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TO220 FETs in offline SMPS's violate creepage & clearance requirement if legs unbent?

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treez

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TO220 FETs in offline SMPS's violate creepage & clearance requirement if legs unbent?

For a TO220 FET used in a 230VAC flyback SMPS the drain and source legs are next to each other. If the TO220 is inserted straight into the PCB , without the legs being bent further apart, then the metal leg of the drain will be at most 1mm away from the metal leg of the source. (and the pads to which they are soldered will be at most that distance apart)

The drain and source could easily be 800V apart from each other during the switching cycle.

Page 9 of the following states that copper that’s that far apart in voltage must be spaced at least 2.5mm apart. –So how come TO220 FETs are regularly seen in offline SMPS’s with unbent legs, and the TO220 simply inserted into the footprint comprising three holes in a line?

PCB layout document
http://www.alternatezone.com/electronics/files/PCBDesignTutorialRevA.pdf

TO220 FET datasheet.
http://www.infineon.com/dgdl/IPP65R...7003b&fileId=db3a30432a7fedfc012a8a961e7158be
 

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