Capacitors for Electronic Equipment

The Selection of Capacitors
for Pulse Applications
D
0
Example
Upp = 350 V
U DC = 140 V
15 µs
~(32 kHz) -1 4 µs
Capacitor: WIMA FKP 1/0.1 µF
Determination of nominal voltage
Calculation is based on an operating
temperature < +60) C unless other data is
given by the user.
U r U 350 V
U rms 85 V (referring to AC voltage share)
Selected nominal voltage:
400 VDC/250 VAC pin spacing 27.5 mm
Permissible voltage gradient
The voltage rise time is:
350 V
w 87.5 V/msec
4 msec.
Value from table “pulse rise time
WIMA FKP 1“, page 66: 7000 V/msec.
The calculated voltage gradient is lower
than the permissible value shown in the
catalogue for this capacitor.
Dissipation
Given: U rms = 85 V
f = 32 kHz
C = 0.1 mF
The frequency determined from the
steepest part of the pulse is:
Pulse width = 15 msec. = 1 cycle
Hence pulse frequency =
1
w 66 kHz
15 x 10-6 The tan d of WIMA FKP 1 at 66 kHz
w 10 x 10 -4 (graph 4).
P d = 85 2 x 2 à x 32 x 10 3 x 0.1 x 10 -6 x
10 x 10 -4 w 0.145 Watts
The selected capacitor has a pin spacing
of 27.5 mm (table 1, page 10 specific
dissipation = 0.025 Watts/K) and the
temperature rise due to self-heating is:
0.145 Watts
Temperature rise = 0.025 Watts/K
w + 6 K
The temperature rise plus the max. ambient
temperature T max. permissible operating
temperature (taking into account the
voltage derating factor as detailed in the
Technical Data). If the permissible temperature
is exceeded, please select a capacitor
with a higher voltage rating.
Optionally a recommendation can
be offered by our engineers upon
receipt of voltage and current
oscillogrammes.
Questionnaire available on
demand.
WIMA FKP 1 Pulse Capacitors
for Very High Current Ratings
The WIMA FKP1 series was developed
for extremely high pulse loads. It has an
internal series connection, the metal foil
electrodes being combined with a floating
electrode metallized on both sides. The
metal foil electrodes are safely contacted
on both sides of the end surfaces and
allow for high current and pulse loading
capabilities. At the same time the capacitor
is fully self-healing due to the floating
electrode metallized on both sides.
As regards pulse loading capability, WIMA
FKP 1 represent the high-end of capacitor
technology.
More information see page 66.
C/C (%)
6
4
2
0
-2
-4
-6
10
9
8
7
6
5
4
3
2
1
0
-55 -40 -20 0 20 40 60 80 100
T(° C)
Capacitance change versus temperature
(f =1 kHz) (general guide).
tan (x 10 -4)
-55 -40 -20 0 20 40 60 80 100
T(° C)
Dissipation factor change versus temperature
(f =1 kHz) (general guide).
M
x µF(s)
106
105
104
-55 -40 -20 0 20 40 60 80 100
T(° C)
60
52
44
36
28
20
12
Insulation resistance change versus
temperature (general guide).
tan (x 10 - 4)
4
0
102 103 104 105 f/Hz 106
Dissipation factor change versus frequency
(general guide).
11.12
11