# NTC and Resistors relationship/usage

#### Lambo Av

Joined Apr 24, 2019
63
Why do we need to connect a resistor with an NTC?
In which situation does the resistance of the resistor have to be lower, equal, or higher than the NTC? (If it is possible to provide a reasoning, that will be great. Thanks)

#### DickCappels

Joined Aug 21, 2008
10,124
It is just for scaling. Often a resistor is put in series with a NTC and that resistor is connected to a voltage source to make a voltage divider which has the characteristic of the output voltage reducing as the temperature goes up, or you could swap the NTC and the fixed resistor and get a voltage with the characteristic of increasing as temperature increases.

NTC's are nonlinear and by putting resistors in series and parallel with it you can affect the shape of the nonlinearity.

The basic answer is it scales the resistance, scales the voltages and affects the shape of the voltage vs temperature curve depending upon your intent.

#### Ian0

Joined Aug 7, 2020
9,529
If you fiddle about with series and parallel resistors long enough, you can make the curve reasonable straight over the range of temperatures you are interested in.
(It generally takes less time to leave it as it is, and write a look-up table for your MCU)