Jesz, any common operational amplifier will work ok at +5V.=20
Take for example the oldest 741.
You have only to do appropriate polarisation: + AO input must be polarised
at +2.5V using a resistor network ( 10k to 47k for the resistors are
good).
Negative feedback reaction through a capacitor from the output to -
operational input. The structure I've described will be an inverted
operational amplifier. V0 =3D - (Z2/r1) * vi where r1 is the input resistor
from AC source to - AO input, z2 is the feedback reaction ( capacitor +
r2 resistor) Take capacitor reactance 10 times less than resistor values an=
d
the gain will be: v0/vi =3D -r2/r1=20
The output will have ac signal straddle to a +2.5DC so don't forget to use
a decoupling capacitorwhen you'll drive the transformer.
Vasile




On Wed, 18 Jul 2001, Jeszs wrote:

> Hi everyone,
>=20
> I have got an audio signal (0.5V AC on top of a 4 V DC level). I need to =
feed the AC part of this signal into a telephone transformer. When I do so =
directly (or through a cap to block the DC) the information is distorted.
>=20
> I need a voltage follower to adapt the impedances. Two problems: first, t=
he only power suply available is 5VDC; second, I have searched on the web f=
or op amplifiers or buffers fed at this level but when I come to the shop t=
hey are never available.
>=20
> Could you recommend a 'generally available' op amplifier or buffer workin=
g at 5VDC?
>=20
> Thanks in advance!
>=20
> --------------------
> Jes=FAs Gonzalo
> INSA, Ingenier=EDa y Servicios Aeroespaciales, SA
> Paseo Pintor Rosales 34
> Tel: +34-915489149
> 28008 Madrid (SPAIN)
> --------------------
> =86=DBi=FB=FF=F0=C3
brX=AC=B5=CA&=86)=ED=F98^<=80=8B=8A=CBb=B1=AA=DC=86+=DEv=D8ky=E7b}=F7=ABz{p=
k+=12y=E8m=B6=9F=BF=FF=0C0=A6'%=8A=CB\=A2o=DA=AD=C8b=BD=EB=1F=A2=B7^=B5=A8=
=A5

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