A Novel Primary-Side Regulation Control Scheme for CCM and DCM LLC LED Driver based on “Magnetizing Current Cancellation Method”

In this article, the primary-side regulation (PSR) technique to achieve accurate output current in an LLC resonant converter has been studied. A novel PSR control scheme for an LLC light-emitting diode (LED) driver based on the “magnetizing current cancellation method” is proposed. The proposed “magnetizing current cancellation method” can effectively eliminate the effect of magnetizing current in the sampled primary resonant current under both the continuous conduction mode and the discontinuous conduction mode. Thus, the accurate output current can be estimated on the primary side of the LLC resonant converter. The magnetizing current cancellation method for the LLC LED driver with symmetric primary resonant current and asymmetric primary resonant current has been analyzed in detail. Some design considerations have also been presented. Then, an LLC PSR control circuit has been designed based on the theoretical analysis. Finally, a 48-to-78-V/1.3-A laboratory prototype for the LED driver has been built up, and experimental results show that good output current regulation has been obtained.