Datasheet

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Fort Lauderdale, FL 33301 USA • 954-766-2800 • www.kemet.com
Single-Ended Aluminum Electrolytic Capacitors – ESC, +105°C
Impedance (Z)
Impedance of an electrolytic capacitor results from a circuit formed by the following individual equivalent series
components:
Equivalent
Capacitance
C
o
R
e
L
C
e
C
o
R
e
L
C
e
C
o
=Aluminumoxidecapacitance(surfaceandthicknessofthedielectric.)
R
e
=Resistanceofelectrolyteandpapermixture(otherresistancesnotdependingonthefrequencyarenotconsidered:tabs,
plates, etc.)
C
e
= Electrolyte soaked paper capacitance.
L = Inductive reactance of the capacitor winding and terminals.
Impedance of an electrolytic capacitor is not a constant quantity that retains its value under all conditions; it changes
depending on frequency and temperature.
Impedance as a function of frequency (sinusoidal waveform) for a certain temperature can be represented as follows:

C
o
R
e
L
C
e
0
.
1
1
1
0
1
0
0
1,000
10,000
0
.
1
1
1
0
1
0
0
1,000
Z
[
o
h
m
]
F
[
K
H
z
]
B
C
A
1
/
ω
ω
ω
ω
C
o
R
e
1
/
ω
ω
ω
ω
C
e
ω
L
• Capacitive reactance predominates at low frequencies.
• Withincreasingfrequency,capacitivereactanceXc=1/ωC
o
decreases until it reaches the order of magnitude of
electrolyte resistance R
e
(A)
• At even higher frequencies, resistance of the electrolyte predominates: Z = R
e
(A - B)
• Whenthecapacitor’sresonancefrequencyisreached(ω
0
), capacitive and inductive reactance mutually cancel each other
1/ωC
e
=ωL,ω
0
= 1/SQR(LC
e
)
• Abovethisfrequency,inductivereactanceofthewindinganditsterminals(XL=Z=ωL)becomeseffectiveandleadsto
an increase in impedance
Generally speaking, it can be estimated that C
e
≈0.01C
o
.