Series Connection of thermal networks

1

Hi,

I’m trying to understand how 2 “Thermal Chains” connected in series are resolved

First, in red, is a thermal chain (Cauer type) and its equivalent network in Foster. Second part, in purple, is another thermal chain and its Foster equivalent. Third part, in black, is the series connection of the two thermal chains and their Foster equivalent.

Plot 1 shows how step responses of thermal chain and its Foster network are identical. Same happens in plot 2 for the second chain.

However, when I connect is series both thermal chains this is not true. Plot 3 shows how the series connection of Foster equivalent networks results in the sum of the individual step response (as I expected). But this doesn’t happen for the thermal chain series connection.

Could anyone help me to clarify this?

BR

Schematic.png
Schematic.png1020×771 16.7 KB

step_response.PNG
step_response.PNG1918×965 14.8 KB

2

My understanding is that due to the nature of the Foster network, any changes to the system, such as to arbitrarily extend the network out from the junction, requires recalculation of all values. So I think this may lead to the discrepancy you are seeing in the synthesized Foster network. This resource may also be helpful for you: https://www.infineon.com/dgdl/Infineon-Thermal_equivalent_circuit_models-ApplicationNotes-v01_02-EN.pdf?fileId=db3a30431a5c32f2011aa65358394dd2

3

Yes, I think that you are right according to the app note you shared.

Many thanls for the feedback