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A novel control technique, called bifrequency pulse-train (BF-PT) control technique, for switching dc-dc converters is proposed. In contrast to the conventional pulsewidth-modulation-based control technique of switching dc-dc converters, which realizes the output voltage regulation by adjusting the duty ratio of the control pulse cycle by cycle, the BF-PT control technique realizes the output voltage regulation of switching dc-dc converters based on the presence and absence of preset high- and low-frequency control pulses. In BF-PT control, the output voltage of switching dc-dc converter is sampled at the beginning of each switching cycle and compared with a reference voltage to determine whether a high- or low-frequency control pulse should be selected as the control pulse. The BF-PT control technique is simple and cost effective and enjoys fast transient response. In addition, two types of control pulses with different switching frequencies spread the emission spectrum over discrete frequencies, resulting in lower electromagnetic interference (EMI) noise and easier EMI filter design. Furthermore, more low-frequency control pulses at lighter load improve the light-load power conversion efficiency. A buck converter operating in discontinuous conduction mode is taken as an example to illustrate the application and benefits of BF-PT control technique. Simulation and experimental results are presented to verify the analytical results.
Date of Publication: Aug. 2011