US 12,119,755 B2
Synchronous rectifier scheme for continuous conduction mode in primary side controlled fly-back converter
Arun Khamesra, Bangalore (IN); Pragyan S. Biswal, Odisha (IN); Hariom Rai, Bangalore (IN); and Saravanan Murugesan, Bangalore (IN)
Assigned to Cypress Semiconductor Corporation, San Jose, CA (US)
Filed by Cypress Semiconductor Corporation, San Jose, CA (US)
Filed on May 31, 2022, as Appl. No. 17/829,130.
Prior Publication US 2023/0387818 A1, Nov. 30, 2023
Int. Cl. H02M 3/335 (2006.01)
CPC H02M 3/33592 (2013.01) 20 Claims
OG exemplary drawing
 
1. A Primary Side Controlled (PSC) fly-back converter comprising:
a transformer having a primary winding coupled to a rectified AC input through a power switch (PS), and a secondary winding coupled to a DC output through a synchronous rectifier field effect transistor (SR_FET), the SR_FET having a drain coupled to the secondary winding and a source coupled to the DC output; and
a fly-back-controller implemented as an integrated circuit (IC) comprising:
a primary-side-controller operable to control a duty cycle of the PS based on power supplied to the DC output; and
a secondary-side-controller operable to turn OFF the SR_FET when the PS turns ON in continuous conduction mode (CCM), the secondary-side-controller including a CCM zero-crossing-detector (ZCD) comparator having a first input coupled to the drain of the SR_FET through a capacitor to receive a first voltage, and a second input coupled to receive a second voltage, the CCM ZCD comparator operable to detect a change in a voltage on the drain of the SR_FET during CCM when the PS turning ON causes a change in secondary current, and to output a signal to turn OFF the SR_FET.