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Op amp help

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I have a DC signal that goes from 0-3V and need an op-amp circuit that converts this to -1V when the input is 0 and +12V when the input is 3V. So my equation will look like, Vout = (13/3)Vin -1. Can this be done with a non-inverting configuration or does it have to be inverting because of the -1? Ive been trying to design this for a few hours but nothing works out.

thanks.
 
I have a DC signal that goes from 0-3V and need an op-amp circuit that converts this to -1V when the input is 0 and +12V when the input is 3V. So my equation will look like, Vout = (13/3)Vin -1. Can this be done with a non-inverting configuration or does it have to be inverting because of the -1? Ive been trying to design this for a few hours but nothing works out.

thanks.

Hi Highlight,
here is my solution: Use a non-inverting configuration with feedback as follows: 10k from output to neg. input and 3k from neg input to a fixed source of +0.3 volts.
Thus you have:

Vout=(1+10/3)*Vin - 0.3*10/3.
 
Last edited:
Are you trying to convert a 0-3 signal to a -1 to 12 V signal?

Or are you interested in a comparitor circuit; i.e. Vin < ~zero; output -1; wjen Vin > ~3V output 12 V; waht do you want in between.
 
Hello,


Here is a simple amplifier that takes 0 to 3v input and puts out -1 to 12v respectively.

In the schematic, the amplifier is set up to work with a stable +5v source voltage (power supply rail). However, you can connect that point to any positive voltage simply by changing the values of R2 and R3. The values of R2 and R3 are calculated from these two simple formulas:

R2=Vs*33333 in ohms
R3=10000*R2/(R2-10000) in ohms

where
Vs is the positive source power supply voltage. This should be a stable voltage over temperature.
 
Last edited:
Hello,


Here is a simple amplifier that takes 0 to 3v input and puts out -1 to 12v respectively.

In the schematic, the amplifier is set up to work with a stable +5v source voltage (power supply rail). However, you can connect that point to any positive voltage simply by changing the values of R2 and R3. The values of R2 and R3 are calculated from these two simple formulas:

R2=Vs*33333 in ohms
R3=10000*R2/(R2-10000) in ohms

where
Vs is the positive source power supply voltage. This should be a stable voltage over temperature.


works great, thanks!
 
works great, thanks!

Hi,

You're welcome. And i also wanted to mention that the limiting value of R2 is 10k and can not go lower than that without changing R1 too, although it's not likely that you would need a value as low as 10k anyway.
 
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