How to raise offset voltage?

[Yoshidk]

Hello everyone

Its not really homework, but needed for a project in school
Our input signal is AC -2.5V to 2.5V from another circuit, and we need to "raise" this signal to 0-5V
(ex. so -2.5V equals 0 and 0.5V equals 3V, and so on)

Is there an easy way to do this?

We tried something with "summing amplifier", and it works in simulation, but in realisation its toally messed up, we might have done several things wrong..

Here is a screenshot of circuit in multisim
**broken link removed**

U4 is a voltage follower
U5 is voltage follower supplying the 2.5V (we only have 15V supply)
U6 is the summing
U7 is an inverter

Can anyone tell either what we are doing wrong, or even better tell us an easier way to deal with this problem?

 

[barry]

Well, you've made this waaaaay more complicated than it has to be. First, U4 is supplying 0 volts to R15; just connect it to ground! But here's a simpler solution, assuming your input comes from a relatively low impedance source.

Connect your 50K/10K voltage divider to the input of a voltage follower. Connect a capacitor to that same input. Connect the other side of that cap to your input. VOILA! your output is now offset by the value of your voltage divider.

 

[Yoshidk]

Edit.
We just tried this in simulation and it works like a charm!

Thank you very much man, this will help us a lot!