Switching power supply control circuit and method and switching power supply system

• Main Author: CHENG DONGBO
• Format: Patent
• Language: Chinese; English
• Published: 24.12.2019
• Subjects: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC,OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWERSUPPLY SYSTEMS; CONTROL OR REGULATION THEREOF; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUTPOWER; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER; ELECTRICITY; GENERATION

The invention discloses a switching power supply control circuit and method and a switching power supply system. When a low bus voltage Vbus is input to a switching power supply, the output voltage Vout of the secondary side is reduced. In this case, the switching power supply control circuit of the invention can detect that the waveform of a feedback voltage VFB used for feeding back the output voltage Vout condition of the secondary side of the switching power supply has a full duty ratio and judge that an output power frequency ripple problem occurs, the peak voltage Vcs of the switching power supply will be increased by K times (K>1), and the ratio Tons/Tsw of the secondary side on time of the switching power supply to the switching period will be reduced by K times, so that the product of Vcs and Tons/Tsw is kept unchanged, and the constant-current output of the switching power supply is maintained. Meanwhile, because Tons/Tsw is reduced (namely, Tons remains unchanged, and Tsw isincreased), the off time