Hold-up Time Extension Method in LLC Converter by Detecting Operation Region

This paper proposed a hold-up time extension method in LLC converter by detecting the operation region. The LLC converter is widely used topology for the medium power application due to the low voltage stress and zero-voltage-switching (ZVS) capability. The LLC converter should operate in the inductive region due to the ZVS operation. For the stable ZVS operation, a sufficient gain margin of the maximum operation gain is required to prevent the operation in the capacitive region because the theoretical peak voltage gain analysis is not accurate. As a result, to satisfy the enough hold-up time, there are many side-effects such as large link capacitor and not optimized design of the LLC converter. The proposed holdup time extension method can use the peak gain without margin by detecting the accurate peak gain point. By using the proposed method, the hold-up time can be extended and the link capacitor can be reduced achieving high power density. The feasibility of the proposed method is confirmed with 500W output prototype.