URGENT

I need the part no. which is suitable for my application if anyone can help me out i will be really thankfull

i require an isolation between a thermistor and a microcontroller

isolation can be in the form of a buffer(or unity gain Opamp)

input to the opamp will be a potential divider arrangement using a thermistor and a resistance, where thermistor value will range from 1K Ω to 275K Ω

output of opamp will be connected to the input of microcontroller.

the specs of opamp should be:-
1) single supply +5VDC
2) high input impedence in the range of mega ohms as the input impedence of thermistor is upto 275K Ω
3) input voltage will vary from .25V DC to 4.75V DC, ouptput should be exactly the same

Presently i was using LM324 but the problem was the output ranges from .25 to 3.6V and not upto 4.75 as required.

 

Hi sundeep,

It would be helpful if you could post a schematic of your present opamp interface circuit.

hgmjr

 

Look at LMC7111.

 

Hi sundeep,

I believe the suggestion by RonH to consider using a rail-to-rail opamp will most likely correct your problem. The LM324 opamp predates the newer generation rail-to-rail opamps and so its positive swing is limited. Your need for the output to reach 4.75V coupled with the use of a +5V supply are requirements that the LM324 will have difficulty meeting.

It would still be helpful if you could post your schematic so that a clearer determination could be made. There may be additional factors responsible for your lower than expected output level.

hgmjr

 

Originally posted by sundeep@Sep 28 2005, 05:10 PM
URGENT

I need the part no. which is suitable for my application if anyone can help me out i will be really thankfull

i require an isolation between a thermistor and a microcontroller

isolation can be in the form of a buffer(or unity gain Opamp)

input to the opamp will be a potential divider arrangement using a thermistor and a resistance, where thermistor value will range from 1K Ω to 275K Ω

output of opamp will be connected to the input of microcontroller.

the specs of opamp should be:-
1) single supply +5VDC
2) high input impedence in the range of mega ohms as the input impedence of thermistor is upto 275K Ω
3) input voltage will vary from .25V DC to 4.75V DC, ouptput should be exactly the same

Presently i was using LM324 but the problem was the output ranges from .25 to 3.6V and not upto 4.75 as required.

[post=10687]Quoted post[/post]​

Hi Sundeep,

Texas Instruments offers very good RRIO OPAMPS like OPA350, OPA355 which have very high input impedence and can drive the microcontroller also.

Best regards,
Sanjeev