Backward-flowing current prevention circuit, backward-flowing current prevention method and power supply system

Abstract

An embodiment of the invention provides a backward-flowing current prevention circuit, a backward-flowing current prevention method and a power supply system. The backward-flowing current prevention circuit comprises a detection circuit, a state keeping circuit, a comparison circuit and a voltage identification circuit. Voltage at the center of a transformer secondary coil is detected through the backward-flowing current prevention circuit, namely the voltage is current output voltage of the bridge type synchronous rectification power supply system. As the current output voltage can change along with input voltage of the bridge type synchronous rectification power supply system, when falling-off of the voltage at the center of the secondary coil is detected, falling-off of the input voltage can be judged, a turn-off signal is output to a driving circuit, the driving circuit controls turn-off of a metal oxide semiconductor field effect transistor (MOSFET) of a secondary side rectifying circuit according to a judgment signal, the bridge type synchronous rectification power supply system is effectively prevented from producing backward-flowing current, and therefore, reliability of application of the synchronous rectification power supply system is improved.

Description

technical field [0001] The invention relates to the technical field of electronic circuits, in particular to an anti-backfeed current circuit, a method for preventing back-feed current and a power supply system. Background technique [0002] In recent years, with the development of electronic technology, many occasions require the working voltage of the circuit to be lower and lower, and the current is higher and higher. In the case of requiring output of low voltage and high current, it was proposed to apply synchronous rectification technology to the power supply system. Synchronous rectification uses a special metal-oxide-semiconductor-field-effect transistor (Metal-Oxide- Semiconductor Field-Effect Transistor, referred to as MOSFET), to replace the rectifier diode to reduce the output voltage and rectification loss, MOSFET is a voltage-controlled device. However, since the volt-ampere characteristic of the MOSFET is linear when it is turned on, when the MOSFET is used a...

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Problems solved by technology

However, this solution can only control the driving of the secondary side MOSFET after detecting the back-feeding current, and the back-feeding current will quickly charge the output junction capacitance of the secondary-side MOSFET. Although the back-feeding current is small, it will still cause certain stress, even avalanche

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