A switching power supply circuit, a synchronous rectification control circuit and a control method thereof

Abstract

Disclosed are a synchronous rectification switching power supply circuit and a control method thereof. The switching power supply circuit includes an energy storage element having a primary side and a secondary side, a synchronous rectification switch coupled to the secondary side, and a synchronous rectification control circuit. The synchronous rectification control circuit provides a driving signal to control the synchronous rectification switch, and the synchronous rectification control circuit controls the synchronous rectification switch to be turned on according to the drain-source voltage at both ends of the synchronous rectification switch after judging that the primary side is effectively turned on. In the setting mode, if the drain-source voltage at both ends of the synchronous rectification switch is continuously greater than a dynamic reference voltage within the preset window duration, it is judged that the primary side is effectively turned on, and when the switching power supply circuit works in the preset mode, the preset Once the drain-source voltage at both ends of the synchronous rectification switch is greater than the dynamic reference voltage, it is judged that the primary side is effectively turned on, thereby ensuring accurate control of the synchronous rectification switch.

Description

technical field [0001] Embodiments of the present invention relate to an electronic circuit, and more specifically, to a switching power supply circuit, a synchronous rectification control circuit and a control method thereof. Background technique [0002] With the development of electronic technology, synchronous rectification circuits are widely used in notebook power adapters, wireless communication equipment, LCD screen power management, Ethernet power supplies and other occasions that require high conversion efficiency due to their high conversion efficiency. [0003] The synchronous rectification circuit usually refers to receiving the input voltage on the primary side of the transformer, and using a controllable switch tube instead of a diode on the secondary side of the transformer to convert the input voltage into the required output voltage. Typically, its topology includes such as figure 1 The flyback converter shown. [0004] In the secondary-side synchronous r...

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Problems solved by technology

However, as the switching frequency increases, the slope of the drain-source voltage of the synchronous rectification switch during oscillation is getting closer and closer to the slope during normal turn-on, and this control method is no longer able to accurately control the conduction of the synchronous rectification switch.

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