Primary-Side Regulation Scheme for LLC Resonant Converter With Improved Resonant Current Sampling Circuit

A primary-side regulation (PSR) scheme for LLC resonant converter with improved resonant current sampling circuit is presented in this letter. An RC branch together with the auxiliary winding of the transformer is added in parallel with the current sampling resistor. The transformer magnetizing current component in the sampled primary current waveform on the sampling resistor can be offset by the generated voltage waveform on the added capacitor of the RC branch. In this way, PSR control for LLC resonant converter can be realized. Detailed operation principle and deviation analysis on the proposed PSR scheme are presented. Furthermore, a deadtime compensation is introduced to improve the output current accuracy caused by the component tolerance. Finally, a 48-78 V/1.3 A half-bridge LLC prototype has been built up to verify the theoretical analysis.