Quasi-resonant mode switching power supply controller and control method

Abstract

The invention discloses a quasi-resonant mode switching power supply controller and a control method thereof. The controller comprises a zero-crossing detection circuit which samples zero-crossing points and generates zero-crossing signals; a valley bottom conduction logic circuit which receives the zero-crossing signal and the maximum frequency signal, generates the valley bottom opening signal,and decides whether to select a new valley bottom for latching according to the preset judgment logic; a PWM logic control circuit which receives a valley bottom opening signal and a minimum frequencysignal, thereby controlling the PWM signal to be turned on, and controlling the PWM signal to be turned off according to the FB voltage signal and the CS voltage signal; and a time setting circuit which receives the PWM signal and the FB voltage signal, generates a maximum frequency signal and a minimum frequency signal, and thereby controlling the maximum frequency and the minimum frequency of the PWM operation. The invention not only can eliminate the audio noise caused by the continuous switching of adjacent valleys when the quasi-resonant mode operates, but also can improve the EMI, and has high use and popularization value.

Description

technical field [0001] The invention relates to a controller and a control method, in particular to a quasi-resonance mode switching power supply controller and a control method, belonging to the technical field of switching power supplies. Background technique [0002] Quasi-resonant mode is a kind of working mode of switching power supply. By controlling the power switch tube to turn on when the source-drain voltage reaches the minimum value, the switching loss can be controlled to the minimum, and the efficiency improvement is especially obvious for heavy load conditions. As the load lightens, both the excitation time and the demagnetization time are shortened, and the switching frequency will continue to increase when it is always turned on at the first valley. For EMI considerations, a maximum frequency is generally set and usually controlled below 150kHz. As the load is further reduced, the switching loss is usually further reduced by reducing the switching frequency....

AI Technical Summary

Problems solved by technology

The disadvantage of this technical solution is that for systems with variable output voltage and output power levels, such as systems with fast charging schemes and USB PD schemes, different output voltages and output power levels are used for charging according to the battery level.

Between different output voltage gears, the same output voltage feedback signal or output current feedback signal corresponds to different load conditions, and its operating frequency will also be different. Therefore, conduction at a fixed valley bottom is not applicable to all output gears bit

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