The UCC24636 SR is a compact, 6-pin secondary-side synchronous rectifier MOSFET
controller and driver for high efficiency Flyback converters operating in Discontinuous (DCM) and
Transition mode (TM). Unlike traditional SR controllers which measure the SR MOSFET drain voltage,
UCC24636 implements a volt-second balance control method to determine the turn off transition of
the SR MOSFET; hence, SR conduction time is independent of the MOSFET RDSON,
parasitic inductance or ringing allowing flexibility to designers in component slelction and PCB
layout. This control method enables maximum SR conduction time and highest rectifier efficiency for
a given MOSFET.
The controller has built in intelligence to detect converter no load operation and
automatically enters standby mode. While in standby mode, it disables the SR MOSFET and lowers its
bias supply current to 110µA to further reduce overall system standby power consumption. The wide
VDD operating range for the controller allows direct bias from the converter output for fixed or
variable output voltage designs. This eliminates the need for an auxilliary winding on the main
transformer, which simplifies the circuit design and reduces the cost.
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