ALUMINUM ORGANIC CAPACITORS
Performance Characteristics
DC Leakage Current is the current that flows
ESR
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.
1
θ
X =
(Ohms)
c
2πfC
δ
Where:
f = frequency (Hertz)
C = capacitance (Farad)
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.
X
c
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-
Figure 2a Total Impedance of the Capacitor
Below Resonance
tive reactance, (X ) and is usually expressed as a
c
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.
X
= 2πfL (Ohms)
L
Z
Where:
f = frequency (Hertz)
L = inductance (Henries)
R
X
L
DF =
= 2πfCR
δ
X
c
Where:
DF = Dissipation Factor
= Equivalent Series Resistance (Ohms)
c = Capacitive Reactance(Ohms)
= Frequency (Hertz)
= Capacitance (Farads)
θ
R
X
ESR
f
Figure 2b Total Impedance of the Capacitor
Above Resonance
C
DF is also referred to as tan δ or "loss tangent."
The "Quality Factor," "Q", is the reciprocal of DF.
To understand the many elements of a capacitor,
see Figure 3.
8. Equivalent Series Resistance (ESR) and
Impedance (Z)
C
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.
R
ESL
ESR
L
C
R
d
d
Total impedance of the capacitor is the vector sum of
capacitive reactance (X ) and ESR below reso
c
nance; above resonance total impedance is the vec-
tor sum of inductive reactance (X ) and ESR.
L
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.
59
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