# NTC voltage divider

#### banzai

Joined Jan 3, 2014
71
HI

I am using an NTC which is at (2,260Kohm at 70c) and (1,980Kohm at 75c) the resistance difference is not that big between these two temperatures and using the NTC in series with a resistor as a voltage divider wont give much of a voltage change when jumping between these tow temps. Is there any trick to increase the voltage change while using a small resistance change ?

Please let me know if i haven't been clear

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#### joeyd999

Joined Jun 6, 2011
4,287
I am using an NTC which is at (2,260Kohm at 70c) and (1,980Kohm at 75c) the resistance difference is not that big...
That's nearly a 12 1/2 % change in resistance going for 70 to 75C -- not that small. What are you trying to accomplish?

#### Dodgydave

Joined Jun 22, 2012
8,569

#### banzai

Joined Jan 3, 2014
71
That's nearly a 12 1/2 % change in resistance going for 70 to 75C -- not that small. What are you trying to accomplish?
I am building a simple temperature controller and i am currently to far away from a place where i can buy NTC electronics so i got to use what i have on hand, i got this NTC from an old Air condition unit so i don't know the specs of it, the way i got the values was by warming water and measuring the temperature with a thermocouple and using an ohm meter for the NTC

#### ericgibbs

Joined Jan 29, 2010
9,036

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#### crutschow

Joined Mar 14, 2008
23,724
Driving it with a current from a constant current source (such as from a transistor collector or drain) will maximize the voltage change with temperature. You can then amplify that with an op amp and offset the voltage (if necessary) to get the voltage change you want.

But even with a resistive (voltage divider) load you should get enough voltage difference to easily trip a comparator, if you an using ON/OFF switch to control the temperature.