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Updated schematic for a popular DIY linear bench power supply

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Hi everybody,

I have recently purchased a popular power supply DIY kit on Aliexpress. It's available on eBay, Aliexpress and Amazon. If you google something like "0-30V 0-5A Adjustable Power Supply Constant Voltage And Current Diy", you'll find all the links. The attached ZIP file contains the image of the empty board, so that you can easily identify it.

The power supply is rather decent, and could serve well on the bench. Howerver, there are two problems with it.

The first problem is that it may not work, because the linear regulators used are not supplemented with dumping capacitors as per the datasheet, and will most probably start oscillating. And the second, more general problem is that the schematic supplied with them is for an old version of the power supply, so if something does not work, it's very hard to debug the problem. That's exactly what happened to me: it did'nt work, and figuring out the reason was a headache, because the schematic was incosistent with the board.

So I went on to draw the updated one, and that's where I figured the problem with the capacitors, and as you may guess, it was in the part that was changed. In doing so, I have also found the original Chinese copy in PDF format, as the one on the sites is translated into English with automatic translation and is converted into a low resolution raster image, so it's sometimes difficult to discern. The alignment instructions that are provided are also poorly translated, so I had to redo the translation and correct it for proper English.

In the attachement there is a drawing of the new version of the schematic, with all the new replaced components, as well as the original high-quality PDF drawing with proper translation from Chinese that comes with the boards when you purchase them. Please note that the C20 and C21 capacitors are not supplied and there are no places on the board for them. As I mentioned above, they are needed to stop the regulators from oscillating. I have soldered them to the legs of regulators before soldering them into their places. I have tried to retain the parts labeling close to the one found in the original shematic and on the silk print.

The ZIP file also contains a proper translation of adjustment instructions. The adjustment is actually rather simple.

Just a quick note the 3DF20 in the redrawn schematic is shown as PNP instead of NPN.


--- Quote from: moffy on February 02, 2024, 09:39:12 am ---Just a quick note the 3DF20 in the redrawn schematic is shown as PNP instead of NPN.

--- End quote ---

Thank you! I have fixed that.

I built the same a while ago,that used two transfo's,do you just use one?,there is a yt vid of a fella building this,also his website has the schematics.

I've used one transformer, happened to have one scrapped from an old transistor amplifier. They are often sold cheaper than a separate transformer. Tried to find vids on youtube when run into the problem, found a couple, none had my problem and was unable to find the schematic. So had to draw the schematic myself. It also helped to understand how it works, which is a good thing.


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