A Smart-Power Synchronous Rectifier by CMOS Process

The usage of power MOSFET functioning as a synchronous rectifier is a much preferred choice in switched-mode converters, especially for those of high-frequency and high-power density with low output voltage, for minimization of power loss and efficient energy management. However, its scope of application and integration as a replacement of diode rectifier is handicapped by the compulsory requirement of external sensing and gating circuits needed for precise on/off timing control and the tedious incorporation to be a dependent part of the overall converter circuit. We report a unique smart-power synchronous rectifier (SPSR) that is a two-terminal diode-alike power-integrated circuit building block that provides ultralow on-state voltage rectification without the need of adding any external sensing and gating control. Therefore, a direct replacement of diode rectifier by the SPSR in any converter circuit is made possible. In this paper, the design and fabrication of a fully CMOS-process compatible SPSR device is presented. The fabricated device achieved a low forward voltage of 0.14 V in comparison with 0.75 V of the body diode at the same rated-current density. It has a low specific input capacitance of 11.8 nF/cm², which makes it suitable for megahertz switching operations. This reported SPSR is CMOS-fabrication-process compatible and can be directly integrated with any power converter circuits on the silicon substrate.