NTC as a Limiter

[parth22]

Hi all,
I have some questions related using NTC as current limiter.
I read that temp. of NTC changes by nearby components heating or self heating of NTC. To see the self heating behavior I want a thermal model of NTC and want to simulate it.
So for thermal model, I need an arbitrary current source (value is coming from power generated by NTC), and a RC model.

So how to select the RC values from datasheet. Below is the data sheet for example.
https://media.digikey.com/pdf/Data Sheets/Epcos PDFs/B57234S0xxxM000.pdf

 

[KlausST]

Hi,

just to clarify:
An NTC is not used as steady current limiter. It is used as "inrush current limiter", like when charging a bulk capacitor.

A PTC may be used as (steady) overcurrent limiter. Like so called "poly fuses"

The thermal behaviour is opposite.

Klaus

 

[parth22]

Hi,

just to clarify:
An NTC is not used as steady current limiter. It is used as "inrush current limiter", like when charging a bulk capacitor.

A PTC may be used as (steady) overcurrent limiter. Like so called "poly fuses"

The thermal behaviour is opposite.

Klaus

Yes I want to use it as a inrush current limiter. I show you some data.
supply voltage 42V, any NTC resistor, a bulk capacitor 500uf (charging time around 300ms )
Maximum inrush current allowed 4A. So to see the exact behavior i need to simulate thermal model.
SO for this how will you design RC values.

 

[KlausST]

Hi,

I can´t see how your schematic from post#1 matches to the described problem.
I see no NTC, no input, no output..

Klaus

 

[parth22]

Hi,

I can´t see how your schematic from post#1 matches to the described problem.
I see no NTC, no input, no output..

Klaus

Now?

 

[FvM]

I read this thread as follow up to this one https://www.edaboard.com/threads/hysteresis-of-capacitor-voltage.402107

I personally suggested a NTC as possible solution. I would expect that the NTC SPICE model represents the resistance variation, which requires behavioral modelling. It can't use constant R model as in post #5. If I remember right, there are ready made models for Epcos/TDK NTC.

 

[parth22]

I read this thread as follow up to this one https://www.edaboard.com/threads/hysteresis-of-capacitor-voltage.402107

I personally suggested a NTC as possible solution. I would expect that the NTC SPICE model represents the resistance variation, which requires behavioral modelling. It can't use constant R model as in post #5. If I remember right, there are ready made models for Epcos/TDK NTC.

Thanks for suggesting the thread. I will go through with this.
But in post 5, R is not constant. it is changing with T_NTC. Where T_NTC is coming from it's self
heating model.
Btw can you suggest how to make behavioral modelling?

 

[FvM]

But in post 5, R is not constant. it is changing with T_NTC. Where T_NTC is coming from it's self
heating model.

Should say, you expect it to change. But the expression isn't evaluated during transient simulation.