Calculation of the number of required PTC elements

Number of required PTC elements (connected in parallel) as function of capacitance and charging

voltage of smoothing or DC link capacitor:

N

Number of required PTC thermistors connected in parallel

C

Capacitance of smoothing or DC link capacitor in F

V

Charging voltage of capacitor in V

Heat capacity in J/K

Reference temperature of PTC in

°C

Expected maximum ambient temperature in

°C

In case of large N values the resulting resistance of the parallel PTC network might be too low for

effective limitation of the charging current. In this case a combination of series and parallel

connected PTC thermistors can be used.

Inrush current limiters

PTC thermistors in phenolic resin plastic case

Page 5 of 10

Please read Cautions and warnings and

Important notes at the end of this document.