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NTC Thermistor noise disturbance

funnyKedougou

New Member
Hello, I am new in this community and I am glad to a membre.
Actually I am bloked since almost 1 mouth on a problem. Look at the circuit below
NTC thermistor_20210225.jpg

the NTC thermistor returns wrong values due to disturbance coming from nearby MOSFET. see below
Noise_from_Mosfet.jpg
I tried to create a filter by changing the C105 value to 200n or to add a 10k R to create a PI RC filter. But noise reduced but stay high.

Can please give some new ideas ?

Thanks
 

crutschow

Well-Known Member
Most Helpful Member
I tried to create a filter by changing the C105 value to 200n or to add a 10k R to create a PI RC filter. But noise reduced but stay high.
Is the filter close to the MOSFET input, where it should be?
Have you tried increasing the value of the capacitor?
 

funnyKedougou

New Member
Yes the CTN and RC very close to the Mosfet, the reason is to have better measure of the Mosfet heating.
increasing the C105 value was my first idea, but this reduce the noise just a little.
 

crutschow

Well-Known Member
Most Helpful Member
increasing the C105 value was my first idea, but this reduce the noise just a little.
What value did you use?
So what's limiting using an even larger capacitor?
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Your circuit shows it having a ground remote to the MCU. If it wired like that, it could well be ground noise.

Try power and ground connections directly at the MCU, and no connections to anything else away from the MCU.
 

funnyKedougou

New Member
I have used 3 values: 10n, 222n (100+100+22n) and 400n (200+200n). In the final try, I added a 10k R and I have now a better result but not good yet :-I
 

crutschow

Well-Known Member
Most Helpful Member
I have used 3 values: 10n, 222n (100+100+22n) and 400n (200+200n). In the final try, I added a 10k R and I have now a better result but not good yet :-I
You can go a lot higher than that since the thermistor resistance changes slowly, so even a large RC value won't affect the measurement accuracy.
 

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