Fig. 26 shows the power conversion efficiency. If the load current is smaller than 30mA, the processor can change the converter to the single-phase operation for high efficiency. The efficiency improvement can be 5%. However, the converter with the dual-phase operation has better efficiency at heavy loads. A peak efficiency of 88 % is derived with the load of 1150 mA. Improved efficiencies are 5% and 10% compared to dual-phase operation without current balance function and single-phase operation, respectively.
Dual-phase operation W/I current balance
Dual-phase operation W/O current balance
Fig. 26. Power conversion efficiency.
C ONCLUSION AND F UTURE W ORK
The proposed PRCB technique for the voltage-mode multiphase DC-DC buck converter is presented with single controller to achieve the area-efficient solution. The pseudo-ramp operation can use only one physical saw-tooth to generate two individual control duties for the dual-phase operation. In addition, the current balance mechanism also forms a current-loop, which can dynamically adjust each of duty cycles, to ensure the identical driving capability in the multiphase structure. Moreover, the mode transition operation is activated when the point of duty cycle determination is around 50 % so as to prevent the unwilling mode transitions and help enhance the load transient response. Experimental results demonstrate the different mode operation with the distinct duty cycles. The current in each phase is well balanced under both light load and heavy load conditions with an improvement of 83 % in current balance.
5.2 Future Work
This thesis proposes a pseudo-ramp current balance technique to achieve single controller for multiphase operation in voltage-mode DC-DC buck converter. In this work, the operation of dual-phase is unchangeable under light load and heavy load conditions. To get the best efficiency solution under different load current, the number of the operating phase should be decided by the controller. For instance, while the load current is light, only one phase is used. On the other hand, when the load current is large, more phases should be used to cope with. Furthermore, since the current balance tends to slow down the load transient response for accurate current balance, how to improve the transient response with proper current balance performance is good topic of research.
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