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Opamp transfer

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dark

Member
Hello Forum,

I have a voltage changing slowly against response to a sensor from
10V----->5V . I have 5V single supply OPamp , now how to scale it down to 0V----->5V .

Thanks
 

ericgibbs

Well-Known Member
Most Helpful Member
Hello Forum,

I have a voltage changing slowly against response to a sensor from
10V----->5V . I have 5V single supply OPamp , now how to scale it down to 0V----->5V .

Thanks
hi,
Whats the type of OPA you have.??
 

OutToLunch

New Member
do you know anything about the sensor? if it has a low output impedance and can source some current without distorting the signal, you may be able to scale down the sensor output prior to the op amp.
 

Thunderchild

New Member
you could use a voltage divider but that would produce 2.5-5 volts output. if you want to transfer 5-10 volts into a 0-5 volts then you want to subtract not divide. I think you need a differential amplifier arrangement with a gain of 1 on both inputs
 

dark

Member
Hi ,

The Opamp I have is OPA2335 , powered with 0V and 5V . The signal I get is reverse 10V------>5V (it can be 5V---->2.5V with a divider) .But even if I subtract that I get a -Ve sign? which cannot be handeled .

Thanks
 

ericgibbs

Well-Known Member
Most Helpful Member
Hi ,

The Opamp I have is OPA2335 , powered with 0V and 5V . The signal I get is reverse 10V------>5V (it can be 5V---->2.5V with a divider) .But even if I subtract that I get a -Ve sign? which cannot be handeled .

Thanks
hi,
Say you used the INV of the OPA, with a 2:1 divider so thats +5V to 0V
and if you made the OPA *1.
Input +2.5V into the NI of the OPA.

So for 0V inp you would get +5V out
and for +5Vinp you would get 0V.

Is this what you want.?:)
 

dark

Member
hi,
Say you used the INV of the OPA, with a 2:1 divider so thats +5V to 0V
and if you made the OPA *1.
Input +2.5V into the NI of the OPA.

So for 0V inp you would get +5V out
and for +5Vinp you would get 0V.

Is this what you want.?:)
Hi,
I am afraid I dont follow you . Do you say to use the difference amplifiers NON-INV input to be heald at 2.5V ,and the INV should be fed the input signal? . If thats the case after divider I get 5V----->2.5V , and when subtraction on the higher side is done I get 2.5-5=-2.5V ? .

Thanks
 

ericgibbs

Well-Known Member
Most Helpful Member
Hi,
I am afraid I dont follow you . Do you say to use the difference amplifiers NON-INV input to be heald at 2.5V ,and the INV should be fed the input signal? . If thats the case after divider I get 5V----->2.5V , and when subtraction on the higher side is done I get 2.5-5=-2.5V ? .

Thanks
hi,
The INV gain is -1 , the NI gain is 2

Dont forget the 10V signal is via a resistive divider 2:1 so it +5V to 0V
 
Last edited:

MikeMl

Well-Known Member
Most Helpful Member
Hello Forum,

I have a voltage changing slowly against response to a sensor from
10V----->5V . I have 5V single supply OPamp , now how to scale it down to 0V----->5V .

Thanks
Here you go.
 

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dark

Member
hi,
The INV gain is -1 , the NI gain is 2

Dont forget the 10V signal is via a resistive divider 2:1 so it +5V to 0V

Hi ,

Thanks , you are right I slipped the '-1' . I think it will require a gain of 2 (or please correct me ) . holding NON-INV end at 5V . now I get 5-5*-2=0V ,5-2.5*-2=5V .

Thanks
-Adi
 

Roff

Well-Known Member
The common mode range of the OPA2335 is -0.1V to +3.5V.
The transfer function is
Vout=10-Vin.
This must be accomplished within the common mode range.
See below.
It could be accomplished with one op amp, but the resistor values get pretty funky.
 

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ericgibbs

Well-Known Member
Most Helpful Member
The common mode range of the OPA2335 is -0.1V to +3.5V.
The transfer function is
Vout=10-Vin.
This must be accomplished within the common mode range.
See below.
It could be accomplished with one op amp, but the resistor values get pretty funky.
hi Ron,
As you advise a dual OPA configuration would be better, the Rin/Rf are 'funky'.

Have to be careful how I type in 'funky'....:rolleyes:
 

MikeMl

Well-Known Member
Most Helpful Member

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MrAl

Well-Known Member
Most Helpful Member
The common mode range of the OPA2335 is -0.1V to +3.5V.
The transfer function is
Vout=10-Vin.
This must be accomplished within the common mode range.
See below.
It could be accomplished with one op amp, but the resistor values get pretty funky.

Hello,


Also, if a small error is acceptable and the loading wont bother the sensor,
then making R3=2k and R4=1k and eliminating U1 also works ok. That gets us
back down to one single op amp.
 
Last edited:

Roff

Well-Known Member
Hello,


Also, if a small error is acceptable and the loading wont bother the sensor,
then making R3=2k and R4=1k and eliminating U1 also works ok. That gets us
back down to one single op amp.
Mike posted an elegant solution.
 

dark

Member
Thanks everybody for your valuable inputs .

Regards
 
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