Integrated transformer (IT) with built-in leakage inductors is a good approach for simplifying the whole system, as it integrates discrete leakage inductors into the transformer for an LLC converter. The integration of leakage inductor saves the volume and magnetic loss of inductor, however, with price of increased core loss as the leakage flux will flow inside the core. This digest discusses the limitations of integrated magnetics for high power LLC converter, and two design examples of IT and optimized discrete inductor and transformer (DIT) were provided and compared through 3D FEA simulation. With the proposed DIT solution with parallel windings for both inductor and transformer, current sharing between parallel windings can be achieved. The volume of the proposed DIT is 53% smaller than IT. The efficiency at Vin=500V for a 30kW LLC converter with DIT is 1% higher than the IT solution.
