A Constant Current Digital Control Method for Primary-Side Regulation Half-Bridge LLC Resonant Converter

Half-bridge LLC resonant converter has been widely used in many applications such as communication power supplies, servers, LED drivers due to its soft switching, high power density and low cost. To avoid the use of opto-coupler which introduces nonlinearity and temperature drift, a constant current digital control method is proposed for primary-side regulation half-bridge (PSR HB) LLC resonant converter in this paper. An auxiliary winding circuit is added and its voltage is applied to produce the magnetizing current with potential dc current bias, where the dc current bias could be compensated considering the symmetry characteristic. The output diode current waveform could be obtained from the auxiliary winding circuit and constant current control is realized accordingly. The proposed control method is verified through digital control by an FPGA-controlled 48V-78V/1.30A dc-dc PSR HB LLC resonant converter. Constant output current is realized and its accuracy is within 2.3%.