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In this paper, a counter-based pulse-frequency-modulated (PFM) control strategy according to the output voltage ripple using a one-comparator scheme without any analog-to-digital converter (ADC) used is presented, which is realized based on the field programmable gate array (FPGA) and applied to DC-DC converters. However, too small or distorted output ripple limits its performance. Consequently, a positive-sloped ramp wave injection method is used to overcome this problem and enhances its application capability significantly. First of all, the details of the positive-sloped ramp wave injection method are illustrated, and second some experimental results are provided to verify the effectiveness of the proposed control strategy.