Synchronous-Rectification Controller for Affordable, High-Efficiency Power Adapters
The STMicroelectronics’ SRK1001 secondary-side synchronous-rectification controller introduces adaptive features that cut bill-of-materials costs, minimize circuit size, and simplify the design of power adapters, chargers, USB power delivery outlets, and lighting power supplies based on flyback topologies.
Designed for fast turn-on with minimum delay, and introducing innovative adaptive turn-off logic, the SRK1001 maximizes synchronous-rectification MOSFET conduction time for optimum efficiency with minimal switching losses. Unlike other controllers in the market, the SRK1001’s advanced design requires no external compensation circuitry to eliminate parasitic-inductance effects.
The SRK1001 also ensures superior converter efficiency at light loads, where synchronous rectification is no longer beneficial. The device automatically enters low-consumption mode when the MOSFET conduction period reaches the programmed minimum on time or when burst-mode operation of the primary controller is detected. The quiescent current in this mode is just 160µA.
Versatility is another strength of the SRK1001, allowing use in quasi-resonant (QR) converters and mixed continuous/discontinuous current mode (CCM/DCM) fixed-frequency operation at up to 300kHz. Robustness is assured, with programmable blanking time after both turn-on and turn-off to prevent noise from inducing spurious behavior.
Suitable for applications with output voltage up to 24V, and capable of maintaining regulation down to 2V output in CCM, the SRK1001 has a wide supply-voltage range of 4.5V to 32V. The output can sink up to 1A and source up to 0.6A to control the gate of the external N-channel synchronous-rectification MOSFET.
A dedicated Disable/Synchronization pin is provided to turn off the synchronous MOSFET and remotely trigger low-consumption mode, or to synchronize MOSFET turn-off during CCM operation. There is also drain-voltage sensing input capable of monitoring the external MOSFET drain-source voltage up to 185V.
The SRK1001 is in production now, packaged as an 8-pin SO8 device, from $0.33 for orders of 1000 pieces.