Flyback converter providing accurate synchronous rectification and method of controlling the same

A flyback converter comprising:

• a transformer comprising:
• a primary winding comprising a first terminal configured to receive an input signal, and a second terminal;
• and
• a secondary winding comprising a first terminal and a second terminal;
• a main switch coupled to the second terminal of the primary winding;
• a synchronous rectifier switch comprising a first terminal coupled to the second terminal of the secondary winding and a synchronous rectifier controller,
• a second terminal coupled to a power output port and the synchronous rectifier controller, and a control terminal coupled to the synchronous rectifier
• controller, and configured to receive a control voltage to generate an output voltage;
• and
• the synchronous rectifier controller comprising:
• an edge detection circuit coupled to the first terminal of the synchronous rectifier switch, and configured to detect a fast falling edge of a voltage difference signal representing a voltage difference between the first terminal and the second terminal of the synchronous rectifier switch to generate a fast falling edge signal, the edge detection circuit comprising:
• a filter coupled to the first terminal of the synchronous rectifier switch, and configured to filter the voltage difference signal to generate a filtered voltage difference signal;
• and
• a third comparator coupled to the filter, and configured to compare the voltage difference signal with a threshold level to generate the fast falling edge signal;
• a blanking time circuit coupled to the first terminal of the synchronous rectifier switch, and configured to detect a peak according to the voltage difference signal to generate an envelope signal, generate a time length control signal according to the voltage difference signal and the envelope signal, and generate a blanking time signal according to the voltage difference signal and the time length control signal, the time length control signal indicating that a difference between the envelope signal and the voltage difference signal exceeds a predetermined threshold;
• and
• an output circuit coupled to the edge detection circuit and the blanking time circuit, and configured to perform a logic operation according to the blanking time signal and the fast falling edge signal to generate an output signal, so as to generate the control voltage.