Optimal design of multi-winding planar transformers in 1 MHz GaN multiple-output forward converters

It is a serious challenge to find the optimal winding configuration that realizes minimum leakage inductance of the multi-winding planar transformers due to the complex coupling relationship. The proposed idea is to build the mathematical model of leakage magnetic field energy and screen out all possible winding configurations to solve minimum value with Matlab programming. Then, only limited winding configurations need to be simulated in Maxwell, which saves a lot of design efforts. By analyzing the inductance matrix, the leakage inductance of multi-winding planar transformer can be obtained. Then, the optimal winding configuration is solved. A full GaN active clamp forward converter with self-driven SRs is presented. The GaN drive chips for high reliable gate voltage are combined with self-driven scheme. A 16-layer 2-oz prototype with 1 MHz, 100 V input, 5 V/ 6 A and ±12 V/ 0.83 A outputs was built. The measured leakage inductance matches the simulated results and is limited as low as 0.5% of the magnetic inductance. The full load efficiency is over 86.2% within input voltage range.

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