Switched mode power supply with synchronous rectifier

Abstract

In a controller (CC2) for controlling a synchronous rectification switch (S2), the controller (CC2) comprises a sensing circuit (SRL) for sensing an output (D2) of the synchronous rectification switch (S2) at an end of a blanking time to obtain a sense signal (Q), and a control signal generating circuit (ANDl) for generating a control signal (G2) for the synchronous rectification switch (S2) in dependence on the sense signal (Q).

Description

technical field [0001] The invention relates to a switched-mode power supply with a synchronous rectifier. Background technique [0002] ST Microelectronics application note AN1804 describes the functionality and operation of the STSR30 device as a secondary synchronous rectifier driver in a flyback topology switch-mode power supply. The IC generates a drive signal with a set dead time relative to the primary side PWM signal from a synchronous clock input taken on the secondary side of the isolation transformer. When the primary switch is turned off, there is usually spikes and ringing at its drain. This voltage reflected to the secondary side determines the noise in the INHIBIT pin that causes false detection of the discontinuous pattern. To avoid this phenomenon, there is a blanking time in the INHIBIT comparator. Once the falling threshold of the clock is detected, the INHIBIT comparator is disabled for 700 ns to avoid any false triggering due to switching noise. This...

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Problems solved by technology

This voltage reflected to the secondary side determines the noise in the INHIBIT pin which will cause false detection of discontinuous mode

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