What role does the thermistor play in a switching power supply?

October 10, 2021

What role does the thermistor play in a switching power supply?

The typical characteristic of thermistor is that it is sensitive to temperature and exhibits different resistance values ​​at different temperatures. If the thermistor is connected in series between the rectifier bridge and the rectifier filter capacitor, it has a slow-start effect, and the purpose is to control the instantaneous impulse current when the electrolytic capacitor is charged to the electrolytic capacitor when it is just turned on, and the fuse is burned.

Choosing the thermistor in the switching power supply needs to consider the temperature of the working environment and the working current loaded on the NTC thermistor to select the resistance of the resistor. AMPFORT specializes in the production of thermistors and has a professional technical team that can help you choose the most cost-effective product for your switching power supply.

The thermistor can not only protect the switch and make the power supply work stably, but also suppress the surge voltage. Generally speaking, in small and medium power power supply circuits, power NTC thermistors are used to prevent the startup surge current. The purpose is to avoid the instantaneous surge current generated by the capacitive load charging at the moment when the electronic circuit is turned on, usually in the power circuit A power NTC thermistor is connected in series.

In this way, the surge current generated when starting up can be stopped. After the effect of stopping the surge current is completed, the resistance of the NTC thermistor will drop to a very small value through the continuous action of the current, and the power consumption is very small and can be ignored. Will affect the normal operation of the circuit.


All in all, the thermistor is very sensitive to heat. The greater the heat, the greater the resistance. It will limit the current and protect the internal components of the circuit from burnout.