Inrush current limiters
PTC thermistors in phenolic resin plastic case
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
C
V
C
th
T
ref
T
A,max
Number of required PTC thermistors connected in parallel
Capacitance of smoothing or DC link capacitor in F
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.
Please read
Cautions and warnings
and
Important notes
at the end of this document.
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