In isolated DC-DC power converters

the equivalent common-mode (CM) port capacitance CQ between the primary and secondary sides of the transformer serves as the main pathway for the flow of common-mode noise current. Existing methods for measuring the transformer's CQ using a network analyzer are only applicable to isolated DC-DC converters with "two static potential points"

such as flyback and forward converters. There is a lack of evaluation methods for the transformers in isolated DC-DC converters with "no static points" and "single static point". Based on the principle of the Wheatstone bridge balance

This paper proposes a novel method of constructing equivalent static potential points by utilizing radio frequency (RF) transformers

this method enables the evaluation of the common-mode electromagnetic interference (EMI) characteristics of the transformers in isolated DC-DC converters with "no static points" and "single static point". Meanwhile

a calculation model for the transformer's CQ that takes into account the influence of leakage inductance is established. Finally

through the insertion loss (IL) experiments of the transformers in dual full-bridge

half-bridge LLC

and full-bridge DC-DC converters

as well as the prototype experiments of the full-bridge DC-DC converter

the feasibility and accuracy of the proposed evaluation method in this paper are verified.