Voltage follower needs solving

[ed5bradley]

Report Post Today, 04:01 PM
hello,
It is an voltage follower Op Amp...
I need to get under 5V for the V.out and also under 10mA for the I.out

What i have is a 10k thermistor and i need to know what the value of the other resistor should be, and what it looks like drawn up

take a look at the pic i attached

 

[BrownOut]

Decide what resistance the therm will be at the center of the temp range of interest, and make the other resistor that value.

 

[Roff]

Decide what resistance the therm will be at the center of the temp range of interest, and make the other resistor that value.

Apparently you understand his requirements. I don't.

 

[MrAl]

Report Post Today, 04:01 PM
hello,
It is an voltage follower Op Amp...
I need to get under 5V for the V.out and also under 10mA for the I.out

What i have is a 10k thermistor and i need to know what the value of the other resistor should be, and what it looks like drawn up

take a look at the pic i attached

Hi there,


This pic was the result of a quick study of linearity and sensitivity vs choice of resistor and just how
good a 10k thermistor (at 25 deg C) would work for sensing at 40 deg F. The thermistor B is about 4000.

The pic is temperature vs 10 bit AD count vs R2 (R2 is the upper resistor you have labeled R1 in your pic).
As R2 increases, the sensitivity goes down a little as the linearity gets better. It's not that different however.

 

[ericgibbs]

Apparently you understand his requirements. I don't.

Hi Ron,
You are not the only one.

hi Al,
Have I missed something.???

 

[Roff]

Hi Ron,
You are not the only one.

hi Al,
Have I missed something.???

Yeah, it seems like BrownOut and MrAl are just doing core dumps.

 

[MrAl]

Hi Eric and Roff,


Not sure what you mean there? I just figured he was looking for the typical technique for using thermistors for sensing temperature.
I also had to delete a pic until i fiind the right data that goes with it

 

[Roff]

Hi Eric and Roff,


Not sure what you mean there? I just figured he was looking for the typical technique for using thermistors for sensing temperature.
I also had to delete a pic until i fiind the right data that goes with it

The baffling sentence in the OPs post is this:

I need to get under 5V for the V.out and also under 10mA for the I.out

I don't see how we can answer his question until he clarifies this.

 

[MrAl]

Hi again Roff,


Oh ok i see what you mean now.

In any case, the linearity and sensitivity comes into question and here is another pic to add to the data presented so
far for using a thermistor for sensing temperature. This particular application had to sense around 40 degrees F and
needed to be relatively linear within a range of plus and minus 15 degrees F from 40 degrees F.
The red line is perfect linearity, and the blue line is the actual response of the circuit as AD count using a 10 bit ADC.

 

[Syed Horr]

R1 ≥ 10k.

I_out is depended on the load.

 

[Syed Horr]

R1 ≥ 10k.

I_out is depended on the load.

 

[Syed Horr]

R1 ≥ 10k.

I_out is depended on the load.