Synchronous rectifying circuit with primary-side swithching current detection for offline power converters

摘要

A synchronous rectifying circuit is provided for offline power converter. A pulse signal generator is utilized to generate a pulse signal in response to a switching current of the power transformer. An isolation device is coupled to the pulse signal generator for transferring the pulse signal through an isolation barrier of the power transformer. A synchronous rectifier includes a power switch and a control circuit. The power switch is coupled between the secondary side of the power transformer and the output of the power converter for the rectifying. The control circuit is operated to receive the pulse signal for turning on/off the power switch. The pulse signal is generated to turn on the power switch once the switching current is higher than a threshold.