Synchronous output rectification and off line power supply Part II

Power converters are now common in the electrical world. Embedded engineers are also facing increasing demands from electrical equipment suppliers and product manufacturers to improve power convertor functions. In this context, you should know about one peculiar type of power supply- the off line flyback power supply. These custom power supplies have unique benefits over other types of power supplies. They are assisted in this by synchronous output rectification.

Off line flyback power supplies are able to achieve as much as 84% efficiency on a full load with the help of synchronous power rectification. EMI filters are also an integral part of these systems.

Synchronous power rectification was adopted in the late 1990s. The rectification function, enabled by diodes, is achieved by using MOSFETs. SR allows you to construct a number of MOSFETs in parallel enabling the system to handle enhanced output currents.

This arrangement has the additional benefit of reducing conduction losses. In high output current-low output voltage systems, synchronous switching power convertors can give you better performance compared to non-synchronous converters. Synchronous rectification improves thermal performance, efficiency, manufacturing ability, power density and reliability. It also reduces the overall cost of building the custom power supply.

Note that the embedded engineer should ensure proper timing of the gate drive signal for the synchronous rectification to enhance the convertor performance.