A core loss analysis method is presented for compact converters generating a high output voltage. The proposed method focuses on analyzing the core loss of asymmetrical and discontinuous current to design compact converters with a high efficiency. Owing to the proposed method, an accurate core loss for asymmetrical and discontinuous current can be analyzed intuitively and practically, without additional measurement data in a wide frequency range. A compact high step-up converter is presented as an example to demonstrate the validity of the proposed analysis method through measurement results. This method can also be utilized for analyzing core losses in various compact switching mode power supplies that operate in discontinuous conduction mode.