Abstract: A fly-back converter and method of operating is provided to eliminate cross-conduction between a power-switch (PS) on a primary side of a transformer and a synchronous-rectifier (SR) on a secondary side when operating in continuous conduction mode. Generally, the method includes turning on the SR when a drain voltage of the SR drops to a negative voltage followed by a 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. When the PS is turned on before the transformer is completely discharged cross-conduction causes a change in the rise of the drain voltage to a second slope greater than the first slope. By turning off the SR within 50 ns of the change in the rise of the drain voltage, cross-conduction is minimized or eliminated without receiving turn-on information from a controller operating the PS.

Abstract: A fly-back converter and method of operating is provided to eliminate cross-conduction between a power-switch (PS) on a primary side of a transformer and a synchronous-rectifier (SR) on a secondary side when operating in continuous conduction mode. Generally, the method includes turning on the SR when a drain voltage of the SR drops to a negative voltage followed by a 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. When the PS is turned on before the transformer is completely discharged cross-conduction causes a change in the rise of the drain voltage to a second slope greater than the first slope. By turning off the SR within 50 ns of the change in the rise of the drain voltage, cross-conduction is minimized or eliminated without receiving turn-on information from a controller operating the PS.