>I need to convert a 7805 based supply from a 230VAC line to 277V

Downconvert using a small additional transformer:


Use a small trafo specified as, say,  230V prim, 35V secondary

Connect the windings in serial, feed 277V across both windings, get 230V=
 across the 230V winding.

You will be *feeding* the winding labeled "secondary", instead of loading=
 it, so it=B4s voltage will be higher than specified for normal use, as this=
 is a small trafo (high loss) it will be significantly higher, say 47V.

So, you feed it 230+47V=3D277V, and you take out 230V to your original=
 tansformer across the 230V winding.

Note also that this downconvertng transformer can have a lot lower VA rating=
 than the main transformer.  The output current is the originally specified=
 current in each (prim and sec) windings *added*, then multiply by 230Volts=
 and you get the new VA.

/Morgan

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