EMC design of Switching Power Converters Part 6 - Design Techniques for HF output rectifiers

All PN-junction rectifiers and diodes generate switching noise. They create brief bursts of noisy reverse current every cycle, while their minority carriers decay in reverse voltage mode.

(Minority carriers are often called “holes”, but according to my Physics of Semiconductors lecturer in 1970they are really electrons orbiting atomic nuclei in forbidden energy bands, i.e. negative-mass electrons –anti-matter!)

While a rectifier is reverse-biased but its minority carriers have not yet decayed completely, it is effectively“shorting-out” the power supply, and it is hardly surprising that this causes EMI.

So the best rectifiers are Schottky types, because they have no minority carriers and so are much quieterthan PN junction “silicon” rectifiers. Schottky rectifiers made of silicon-carbide (SiC) are now available up to1.2kV, and when used in existing designs

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