op-amp design advice

Thread Starter

raffter

Joined Feb 28, 2008
113
Hello all,

how do I design about this:

input will (example) accept +/-5v and output will be 0V->5V only.... for a -5 input, output will be 0V....0V input would be 2.5V..and +5V input would be 5V out...

:rolleyes:

-Ralph
 

thingmaker3

Joined May 16, 2005
5,084
I might do this by first using an inverting summing amplifier with +5V on the second input and unity gain. Output of the first amp I would send to a second inverting amp with gain of 0.5.
fivefive.jpg
Obviously, this will need a negative rail of -10V or more.


Another option might be to use a voltage divider to get the i/p down to +/- 2.5V and sum with 2.5V.
 

SgtWookie

Joined Jul 17, 2007
22,220
See the attached schematic for one approach.

An LF353 is a dual opamp with similar characteristics to a TL072.
I used the first opamp as a unity gain buffer to avoid loading the input signal. If loading is not a factor to the input, it could be omitted.

The remaining resistors act as a voltage divider network.

The 2nd opamp is also a unity gain buffer. If loading on the output is not a factor, it could also be omitted.

Note that for this scheme to work, a dual polarity supply is necessary. It might be done with a single positive supply and an opamp that had rail-to-rail inputs and outputs, but the input signal would have some loading on it.
 

Attachments

Thread Starter

raffter

Joined Feb 28, 2008
113
thanks for the addtl inputs guys.. :)

I did mine non-inv, and with single supply only(but had to do some voltage boosting for the op-amp..too bad I cant find rail2rail o/p op-amps here(but its all OK now with raising up the supply for op-amp)...

now im thinking a way for an easy switching between level shifted into a plain unity gain(voltage follower)... oh well :) back to simulations...
 
Top