KP/MKP 375
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Vishay BCcomponents
Revision: 10-Aug-15
24
Document Number: 28127
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MEASURING THE COMPONENT TEMPERATURE
A thermocouple must be attached to the capacitor body as in:
The temperature is measured in unloaded (T
amb
) and maximum loaded condition (T
C
).
The temperature rise is given by T = T
C
- T
amb
.
To avoid radiation or convection, the capacitor should be tested in a wind-free box.
APPLICATION NOTE AND LIMITING CONDITIONS
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
PP
) shall not be greater than the maximum (U
p-p
) to avoid the ionization inception level.
3. The voltage pulse 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.
Example
C = 10 nF 1600 V, KP/MPK
This is a signal as in the drawing below
U
P-P
= 1200 V; U
P
= 1100 V; T
1
= 12 µs; T
2
= 64 µs
The ambient temperature is 50 °C
Checking conditions:
1. The peak voltage U
P
= 1100 V is lower than 1600 V
DC
2. The peak-to-peak voltage 1200 V is lower than 202 x 550 V
AC
= 1414 U
P-P
3. The voltage pulse slope (dU/dt) = 320 V is much lower than 7000 V/µs
4. The dissipated power is 170 mW as calculated with fourier terms
This gives a temperature rise of 170 mW/(17 mW/°C) = 10 °C which is allowed according Fig. “Max. allowed temperature
rise as a function of ambient temperature” for an ambient temperature of 50 °C
Thermocouple
2 x
dU
dt
-------
2
x dt U
RDC
x
dU
dt
-------
rated
0
T
U
P
Time
U
P-P
T
1
T
2
_width)
Voltage
