Temperature

Capacitance temperature dependance

Capacitance will undergo a reversible change within a range of temperatures between the upper and lower category temperatures. The gradient of the capacitance/temperature curve is given by the temperature coefficient a of the capacitance, which is defined as the average capacitance change, in relation to the capacitance measured at (20 2) C, occurring within the temperature range T₁ to T₂. It is expressed in units of 10^-6/K.

a = (C₂-C₁)/C₃/(T₂-T₁)
C₁ Capacitance measured at temperature T₁ C₂ Capacitance measured at temperature T₂ C₃ Reference capacitance measured at (20 2) C

The temperature coefficient is essentially determined by the properties of the dielectric, the capacitor construction and the manufacturing parameters. Polypropylene capacitors have negative temperature coefficients, polyester capacitors have positive temperature coefficients.

P

Dielectric		PP	PET	PEN
C temperature coefficient a	10-6/K	-250	+600	+200

Reversible changes of capacitance with temperature are usually expressed as DC/C.

If a capacitor is subjected to a temperature cycle from the reference temperature to T_min, then up to T_max and back to the reference temperature, a small irreversible change may be observed between the initial and the final capacitance. This deviation is called temperature cyclic capacitance drift, and is expressed as a percentage of the reference capacitance. For film capacitors it is usually very small.

Source: Epcos-TDK, modified by Garmanage: Roland Gallay