US 12,255,540 B2
Synchronous rectifier scheme to avoid cross-conduction in a fly-back converter
Viral Kishorkumar Brahmbhatt, Vadodara (IN); and Arun Khamesra, Bangalore (IN)
Assigned to Cypress Semiconductor Corporation, San Jose, CA (US)
Filed by Cypress Semiconductor Corporation, San Jose, CA (US)
Filed on Mar. 20, 2023, as Appl. No. 18/186,859.
Prior Publication US 2024/0322699 A1, Sep. 26, 2024
Int. Cl. H02M 3/335 (2006.01); H02M 1/44 (2007.01)
CPC H02M 3/33592 (2013.01) [H02M 1/44 (2013.01)] 20 Claims
OG exemplary drawing
 
1. A method of operating a fly-back converter, the method comprising:
turning on a synchronous-rectifier (SR) field effect transistor (SR_FET) on a secondary side of a transformer when a SR-drain-voltage on a drain of the SR_FET quickly drops to a negative voltage, followed by a gradual rise in the SR-drain-voltage at a first slope as a current is drawn from the secondary side of the transformer through the SR_FET;
turning on a power-switch (PS) in a primary side of the transformer before the current drawn from the secondary side of the transformer is completely discharged causing a change in the rise of the SR-drain-voltage to a second slope greater than the first slope; and
turning off the SR_FET following the change in the rise of the SR-drain-voltage, eliminating cross-conduction between the PS and the SR_FET when the fly-back converter is operating in a continuous conduction mode,
wherein turning off the SR_FET does not depend on receiving turn-on information from the PS.