NTC thermistor LTSpice simulation

[danny92]

Hi everyone,

I need to simulate the behaviour of an NTC thermistor that I will use in the thermal shutdown system of my amplifier, it's possible to do that in LTSpice?
And what about a comparator with hysteresis, it's possible to simulate?

That could be helpful in the shutdown circuit, to have a higher threshold temperature of the heatsink, like 70 or 75ºC activating the thermal shutdown system and 60 or 65ºC to reactivate the amp. What do you think?

Best regards,
Daniel

 

[bill_a]

Of course it possible to do both. I'd check in with the Yahoo forum for ltSpice - I think there's a thermistor model with different curves on the forum someplace. As for a comparator, just build the circuit you want - it'll simulate just fine.

 

[jcx]

not completely trivial - temperature is not a "live" variable in Spice - so you need to model any heating effects in explicit behavioral source equations for power, thermal resistance, any heat capacity effects
use the modeled temperatures in further behavioral equations for the NTC resistance

the usual thermal modeling analogy uses V for T, I for Power, R is degrees/watt, C models thermal mass/heat capacity

 

[danny92]

Hi everyone thank you very much for your help,

It's possible to change the temperature of the thermistor only, or I have to change the temperature for the whole circuit?
I'm sorry I don't understand what you've said jcx, I'm a newbie at this subject.

Best regards,
Daniel

 

[jcx]

for native device models, diodes, transistors which have some T dependence all Spice based simulators have a global Temperature setting - a constant, common to all parts on the schematic - not too bad an assumption for low power integrated circuit devices the sw was developed for

if you want to model varying temperature effects you have to add your own calculations of both the varying temp and the behavior that is a function of the local varying temperature variable you calculate