Circuit and Method for Driving Synchronous Rectifiers for High-Frequency Flyback Converters

摘要

A voltage waveform similar to a waveform of a magnetizing current of an isolation transformer and immune to high frequency oscillatory resonant behavior is developed across a capacitor of a series resistor and capacitor connection connected in parallel with a synchronous rectifier. A simple logic circuit produces a waveform for controlling the synchronous rectifier which is not subject to significant turn on delay or early turn off caused by oscillatory resonances among parasitic inductances and capacitances. Improved timing accuracy of a synchronous converter provides improved power converter accuracy, particularly for flyback converters which are commonly used in converters for supplying power to offline electrical device but are subject to oscillatory resonant behaviors that cannot be adequately damped at switching frequencies sufficiently high to support miniaturization of adapters.

主权项

1. A transformer isolated power converter comprising
a transformer, a synchronous rectifier connected in series with a secondary winding of said transformer, a series connected resistance and capacitance connected in parallel with said synchronous rectifier, and a circuit responsive to a voltage developed across said capacitor for developing a signal to control said synchronous rectifier.