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0 to 2.5 scaling to 10v to 0v

Danish Ahmed
Prodigy 205 points
Other Parts Discussed in Thread: OPA171

Hi, 

I am building a sensor to measure the distance, sensor give output from 0 to 2.5 v DC. I want to convert these voltages into 10v to 0 V range.

0v in ---> 10v out

2.5 v in ----> 0 V out

So that sensor can easily talk with Inverter ( AC DRIVE ) to control motor speed.

I know it can be done by opamp, but i dont have any negative supply and nor i want to go into all the dcdc converters and inverters. I want to keep it simple. I have wasted a lot of money on inverters. :(

Is it possible to do it by just a single positive supply line ? then i will be more than happy to go with it....

Any help or advice will be appreciated.

Best Regards

Danish 

  • 0
    TI__Genius 14940 points

    Try this circuit.  Power the amplifier from a single 10V supply.

    Reasonable values for Ri would be in the 10k to 20k range and for Rb in the 1k to 2k range.

    The transfer function is Vo = 10 - 4 Vi

    Jim Noxon

     

  • 0 in reply to Jim Noxon
    Guru 21975 points

    Danish,

    Jim's circuit seems to have a problem with the resistor values. The circuit below uses 4 resistors instead of 5.

    R1 and R2 set a gain of -4 to amplify the 2.5V span to a 10V span at the output. The gain at the non-inverting (+) input of the op amp is +5, so 2V at this input creates a 10V positive shift in the output. I've shown the 2V created by dividing a 5V reference voltage down to 2V with R3 and R4. The 2V could be created from another voltage source (including the power supply, if it is stable enough) by changing the R3, R4 ratio.

    The OPA171 would be a reasonable choice for the op amp.

    Regards, Bruce.

  • 0 in reply to Bruce Trump
    TI__Genius 14940 points

    Uh oh!  What was I thinking.  I've since tossed the equations so I cannot even recognize where I made my mistake.  In order for my circuit to work the 4Ri/27 resistor would have to have been tied to 10/9 volts.  Bruce's circuit is the one you should use.  It is a more elegant design from the start.

    Let this be a lesson to everyone, always verify your design before publishing it.

    Jim Noxon