EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: eamoex on May 17, 2020, 07:48:00 pm
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I see these power supplies on eBay
https://www.ebay.com/itm/Ultra-Low-Noise-linear-power-supply-LPS-PSU-KIT-5V-9V-12V-15V-18V-24V-/121940137982 (https://www.ebay.com/itm/Ultra-Low-Noise-linear-power-supply-LPS-PSU-KIT-5V-9V-12V-15V-18V-24V-/121940137982)
but I don't understand how they work. Where is the bridge rectifier, where is the transformer?
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It's a kit, you have to supply the transformer yourself.
And I guess the four TO-220s mounted on heatsinks are the rectifier.
Some more info which may be this supply:
https://www.amb.org/audio/sigma11/ (https://www.amb.org/audio/sigma11/)
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According to schematic, transformer AC in goes into where it shows AC on left bottom of PCB. Bridge rectifiers are on heatsink. Kind of an odd design....
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It then looks like you have to bolt the whole unit to a subsequent heatsink. It looks like the pass transistors stick out the bottom.
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That's MOSFET, and yes, it is meant to be bolted to the bottom of the case or heat sink.
In the page itself, there is a reference to a project that this product is based on. If you go there, you can see the whole thing. There are two MOSFET devices that sticks out and are meant to bolt to the chasis. I've seen hundreds of these offers on eBay, including dis-similar designs but all stating it is for the audio low noise applications.
What I got was a PCB and pile of parts. No instruction. The regulator IC was an obvious PULL and recycled parts AND different from the one that's advertised. It was lower rated (current wise) version. It also did not match the PCB. (3 pin device into 5 hole PCB pattern) NO instructions. When I complained, the seller put up a wall but when I pressed on, he quickly refunded the full amount and went away.
I advise caution on these.... or at least expect all kinds of issues.
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I would expect fake transistors and also I would be very sceptical of the provenance of those large caps. They would be expensive if genuine and would be an obvious item to be faked as well.
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The kit I bought had multiple of those large caps by NICHICON. I put it on my capacitor tester. At least capacity was correct and leakage was reasonable. But I have no reason to believe they were actually NICHICON 105C version. I'm starting to develop an aversion to those kits from these regions. Prices are too good to be true.
I've actually didn't build mine. Patterns on PCB was wrong for the IC and didn't feel like spending time and working with substandard products.
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Thanks everyone. That's enough to steer me away from these.