Quote:
Originally Posted by ms660
Another way to figure out what VA rating is needed is by using Schades curves.
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Quote:
Originally Posted by kalee20
It would, and that would be the way to go if a transformer is being designed.
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You don't have to design the transformer in order to figure out what VA rating is likely to be required (give or take a few percent) using Schades curves.
I've done a comparison for 15 VDC @ 3 Amps using a guide from a transformer manufacturer and Schades curves.
Manufactures guide:
VAC = 0.85*VDC + 2*Vdrop = 14.75 Volts (Vdrop being the DC RMS voltage across one diode)
IAC = 1.65*IDC = 4.95 Amps
VAC*IAC = 73 VA
Schades curves.....75.8 VA....Based on Rs/Rload of 6% and a ripple factor of 1%
Near enough, given the errors that can be incurred when reading Schades curves.
Lawrence.