Adaptive frequency adjustment technique in current mode DC–DC converters for input voltage range extension

Abstract

This study presents a switching frequency adjustment technique that helps widen the input voltage range of a current mode DC-DC converter. Conventional current-mode switching converters suffer the minimum on/off time restrictions that limit the input-to-output conversion ratio. This work introduces an additional regulation loop on top of an existing converter that regulates the switching period when the minimum on/off time limit is approached. Compared with a converter with fixed switching frequency, the proposed approach allows the free-running switching to be set without being limited by the minimum on/off time. A boost topology with output voltage of 24 V was built based on the proposed approach, and the measured valid input voltage range was extended from 8-16 to 3-21 V by the proposed scheme under 1 MHz preset frequency. Since the slope-compensation current, the inductor size, and the output capacitor are all optimised at 1 MHz and is not limited by the minimum on/off time which may lower the switching frequency of a conventional converter down to 450 kHz, the measured maximum available output current and the typical output voltage ripple under 12 V input achieved 1.57 A and 57 mV, respectively.