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A Buck Converter with PLL-based PWM/PFM Integrated Control  

Heo, Jung (Division of Electrics & Information Engineering, Chonbuk National University)
Jeong, Hang-Geun (Division of Electrics & Information Engineering, Chonbuk National University)
Publication Information
Journal of the Institute of Electronics Engineers of Korea SD / v.49, no.8, 2012 , pp. 35-40 More about this Journal
Abstract
In DC-DC converters, a PWM/PFM dual mode control method is commonly used to maintain a high efficiency over a wide range of load variation. Since the control mode is selected according to the load condition, the chip area is increased due to additional circuit for mode control and the optimum efficiency cannot be achieved around the mode transition point. To solve such problems, a new integrated control method is proposed in this paper, in which a PLL is used in the current mode PWM control circuit instead of an oscillator. The proposed integrated control method is verified through a design of a buck converter using PSIM simulation. Simulation of the complete buck converter circuit by Cadence Spectre showed a maximum efficiency of 94.7% at a load current of 250mA and an efficiency of 85.4% at a load current of 10mA under the light load condition.
Keywords
PWM control; PFM control; wide load range; Buck converter; PLL-based oscillator;
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