This is about as simple as it gets ............
.
.
.
View attachment 322760

Nice little DC circuit ) So how would you do the same thing, yet not have the "+" power tied to the load until the opto is "ON"? My similar application is for PWM of a 12 Vdc fan motor on my RV. I prefer not to have the live power at the load until the output is turned "ON" by the opto. I am assuming from the diagram that the load always is hooked to the "+". Probably to avoid the loss of voltage across the MOSFET.

 

I give-up.
.
.
.

 

I wasn't finding the correct term in English to represent this device I'm designing, I believe the right name is "Active Dummy Load"

 

Active Dummy Load

Do you have power stored in a capacitor, and you want it discharged fast? The capacitor might be in a power supply.

 

I would advise against deriving the gate voltage from the supply that you are testing. If the supply shuts down, then you lose control of the dummy load. You could easily power the drive circuitry from a PP3, because it just has to supply the op-amp and the MOSFET gate.
As your minimum voltage spec is 5V, if you drop 4V across the source resistor, you reduce the power dissipation in the MOSFETs, you also boostrap the gate drive to some extent, making it less of a capacitive load on the op-amp and also don't need the second op-amp to amplify the voltage across the sense resistor.
Resistors are designed for dissipating power. MOSFETs, these days, are really designed only for switching. I would recommend some old MOSFETs such as IRFP140, IRF540 etc, not some modern designs.

 

I liked the solution given by @LowQCab, it seems to be the appropriate option for the problem in question.

However, in this first stage, for didactic reasons, I need to make the example and functional circuit with the 4n25. I understand the implications regarding the absence of load, but as long as in the first instant (first second) when coupling the load (source) the mosfet is turned off, then turning on, this will be controlled by the control side with the operational amplifiers.

 

I liked the solution given by @LowQCab, it seems to be the appropriate option for the problem in question.

However, in this first stage, for didactic reasons, I need to make the example and functional circuit with the 4n25. I understand the implications regarding the absence of load, but as long as in the first instant (first second) when coupling the load (source) the mosfet is turned off, then turning on, this will be controlled by the control side with the operational amplifiers.

.
Well .........
Thank You for your endorsement,
but I still have no idea about what You are trying to accomplish with your Project.
I was making "assumptions" just like everyone else.
.
.
.

 

but I still have no idea about what You are trying to accomplish with your Project.
I was making "assumptions" just like everyone else.

I think what's making it difficult is the language, I'm not a native English speaker and I'm using a translator.

I am trying to design a Smart Active Load controlled by Operational Amplifiers to test sources and batteries, for didactic reasons, this project will be used to teach how optocouplers, operational amplifiers, mosfets, shunt resistors and other voltage and current concepts work, I need the part that controls the load, be galvanically isolated from the load composed of the mosfet and the shunt resistor, in the control part I will carry out several analyzes using OpAmps and control the MosFET which must, as I said, be galvanically isolated from the control part.

 

I think what's making it difficult is the language, I'm not a native English speaker and I'm using a translator.

I am trying to design a Smart Active Load controlled by Operational Amplifiers to test sources and batteries, for didactic reasons, this project will be used to teach how optocouplers, operational amplifiers, mosfets, shunt resistors and other voltage and current concepts work, I need the part that controls the load, be galvanically isolated from the load composed of the mosfet and the shunt resistor, in the control part I will carry out several analyzes using OpAmps and control the MosFET which must, as I said, be galvanically isolated from the control part.

I understand what you are trying to make, but I still think that the galvanic isolation is, to use an idiom that won't translate well, is creating a rod for your own back. It will certainly teach anyone who is thinking of trying it, that optoisolators inside a feedback loop doesn't make life easy.

 

Your requirement that the maximum-Voltage may go all the way to ~60-Volts
complicates matters immensely.

You can find Op-Amps that can handle ~60-Volts ( $$$ ),
or You can use a Voltage-Regulator,
but that would require around ~15-Volts minimum Input.

Projects are generally designed around a specific Voltage-range,
not anything between ~5 and ~60-Volts.

FETs are NOT Linear-Resistors.
Opto-Isolators are not truly Linear, ( but they can be made Linear with more external Circuitry ).

The request You have made is not a simple one ...........
How much Time and Money do You want to spend ?
.
.
.

 

time is not a problem, knowledge is more important, money is a problem but at this stage I am just working with the simulator, demonstrating the operation and interaction of each component.

 

Unfortunately, Components don't smoke and explode in a Simulator,
but they do it all the time in real-life.

I would suggest that You spend most of your time figuring-out why
there may be ~3,000, ( or even more ), different versions of the same basic part.
Some are dirt-cheap, and some are brutally-expensive.
Some are quite universal, and some only do one exact job, and some are in between.
This is also why any project must start-out with an outline of the environment that it will be operating in,
and usually, this starts-out with the character and specifications of the Power-Supply that will be used.
Then, all of the Components can be selected based on their working well with that Power-Supply-Voltage.

The Power-Supply is the most important part of any Project.

You can start figuring this stuff out by performing a "Parametric-Search" on the
websites of any of the the big Electronics-Distributors,
then studying Specification-Sheets which all contain a ton of valuable information,
including proven example Circuits that work well with that particular Part-Number.

If a finished electronic-product doesn't have an extensive Specification-Sheet, it's probably junk,
this is especially true of some of the ultra-cheap-"Modules" from China.
.
.
.

 

Regarding the simulation, I agree that we don't have the experience of the component exploding in our faces, but that doesn't stop it from happening when it goes to the bench and is put to the test. Simulation is a second step, the first being the idealization of the circuit you want to create.



The choice of the 4N25 is a didactic question, it is not because we are unaware of the existence of other options, it is necessary that the circuit be made with it to test various knowledge surrounding its operation and the other subcircuits involved.