Another Vishay’s app note about power factor correction this time about the component used and their effects. Link here (PDF)
PFC devices are generally selected base on the speed of their reverse recovery time (trr). Currently for CCM (Continuous-Conduction-Mode) and CRM (Critical Conduction-Mode) PFC devices in market, rectifiers up to 600 V with trr smaller or equal to 35 ns are generally used as CCM PFC; rectifiers up to 600 V with reverse recovery time between 35 ns to 60 ns are used as CRM PFC.
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It should be noted there is a tradeoff between forward voltage drops and switching speed; when the reverse recovery time of Ultrafast rectifiers are less than 35 ns, their forward voltage drops would increase significantly, in turn the devices’ forward surge current abilities would be diminished, therefore cautious attention should be taken when selecting the appropriate CCM or CRM PFC devices for various switch mode power supply applications, such that expected performance could be achieved and better reliability would still be ensured.
