Control circuit, control method and switching power supply

Abstract

The present invention provides a control circuit, a control method and a switching power supply, so that the frequency of the conduction signal used to control the conduction of the main switch tube is Preset frequency, and when the turn-off time required by the main switch tube is less than the minimum turn-off time, it is a frequency that is positively correlated with the turn-off time required by the main switch tube, so that the fixed frequency working mode can be realized The smooth switching between frequency conversion and fixed-off working modes does not require a special mode judgment circuit to provide a mode switching signal, so the implementation method is simple, and it can stably and continuously realize the expansion of the duty cycle of the switching control signal of the main switching tube . In addition, since the power supply is also in a constant off-time operation mode during the frequency conversion process, the problem of sub-harmonic oscillation caused by insufficient sub-harmonic compensation due to frequency conversion will not be caused.

Description

technical field [0001] The invention relates to the technical field of power electronics, and in particular relates to a control circuit, a control method and a switching power supply. Background technique [0002] Switching power supplies are widely used in portable electronic devices, and they are mainly composed of power stage circuits and control circuits. The control circuit controls the switching power supply to convert the input voltage into a corresponding output voltage by controlling the duty ratio of the driving signal of the main switching tube in the power stage circuit. [0003] Based on the inherent delay in the logic circuit and the driving circuit in the switching power supply, and in order to prevent false triggering of the main switching tube, it is usually necessary to make the main switching tube of the switching power supply have a minimum off time. Due to the existence of the minimum off time, in the switching power supply controlled by fixed frequenc...

AI Technical Summary

Problems solved by technology

Due to the existence of the minimum off time, in the switching power supply controlled by fixed frequency, the duty cycle of the driving signal of the main switching tube will be limited, and the higher the switching frequency of the main switching tube, this limitation will be more obvious

For example, for a step-down switching power supply, when the output voltage is required to be relatively close to the input voltage, the duty cycle of the driving signal of the main switch tube needs to be as close to 1 as possible. However, the existing fixed frequency control method, Due to the existence of the minimum off time, the maximum duty cycle of the driving signal of the main switch is limited and cannot be further expanded, making it difficult for the switching power supply to maintain the required output voltage

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