ESW157M6R3AC3AA Datasheet, PDF (16/24 Pages) Kemet Corporation – Single-Ended Aluminum Electrolytic Capacitors ESW Series

Single-Ended Aluminum Electrolytic Capacitors – ESW Series, +105ºC
Impedance (Z) cont’d
Impedance as a function of frequency (sinusoidal waveform) for different temperature values can be represented as follows (typical
values):
Z (ohm)
1000
10 µF
100
-4 0°C
10
2 0°C
1
8 5°C
0.1
0.1
1
10
100
1000
10000
F (KHz)
R_e is the most temperature-dependent component of an electrolytic capacitor equivalent circuit. Electrolyte resistivity will decrease if
temperature rises.
In order to obtain a low impedance value throughout the temperature range, R_e must be as little as possible. However, R_e values
that are too low indicate a very aggressive electrolyte, resulting in a shorter life of the electrolytic capacitor at high temperatures. A
compromise must be reached.
Leakage Current (LC)
Due to the aluminum oxide layer that serves as a dielectric, a small current will continue to flow even after a DC voltage has been
applied for long periods. This current is called leakage current.
A high leakage current flows after applying voltage to the capacitor then decreases in a few minutes, e.g., after prolonged storage
without any applied voltage. In the course of continuous operation, the leakage current will decrease and reach an almost constant
value.
After a voltage-free storage the oxide layer may deteriorate, especially at high temperature. Since there are no leakage currents to
transport oxygen ions to the anode, the oxide layer is not regenerated. The result is that a higher than normal leakage current will flow
when voltage is applied after prolonged storage.
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