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Adaptive-coupled Inductors for Multiphase Voltage Regulators

Circuit scheme
Fig. 1. Multiphase buck with an adaptive-coupled inductor. (a) Equivalent circuit. (b) Inductor structure.
  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 (also named TLVR) can dramatically improving the circuit transient response without increasing the inductor current ripple and sacrificing the efficiency. However, a design conflict between the steady-state performance and transient response exists for the traditional indirect-coupled inductor structure with a given inductor size.

  To solve this issue, this paper proposes an adaptive-coupled inductor structure as shown in Fig. 1. This is realized by applying a variable inductor in the additional winding loop of an indirect-coupled inductor. By varying the coupling coefficient during the steady-state operation and load transients, the proposed inductor structure can help the multiphase buck converter achieve a faster transient speed while maintaining the same steady-state current ripple, as compared with the traditional indirect-coupled inductor. The coupling coefficient in the proposed structure is self-adjusted according to the circuit working conditions. Therefore, the proposed structure can be easily implemented without increasing the control complexity and cost. Furthermore, the inductor size of Lc can be dramatically reduced.

  A four-phase buck converter with the proposed inductor structure is experimentally tested, and a 25.6 % output voltage overshoot reduction can be realized by the proposed coupled inductor structure as shown in Fig. 2.
Testing waveform
Fig. 2. Load transient response comparison. (a) Traditional coupled inductor. (b) Proposed coupled inductor.

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