Analog Dummy Load..!!

[tuxitheone]

hey Dave, I've looked a little on your schematic on the dummy load, and i have also made a test version, but I could not quite understand way it could not adjust as I expected, so I was forced to look at schematic again .
I came to change shunt resistance to a 0.10R 1W SMD resistor, in order to get it to work as I would like.
Now I can adjust from 0-20 AMP without problem. So I have made a small pdf with my / your schematic in with the changes is made. Take a look at it and say what you think about it, and if there is something you think i could change, to get it to work more effectively, then just write in the forum. i'm glad to have this little thing of awesomeness, because i´m working on a Big Power Supply 0-48Vdc and 15 Amp, because i have some big motors i would like to run at full capacity, and this well do..

so thanks for the schematic...

[tom66]

Your 0.1R 1W resistor will dissipate 40 watts at 20 amps. This may shorten its life somewhat.

You will need a very large heatsink to dissipate 48V * 15A = 720W. Certainly need more than one MOSFET as otherwise the SOA is going to be massively exceeded. I am assuming you do not require full current at full load voltage, but you don't say if you do.

Your 10uF capacitor on the leg of your potentiometer has an effective ~6second 3RC factor, which will create a considerable "lag" when changing the load current. At best this will be irritating, but at worst it will make it hard to set the right current.

You may need to add some compensation to the control loop to prevent the circuit oscillating, typically IC2A would be converted into an inverting integrator with gain, using a capacitor and resistor in parallel as feedback. IC2B would calculate the error voltage to feed into the integrator.

What's with the 8uH inductor & 10uF capacitor? I take it's a noise filter but you'd do better with a good voltage regulator. The inductor and capacitor need to be bigger to have the desired effect.

[tuxitheone]

hi yes I test at 1 Vdc and maximum 15 Amp else would be sick, compared to the noise damping is to avoid my internal power supply doing strange things. compared to my shunt resistor may well be that it does not hold so long, but if you have a 1R 7W resistance instead it does not work as I thought it should.
and thanks for the feedback, i well look a little more on my op amps ...