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Thread: Low-ripple (120Hz) 5V 3A AC adapter?

  1. #11
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    Quote Originally Posted by Chuck(G) View Post
    No, but I solved this one by inserting a pi-section filter to the analog stage 5V rail. The voltage wasn't too critical, so a bit of loss could be tolerated. Saves me from having to scrounge a PSU that I like.
    Thinking about this, is it not possible that the mfr designed the thing for a specific purpose and wasn't at all concerned with a small amount of noise/ripple? What would have been the added cost for your mod?
    Surely not everyone was Kung-fu fighting

  2. #12
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    I don't believe that most switching cheap wall wart DC supplies are designed for much more than charging batteries (most common) or running purely digital hardware. I'll have to dig through my "big box o' warts" to see if I've got a linear wart with decent filtering and regulation. Of course, you pay a penalty for loss of efficiency, but that shouldn't matter here.

  3. #13
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    Quote Originally Posted by Chuck(G) View Post
    I'll have to dig through my "big box o' warts" to see if I've got a linear wart with decent filtering and regulation.
    Key point being the "regulation" part.

    I've not come across an old linear transformer that was ever within spec. My old game console wall warts from 30 years ago output almost triple the voltage they were once rated for.

  4. #14
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    That's pretty common--the idea is that the voltage delivered will fall within a loose spec once loaded. Regulated warts tend to be in the 0-1A current range, mostly due to using the venerable 7805 regulators. After that, heat becomes an issue...

  5. #15
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    Quote Originally Posted by Chuck(G) View Post
    That's pretty common--the idea is that the voltage delivered will fall within a loose spec once loaded. Regulated warts tend to be in the 0-1A current range, mostly due to using the venerable 7805 regulators. After that, heat becomes an issue...
    I've never seen an old transformer style wall wart with a linear regulator in them. All the ones I have seen are a transformer, some sort of bridge rectifier and a capacitor.

    And I assure you they fall nowhere near any spec when loaded, once the voltage drifts up, it stays there whether loaded or not. It's caused by a failure condition in the transformer where the windings short together from the varnish insulation breaking down due to age and heat.

  6. #16

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    most cheap chinese SMPS have noticeable ripple on the output, thing is most applications don't care so they save money where they can

  7. #17
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    Quote Originally Posted by GiGaBiTe View Post
    I've never seen an old transformer style wall wart with a linear regulator in them. All the ones I have seen are a transformer, some sort of bridge rectifier and a capacitor.
    Do you want to see the inside of one such wart with 7805? I think I can manage it.

  8. #18
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    Quote Originally Posted by Chuck(G) View Post
    Do you want to see the inside of one such wart with 7805? I think I can manage it.
    I mean if you don't mind smashing one open just to take pictures, it'd be interesting to see.

    I've broken open hundreds of transformer type wall warts and never seen one with a linear regulator in them. Though I have opened up a couple of 3A linear bench supplies designed to float charge batteries, and they had the same problem where the transformer voltage drifted up from shorting windings, and the regulation circuitry couldn't compensate and subsequently burned up. I tried to repair one of them, but the voltage wouldn't go below 21.37v, even fully loaded. They weren't worth rewinding so I trashed one of them and re-purposed the case of the other with a 12v switching power supply.

  9. #19
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    I was thinking about opening an old Zip drive wart. I'm pretty sure that that has a regulator in it. I've got a few modem linear "warts" with +5 -12 and +12 regulation. I'm looking at a switching 'wart here from an old Compaq LCD wart that has regulated +12 and +5 (I use it to power floppy drives, but it's got enough to handle a 3.5" hard drive). Some are corded, but others are plug-in type.

    I've got to be pretty good at opening warts that have screw-less closures (welded or glued plastic). Just a little patience with a rawhide mallet eventually opens the seam, allowing for servicing of the innards, then closing up using a little solvent cement.

  10. #20

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    Quote Originally Posted by Chuck(G) View Post
    then closing up using a little solvent cement.
    what's the best chemical to use for that?

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