T
We have a D2PAK FET (SPB07N60) in our 146W offline LED light. In our thermal test, the thermocouple on the metal drain was at a temperature of 125 degC. The thermocouple on the plastic case of the same FET was at 118degC.
The FET was dissipating 11.8W
Do you think these temperatures are unrealistically close to each other?
You calculations seem to assume that 11.8W is flowing through each path (for a total dissipation of 23.6W). In reality, the dissipated power will be divided among each path depending on the temperature difference between them. Assuming your measurements (and interpretations on the meaning of the two Rjc values) are accurate, 7.23W is flowing through the metal tab, 4.57W is flowing through the plastic case, and Tj=135.82C.Thanks
Rth(jc) is 1.5 degc/w for the metal drain, but is 3.9degC/w for the Fullpak case (datasheet page 2).
Therefore the drain should have been at Tj + 17.7 degC.
The Fullpak case should have been at Tj + 46 degC.
In other words, there should have been 28 degrees difference between the temperature of the Fullpak case , and the metal drain,…….but we only saw a difference of 7 degrees.
Do you know what’s wrong.?
Thanks, i thought it must be something like that. But i wonder why the TO220 has such a poorer Rth(jc) than the D2PAK? (3.9K/W vs 1.5K/W)However this is moot because the two numbers you referenced describe completely different packages (fullpak is the name of infineon's TO220 with an insulated tab and wider pitch). Presumably the Tc values describe heat transfer through the tabs, not the plastic cases.
Regular TO220 has Rth of 1.5 K/W as well, TO220FP is fully isolated.But i wonder why the TO220 has such a poorer Rth(jc) than the D2PAK? (3.9K/W vs 1.5K/W)
Also, the graph 2 on page 5 (kndly pointed out by C_Mitra) says we shoudl not go above 110degC....but our drain is at 125degC. ... ...
Not sure what you're referring to. Available power dissipation should be Ptot=(Tjmax-Tc)/Rjc. That's how the graph is derived.In the light of more recent information, I now think that we should be discussing about graph 1 instead; but the D2PAK is supposed to handle 20W at 120C!
Something is not apparently not right. At 100C it can handle 35W.
While the lack of clarity about the FullPak package is annoying, everything else seems fairly normal.But anyway, the datasheet is badly written; it could have been as well in Chinese.
Not sure what you're referring to. Available power dissipation should be Ptot=(Tjmax-Tc)/Rjc. That's how the graph is derived....
Thanks, myself also.By the way, I am still confused whether the case temp refers to the metal mount underneath the belly or the black top?
Imagine you can perfectly control the case temperature by use of an external temperature controller. It basically means "if the case temperature is Tc, how much power can the device dissipate before Tj goes over Tjmax."But what is available power dissipation? I always assumed that it is Total power dissipation.
If your case temperature is already at Tjmax, you can't dissipate any power without Tj exceeding Tjmax.At 150C (that is the Tjmax) case temp it does not dissipate any power. It suddenly appears counter intuitive.
Right, they're not very practical, since you don't have a perfectly controlled Tc. And IMO you should stay 20C left of the curve if you want something reliable....In reality the computed graphs are of little use but they provide a go/ no-go rapid test for the engineers. If your point (Tc,Ptot) falls on the left hand side of the graph you are ok (else you are on your own!)
Certainly the metal tab. In practice nearly all the thermal flux is going to take that path, so the plastic temperature is practically irrelevant.By the way, I am still confused whether the case temp refers to the metal mount underneath the belly or the black top?
I don't see anything implausible about your result. You could probably reverse the difference by blowing on the other side of the PCB, or covering the package with some a convection barrier.Thanks, myself also.
As discussed, in our test, the D2PAK was dissipating 11.8W, and the black case was at 118degC and the metal tab was at 125degC. I think something was wrong with our readings....possibly thermocouple too close to metal case, and noise getting capacitively coupled into it.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?