# Interpretation of the thermal model - conduction loss graph

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Hello,

After adding the manufacture thermal model in the MOSFET, I found the "Turn-on loss" and "Turn-off loss" tabs show graphs of E vs. V, I. While they make perfect sense, the "Conduction loss" tab shows the graph below which has NO "E" at all. So w/o. E values, how the conduction loss is calculated in the model??

(My understanding of the conduction loss is = Ion^2 * Ron where Ron = dVon/dIon. Is it correct??)

Thank you.

asked Mar 23, 2022

## 1 Answer

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The conduction losses are P=v*i, or more clearly in this context P=v(i,T)*i where v(i,T) is from the look-up table posted with i as the current through the device and T is temperature.
answered Mar 25, 2022 by (1,795 points)
selected Mar 28, 2022

Thank you for the answer Bryan.

May I ask in your eqn. "E=v*i" - Is "E" denoting the power (in W) or energy (in J)? Do you mean power P(in W)? If so, my another question is why the energy E (in J), in stead, is used in "Turn-on loss" and "Turn-off loss" (attached below)?

Thank you agian!

It would better to use "P" since v*i returns a power in watts.  I revised my response above.  Switching losses are joules since they are dirac-type impulses representing the total amount of energy emitted during the switching transient, which is instantaneous in PLECS.

So it means, in the graph, the given E(uJ) = P(uW) actually?

Assuming you are referring to the switching loss graph, the data entered in the table and Z axis in the graph is in energy (J, mJ, or uJ).  The voltages and currents in the graph are not multiplied since switching loss energy is a function of the voltage and current transients, as shown below. The Eon/Eoff values in the figure below would correspond to the entries in the table for a given voltage and current condition. The figure is from the thermal modeling section of the PLECS Manual.

It does make sense to me Bryan. I really appreciate your patience. So, actually E = integral of P(t) and the E in the graph the value for one switching cycle.

Thanks,