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EDN 1994 Design Idea: Spice does thermal analysis - missing files

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busaboy:
EEVblog member @mawyatt wrote an EDN Design Idea in 1994 titled "Spice does thermal analysis". Unfortunately EDN doesn't provide access to old content and Mike doesn't have the Spice files anymore.

Can anyone help with di1576z.zip?

https://www.edn.com/edn-access-08-18-94-spice-runs-thermal-analysi/

CatalinaWOW:
What are you looking for?  Values for components?  Only a little that was in use at the time this article was written would be pertinent to todays components.

The idea is simple enough.  Model thermal masses as capacitances and heat conduction paths as resistances.  Heat capacities of common materials are readily available on line, as are conductivities.  Thermal resistance of many packages can be found in data sheets.  Some things need to be fudged.  Radiative and convective heat transfer don't really model simply and are probably best dealt with by a rational approximation to measured data.  And three dimensional heat flow such as lateral flow in a circuit board, or transfer to a large heat sink from a dimensionally small heat source will have to be simplified to a network of thermal resistors.  But when you get that complex it probably makes sense to use more traditional thermal model. 

As always models are simplifications of the real world and need to be validated by comparison with measured data before you really believe the results.

busaboy:
Looking for the original Spice sub-circuits with formulas.

Trying to add more simulation examples for Qucs-S. I already have examples using the rare Manufacturer supplied "thermal" Spice models. The issue is how to do thermal modeling using old Spice models or the vast majority of power devices that don't come with a thermal Spice model. It's useful for Hobbyists building audio power amplifiers.

https://github.com/ra3xdh/qucs_s/discussions

RoGeorge:
You started this topic twice.  :)
Please do not duplicate the same subject (it's one of the rules to keep this forum clean).

If you forgot where did you wrote before, go to "Profile" -> "Summary" -> "Show Posts", or bookmark this link:  https://www.eevblog.com/forum/profile/?area=showposts

It is also possible to edit your own posts, or to move your own topics to another section of the forum (in case you accidentally opened them in a wrong section).


@ in front of a username doesn't work on this forum, so it doesn't send a mention notification.


That simulation looks like it doesn't depend on any specific/custom files or models.  The thermal model is in the topology of the schematic itself, and in the values for the particular thermal R and C.

Should be enough to just redraw the schematic in your preferred simulator.


Spice can do temperature simulations, for example can account for Vbe variations with temperature, or for the thermal coeficients of resistors, etc., but that is something else.

I think the article is not about those spice features, but rather about modeling the thermal effects using an electric analog.  Random link example for an analog of thermal effects using electric circuits:
http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node118.html

In a similar way, there is an equivalence between mechanical and electrical circuits, so for example mechanical behavior can be also simulated with a SPICE model:
https://en.wikipedia.org/wiki/Mechanical%E2%80%93electrical_analogies

iMo:
FYI - https://www.eevblog.com/forum/metrology/lm399-heat-loss-within-a-vacuum/msg4392685/#msg4392685

PS: one of the great issues with Spice (LTspice, etc.) since ever is there is none "on-the fly" feedback of the actual Temperature (the temperature of a particular part) into its intrinsic models.

Having that would be a fundamental breakthrough.

You may easily model a schematics where, for example, a power loss of a 2N2222 transistor will be 100W (and its temperature say 700C) and it still will show nice results. Today LTspice assumes everything in your schematics is "kept" at the set global Temperature, like the default 27degC. You may "step" through temperature, but each individual step means that you change the global temperature to a certain value, and again, all in your schematics is kept at that temperature during the entire simulation run within the set step.. Also you may assign an individual temperature to a certain part, but again, it will stay constant during the entire simulation run.
That is a real world nonsense, of course..

To create an actual temperature of something is easy in the Spice as you may derive it from the power loss which is accessible anytime, but there is none mechanism to feed it back into the intrinsic models (diodes, transistors, resistors, etc.).. Also modeling of the temperature gradients and flows in the Spice is easy even today (provided you have on the actual temperature based behavior of the parts handy, what is not the case today).

I asked on this problem at the ADI's EZone forum (where LTspice developers sit), after a short discussion the guys there indicated "..it would require almost complete rewrite.." :palm: of the LTspice.

Btw., there is everything you need in the Spice to do it, as all its intrinsic models ARE ALREADY a function of Temperature (the temperature is an internal variable in the models, like any currents/voltages)..

Thus all what needs to be done is to SIMPLY expose the internal intrinsic model's temperature variable such we may wire it somewhere (where we created the actual temperature value).

So instead of a single global CONSTANT Temperature (as is today) we will have N_x temperature VARIABLES (where N is the number of the LTspice's intrinsic models, perhaps 15-20), applicable to each specific part in the schematics individually (as the part's parameter into which we will wire our temperature_value generating node).
Like Q1_Q_BIP3_temp, Q23_Q_MOS2_temp, D3_D_temp, D6_D_temp, R7_R_temp..
When not wired/set by the user in the schematics the default global Temperature will be used.

I encouraged them to go for it..  :D

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