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Secondary Side Switch-Mode Power Supply Control Slide 23

This slide discusses a smart driver for Flyback converters, the STSR30. It features a supply voltage range of 4 to 5.5 V with a typical peak output current capability to drive the MOSFET of 1.5 A source/sink. The MOSFET is a voltage-dependent device that has a gate capacitance that must be driven with this current. This does not mean it can dissipate and drive 1.5 A continuously, it means it allows driving 1.5 A peak into charging and discharging the capacitance of the MOSFET gate. The STSR30 is capable of an operating frequency of 30 to 750 kHz for the power supply and it has smart turn-on anticipation timing; therefore it knows precisely when to turn the MOSFET on. The body diode almost never conducts, eliminating the additional losses of the voltage drop across the body drain diode in the MOSFET. It also has automatic turn-off for duty cycles of less than 14% to reduce light load losses, as well as a disable pin. This device is meant for use in high-power adapters. Additionally, it has an inhibit pin, an output gate pin to drive the MOSFET, a signal ground as well as a power ground pin, plus the Vcc pin for the supplied voltage and a disable, set anticipation, and clock pins. This device can operate in discontinuous mode, continuous conduction mode, and quasi-resonant configurations. There is no need for a current sense transformer in the application. It can do standalone operation on the secondary side, as there is no requirement to receive signals from the primary side controller across an isolation barrier to handle the synchronous rectification, simplifying operation.

PTM Published on: 2015-04-06