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CurrentSense Comparators for electronic load

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Jwillis:
I managed to get 4 Mosfets working equally through varying Currents and Voltages  by using one current sense of a Master reference Comparing the current sensors of each remaining Mosfet to drive those the remaining  Mosfet drivers in parallel . But calibrating them was complicated. I was wondering if I could reference of each current sense in series to make calibration easier. I don't have an accurate  circuit diagram with all the information available at this time So I drew up this simplified block diagram to explain what I want to try. Would this work to make calibrating each block easier? 

Dave:
Compare every slave branch to a single master reference, otherwise your errors are just going to accumulate.

Vovk_Z:
I don't understand why comparators?
May be something like that (here is usual way to make el. load, X4 is for 1k potentiometer):

Jwillis:

--- Quote from: Dave on January 30, 2020, 12:26:18 pm ---Compare every slave branch to a single master reference, otherwise your errors are just going to accumulate.

--- End quote ---

Thanks Dave. the way you describe is the way I have it right now. I see your point now how errors will occur and compound across the series .


--- Quote from: Vovk_Z on January 30, 2020, 09:23:53 pm ---I don't understand why comparators?
May be something like that (here is usual way to make el. load):


--- End quote ---

Your right that that is is the common way of paralleling but the problem still arises that one will load hog more than the others . This is do to each Mosfets having  a different Vgs .Even when selecting  Mosfets to have a Vgs  as close as possible ,the problem of load hogging still occurs.This seems to be much worse when running Mosfets in linear mode as opposed to pulsing .
The idea of the comparators is to make  the currents passed be each Mosfet  equal by automatically adjusting the gain of each driver. So far the concept works but calibration of the gain on the drivers becomes a nightmare . Its easy to calibrate the gain of 2 .But with 4 it gets more complicated. Adjusting the gain of one will change the gain of all others.
Once all banks are balanced the comparators are able to keep them balanced as the voltage the current demands increase.

I have tried to use a simulator but I just can't get the program to work even on simple circuits. Still trying.

hli:

--- Quote from: Jwillis on January 31, 2020, 01:20:15 am ---Your right that that is is the common way of paralleling but the problem still arises that one will load hog more than the others . This is do to each Mosfets having  a different Vgs .Even when selecting  Mosfets to have a Vgs  as close as possible ,the problem of load hogging still occurs

--- End quote ---
No. In Vovk_Z's schematic, each MOSFET has its own shunt resistor, own feedback loop. This means each MOSFET draws current according to the shunt resistor, no matter what its Vgsth is. You even can use different MOSFETs - as long as they can handle the load you are fine.

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