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DC dummy load circuit calibration
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VEGETA:
Take a look at this one too:

This is its schematic: https://raw.githubusercontent.com/frank26080115/DummyLoad/master/Hardware/dummyload.png

It uses IRFB7430PBF MOSFET which has the DC curve at SAO, like my IRL640A and unlike my IRLI44Z.

However, I don't understand the concept here. If the C per W is nearly the same for all these mosfets, how come the ones with DC curve at SOA can work perfectly but the ones that don't have it cannot? I mean even with sharing between 4 mosfets while the other one with DC curve can do the job alone.

The problem with IRL640A is that it is not in isolated package like IRIL44Z. So I need to isolate them from each other if I wanna parallel them. I have this: https://www.banggood.com/30pcs-Silicone-Thermal-Conductive-Pads-10x10x1mm-Heatsink-Chip-Compound-Pad-p-1120597.html for the job + the thermal compound (cheap one from Aliexpress).
VEGETA:
Also, if I got 4 mosfets with 4x0.33R for each one -> how can I set the global current by 1v per 1a method that I want?

I don't want any arduino or MCU for now... just a panel meter with 10-turn pot.
Ian.M:
I'll get back to the non-DC S.O.A rated MOSFET failure issue when I've found a good link that explains it.   Quick summary:  Many power MOSFETs consist of a number of MOSFET 'cells' that are internally paralleled by the metalization on the silicon die.  Just like paralelling discrete MOSFETs, the individual cells can suffer from hot-spotting, current hogging and resulting thermal runaway.

To get 1A/V from four CC MOSFET + OPAMP circuits combined is very simple.  Each has a native response of 3A/V, so the combo gives 12A/V.   Therefore all you need is a 12:1 ratio divider for the control voltage, probably with +/-10% trim range via a preset to enable you to compensate it for component tolerances.   
VEGETA:
The 4*0.33 resistor per each mosfet is about 0.0825 ohms =~ 0.08 Ohms. So 1v/0.08 = 12A!

However, for 3x1R = 0.33 then yes. but this is gonna composed with 1/4 watts resistors which is terrible... will it handle the required power? perhaps 5x1 ohms resistors is better? this is gonna be about 0.20 ohms\1.25 watts per "branch".

^
I will try this via LTSpice and let you know tomorrow. I will update the Kicad project too. This way, I will get rid of the power resistor and by doing this anyone will be able to do this project with jelly bean component. I would need to buy more 1R resistors locally though!

So now we need the 10-turn pot to have 1v per 1a -> divide that by 5 to get it to work with 0.2R per branch resistor. This means getting a 10k pot after the 10-turn pot and adjust it to be /5. No need for extra accuracy since there is no software or measurement... just a panel meter which is the one to be calibrated. Or I can just put (1k+1k+1k+1k) + 1k to be /5 since no need to trimming. this could work right?

How about using one of those heatsinks in the picture for this?

Anyway, what about using IRB640A which has a DC curve? can it work?
Ian.M:
If I was using 0.33R resistors, I'd use three per MOSFET - it comes out nearer 0.1R that way, which is a good value to compromise between dissipation in the sense resistor and enough feedback voltage for good accuracy.

Even with 3x 1R 1/4W resistors they can tolerate 0.5A each for a total of 1.5A.     If you go for 0.33R 1/4W resistors, each can tolerate 0.87A.   In all cases its probably a good idea to derate it a bit as at full current they will run rather hot but they are within their rated dissipation.

Another way to handle the 10K multiturn pot would be to put 40K in series with the top end of it so there is only 1V across it.  However if you intend to use a voltmeter on the pot wiper for a digital readout of the setpoint, you'll want to put the scaling divider after the pot.   You'll probably also want a unity gain OPAMP buffer between the pot wiper and the scaling divider so it doesn't excessively load the pot.
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