Select a higher voltage rated part (30% to 70%) than the maximum line voltage. In the case of low impedance circuits, the tantalum capacitor is likely to be stressed by current surges. In circuits which undergo rapid charge/discharge, a protective resistor of 1.0 ohm per applied volt is recommended. If this is impossible, a voltage-derating factor of up to 70% is recommended. A combination of tantalum capacitors can be connected in series to increase working voltage of the equivalent capacitor. In many power supply topologies where the di/dt through the capacitor is limited, such as most implementations of buck (current mode), forward converter and flyback, the requirement for series resistance is decreased to 0.1 ohm per applied volt. 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. Certain test circuits such as ICT are likely to subject the capacitor to large voltage and current transients, which will not be seen in normal use. This should be taken into account when considering the capacitors rated voltage.