Hi,
I recently acquired this 60W dummy load from China. It can be found from various sellers on ebay and from banggood.
Since I am also working on my own design of a dummy load, I figured it would be a good idea to see how this one does the job so I went ahead and reverse engineered the circuit. The whole process is described in this video:
I also go over each block and I explain how I think it works. I think I got most of the things right, because I have been dealing with them in my own design. However I am left with a couple of questions towards the end of the video:
Question 1: I wasn't sure what kind of configuration they used on the op-amp, but as users suggested in the comments, it appears to be an integrator and that should help by avoiding rapid changes in the control loop which would cause large current surges through the mosfet. I would like to hear your input on my assumption.
Question 2: What do you think is happening with pin 16 which looks like an ordinary IO pin. Keep in mind this dummy load monitors it's own dc input and it will give an error if it's not within an accepted range around 12V.
Question 3: Why are they biasing the positive input for the voltage sensing with 0.096V obtained from VDDA? both the single ended one and the second one for the 4 wire mode. How is that helping?
I would also appreciate any other comments or things you might want to mention.
Thank you.
PS: There is also a review video if you are interested in this dummy load and what it can do, look for Voltlog #38.