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PICList Thread
'[EE]:Adding a DC Bias to An AC Signal'
2002\02\05@195238 by Steve Kasm

Put together the circuit you attached, my original circuit just had the
output (primary) of a 120/12v 300ma transformer with a 4.7uf non
polarized cap across the output going to the phone; this gave me 37.8
volts ac and rang the phone. Your circuit gives me 20 AC with only 3.2
D.C at the phone connections using your instructions. I built the
circuit according to your schematics; I can only assume I have done
something wrong, perhaps the phone is connected to the wrong place? The
only component I did not have from your schematic was the 2.2uf cap I
used a 4.7uf 50v is this critical? At the off-hook connection if I place
a meter here the voltage seems to fluctuate between 1.9v and 0dc with
the phone on-hook if that helps. I tried a 4.7uf Non Polarized and a
10Uf Non Polarized in your circuit and it seems to give a higher output
with the 4.7uf Non Polarized but still won't ring the phone.


{Original Message removed}

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