Dummy Load Reverse Engineering - Page 1
Forum section: electronics / general

author: voltlog
author_rank: Regular Contributor
timestamp: March 17, 2016, 08:31:53 pm
content: 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.

author: dadler
author_rank: Unknown
timestamp: March 18, 2016, 12:36:53 am
content: I'm subscribed to your channel and enjoy your videosPerhaps you could post inhttps://www.eevblog.com/forum/other-blog-specific/instead/as well?

author: voltlog
author_rank: Regular Contributor
timestamp: March 18, 2016, 06:00:30 am
content: I think it's better to avoid duplicate posting, to avoid being considered a spammerI think it's a good fit in this category because, well, there are design technical questions that I am searching answers for.Thank you for being a subscriber!

author: dadler
author_rank: Unknown
timestamp: March 24, 2016, 08:39:47 pm
content: I am interested in your dummy load project as well. You also asked a while back if people would be interested in your PSU project, and I would like to reiterate that I would enjoy more information/details--or a video!Your videos are professional and well-presented

author: voltlog
author_rank: Regular Contributor
timestamp: March 25, 2016, 06:01:58 am
content: Thank you for getting back to me on that subject. The dummy load is certainly a subject I will do a video on soon. The problem is the lack of time, I haven't worked on the dummy load project at all lately. Since it's my first project on the stm32 I need a full day to get my development environment setup and get started writing code.The power supply project is an older project of mine, it had some oscillation problems in the current control loop if I remember correctly. I will also do a video on that but the dummy load is the priority here.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: March 29, 2016, 01:39:26 pm
content: I really need to build a dummy load myself. Find I need it more and more.Good video as always.

author: voltlog
author_rank: Regular Contributor
timestamp: March 30, 2016, 05:13:34 am
content: The one I reviewed is pretty good for most purposes but if you need to go higher power, better precision, more functionality then yes you probably need to buy a commercial expensive one or build it yourself