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Rectifiers for power factor correction (PFC)

Posted: 21 Jan 2010     Print Version  Bookmark and Share

Keywords:power factor correction  conduction mode  PFC rectifier 

Continuous-conduction mode (CCM) and critical conduction mode (CRM) devices are most widely adapted in commercial applications for power factor correction (PFC). CCM devices are often used in SMPS with output power ratings greater than 300W; while CRM devices are often used in SMPS with output power ratings less than 300W. CRM PFC devices operate in the boundary mode between CCM PFC and discontinuous conduction mode (DCM) PFC devices.

PFC devices are generally selected base on the speed of their reverse recovery time (trr). Currently for CCM and CRM PFC devices in market, rectifiers up to 600V with trr smaller or equal to 35ns are generally used as CCM PFC; rectifiers up to 600V with reverse recovery time between 35ns to 60ns are used as CRM PFC. It should be noted there is a trade-off between forward voltage drops and switching speed; when the reverse recovery time of Ultrafast rectifiers are less than 35ns, 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.

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