Digital Voltage-Mode Controlled Buck Converter With Dual-Edge Pulse Frequency Modulation

Pulse frequency modulation (PFM) includes constant on-time (COT) modulation and constant off-time (CFT) modulation. Compared with pulse width modulation (PWM), there are advantages of high light-load efficiency and fast transient response in PFM, so it has been widely aroused attention from domestic and foreign scholars. However, it behaves some disadvantages, such as low output-regulation accuracy, variable switching frequency, and so on.In order to improve the output-regulation accuracy of switching converter with PFM, dual-edge pulse frequency modulation (DPFM) for switching converter in a continuous conduction mode (CCM) was investigated. The principle of digital voltage-mode controlled buck converter with DPFM was introduced, and its steady-state performances were analyzed and compared with digital voltage-mode controlled buck converter with PFM, which are validated by the simulation results. The results show that DPFM modulation provides better transient performance for switching converter and improves output-regulation accuracy of switching converter.In order to improve the output-regulation accuracy and keep switching frequency constant of switching converter with PFM, improved pulse frequency modulation (IPFM) is proposed to improve the output-regulation accuracy of switching converter at first. On this basis, quasi-constant-frequency variable duty-cycle modulation (QCF-VDM) is proposed to keep switching frequency constant of switching converter. The principle of IPFM and QCF-VDM modulation was introduced. Simulation results are provided to validate the correctness of the theoretical analysis.Finally, the digital experimental platform based on the field programmable gate array is established and the experiment results verify both the theory and simulation analysis. Experimental results show that digital voltage-mode controlled buck converter with dual-edge constant on-time modulation provides better transient performance and improves output-regulation accuracy for switching converter, comparing with COT modulation. Voltage-mode controlled buck converter with improved constant on-time modulation provides better output-regulation accuracy than COT modulation, and keeps transient performance well.