General Description
Effects of Voltage –
Variations in voltage have little effect
on Class 1 dielectric but does affect the capacitance and
dissipation factor of Class 2 dielectrics. The application of
DC voltage reduces both the capacitance and dissipation
factor while the application of an AC voltage within a
reasonable range tends to increase both capacitance and
dissipation factor readings. If a high enough AC voltage is
applied, eventually it will reduce capacitance just as a DC
voltage will. Figure 2 shows the effects of AC voltage.
Cap. Change vs. D.C. Volts
AVX X7R T.C.
Capacitance Change Percent
2.5
0
-2.5
-5
-7.5
-10
25%
50%
Percent Rated Volts
75%
100%
Cap. Change vs. A.C. Volts
AVX X7R T.C.
Capacitance Change Percent
50
40
30
20
Figure 4
Typical Cap. Change vs. Temperature
AVX X7R T.C.
Capacitance Change Percent
+20
+10
0VDC
0
-10
-20
-30
-55 -35
-15
+5
+25 +45 +65 +85 +105 +125
RVDC
10
0
12.5
25
37.5
Volts AC at 1.0 KHz
50
Figure 2
Capacitor specifications specify the AC voltage at which to
measure (normally 0.5 or 1 VAC) and application of the
wrong voltage can cause spurious readings. Figure 3 gives
the voltage coefficient of dissipation factor for various AC
voltages at 1 kilohertz. Applications of different frequencies
will affect the percentage changes versus voltages.
Temperature Degrees Centigrade
Figure 5
D.F. vs. A.C. Measurement Volts
AVX X7R T.C.
10.0
Dissipation Factor Percent
Curve 1 - 100 VDC Rated Capacitor
8.0 Curve 2 - 50 VDC Rated Capacitor
Curve 3 - 25 VDC Rated Capacitor
6.0
4.0
2.0
0
.5
1.0
1.5
2.0
2.5
AC Measurement Volts at 1.0 KHz
Curve 1
Curve 3
Curve 2
Figure 3
The effect of the application of DC voltage is shown in
Figure 4. The voltage coefficient is more pronounced for
higher K dielectrics. These figures are shown for room tem-
perature conditions. The combination characteristic known
as voltage temperature limits which shows the effects of
rated voltage over the operating temperature range is
shown in Figure 5 for the military BX characteristic.
Effects of Time –
Class 2 ceramic capacitors change
capacitance and dissipation factor with time as well as tem-
perature, voltage and frequency. This change with time is
known as aging. Aging is caused by a gradual re-alignment
of the crystalline structure of the ceramic and produces an
exponential loss in capacitance and decrease in dissipation
factor versus time. A typical curve of aging rate for semi-
stable ceramics is shown in Figure 6.
If a Class 2 ceramic capacitor that has been sitting on the
shelf for a period of time, is heated above its curie point,
(125°C for 4 hours or 150°C for
1
⁄
2
hour will suffice) the part
will de-age and return to its initial capacitance and dissi-
pation factor readings. Because the capacitance changes
rapidly, immediately after de-aging, the basic capacitance
measurements are normally referred to a time period some-
time after the de-aging process. Various manufacturers use
different time bases but the most popular one is one day
or twenty-four hours after “last heat.” Change in the aging
curve can be caused by the application of voltage and
other stresses. The possible changes in capacitance due to
de-aging by heating the unit explain why capacitance
changes are allowed after test, such as temperature cycling,
moisture resistance, etc., in MIL specs. The application of
high voltages such as dielectric withstanding voltages also
37
ETC [ ETC ]
