Hi All,

I'm trying to understand how you would estimate the junction temperature of an IGBT and i am getting myself all confused.

Im trying to use the attached IGBT datasheet tutorial provided by ST.

It is based on the STGFW40V60D datasheet. https://www.st.com/en/power-transistors/stgw40v60df.html

It mentions that PToT (the maximum power dissipation for a given case temperature) is as follows :. PTOT = (TJmax - TC )/ Rth J-C

Where TJmax = 175

This further leads on to looking at section "2.4.9 Maximum transient thermal impedance (ZthJC)" where TJstart == Tc

Tj = TJstart + ΔTj = TJstart + ZthJc (tp,δ) * Ptot = TJstart + k(tp,δ) * RthJc * Ptot

Looking at the provided graph assuming

δ = 0.5

tp = 0.000025

fs = 0.00005

TC = 25

so for Tj = TJstart + k(tp,δ) * RthJc * Ptot = 25

I'm trying to understand how you would estimate the junction temperature of an IGBT and i am getting myself all confused.

Im trying to use the attached IGBT datasheet tutorial provided by ST.

It is based on the STGFW40V60D datasheet. https://www.st.com/en/power-transistors/stgw40v60df.html

It mentions that PToT (the maximum power dissipation for a given case temperature) is as follows :. PTOT = (TJmax - TC )/ Rth J-C

Where TJmax = 175

**°C, TC = measured case temperature, Rth J-C igbt = 0.53****°C. Where TC = 25****°C .:. PToT = 283W**

PToT can also be worked out by PToT = Vce * Ic

Question A) ( I am unsure whether Vce is the average voltage accross the collector and emitter or this is the saturation voltage of the IGBT, if so how do i measure this?)

PToT can also be worked out by PToT = Vce * Ic

Question A) ( I am unsure whether Vce is the average voltage accross the collector and emitter or this is the saturation voltage of the IGBT, if so how do i measure this?)

This further leads on to looking at section "2.4.9 Maximum transient thermal impedance (ZthJC)" where TJstart == Tc

Tj = TJstart + ΔTj = TJstart + ZthJc (tp,δ) * Ptot = TJstart + k(tp,δ) * RthJc * Ptot

Looking at the provided graph assuming

δ = 0.5

tp = 0.000025

fs = 0.00005

TC = 25

**°C**

i would say k(tp,δ) doesn't show on the graph. So wrongly or rightly i would assume K = 0.5 as the response looks fairly flat for 10^-5.**Rth J-C igbt = 0.53****°C**i would say k(tp,δ) doesn't show on the graph. So wrongly or rightly i would assume K = 0.5 as the response looks fairly flat for 10^-5.

so for Tj = TJstart + k(tp,δ) * RthJc * Ptot = 25

**°C + 0.5 *****0.53****°C * Ptot.**

Question B) : For Ptot can i use the 283w i calculated earlier or do i need to measure Vce and Ic?

If Ptot == 283w then Tj == 99.995

Question B) : For Ptot can i use the 283w i calculated earlier or do i need to measure Vce and Ic?

If Ptot == 283w then Tj == 99.995

**°C is this correct? and is this telling me the peak junction temperature or the steady state temperature?**

Thanks for your help!Thanks for your help!