Pulse transformer gate drive for offline half bridge SMPS

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treez

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On page 125 of Power supply cookbook by Marty Brown (2nd Ed), Brown designs a pulse transformer gate drive for an offline half bridge converter. Brown states that the gate drive transformer would have the same voltage stresses as the main half bridge transformer…surely this is not correct?
(the drive transformer is driving primary hi side fet from the primary side)
 

The drive transformer windings must be isolated for the full converter operation voltage, same as the output transformer. Nevertheless the drive transformer provides only functional isolation. The output transformer typically needs reinforced isolation, hence higher creepage, clearance and test voltages.

If voltage stress refers to the isolation working voltage, particularly high frequent AC, the author is right though.
 
the GD Tx sees the pri side rail volts at switching frequency - so some pretty decent insulation needed for 10 year service life

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except under lightning and impulse test conditions the main Tx sees the same stresses to o/p - assuming output grounded ( earthed ).
 
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