Nemco Electronics Performance Info - Manual (Page 9)

General Performance Information
z Operating Voltage/Voltage Derating If a capacitor with a higher
voltage rating than the maximum line voltage is used, then the operating
reliability will be improved. This is known as voltage derating. The graph
shows the relationship between voltage derating (the ratio between
applied and rated voltage) and the failure rate. The graph gives the
correction factor F
U
for any operating voltage.
Effect of applied voltage on basic failure rate for typical component
(60% confidence level).
z Operating Temperature If the operating temperature is below the rated
temperature for the capacitor then the operating reliability will be improved
as shown. This graph gives a correction factor Ft for any temperature of
operation.
Correction Factor to Failure Rate F for Ambient Temperature T
for typical component
z Circuit Impedance All solid tantalum capacitors benefit from current limiting to
prevent burning of the device. A series resistor is recommended for this purpose.
A lower circuit impedance may cause an increase in failure rate, especially at tem-
peratures higher than 25°C. An inductive low impedance circuit may apply voltage
surges to the capacitor and similarly a non-inductive low impedance circuit may
apply current surges to the capacitor, causing localized over-heating and failure.
The recommended circuit impedance is 1 ohm per volt. Where this is not feasible,
equivalent voltage derating should be used. The graph shows the correction factor,
F
R
, for increasing series resistance.
Correction Factor to Failure Rate for Series Resistance R on Basic
Failure Rate F
B
for typical component
Correction Factor F
R
(Failure Rate 1% / 1000 hrs.)
Correction Factor F
U
Correction Factor F
T
Temperature °C
Percent Rated Voltage U/U
R
(%)