Nemco Electronics Performance Info - Manual (Page 2)

General Performance Information
z Working DC voltage range - 4 to 50 WVDC
Rated voltages are the maximum recommended peak DC operating
voltages for continuous use from -55°C to +85°C. Operation above
+85°C requires linear derating to 2/3 rated voltage at +125°C.
To improve operating reliability select higher voltage ratings (30% to 70%
recommended) than the maximum line voltage. This is known as
voltage derating. The effects of voltage derating can be seen by
referring to the section on reliability, failure rate.
Temperature °C
z Surge Voltage VDC Surge voltage includes the sum of
peak AC ripple, DC bias and any transients. This is the
highest voltage that may be applied to a capacitor for a short
period of time. The surge voltage may be applied up to ten
times in an hour for periods up to 30 sec. at a time. These
values are not intended to apply to continuous operation.
The surge voltage must not be used as a parameter in the
design of circuits in which, in the normal course of operation,
the capacitor is periodically charged and discharged.
The solid tantalum capacitor has a limited ability to
withstand surges due to the fact that they operate at very
high electrical stress within the oxide layer. It is important to
insure that the voltage across the terminals of the capacitor
does not exceed the surge voltage rating at any time. This
is particularly so in low impedance circuits where the
capacitor is likely to be subjected to the full impact of surges.
Even an extremely short duration spike is likely to cause
damage. In such situations it may be necessary to use a
higher voltage rating such as an extended range value and/or a lower ESR device.
Solid tantalum capacitors have a self healing ability due to the manganese dioxide semicoducting layer used as the negative
plate. In the case of low impedance circuits, the capacitor is likely to be stressed by current surges. Derating the capacitor
voltage by 50% or more increases the reliability of the component. In circuits which undergo rapid charge or discharge a
protective resistor of 1
Ω/V is recommended. If this is impossible, a derating factor of up to 70% is recommended. In such
situations a higher voltage may be needed than is available as a single capacitor. A series combination can be used to
increase the working voltage of the equivalent capacitor: For example two 22
μF 25V parts in series is equivalent to a 11μF
50V part. 1 ohm per volt series resistance is recommended for dynamic conditions which include current in-rush applications
such as inputs to power supply circuits. In many power supply topologies where the di / dt through the capacitor(s) is limited,
(such as most implementations of buck (current mode), forward converter, and flyback), the requirement for series resistance
is decreased. 0.1 ohm per volt series resistance is recommended for steady state conditions. This level of resistance is used
as a basis for the series resistance variable in a 1% /1000 hours 60% confidence level reference. This is what steady state life
tests are based on.
NOTE: Certain test circuits (i.e. ICT) are likely to subject the capacitors to large voltage and current transients, which will not
be seen in normal use. These conditions should be taken into account when considering the capacitor’s rated voltage for use.
This can be controlled by ensuring a correct test resistance is used.
% Rated V
olt
age
Rated Derated
Working Surge DC Surge
Volts Voltage Volts Voltage
+85°C +85°C +125°C +125°C
4 5.2 2.7 3.2
6.3 8 4 5
10 13 7 8
16 20 10 12
20 26 13 16
25 32 17 20
35 46 23 28
50 65 33 40