Inrush limiting resistors
Inrush limiting resistors of a few Ohms or less in series with the AC line can address a problem with AC-DC converters where a large surge current may occur as the device powers up and the bulk storage capacitors initially charge. One alternative, especially for higher-wattage supplies, is to use a negative temperature coefficient (NTC) resistor, which decrease in resistance as the device self-heats. This means that for optimal operation the NTC device will need to remain at that higher temperature which may not be tolerable to the surrounding components. A properly designed pulse withstanding resistor rated in Joules rather than continuous power may be the better solution in many cases.
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