Coupled Inductors With an Adaptive Coupling Coefficient for Multiphase Voltage Regulators

As modern microprocessors continuously advance, a high-efficiency, high-power-density voltage regulator design with fast transient response is a must. Compared with the non-coupled-inductor-based solution, a multiphase buck converter with an indirect-coupled inductor (ICL) can dramatically improve the circuit transient response without increasing the inductor current ripple and sacrificing efficiency. However, a design conflict between the steady-state performance and transient response exists for the conventional ICL structure with a given inductor size. This article first analyzes the benefits and limitations of the conventional ICL based on a detailed modeling process. Then, an adaptive-coupled inductor structure is proposed to solve the issue. This is realized by applying a variable inductor in the extra winding loop of an ICL. By self-adjusting the coupling coefficient, the proposed structure can further improve the circuit transient response without increasing the phase inductor current ripple. A four-phase buck converter with the proposed inductor structure is experimentally tested, and it shows that a 25.6% output voltage overshoot reduction or a 21.8% output capacitance reduction can be realized by the proposed coupled inductor structure.