KEMET®
APPLICATION NOTES FOR TANTALUM CAPACITORS
Capacitance typically changes with temperature
according to the curve of Figure 2.
percent in this calculation). Another expression, rarely
ESR
used, is the “power factor,” or
while DF is ctn u.
Power factor is cos u,
⌮
.
+20
+10
0
7. DC LEAKAGE (DCL)
DC leakage is affected by voltage to a much larger
extent, and this effect can frequently be used to advantage
in circuits where only very low leakage currents can be tol-
erated. Typical response of DCL to applied voltage is illus-
trated in Figure 4.
-10
-20
1.0
1.0
-80 -60 -40 -20
0 +20 +40 +60 +80 +100 +120
Operating Temperature °C
0.1
Figure 2. Typical Effect of Temperature upon Capacitance
6. DISSIPATION FACTOR (DF)
0.1
DF is measured at 120 Hz and 25° C with up to 1 volt
rms applied. Note that, in either operation, peak AC plus
DC bias must not exceed either rated voltage (normally
polarized) or 15% of rated voltage in the reverse direction
at 25°C. Measurement circuits are of high impedance,
however, and under these conditions 1 volt rms may be
applied even to 6 volt capacitors (23% peak reversal) with-
out a DC bias. DC bias is thus normally not used, except
when rated voltage is below 6 volts and the AC signal level
exceeds 0.3 vrms. However, MIL-C-39003 provides for up
to 2.2 volts DC.
0.01
0.01
0.000.00011
0
10 20
30 40 5500 60 770 0 80 90 101000111010
30 40 60 80 90
0
10
20
Temperature -°C
Percentage of Rated Voltage
Dissipation Factor (DF) is a useful low-frequency
measure of the resistive component in capacitors. It is the
ratio of the unavoidable resistance to the capacitive reac-
tance, usually expressed in percent. DF increases with
temperature above +25° C and may also increase at lower
temperatures. Unfortunately, one general limit for DF can-
not be specified for all capacitance/voltage combinations,
nor can response to temperature be simply stated.
Catalogs for the respective series list DF limits under var-
ious conditions.
Figure 4.
Typical Range of DC Leakage as
a Function of Applied Voltage
DC leakage current (DCL) increases with increasing
temperature according to the typical curve of Figure 5.
10.0
Dissipation factor increases with increasing frequen-
cy as would be expected from the decreasing capacitive
reactance. DF is not a very useful parameter above about
1 kHz. The DF of larger capacitance values increases
more rapidly than that of smaller ratings. Figure 3 shows
typical effect of frequency on DF.
Reference 1.0
at + 25°C
20.0
1.0
10.0
0.1
-60 -40 -20
0
+20 +40 +60 +80 +100 +125
Operating Temperature –˚C
1.0
100
1K
10K
Figure 5.
Typical Effect of Temperature
upon DC Leakage Current
Frequency - Hertz
Figure 3.
Normal Effect of Frequency upon
Dissipation Factor
Leakage current is measured at a rated voltage
through +85°C and may also be measured at +125°C with
2/3 of rated voltage applied.
DC bias causes a small reduction in capacitance, up
to about 2% when full rated voltage is applied, as bias. DF
is also reduced by the presence of DC bias. Rated voltage
may cause a decrease in DF of about 0.2% (e.g., a
decrease from 3.6 to 3.4% DF).
8. RATED VOLTAGE
This term refers to the maximum continuous DC
working voltage permissible at temperatures of +85° C or
below. The lower operating temperature is specified as
-55° C. Operation above +85° C is permissible, with
reduced working voltage. Typical working voltage reduc-
tion is to 2/3 of rated voltage at +125° C.
ESR
DF is defined as
and is also referred to occa-
c
sionally, as tan d or “loss tangent.” The “Quality
Factor,” Q, is the reciprocal of DF (DF is not expressed in
76
KEMET Electronics Corporation, P.O. Box 5928, Greenville, S.C. 29606 (864) 963-6300
KEMET [ KEMET CORPORATION ]
