Mine is meant to be only a contribution from an enthusiast.
If we look in the forums and on Youtube there are many cases of Mosfets that sometimes explode in a pyrotechnic and dangerous way.
We neglect the case of FAKE components and limit the discussion to the original ones.
In products such as the DL24, in its various versions; powerful but cheap Mosfets are used: currently comes with IRPF264.
Enthusiasts who go to replace the mosfet often rely on the most visible parameters such as Amps and Watts supported. The voltage is related to the type of source to be tested.
If we want to give an example, the IRFP90N20D 200v 94A and 580W type il Mosfet is certainly considered better than the IRFP264 currently mounted in the DL24pcb and which has the following data 250v 38A and 280W.
In reality both of these Mosfets are intended for common use for MOSFETs, i.e. as switches and therefore in dynamic regime and not to act as a static resistor in an electronic load and this, wanting to simplify a lot, means that currents and dissipations are possible only for very short instants in which the MOSFET works in switching therefore in conditions where in most of the time the Mosfet is either closed or open and therefore dissipates very little.
In an electronic load this thing is not respected and the MOSFET is asked to behave like a resistor, returning to a state of partial conduction and therefore of dissipation for even very long times.
To evaluate these things in the Mosfet Datasheets, the manufacturer puts a graph called briefly "SOA" or in full "Forward bias Safe Operating Area" or even "Maximum Safe Operating Area" where there are curves remaining "under" which the manufacturer guarantees "survival" of the Mosfet under those indicated conditions.
Below is an image where there are both MOsfets we just talked about
The first IMPORTANT, indeed very important, thing to note is that the curve with the longest time is 10 msec, ie the manufacturer does not supply any data for continuous operation in "DC"; this makes it clear that we will not be able to have guarantees, quite the opposite.
I have traced some curves in red imagining a deterioration which generally exists with the increase of time, but it is only my hypothesis: no guarantee from the manufacturer.
We can make comparisons with the curve at 10msec but perhaps it is better to use my curve to get values which, even if not guaranteed, are more compatible with continuous use.
let's take a trivial voltage of 20 v the IRFP90n20D at the crossing on the red line will give about 8 A while the "less powerful" IRFP264 will give 20A; the same difference can be found using the manufacturer's official curves at 10 msec.
This means that the IRFP264 is more suitable for use, always improper let us remember, what we want to do with it even if it has lower general data.
But it's not exactly always true; for example at 4 volts (just the voltage of a lithium element) we see that the IRFP90n20D will carry 70A while the IRFP264 only 50 and if we use the official curves at 10 msec at 7v the IRFP90n20D will carry 200A while the IRFP264 will it will stop just above 100 A.
In short, the comparison is not as successful as looking at the main current and wattage specifications where the IRFP90n20D clearly doubles the IRFP264.
In practice, who can say with which voltage and current pairs it will be used and since the "DC" curve is invented, the result will be ...any. But we have found that the general data "alone" is not enough to find the best MOsfet and it is necessary to look at the SOA graph.
Let's take a step forward, armed with these considerations, let's look for Mosfets that have large currents, large wattages but also a nice "DC" curve in the SOA graph and we exaggerate to be clearer.
Here is a good example IXFB100N50P, a real monster with 500v 100A and 1890W of dissipation, with a large plus264 container and with an impressive weight of 10.28gr (IRFP90n20D or IRFP264 weigh just under 6g and incidentally their fake 4,4gr)
This "monster" as seen from the SOA graph also has the DC curve
and at 20 v we read 100A, in short we arrive almost at 2000W and we will be limited to 1890W by the dissipation.
let's take into account that the initial mosfets are still available and cost from 5 to 7 €, I'm always talking about the original ones; this monster is instead more difficult to find in this period (so beware of fakes) and costs between €25 and €30.
So is everything okay? do we have the solution? just pay?
Yes and no
There's still one thing that can escape and instead it's VERY IMPORTANT.
If you look at the SOA graph of the IXFB100N50P, if it is true that there is a DC curve BUT it is also true that the whole SOA graph refers to these two temperature conditions
Tj of 150°C and Tc of 25°C.
If you think about it for a moment in an electronic load and in a situation of continuous dissipation how do you keep the case at 25 °C?
It is practically impossible except by liquid cooling, and not like water but strong things like nitrogen and the like.
This happens because even the IXFB100N50P monster has not been designed to work in a linear way and therefore the manufacturer is not able to give guarantees if you put it in an electronic load with the case at 50°C for example, a rather normal situation instead.
Here is the last point.
There is a category of MOSFET called linear, born to do the work like of the electronic load.
Let's take an example here too
the IXTK110N20L2 less powerful than the previous one with "only" 200V 110A and 960W and weighing only 6.8 gr but which costs at least another 10€ more and is even less easy to find in this period.
here is its curve
Before you tell me the monster was better, look at the test conditions: Tj equals 150°C but Tc is 75°C. Here's the BIG difference is this; the "survival" of this Mosfet is guaranteed by the manufacturer in the real conditions in which an electronic load works and therefore this Mosfet if cooled well but with feasible things will be able to give a real 600W electronic load coupled with a heatsink of those for very high-end PCs powerful. We must remeber that il DL24 Atorch mosfet is not the only limit for 600W, many other things must be enforced like diode schottky , shunt resistors and also some parts of PCB
I don't know how clear and useful it was but I'll stop here, any insights on this question.
I apologize to those who already knew these things.