causes significant CM current on the power lines. By removing the power transformer and powering the modem circuitry with an isolated DC source, we have demonstrated that the CM current on the power lines could be reduced by as much as 15 dB.