Why is this (normal looking) switched mode power supply advertised for LEDs? - Page 1
Forum section: electronics / projects

author: Pinkus
author_rank: Frequent Contributor
timestamp: July 12, 2022, 09:33:09 am
content: I need 24V 5A (for some electronics and some stepper motors) and have a 24V 200W (=>8A) power supply laying around. However, the manufacturer announces it as a LED power supply. It looks and acts like a regular switch mode power supply. There are many other suppliers with usual/regular looking power switched mode supplies out there but they all show theirs as LED power supplies. I've been wondering about this for a long time and wanted to finally get some input.Why is it so? I can only guess things such as lower certification levels needed or that the power supply can not regulate load fluctuations so well. Maybe somebody has insights or better reasons?Any reason I should not use it for general electronics?If helpful: more information about my power supply (DT-NT24V-200W):https://www.alibaba.com/product-detail/DUSKTEC-12-V-30v-10a-Slim_1600492146358.htmland I attached a photo of the PCB (top side only, I was too lazy to dismount completely to be able to make a photo of the bottom side with the chips

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 12, 2022, 10:17:55 am
content: Can't tell from just a picture, whether it's a CC or CV characteristic. Other things: it might have tons of ripple, or poor transient response -- neither of which matter to LEDs. (It's got to be well enough filtered to not fail EMI -- mind, there's no guarantee of that either, especially from Ali -- so it's probably not bad in that regard at least.)Tim

author: Pinkus
author_rank: Frequent Contributor
timestamp: July 12, 2022, 11:24:26 am
content: CV of course. You are right.In the meantime I connected it to my electronic load and let it run in an alternation 8A for 100ms / 1A for 200ms. Result: I have seen much better power supplies. See first two scope pics. It will probably work for testing etc. but it is not really great; this is not a very stable voltage. I better order a regular power supply.Just a note: As a comparison, I connected a similar (but regular, thus non-LED) switched mode power supply: here the voltage is absolutely stable, the scope just shows a flat line when running the same load test as above.The last picture shows, the LED supply is even shutting down for a short moment if the load (here: 5A) goes away completely for a moment. Probably this is a kind of emergency shutdown as a moment before, the voltage raised above 25V due to the load dump.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 12, 2022, 02:18:13 pm
content: Actually that's probably more like: the output is too high so the controller throttles off, but then it doesn't have any aux power so it shuts down completely until the startup circuit wakes it again. Though I don't have a clue what's suddenly discharging the output, unless that's you -- or there's a downprogramming feature perhaps to ensure LEDs don't glow on forever when shut off. Or a crowbar, but delayed after peak voltage somehow, so probably not.Oh yeah, there's not just an output choke, but also a, probably gate drive transformer, on the primary side; that must be 2-switch forward. Not bad. Perhaps better efficiency and EMI than flyback.Tim

author: TimNJ
author_rank: Super Contributor
timestamp: July 12, 2022, 04:49:40 pm
content: Maybe it's related to form factor? I don't really have much experience with LED lighting installations, but has the long rectangular shape that most of these drivers use. Maybe it follows the shape of fluorescent ballasts?Other ideas, which I am not optimistic this power supply has implemented, involve line current harmonics per IEC61000-3-2. LED drivers are supposed to have high power factor and low harmonic current distortion. Maybe the controller is one of those all-in-one types which does PFC and control of output power in a single stage.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 12, 2022, 06:58:28 pm
content: Quote from: TimNJ on July 12, 2022, 04:49:40 pmAlso good points.Looks like the latter is out, at least: there's no front end stage for PFC, and the output shows no ripple. There could be an analog CC (gyrator sort of thing) to supply low ripple (current) to an LED load, but that's not supported by the measured source impedance, either. (Would also be difficult to get PFC through a forward converter; I mean, some improvement could be made, if not necessarily meeting regs?)Tim