If the field effect transistor T is cut off, a voltage is present at the drain electrode D of the field effect transistor T, which voltage is composed of {HEAD ~ the sum} of the input voltage UE and {TAIL ~ a voltage} present across the primary winding N1 which also exhibits an overvoltage peak generated by the stray inductance between the primary and secondary winding 
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If the field effect transistor T is cut off , a voltage is present at the drain electrode D of the field effect transistor T , which voltage is composed of { HEAD ~ the sum } of the input voltage UE and { TAIL ~ a voltage } present across the primary winding N1 which also exhibits an overvoltage peak generated by the stray inductance between the primary and secondary winding
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH