Datasheet

Document Number: 28109 For technical questions, contact: [e-mail]
www.vishay.com
Revision: 22-Dec-10 117
MKT371, MKT372, MKT373
DC Film Capacitors
MKT Radial Potted Type
Vishay BCcomponents
APPLICATION NOTE AND LIMITING CONDITIONS
These capacitors are not suitable for mains applications as across-the-line capacitors without additional protection, as described
hereunder. These mains applications are strictly regulated in safety standards and therefore electromagnetic interference
suppression capacitors conforming the standards must be used.
For capacitors connected in parallel, normally the proof voltage and possibly the rated voltage must be reduced. For information
depending of the capacitance value and the number of parallel connections contact: [e-mail]
To select the capacitor for a certain application, the following
conditions must be checked:
1. The peak voltage (U
P
) shall not be greater than the rated DC voltage (U
RDC
)
2. The peak-to-peak voltage (U
P-P
) shall not be greater than 2√2 x U
RAC
to avoid the ionisation inception level
3. The voltage peak slope (dU/dt) shall not exceed the rated voltage pulse slope in an RC-circuit at rated voltage and without
ringing. If the pulse voltage is lower than the rated DC voltage, the rated voltage pulse slope may be multiplied by U
Rdc
and
divided by the applied voltage.
For all other pulses following equation must be fulfilled:
T is the pulse duration
.
4. The maximum component surface temperature rise must be lower than the limits (see graph Max. Allowed Component
Temperature Rise).
5. Since in circuits used at voltages over 280 V peak-to-peak the risk for an intrinsically active flammability after a capacitor
breakdown (short circuit) increases, it is recommended that the power to the component is limited to 100 times the values
mentioned in the table: “Heat Conductivity”
6. When using these capacitors as across-the-line capacitor in the input filter for mains applications or as series connected with
an impedance to the mains the applicant must guarantee that the following conditions are fulfilled in any case (spikes and
surge voltages from the mains included).
Voltage Conditions for 6 Above
EXAMPLE
C = 330 nF - 63 V used for the voltage signal shown in next drawing.
U
P-P
= 40 V; U
P
= 35 V; T
1
= 100 µs; T
2
= 200 µs
The ambient temperature is 35 °C
Checking conditions:
1.The peak voltage U
P
= 35 V is lower than 63 V
DC
2.The peak-to-peak voltage 40 V is lower than 2√2 x 40 V
AC
= 113 U
P-P
3.The voltage pulse slope (dU/dt) = 40 V/100 µs = 0.4 V/µs
This is lower than 60 V/µs (see specific reference data for each version)
4.The dissipated power is 16.2 mW as calculated with fourier terms
The temperature rise for W
max.
= 3.5 mm and pitch = 5 mm will be 16.2 mW/3.0 mW/°C = 5.4 °C
This is lower than 15 °C temperature rise at 35 °C, according figure max. allowed component temperature rise
5.Not applicable
6.Not applicable
ALLOWED VOLTAGES
T
amb
≤ 85 °C 85 °C < T
amb
≤ 105 °C
Maximum continuous RMS voltage U
RAC
See “Max. AC Voltage as Function
of Temperature” per characteristics
Maximum temperature RMS-overvoltage (< 24 h) 1.25 x U
RAC
U
RAC
Maximum peak voltage (V
O-P
) (< 2 s)
1.6 x U
RDC
1.3 x U
RDC
2
dU
dt
--------


2
0
T

dt U
Rdc
dU
dt
--------


rated
×<××