Quote of the Day
Being defeated is often a temporary condition. Giving up is what makes it permanent.
— Marilyn vos Savant
In my previous post, I provided some definitions of thermal resistances and thermal characteristics. In this post, I want to show the problem that got me interested in this subject. An engineer misused the numbers and got answers that did not make sense. I require the folks in my group to estimate the junction temperatures of the parts they use so that the know if there design may have a temperature problem. In this case, the calculation required the use of the ψJT thermal characteristic. The basic problem is straightforward:
- Estimate the junction temperature of a part that dissipates 1.25 W.
- We have a large number of thermal parameters available. Which one do we use?
Figure 1 shows how the calculation went.
Figure 1: Three Wacks at Estimating Junction Temperature.
I thought this was a good example to illustrate the importance of understanding the thermal parameters and using them properly.
As an aside, I also looked at estimating the ψJT using the estimating formula from the previous post (Figure 2).
Figure 2: Psi-JT Esimate with Comparison to the Measured Value.
The result is not too bad considering the limited data I have.