Dc-dc Flyback Topology Of The Secondary Side Synchronous Rectifier Control Chip To Achieve

DC-DC convertor is the core of switch–on power supply, moreover, an imporant aspect is to deduce the wastage, increase the efficiency of the DC-DC convertor. Schotty diode rectification wastage occupy the most of wastage, and rectification wastage can debase and efficiency can improve observably. A synchronous rectification chip is designed in the application of flyback convertor in the paper.The key technology for flyback synchronous rectification is as follows:1: How to control dead time reasonly dead time is meant that PWM transistor and rectifying transistor is cut-off in the flyback convertor. Dead time is almost presence in the flyback schotty diode rectification.The body diode for synchronous rectifier is turn on in the dead time when it is in the CCM mode. If dead time is too short, secondary roll will be short circuit. Load doesn't gain energy. If dead time is too long, synchronous MOSFET rectification transistor is cut-off prematurely and efficiency is debase. Thereby, chip itself need to design the tracking dead time circuit automatically.2: Flow backwards wastage when the energy of high frequency pulsant transformer is discharged completely, if synchronous MOSFET rectification transistor is still turn-on, energy storage for C will flow backwards through it, consequently, leading to useless energy wastage. So, synchronous MOSFET rectification transistor must cut-off when the energy of high frequency pulsant transformer is discharged fully.3: Parasitically oscillate the secondary roll of high frequency pulsant transformer and parasitical capacitance of synchronous MOSFET rectification transistor will take place resonance when synchronous MOSFET rectification transistor is turn-on, as may make that synchronous MOSFET rectification transistor is cut-off as soon as it is turn-on. So, a circuit need to be designed to ensure that synchronous MOSFET rectification transistor is turn-on reliably.A synchronous rectification chip is designed in the application of flyback convertor to solve the above problems preferably in the paper.