SRK1000/SRK1000A/SRK1000B Adaptive Synchronous Rectification Controller

STMicroelectronics' SRK1000/SRK1000A/SRK1000B is a controller intended for secondary-side synchronous rectification (SR) in flyback converters, suitable for operation in QR and mixed CCM/DCM fixed frequency circuits. It provides a high-current gate-drive output capable of driving N-channel power MOSFETs.

The control scheme of this IC is such that the SR MOSFET is switched on as soon as current starts flowing through its body diode and it is then switched off as current approaches zero. The fast turn-on with minimum delay and the innovative adaptive turn-off logic allow for maximizing the conduction time of the SR MOSFET and eliminate the effect of parasitic inductance in the circuit.

SRK1000/SRK1000A/SRK1000B features a programmable blanking time after turn-on and a fixed min blanking time after turn-off is available with three options corresponding to three different part numbers SRK1000, SRK1000A, and SRK1000B in order to cope with different applications.

The device enters low consumption mode when it detects primary controller burst-mode operation or when the SR MOSFET conduction becomes lower than the minimum time programmed. In this way, converter efficiency improves at light load where synchronous rectification is no longer beneficial.

After the converter restarts switching or the IC detects that the current conduction in the rectifiers has increased 20% above the minimum time programmed value, the IC exits low consumption mode and resumes switching operation. SRK1000/SRK1000A/SRK1000B are in 6-pin package SOT23-6L.