Thermistor

thermistor-ntc.pdf

http://www.ametherm.com/

Just a word of caution. Thermistors are designed to approx maintain a constant power dissipation over a specific range. This means that they will, by design, run hot and should not be forced air cooled. However enough space should be given around the part to allow for convection cooling. Also don't mount the thermistor near other heat sensitive parts.

 

In most transformer input designs (as opposed to off the line rectification) the inrush current is limited by the leakage reactance of the transformer, except for the magnetizing (excitation) current in the transformer. Inrush limiters will help reduce the stress on the transformer but not do much for the rectifier, caps, etc. unless the thermistor value is chosen so that it provides a comparable cold impedance to that of the leakage reactance of the transformer. This may result in excessive hot dissipation in the thermistor.

 

Without knowing the transformer characteristics, selection of the thermistor becomes a trial and error process unless others have already done it and can provide the proper part information.