ALUMINUM ORGANIC CAPACITORS
Performance Characteristics
DC Leakage Current is the current that flows
through the capacitor dielectric after a five minute
charging period at rated voltage. Leakage is meas-
ured at 25°C with full rated voltage applied to the
capacitor through a 1000 ohm resistor in series with
the capacitor.
DC Leakage Current does increase with tempera-
ture. The limits for 85°C @ Rated Voltage and
125°C are both 2 times the 25°C limit.
7. Dissipation Factor (DF)
Refer to part number tables for maximum DF limits.
Dissipation factor is measured at 120 Hz, up to 1.0
volt rms maximum. Dissipation factor is the ratio of
the equivalent series resistance (ESR) to the capaci-
tive reactance, (X
c
) and is usually expressed as a
percentage. It is directly proportional to both capaci-
tance and frequency. Dissipation factor loses its
importance at higher frequencies, (above about 1
kHz), where impedance (Z) and equivalent series
resistance (ESR) are the normal parameters of con-
cern.
R
DF = X = 2πfCR
c
Where:
DF = Dissipation Factor
R = Equivalent Series Resistance (Ohms)
Xc = Capacitive Reactance(Ohms)
f
= Frequency (Hertz)
C = Capacitance (Farads)
DF is also referred to as tan
δ
or "loss tangent."
The "Quality Factor," "Q", is the reciprocal of DF.
8. Equivalent Series Resistance (ESR) and
Impedance (Z)
The Equivalent Series Resistance (ESR) of the AO-
CAP is much lower than standard Tantalum caps
because the polymer cathode has much higher con-
ductivity. ESR is not a pure resistance, and it
decreases with increasing frequency.
Total impedance of the capacitor is the vector sum of
capacitive reactance (X
c
) and ESR below reso
nance; above resonance total impedance is the vec-
tor sum of inductive reactance (X
L
) and ESR.
ESR
Xc =
1
2πfC
(Ohms)
θ
δ
Where:
f = frequency (Hertz)
C = capacitance (Farad)
X
c
Figure 2a Total Impedance of the Capacitor
Below Resonance
XL = 2πfL (Ohms)
Z
X
L
δ
θ
ESR
Figure 2b Total Impedance of the Capacitor
Above Resonance
To understand the many elements of a capacitor,
see Figure 3.
C
ESL
ESR
R
L
C
d
R
d
Figure 3 The Real Capacitor
A capacitor has a complex impedance consisting of
many series and parallel elements, each adding to
the complexity of the measurement system.
ESL
- Represents inductance. In most instances it is
significant at the basic measurement frequencies of
120 and 1000 Hz.
ESR
- Represents the ohmic resistance in series
with the capacitance. Lead attachment and capacitor
electrodes are contributing sources.
©KEMET Electronics Corporation, P.O. Box 5928, Greenville, S.C. 29606, (864) 963-6300
59
Aluminum Organic Capacitors
Where:
f = frequency (Hertz)
L = inductance (Henries)
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