A novel accurate primary side control (PSC) method for half-bridge (HB) LLC converter

Until now, several researches have been progressed on the primary side control (PSC) methods which decrease the size and cost of the overall system. However, all of them have been applied to the flyback converter, and it is difficult to apply them to the half-bridge (HB) LLC converter due to the large voltage across the secondary leakage inductor of the transformer. In this letter, a new PSC method for the HB LLC converter is proposed to obtain accurate output voltage. In the proposed method, the output voltage is regulated by obtaining the voltage across the primary side of the transformer when the external resonant inductor voltage becomes 0V. At this time, since the voltage across the transformer secondary leakage inductor is small, the proposed method can accurately regulate the output voltage. A 400V input and 20V/85W output laboratory prototype is built and tested to verify the effectiveness of the proposed PSC method.