KEMET®
APPLICATION NOTES FOR TANTALUM CAPACITORS
9. WORKING VOLTAGE
Total impedance of the capacitor is the vector sum of
capacitive reactance (XC) and ESR, below resonance;
above resonance total impedance is the vector sum of
inductive reactance (XL) and ESR.
This is the maximum recommended peak DC operat-
ing voltage for continuous duty at or below 85°C without
DC voltage surges or AC ripple superimposed. No voltage
derating is required below 85°C. Capacitors may be oper-
ated to 125°C with working voltage linearly derated to 2/3
of the 85°C rating at 125°C as shown in Figure 6.
ESR
150
125
100
75
θ
δ
1 ohm
X
=
X
C
C
50
Ζ
2πfC
25
0
where:
f = frequency, Hertz
C = capacity, Farad
-75
-50
-25
Temperature -°C
Working Voltage Change with Temperature
0
+25
+50
+75 +100 +125
Figure 6.
10. SURGE VOLTAGE
Surge voltage is defined as the maximum voltage to
which the capacitor should be subjected under transient
conditions, including peak AC ripple and all DC transients.
Figure 7a Total Impedance of the Capacitor
Below Resonance
DC Working
15/
Voltage @ 85°C
2
3
4
6 10 16 20 25 35 50 60 75100125
Surge Voltage
@ 85°C
2.6 4 5.3 8 13 20 26 33 46 65 78 98130140
TABLE 1 Surge Voltage Ratings
Ζ
A typical surge voltage test is performed at +85°C
with the applicable surge voltage per Table 1. The surge
voltage is applied for 1000 cycles of 30 seconds on volt-
age through a 33 ohm series resistor and 30 seconds off
voltage with the capacitor discharged through a 33 ohm
resistor. Upon completing the test, the capacitors are
allowed to stabilize at room temperature. Capacitance, DF,
and DCL are then tested:
X = 2πfL
X
L
L
where:
f = frequency, Hertz
L = inductance, Henries
δ
θ
1. The DCL should not exceed the initial 25°C limit.
ESR
2. The capacitance should be within ±10% of initial
value.
3. The DF should not exceed the initial 25°C limit.
Figure 7b Total Impedance of the Capacitor
Above Resonance
11. REVERSE VOLTAGE
Although these are polar capacitors, some degree of
transient voltage reversal is permissible, as seen below.
The capacitors should not be operated continuously in
reverse mode, even within these limits.
To understand the many elements of a capacitor, see
Figure 8.
Percentage of
Temperature, °C. Rated Voltage
L
R
S
C
+25
+85
+125
15
5
1
R
L
TABLE 2 Reverse Voltage Ratings
C
d
R
d
12. EQUIVALENT SERIES RESISTANCE (ESR)
Equivalent Series Resistance (ESR) is the preferred
high-frequency statement of the resistance unavoidably
appearing in these capacitors. ESR is not a pure resis-
tance, and it decreases with increasing frequency. Typical
ESR limits are established in each specific product series.
However, the ESR limits provided are for reference only,
and are not necessarily the actual value that a particular
Series product will attain.
Figure 8.
The Real Capacitor
A capacitor is a complex impedance consisting of
many series and parallel elements, each adding to the
complexity of the measurement system.
L — Represents lead wire and construction induc-
tance. In most instances (especially in solid tantalum and
KEMET Electronics Corporation, P.O. Box 5928, Greenville, S.C. 29606 (864) 963-6300
77
KEMET [ KEMET CORPORATION ]
