Hello,
Take, for example, this MOSFET called IRF4104PBF .
The Maximum Safe Operating Area, figure 8, mentions that Tc == 25C and TJ == 175C in the figure. The datasheet also specifies that this MOSFET can do 75A with VGS at 10v. RDS(on) is 0.0055ohms, the power dissipation is 140W, and TJC == 1.05C/W.

(I tried to align the terms, but the forum keeps eating my extra whitespace. Ugh.)
I Rds(on) C/W C
(75**2)*0.0055*1.05+25 = ~57.5C TJ assuming you can keep the case at 25C.

So isn't the Maximum Safe Operating Area graph a bit unrealistic?*
I mean, they don't even list DC in the graph and the MOSFET can clearly do DC.

Am I missing something?

Thanks!

EDIT: * I mean with respect to the junction being at 175C while the case is at 25C. You might be able to push the junction that far, but you'd need an industrial chiller to keep the case at that temperature.

 

First, notice that the SOA graph says that it is for a single pulse.

Where are you seeing that it says that if can do 75 A with VGS = 10 V? Are you referring to Fig 10?

RDS(on) is a max of 5.5 mΩ at Vgs = 10 V, ID = 75 A, and TJ = 25°C. That does NOT say that the device can sit there continuously under those conditions, only that those are the conditions that were established, however briefly, and at which that parameter was measured.

 

First, notice that the SOA graph says that it is for a single pulse.

Where are you seeing that it says that if can do 75 A with VGS = 10 V? Are you referring to Fig 10?
<snip>

Actually, I was looking at page 2->RDS(on) value, which says the value is measured under Vgs == 10v, Id == 75A.

Hello I am expert in this Computer Science and Electrical Comunication so you can consider as perfect answer ,
The values of Tc (case temperature) and TJ (junction temperature) specified in the graph are important considerations for understanding the safe operating limits. In this case, Tc = 25°C and TJ = 175°C. The graph assumes a constant case temperature of 25°C while varying the junction temperature up to 175°C.

I figured as much.

The

Stray "the"?

To calculate the approximate junction temperature (TJ), you can use the formula:
TJ = Tc + (RDS(on) * ID^2 * TJC) + Tamb
where:
TJ is the junction temperature,
Tc is the case temperature,
ID is the drain current,
RDS(on) is the on-state resistance,
TJC is the thermal resistance from junction to case, and
Tamb is the ambient temperature.

Aside from Tamb (which I omitted because it wasn't really part of the question, given that I still didn't calculate the heatsink thermal parameters), that's exactly the formula that I was using.

It's important to note that the MSOA graph represents the safe operating limits under specific conditions and is not intended to indicate continuous operation at the specified limits. The graph provides insights into the device's capabilities but should be used in conjunction with other considerations such as thermal management, derating, and other electrical parameters to ensure reliable operation.

If you have specific requirements or concerns regarding the operating conditions of the MOSFET, it is recommended to consult the manufacturer's application notes, guidelines, or contact their technical support for further clarification.

Well, I was trying to use their information in their MOSFET datasheet so that I wouldn't need to contact tech support. I'm a student, so I would probably just be ignored, as has happened in the past with other companies from which I've made purchases (I'm talking to you, Rigol).

And thanks for the answer. That pretty much sums up what I was asking.

 

Well, I was trying to use their information in their MOSFET datasheet so that I wouldn't need to contact tech support.

Look at other datasheets of mosfets the same named chart is almost always the same. like it was copied and pasted.