I just love your insights, Kleinstein. Excellent, always excellent. I wish you were my next door neighbor... LOL.
I have changed the v ref component, on the schematic. The new one is better, for this application, IMHO. Cheaper, I think, and less complicated. This changed the component reference numbers.
The supply for the circuit does not need much current. So I don't see a real need for a high current regulator.
I was thinking to try to use the 12v positive regulator, for the fan, too. But, this would put quiet different loads on the positive and negative regulators and that might not be a good thing?
The 2 MOSFET version uses relative low power Shunts, so this would mean a rather low drop at the shunt and thus not very precise regulation.
Well, I had wanted to use a higher wattage, single resistor, just like the single-MOSFET version, only slightly larger. From your earlier reply, about that, I thought you said that this wasn’t a great idea. Did I misunderstand? If so, what would needs to be done?
If a single shunt is difficult, or costly, I think, IIRC, that the cost of the first single shunt was not too bad. So, I would use two of those, instead of the SMDs.
The Shunts are also rather close to the MOSFETs, so there would be extra heat in this area. Those SMD resistors only get there nominal heat resistance with a relatively large copper area - so 2 SMD resistors close together only provide a slightly higher power rating, not twice the value. So the size for the SMD shunts is misleading - it's not just the small chip, but should include 1-2 cm² or copper on the board.
We had that discussion before and there is a reason the commercial electronic loads usually use quite large shuns, like quite a large (e.g. maybe bare wire shunt extending well above the board. So the resistor size for the 1 FET version is not that bad.
Designing to have a tight board stemmed from the op amps requiring the shortest trace runs possible, the habit to limit board cost and the dimensions of the (cheap) flat-rate 100mm x 100mm boards. But, you are exactly correct. I will spread things out, a bit.
The shunts were moved to the FETs, because I thought it would improve accuracy. Does their location matter, other than providing them with enough copper and keeping them away from other heat sources? These two concerns are why the one-FET version had the shunt placed away from the FET. What about the long traces, for them?
The position of the shunt's, shape of the ground plane is also not really good, especially for the left channel there is no clear, direct ground connection from the shunt to the OP. For a precision circuit a ground plane can be tricky, as it gets difficult to see where the current actually flowing. So a ground pour is a poor ground if there are cuts from other traces.
Agreed. I moved the ground plane to the bottom, to try to improve directional access, but it did not help. I really don’t know what else to do. A multi-layered board is just too expensive, for me, for a hobby project.
I don't understand the desire to make an electronic load so small - with power electronics is helps to have the heat sources a little apart. For a prototype is also helps if there is at least space for the probes and space for possibly needed bodges.
Agreed, per above.
A 7812 for the voltage regulation is large enough. If really on the squeeze one could add some resistance between the rectifier and cap to improve on the power factor and this way reduce the raw voltage and get away with less heat from an LDO.
I do not know this trick. Is there a name, for the technique, so that I could look it up, to study it?
Thinking on cost... As usual, DIY (especially DIY development) is not necessarily cheaper than a manufactured unit. But, I do it, for fun and education. From that perspective, it is a good value...
As always, I am s-o-o grateful. Thank you.