Synchronous rectifying circuit and implementing method

Abstract

The invention provides a synchronous rectifying circuit which comprises two MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistor) respectively connected to the different polarity ends of one transformer full-wave rectification winding. A diode is connected in parallel between a source electrode and a drain electrode of each MOSFET; after being connected in series with a divider resistance, the drain electrode of each MOSFET is connected with the input end of a differential amplification circuit; the output end of the differential amplification circuit is connected with the input end of a comparison circuit; an output of the comparison circuit is connected with a driving circuit of the MOSFETs; an output of the driving circuit is connected with grid electrodes of the MOSFETs; after being connected in series, the different polarity ends of the other transformer full-wave rectification winding are connected with an output filter inductance; the output filter inductance is connected in series with a power supply load resistance. The synchronous rectifying circuit has the advantages of simplicity and practicality, does not depend on a primary control signal during operation, has the obvious advantage for a half-bridge topology, a phase-shifted full-bridge topology and the like which lose the duty ratio, can allow an input voltage to have a wider range, can be suitable for the place with large load variation and is low in cost.

Description

technical field [0001] The invention relates to synchronous rectification technology, in particular to a synchronous rectification circuit and a realization method. Background technique [0002] As a switching converter, there must be a rectification link at the output end for better DC output. As the main switching device of the output circuit, a diode is usually used (using its unidirectional conductivity). It can be understood as a switch that turns on as long as there is sufficient forward voltage without the need for additional control circuits. However, its conduction voltage drop is relatively high, and the conduction voltage drop of a fast recovery diode or an ultra-fast recovery diode can reach 1.0-1.2V. Even if a low-drop Schottky diode is used, the voltage drop is about 0.6V. This voltage drop generates power dissipation, and the rectifier diode is a fixed voltage drop device. The loss of such devices is very large in the working environment of low voltage and ...

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Problems solved by technology

[0004] The main disadvantage of synchronous rectification in the voltage-type self-driven mode is that the driving voltage of the SR is proportional to the input voltage of the switching converter. When the input voltage range is wide, it is difficult to drive the SR safely and reliably in the entire voltage range; the current The main disadvantage of the self-driven synchronous rectification method is that it is difficult for the converter to obtain the control signal when it is light-loaded or no-loaded; Some topologies where the secondary side loses the duty cycle are not suitable; the synchronous rectification of the control IC method solves some of the above-mentioned shortcomings due to the integration of the internal circuit, but the cost of the control IC is relatively high

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