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A4018_ELH • 2/10/2016

Snap-In Aluminum Electrolytic Capacitors – ELH Series, +85ºC

Impedance (Z) cont’d

Impedance as a function of frequency (sinusoidal waveform) for different temperature values can be represented as follows (typical

values):

0.1

1

10

100

1000

10000

0.1

1

10

100

1000

Z (ohm )

F (KHz)

85°C

20°C

10 µF

-40°C

R

temperature rises.

In order to obtain a low impedance value throughout the temperature range, R

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.