Synchronous rectification controller and synchronous rectification control method

Abstract

The invention discloses a synchronous rectification controller and a synchronous rectification control method. The controller comprises a sampling module, a driving module and a control module, wherein the sampling module is used for sampling a source voltage and a drain voltage of a synchronous rectification metal-oxide-semiconductor (MOS) tube and acquiring a voltage difference value between thesource voltage and the drain voltage, the driving module is used for adjusting a grid voltage of the tube, and the control module is used for comparing the voltage difference value, a first thresholdvalue and a second threshold value, controlling the driving module to adjust the grid voltage of the tube to maximum output voltage when the voltage difference value is smaller than the first threshold value, controlling the driving module to adjust the grid voltage of the tube to change between 0 and the maximum output voltage when the voltage difference value is larger than the first thresholdvalue and smaller than the second threshold value so that the voltage difference value is adjusted to be equal to the first threshold value, and controlling the driving module to adjust the grid voltage of the tube to 0 when the voltage difference value is larger than the second threshold value. By the controller, the switch-on and switch-off speed of the synchronous rectification MOS tube can beincreased, so that the efficiency is obviously improved, and the loss is obviously reduced.

Description

technical field [0001] The invention relates to the field of basic electronic circuits, in particular to a synchronous rectification controller and a synchronous rectification control method. Background technique [0002] Due to the gradual increase in the requirements for energy conservation and environmental protection, countries have also formulated higher energy efficiency standards to regulate the efficiency and energy consumption of power supply products and household appliances. However, in some high-current output applications, the general flyback topology application The rectifier diodes used have problems such as large conduction voltage drop, unsatisfactory withstand voltage, and large parasitic resistance, which lead to failure to meet the requirements of energy efficiency standards. [0003] The synchronous rectification circuit is specially applied for high current output conditions. It uses synchronous rectification MOS tubes to replace the rectifier diodes in...

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Problems solved by technology

[0004] However, since the synchronous rectification MOS transistor is used in a high-current system, the area of ​​the synchronous rectification MOS transistor is large and the gate parasitic capacitance is large

The current synchronous rectification control method is generally a fixed voltage shutdown mode, which will cause inappropriate current shutdown timing, or difficulties in matching or selecting synchronous rectification MOS tubes, and the turn-on and turn-off delays of synchronous rectification MOS tubes are relatively long , making the system efficiency less

In the current continuous state, the turn-off delay of the synchronous rectification MOS tube will cause the power switch tube and the synchronous rectification MOS tube to be turned on at the same time, which will lead to transformer saturation and other phenomena, which will reduce efficiency or cause damage to the power system.

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