There are two resonant approaches for an active clamp flyback (ACF) converter, primary resonance and secondary resonance, which affect the design guidance on the clamp capacitor (C_CLAMP). Referring to Figure 9-1, if C_O1 serves as the main energy-storage capacitor at the output with large capacitance and C_O2 is a smaller high-frequency decoupling capacitor, leakage inductance of transformer (L_K) mainly resonates with C_CLAMP during the demagnetization time of L_M. This configuration is called the primary-resonance ACF converter. On the other hand, if C_O2 serves as the main energy-storage capacitor at the output with larger capacitance and C_O1 is much smaller than the equivalent capacitance of C_CLAMP reflected to the secondary side (C_CLAMP*N_PS²), L_K mainly resonates with C_O1. This configuration is called the secondary-resonance ACF converter.