Apparatus and methods for sensing resonant circuit signals to enhance control in a resonant converter are described herein. A buffer circuit coupled in parallel with or across a resonant component (e.g., a transformer) input port avails a buffered primary port signal for use in resonant conversion. The buffered primary port signal is a comprehensive signal including information relating to both input voltage and input power; and it may be used to advantageously enhance switching and power conversion in an inductor-inductor capacitor (LLC) converter. Additionally, the LLC converter uses a sense interface circuit to provide a scaled replica of the buffered primary port signal. In one example the scaled replica can advantageously be used with a secondary side controller to control output power based on the comprehensive information contained within the buffered primary port signal.