Hey there,
this is my first post, so hello everybody!

im looking for a circuit allowing me to apply min/max settings for a varying 0-10v analog control voltage. i need to limit the 10v range to a 2v range between 1v-3v.
i would like to be able to vary these limits with trim pots if possible.
i found a circuit for a fixed supply voltage, but nothing for a varying one. it would be great, if anyone could point me to a fitting circuit.

thanks a lot!
jakob

 

If I understand correctly, you want to convert a 0-10V signal to a 1-3V signal?

 

You can run the 0-10V signal through a gain stage with a gain of 0.2 which will convert it to a 0-2V signal and the add it to a constant value of 1 volt to get a signal that varies from 1-3 volts. Completely standard opamp stuff.

 

To be clear, do you want to scale the input or limit it?
Scale: 1V in gives 1.2V out, 9V in gives 2.8V out.
Limit: Anything less than 1V in gives 1V out, anything more than 3 V in gives 3V out, 2.5V in gives 2.5V out.

 

i found a circuit for a fixed supply voltage, but nothing for a varying one.

ok post the circuit.

i would like to be able to vary these limits with trim pots

"trim pot" What is the range? 0 to 10V or can you live with 0 to 5V?
What supply voltages do you have? Is there a negative supply?

 

Hey thanks for the replies
i want to scale them just as described by AlbertHall. It would be great if i could somehow set the limits with trim pots. my supply voltage is either 24v or +-15v. My max limit will never be above 5v. My min limit never below 1v. The input range will always vary between 0-10v. Thanks!

 

Hey thanks for the replies
i want to scale them just as described by AlbertHall. It would be great if i could somehow set the limits with trim pots. my supply voltage is either 24v or +-15v. My max limit will never be above 5v. My min limit never below 1v. The input range will always vary between 0-10v. Thanks!

This circuit will do a linear transformation on a 0-10V signal. It can be reconfigured to perform any similar transformation and can also be adjusted with potentiometers. The first amplifier inverts and scales the incoming control signal. The second amplifier inverts and sets the offset via resistors R7 & R8. Any linear function of the form y = mx + b can be realized in this fashion. It is necessary to use an inverting configuration because the non-inverting configuration cannot realize a gain of less than 1, when configured as a unity gain follower.

 

Papabravo beat me by a minute.

Below is the LTspice simulation of a two op amp circuit that I think does what you want.
The output is shown for both limits of the gain and offset adjustment pots with a 0-10V input (horizontal axis).
I used the ±15V supplies you have available.

 

It may be worth pointing out that you can realize the same behavior with either a single supply or a dual supply.

 

Thanks a lot guys, you are awesome! I will give this a shot on the weekend and let you know how it goes. Best

 

Papabravo - thanks!
what value would i use for r7 and r8 if id want this to be 1v-5v instead? I just want to see what size of trimmers i need in order to fit my range.

 

Crutshow - say i want to lower the starting point back to 0v - is that possible with the given resistors? Or would i need to change anything?

 

Papabravo - thanks!
what value would i use for r7 and r8 if id want this to be 1v-5v instead? I just want to see what size of trimmers i need in order to fit my range.

The span is set with resistors R1 & R2
To map 0-10V into 1-5V, you compute the gain as (5-1) / (10-0) = 0.4. You could change R1 from 4K to 8K and 8K/20K = 0.4

To get the reference voltage Vr at the junction of R7 & R8 you proceed as follows, by writing KCL :

​

(Vi - Vr)/10K = (Vr - Vo)/10K​

Vo = 2*Vr - Vi​

In the first amplifier you know several points:

0V -> 7V,​

5V -> 5V, &​

10V -> 3V​

​

because there is an inversion about the midpoint of the range. In the second amplifier you want to map the outputs from the first amplifier as follows:

7V -> 5V,​

5V -> 3V,​

3V -> 1V​

​

Pick any of those mappings and substitute

3V = 2*Vr - 5V​

8V = 2*Vr​

Vr = 4V​

​

You can keep R8 equal to 15K and change R7 to 22.6K, Vr will be equal to 4 Volts and the DC transfer function will be y = 0.4*x + 1
Note: The values of R7 & R8 are not unique. Any pair of values that gives 4V at the non-inverting input will do.

​

 

Crutshow - say i want to lower the starting point back to 0v - is that possible with the given resistors? Or would i need to change anything?

You need to change the configuration of the offset adjustment pot U3 slightly (below):

 

Thanks again. I really appreciate your help!