LC filters(LCFs) play a crucial role in DC-DC converters, serving to filter out high-frequency switching noise and reduce input/output ripples. However, existing LCF solutions in converters rely heavily on a limited number of traditional configurations, with little exploration of new and potentially valuable configurations. To address this limitation, this paper proposes a systematic method to integrate DC-DC converters and second-order LCFs(SO-LCFs). The method begins with analyzing the behavior of inductors and capacitors in SO-LCFs to establish conditions under which an LC pair can function effectively as an SO-LCF. Then, with this condition, a three-step method is proposed to determine how to strategically incorporate an LC pair into a DC-DC converter to achieve effective current filtering without changing the converter’s key performance, like voltage gain. The proposed method is successfully applied to Buck, Boost, and BuckBoost DC-DC converters, resulting in 5, 5, and 6 distinct SO-LCF solutions, respectively. These solutions include not only existing configurations but also uncover several new ones, demonstrating that the proposed systematic method is more comprehensive and offers the potential for more valuable filtering solutions in practical applications.