Protection of the Transformer
This application note provides a convenient solution (see Figure 2) to deal with the problem of inrush current exceeding saturation current in transformers.
The solution uses an NTC Thermistor in series with the primary.
This NTC Thermistor offers high resistance at the beginning of switching and limits the inrush current.
After a short time, the NTC Thermistor resistance decreases to a low value due to self heating and does not affect normal operation.