Electrical resistance Temperature coefficient

1 electrical resistance

1.1 positive temperature coefficient of resistance
1.2 negative temperature coefficient of resistance
1.3 negative temperature coefficient of resistance of semiconductor

electrical resistance

the temperature dependence of electrical resistance , of electronic devices (wires, resistors) has taken account when constructing devices , circuits. temperature dependence of conductors great degree linear , can described approximation below.

ρ

⁡
(
t
)
=

ρ

0


[
1
+

α

0


(
t
−

t

0


)
]


{\displaystyle \operatorname {\rho } (t)=\rho _{0}[1+\alpha _{0}(t-t_{0})]}

where

α

0


=


1

ρ

0






[



δ
ρ


δ
t



]


t
=

t

0






{\displaystyle \alpha _{0}={\frac {1}{\rho _{0}}}\left[{\frac {\delta \rho }{\delta t}}\right]_{t=t_{0}}}

ρ

0




{\displaystyle \rho _{0}}

corresponds specific resistance temperature coefficient @ specified reference value (normally t = 0 °c)

that of semiconductor exponential:

ρ

⁡
(
t
)
=
s

α


b
t





{\displaystyle \operatorname {\rho } (t)=s\alpha ^{\frac {b}{t}}}

where



s


{\displaystyle s}

defined cross sectional area ,



α


{\displaystyle \alpha }

,



b


{\displaystyle b}

coefficients determining shape of function , value of resistivity @ given temperature.

for both,



α


{\displaystyle \alpha }

referred resistance temperature coefficient.

this property used in devices such thermistors.

positive temperature coefficient of resistance

a positive temperature coefficient (ptc) refers materials experience increase in electrical resistance when temperature raised. materials have useful engineering applications show relatively rapid increase temperature, i.e. higher coefficient. higher coefficient, greater increase in electrical resistance given temperature increase. ptc material can designed reach maximum temperature given input voltage, since @ point further increase in temperature met greater electrical resistance. unlike linear resistance heating or ntc materials, ptc materials inherently self-limiting.

some materials have exponentially increasing temperature coefficient. example of such material ptc rubber.

negative temperature coefficient of resistance

a negative temperature coefficient (ntc) refers materials experience decrease in electrical resistance when temperature raised. materials have useful engineering applications show relatively rapid decrease temperature, i.e. lower coefficient. lower coefficient, greater decrease in electrical resistance given temperature increase. ntc materials used create inrush current limiters (because present higher initial resistance until current limiter reaches quiescent temperature), temperature sensors , thermistors.

negative temperature coefficient of resistance of semiconductor

an increase in temperature of semiconducting material results in increase in charge-carrier concentration. results in higher number of charge carriers available recombination, increasing conductivity of semiconductor. increasing conductivity causes resistivity of semiconductor material decrease rise in temperature, resulting in negative temperature coefficient of resistance.