It's a thermistor. Its purpose is to limit inrush current at power on. It has a negative temperature coefficient, or NTC: a high resistance on start-up, which goes down as it heats up.

The NTC value you choose will depend largely on the typical current your supply needs.

Here's a write-up that discusses this: https://www.powerelectronics.com/community/article/21860750/how-do-you-choose-the-right-type-of-ntc-thermistor-to-limit-inrush-current-for-capacitive-applications

It's a thermistor. Its purpose is to limit inrush current at power on. It has a negative temperature coefficient, or NTC: a high resistance on start-up, which goes down as it heats up.

The NTC value you choose will depend largely on the typical current your supply uses and the size of the input filter cap (that is, the expected worst-case inrush.)

Here's a write-up that discusses this: https://www.powerelectronics.com/community/article/21860750/how-do-you-choose-the-right-type-of-ntc-thermistor-to-limit-inrush-current-for-capacitive-applications

It's a thermistor. It has a high resistance on start-up, which goes down as it heats up. Its purpose is to limit inrush current at power on.

It's a thermistor. Its purpose is to limit inrush current at power on. It has a negative temperature coefficient, or NTC: a high resistance on start-up, which goes down as it heats up.

The NTC value you choose will depend largely on the typical current your supply needs.

Here's a write-up that discusses this: https://www.powerelectronics.com/community/article/21860750/how-do-you-choose-the-right-type-of-ntc-thermistor-to-limit-inrush-current-for-capacitive-applications