Korad KD3305D Look inside and measurement - Page 1
Forum section: electronics / testgear

author: hp3310a
author_rank: Regular Contributor
timestamp: February 19, 2025, 06:05:54 pm
content: Hi everyone,I have a Korad KD3305D, a dual channel 0-30V 5A lab power supply (+ 3rd channel with fixed voltages at 2.5V, 3.3V and 5V). Since I now have a usable electronic load I wanted to see how well it does under load and documented it all. I also took a look inside to find out whether it can be calibrated and while I was there I took some pictures.Since reports about this power supply are rather underrepresented I though I'd post the hole thing.The measurement was done using my 34401a and the ET5410A+ electronic load.I went through the entire range of the supply in 0.1V steps and took 5 measurements for each set voltage at 0A, 0.5A, 1A, 2A and 5A. I didn't turn off the load at 0A, so there was a tiny load between 0-3mA attached there as well. I did some spot checks and there was no difference in output voltage whether the load was turned on at 0A or not.I wrote down all 1500 values manually into a spreadsheet (also attached here). I now know why one needs a programmable power supplyAnyway, maybe someone in need of a cheap and robust power supply finds this interesting.

author: hp3310a
author_rank: Regular Contributor
timestamp: February 19, 2025, 06:07:00 pm
content: Additional pictures

author: hp3310a
author_rank: Regular Contributor
timestamp: February 19, 2025, 06:19:40 pm
content: Forgot the error charts, those are also in the spreadsheet. Pretty sure this is not how professionals do it, but I think it is useful nonetheless. I split up the relative error chart into 0-2V and 2-30V because the large error in the lower 2V distorts the chart so you can't make out values of higher output voltages.

author: Gyro
author_rank: Super Contributor
timestamp: February 19, 2025, 07:36:55 pm
content: Congratulations on sneaking in the 3310A at the top of the stack.It looks a nice solid linear supply, a bit unusual to find one with a traditional mains transformer rather than a lighter (shipping cost) toroidal.One of the most important 'parameters' is the overshoot and undershoot on step load and output on/off. This is trickier to do with an active load as it may have its own artifacts, and of course needs a scope. Significant issues are much less likely in a linear supply than a switchmode one though. I'm not sure if anyone has characterized this model.

author: hp3310a
author_rank: Regular Contributor
timestamp: February 20, 2025, 01:15:14 pm
content: Thanks for the comments. I took the opportunity to put my scope to good use, though I'm sure better skilled people would be able to extract better results.With the above setup I took two measurements for different output voltages both at no load (load turned off) and against active load set to 2A. Not sure where the step in most shots comes from, I assume it is when the load finally turns on and the power supply takes a little to regulate.At higher voltages there sometimes was some overshoot but most of the time there was none.Finally I tried (and failed) to record load-changing but I couldn't get the scope to trigger on the step because of all the noise. There's probably a trick to do that.Image names should give a hint what it is showing.

author: hp3310a
author_rank: Regular Contributor
timestamp: February 20, 2025, 01:17:49 pm
content: More scoping action

author: hp3310a
author_rank: Regular Contributor
timestamp: February 20, 2025, 01:18:47 pm
content: last part

author: Gyro
author_rank: Super Contributor
timestamp: February 20, 2025, 08:09:51 pm
content: Turn-on isn't exactly tidy, particularly at higher voltages but I can't see anything that would cause damage to the load. That's the main concern of course.Step load change looks nice and clean. It would be interesting to know where the noise spikes are coming from, it could be the active load or general noise pickup on the ground lead. Only a resistive load test would tell that.Overall it looks pretty good.

author: Furna
author_rank: Frequent Contributor
timestamp: February 20, 2025, 08:34:23 pm
content: A couple of old but usefull videosEEVblog #594 – How To Measure Power Supply Ripple & Noisehttps://www.eevblog.com/2014/03/21/eevblog-594-how-to-measure-power-supply-ripple-noise/The next one regarding coaxial cable impedance matching and compensation.EEVblog #1266 – PSU Probing Screw Up!https://www.eevblog.com/2019/12/02/eevblog-1266-psu-probing-screw-up/

author: hp3310a
author_rank: Regular Contributor
timestamp: February 21, 2025, 02:38:19 pm
content: OK, armed with that knowledge I can continue this series...Because I don't have a BNC-to-Probe adapter like Dave showed (yet), I tried the next best thing at my disposal so I could measure noise at different loads.First set is at 5V with 0.1-5A. No load means the electronic load was turned off.

author: hp3310a
author_rank: Regular Contributor
timestamp: February 21, 2025, 02:39:54 pm
content: Then at 30V again no load, 0.1-5A.

author: hp3310a
author_rank: Regular Contributor
timestamp: February 21, 2025, 02:46:28 pm
content: Finally I tried to measure using a 56Ω 300W resistor at 30V but that didn't really work. I did measure something, only what it was I don't know because it also appeared on the scope with the power supply turned off completely.When I short the probe tip I get less than 0.5mVpp, so it is not the scope.

author: Furna
author_rank: Frequent Contributor
timestamp: February 21, 2025, 05:09:22 pm
content: I would attach the banana to BNC adapter to the PSU and the cables to the adapter ...oscilloscope probe(s) must be as much as possible near to PSU output.Also, as already someone else noted, the best is a pure resistive load.Nice job!