SBOS872A May 2018 – June 2018 OPA521
PRODUCTION DATA.
Most power-line communication transformers are compact, with turns ratios between 1:1 and 4:1, low leakage inductance, and approximately 1-mH of winding inductance. It is the voltage divider formed by the HV Cap and winding inductance that divides down the ac mains voltage and reduces it to negligible levels at the modem output. Figure 21 shows the equivalent circuit formed with the HV Cap and the line coupling transformer.
Where:
For the purposes of analysis, this circuit can be simplified as shown in Figure 22.
Where:
In a typical line coupling circuit the ac mains voltage injected into the modem is approximately 20 mVPP.
Determining the optimal turns ratio (N1/N2) for the power-line communication transformer is simple, and based on the principle of using the maximum output swing capability of the power amplifier together with the maximum output current capability of the power amplifier to achieve maximum power transfer efficiency into the load. Assuming the power-supply voltage and target load impedance are known, the turns ratio is determined as shown in Figure 17, and calculated with Equation 11 and Equation 12.