Author Topic: FF on Thermisters  (Read 1936 times)

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Offline techie1234Topic starter

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FF on Thermisters
« on: July 12, 2016, 12:15:41 pm »
What about a Fundamentals Friday on thermisters: some rules of thumb for when should you use them to limit inrush, how to pick the right one for a particular application, etc.?  For example, when I've modeled circuits in LTSpice (yes I know there are a lot of idealizations inherent) if you zoom in on the first ms or two you can see some very high amperage drawn into the circuit.  If that's anything like how the circuit operates in the real world, it would seem that one is over-drawing past many components' specs if only for a very short period of time - in which case, why don't we use them on virtually everything?  Or is the effect simply negligible?
« Last Edit: July 12, 2016, 12:35:57 pm by techie1234 »
 

Offline uncle_bob

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Re: FF on Thermisters
« Reply #1 on: July 13, 2016, 01:16:25 am »
Hi

Simple answer to the last part "why don't we use them on everything?":

There are other, (generally easy) ways to reduce the issues related to inrush to negligible levels. Inrush limiters have their own failure modes / drop efficiency / add cost. Consider: The beast is a temperature dependent device. It works by getting hot and staying hot. Hot stuff fails, energy is used to keep it hot.

Bob
 
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Offline techie1234Topic starter

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Re: FF on Thermisters / Inrush Current Protection
« Reply #2 on: July 13, 2016, 11:52:00 am »
There are other, (generally easy) ways to reduce the issues related to inrush to negligible levels. Inrush limiters have their own failure modes / drop efficiency / add cost. Consider: The beast is a temperature dependent device. It works by getting hot and staying hot. Hot stuff fails, energy is used to keep it hot.
Good point - perhaps the better FF is on various techniques for limiting inrush currents, when to use one vs. another, etc.?
 

Offline uncle_bob

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Re: FF on Thermisters / Inrush Current Protection
« Reply #3 on: July 14, 2016, 12:53:50 am »
There are other, (generally easy) ways to reduce the issues related to inrush to negligible levels. Inrush limiters have their own failure modes / drop efficiency / add cost. Consider: The beast is a temperature dependent device. It works by getting hot and staying hot. Hot stuff fails, energy is used to keep it hot.
Good point - perhaps the better FF is on various techniques for limiting inrush currents, when to use one vs. another, etc.?

Hi

It's part of the basic design for whatever you are designing. The techniques you use are highly dependent on the gizmo. The most basic of them date to the 1800's when they figured out how to *not* wind transformers ....M= 1.0 is not as good as M = 0.98 or 0.96.

Bob
 


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