The switched-mode power supply market has shown an interesting trend in recent years, mainly driven by a new demand in PCs and Telecom applications. The implementation of new circuit topologies and a tremendous increase in switching frequency to meet new limits, have been the driving factors in the development of new semiconductor components.
Fast rectifiers are today playing a key role in these new topologies and in the trend of increased frequency of operation. As switching speeds or frequency of operation increase well beyond 400Hz, rectifiers can become inefficient or notably handicapped to a variety of applications unless designed and selected with added performance features. This is most often given in terms of Reverse Recovery Time Trr. Applications may include switched mode power supplies or others requiring high speed rectifier response. In these examples, rectifiers are often expected to respond as ideal switches or "one-way-current-flow valves" to meet functional circuit requirements when subjected to forward and reverse voltage environments. High speed rectifiers best approach this ideal by minimizing switching energy losses and heat that can otherwise be generated in other circuit components and in switching rectifiers themselves.
The industry generally identifies a rectifier as "fast" if it is rated with reverse recovery of 500ns or less (approx. 1/10 that of standard rectifiers). If further improved to 100ns or less, it is often termed "ultrafast" or "superfast". Low current small signal diodes with 10-100 volt VRRM are in the Trr range of 0.75 to 5 ns. Medium to high current ultrafast / superfast rectifiers are available in a range of 15 to 60 ns as voltage rating is increased from 50 to 800 volt VRRM operation.
Surface Mount Devices