SYNCHRONOUS RECTIFICATION IN A FLYBACK CONVERTER

摘要

A flyback converter (100) has a primary side (112) comprising a main switch (Q1) and a control device (116) and a delay circuit (110). The converter has a secondary side (114) comprising a drive circuit controlling a rectifying switch (Q4). The drive circuit comprises a first part including a first transistor (Q2), a first discharge diode (D2) and an on-node (D_ON) and a second part including a second transistor (Q3), a second discharge diode (D3) and an off-node (D_OFF). The control device is connected to the drive circuit via at least one drive capacitor (C1, C2) to the on- and off-nodes. The control device issues drive pulses to the main switch through the delay circuit and to the drive circuit. The drive circuit has a first mode of operation in a flyback phase, which is triggered when the main switch is turned off and the rectifying switch is rendered conducting. A second mode of operation is a forward phase, which is triggered when the main switch is turned on and the rectifying switch is rendered non-conducting. The flyback converter comprises few components and the main switch is efficiently prevented from conducting simultaneously with the rectifying switch.