what do you think about this lab psu project? - Page 1
Forum section: electronics / beginners

author: digik
author_rank: Regular Contributor
timestamp: January 15, 2025, 12:51:24 pm
content: i want to build this lab psu that looks quite good on paper. however it lacks a backfeed protection if you want to use it as a charger. what do you think about?https://www.pcbway.com/project/shareproject/0_30V_0_3A_DC_DC_Regulated_Power_Supply_Circuit.html

author: BILLPOD
author_rank: Frequent Contributor
timestamp: January 15, 2025, 02:06:44 pm
content: Good Morning Digik, I remember, many years ago, early in my electronics hobby, I often looked for projects to do on weekends. I would go to the local Radio Shack and shop for something to build. I once brought home an analog VOM kit and that was fun, but not terribly educational. This project would have been great, and a useful device when finished. All the hard design work has been done, so those just starting out should be able to build it with little problem.

author: jwet
author_rank: Frequent Contributor
timestamp: January 15, 2025, 03:43:15 pm
content: Its basically a very old National Simple Switcher IC with some current and voltage feedback wrapped around it. If you want to charge batteries, etc, at medium currents, its probably ok generally- I would find a place to put a diode, probably after the inductor inside the loop. Ripple and noise won't be very good. Transient load response won't be great and I can't imagine it might oscillate at certain V and I's. You can buy a pretty competently designed chinese switcher PSU in a box with meters, etc for about $50.The problem with making a variable buck like this is that the inductor value or the current limits really needs to change to cover such a wide range of I's and V's. The buck converter is a fixed frequency type with cycle current limiting, at reasonable loads, it will find a PWM value that will work well but if it kind of falls apart at lighter loads and will get into a pulse skipping at lower frequencies where you'll get lots of ripple.Its ok for the garage but its far from a lab supply.

author: Jwillis
author_rank: Super Contributor
timestamp: January 15, 2025, 04:10:20 pm
content: The LM2576 is not bad, but the LM2596 is much better. The LM2596 is a direct replacement for the LM2576. The LM2596 also has a much higher switching speed (150kHz) than the LM2576 (50kHz). This allows for much smaller values on the input and output capacitors and smaller values for the inductor. For even cleaner output, I would also suggest a second LC filter after the final output capacitor.

author: digik
author_rank: Regular Contributor
timestamp: January 15, 2025, 05:11:18 pm
content: thanks, i'm aware of the limitations of the ic used. i was more referring to the whole circuit project: for example at first glance it lacks a backfeed protection in case is used as a charger. i will replace the ic with the lm2596adj, reduce the inductors and capacitors accordingly as per datasheet, but i will keep the current adjust part of the circuit exactly as it is.yes, it's a "very old" chip jwet...but in the meantime can you suggest a modern direct replacement that is simple to implement like this? as the ripple part, although i have not jet build it i think it should be very good and stable.

author: kripton2035
author_rank: Super Contributor
timestamp: January 15, 2025, 06:26:53 pm
content: https://www.aliexpress.com/w/wholesale-lm2596adj.html

author: Jwillis
author_rank: Super Contributor
timestamp: January 15, 2025, 06:37:18 pm
content: Quote from: kripton2035 on January 15, 2025, 06:26:53 pmThose are ok. But won't handle the advertised 3A without a heat sink.

author: digik
author_rank: Regular Contributor
timestamp: January 15, 2025, 07:16:29 pm
content: no. if those crap are ok, then the one proposed must be great.those module not only won't handle 3A but they also lack current control.

author: jwet
author_rank: Frequent Contributor
timestamp: January 16, 2025, 01:32:26 am
content: The issue isn't new or old. The newer simple switchers use the same simple scheme just a bit faster. This isn't the real problem, the problem is the variability and feedback. You could make a fine supply that will take in something like 30v and make a fixed supply at any voltage in between 1 and near 30v at 1- 3 amp with the equations and correct parts selection in the data sheet. You can't however make a supply that is variable over all these corners and will behave. Use their design method and try to make a supply that will do 4v at 1 amp and then try the same values at 30v 3 amps. TI has a simulator called Webbench that will do the work for you. It will be a mess.On the current and voltage control, it uses comparators that will fire on ripple current and ripple voltage, there is no hysteresis and no HF limiting in the feedback. Its not a very good design, I was just trying to answer your question, "I don't think much of it"- no offense. I don't have a good alternative though others might. Even with my near 50 years of experience, I would buy something like this myself off the shelf- I can't build something half as good for the money they charge that would make sense for my time investment.

author: digik
author_rank: Regular Contributor
timestamp: January 16, 2025, 12:20:30 pm
content: in the meantime i have found another project:https://www.pcbway.com/blog/technology/0_30V__0_7A_Adjustable_Switching_Power_Supply.htmlthis time the autor takes some measurements and the ripple looks quite good. what do you think?

author: radiolistener
author_rank: Super Contributor
timestamp: January 16, 2025, 01:02:17 pm
content: Quote from: jwet on January 15, 2025, 03:43:15 pmAh, when I read this 'competently designed Chinese', I remember those 'competently designed' Chinese battery chargers for LED lamps - you know, the ones that are essentially just a ballast capacitor and a rectifier diode which connects the battery directly to the mains and soldered together with wires, rattling around in a casing with no insulation, designed for direct charging from a 220V mains. A real masterpiece of minimalism, good price and... electrical safety.

author: macboy
author_rank: Super Contributor
timestamp: January 16, 2025, 01:19:31 pm
content: One glaring problem with this circuit is that the current sense resistor creates a voltage drop which is not sensed nor compensated for by voltage regulator. This means that when it delivers 3 A output current, the voltage will be 0.3 V too low, no matter what the set voltage is. In other words, the design's "load regulation" specification will be very poor.

author: digik
author_rank: Regular Contributor
timestamp: January 16, 2025, 01:50:18 pm
content: Quote from: macboy on January 16, 2025, 01:19:31 pmdid you mean with the first one that i've posted or with this?:https://www.pcbway.com/blog/technology/0_30V__0_7A_Adjustable_Switching_Power_Supply.html

author: silly sausage
author_rank: Regular Contributor
timestamp: January 16, 2025, 03:30:05 pm
content: i wouldnt want those noisy buts of junk anywhere near my radios or antennas, linear is king.