FFLC31MA4427 Datasheet, PDF (2/9 Pages) AVX Corporation – Medium Power Film Capacitors

Medium Power Film Capacitors
FFLC
LIFETIME EXPECTANCY VS HOT SPOT TEMPERATURE AND VOLTAGE
1.4
1.3
1.2
θ_HS = 55ºC
1.1
θ_HS = 70ºC
1.0
θ_HS = 85ºC
0.9
0.8
100
1,000
10,000
100,000
Lifetime Expectancy (hours)
1,000,000
HOW TO CHOSE THE RIGHT CAPACITOR
The capacitor lifetime depends on the working voltage and the hot spot temperature.
Our caps are designed to meet 100000 hours lifetime at rated voltage and 70°C hot spot temperature. In accordance with
operating conditions, please calculate the hot spot temperature and deduce from this calculation if the obtained lifetime can suit
the application.
1. From the tables, select a capacitor with required capacitance
Cn and voltage Un.
U_n
U_w
Calculate the maximum ripple voltage allowed for the selected cap:
Urmax = 0.2Un
If Ur>Urmax, select a capacitor with higher rated voltage
Make sure Irms application < Irms table
Copy out:
• serial resistance (Rs): see table of values
• thermal resistances Rth1 and Rth2 (depending on cooling conditions)
2. Hot spot temperature calculation
Total losses are calculated as follow: Pt=Pj+Pd
Joule losses: Pj = Rs x Irms²
Dielectric losses: Pd = Q x tgδ0 with
• Q(reactive power) = Irms² for a sinusoidal waveform
–––––
C␻
• tgδ0 = 2 x 10^-4 (dielectric losses of polypropylene)
Hot spot temperature will be:
␪HS = ␪amb + (Pj + Pd) x (Rth1 + Rth2)
␪HS absolute maximum is 85°C
If temperature is higher than 85°C, come back to #1 and start again
with another selection.
Rth1: thermal resistance between hot spot and case
Rth2: thermal resistance between case and ambient air
U_r
1/f
Tim e
R_th1
R_th2
HS
CASE
AMB
width
JUNE 2015 ■ 43