OMG... I sure hope I NEVER see this in a circuit I buy...

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  • eccerr0r
    Solder Sloth
    • Nov 2012
    • 8673
    • USA
    #1

    OMG... I sure hope I NEVER see this in a circuit I buy...

    I was browsing around how USB OTG power negotiation works and how it deals with wall wart "dumb" supplies (since these OTG need to both supply and sink) and ran across this fairly irrelevant webpage from Google:

    http://emproj.com/AC_DC_LM2575

    OUCH OUCH OUCH OUCH...

    Ok, back to our normally scheduled programming...

    Tags: None
    • stj
      Great Sage 齊天大聖
      • Dec 2009
      • 30941
      • Albion
      #2
      Re: OMG... I sure hope I NEVER see this in a circuit I buy...

      lol - that's why they glue the case shut!!!

        Comment

        • mariushm
          Badcaps Legend
          • May 2011
          • 3799
          #3
          Re: OMG... I sure hope I NEVER see this in a circuit I buy...

          Technically, it's a correct circuit (if you're nitpicking, i'd be concerned about the fuse being too large but whatever)...

          In real world, the lack of isolation makes this a killer circuit. For example, someone could plug his mp3 player in the charger and get killed due to metal contact in some faulty headphones or something like that.

            Comment

            • Th3_uN1Qu3
              Believe in
              • Jul 2010
              • 6031
              • Romania
              #4
              Re: OMG... I sure hope I NEVER see this in a circuit I buy...

              Due to the lack of mains isolation, this circuit will never make it in a wall wart type supply.

              However, it's not like cheapo Chinese wallwarts are any better - if you took apart a transformer from one of those, what's keeping the mains away from your 5V-powered device is literally ONE LAYER of ridiculously thin yellow tape on the transformer, plus the enamel coating on the wires. Yet they work fine... for the most part. Occasionally they blow up, taking your device with them, and sometimes they even electrocute somebody. But as long as dumb, uninformed penny pinchers will keep buying them, the Chinese will keep making them.

              The wall warts that have (real) safety markings on them use much thicker insulation on the transformer, and have all the required input and output filtering components, making the supplies intrinsically safe under all operating conditions specified in the manual.
              Last edited by Th3_uN1Qu3; 12-06-2014, 10:53 PM.
              Originally posted by PeteS in CA
              Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
              A working TV? How boring!

                Comment

                • eccerr0r
                  Solder Sloth
                  • Nov 2012
                  • 8673
                  • USA
                  #5
                  Re: OMG... I sure hope I NEVER see this in a circuit I buy...

                  Yes, it was the isolation and the fact the first "preregulator" is linear, which would basically drop the efficiency...

                  The cheap Chinese wall warts at least tried to isolate, this PSU doesn't even try, plus it has awful efficiency (I'd think that the more common capacitive reactance transformerless PSUs would be more 'efficient' than this circuit...)

                    Comment

                    • ben7
                      Capaholic
                      • Jan 2011
                      • 4059
                      • USA
                      #6
                      Re: OMG... I sure hope I NEVER see this in a circuit I buy...

                      Don't the russians have different electrical wiring systems in their buildings? It might be OK for their buildings. Would never pass for manufacture/retail in the US, etc... though!
                      Muh-soggy-knee

                        Comment

                        • stj
                          Great Sage 齊天大聖
                          • Dec 2009
                          • 30941
                          • Albion
                          #7
                          Re: OMG... I sure hope I NEVER see this in a circuit I buy...

                          no, electricity flows the same way in the ussr.

                          it's just the car/truck drivers that seem to make the place look like a different planet!

                            Comment

                            • ben7
                              Capaholic
                              • Jan 2011
                              • 4059
                              • USA
                              #8
                              Re: OMG... I sure hope I NEVER see this in a circuit I buy...

                              Originally posted by stj
                              no, electricity flows the same way in the ussr.
                              Well I'm talking about maybe different grounding etc... hey, I was just an idea/thought.
                              The only way I'd see this as an acceptable circuit is if the WHOLE load on it is isolated (and isolated well enough) from any possible electrical contact with the outside world. Like, in an LED light bulb. They use high voltage buck converters, with no isolation transformer. It's acceptable because the LED is protected from any contact with the outside world.

                              Originally posted by stj
                              it's just the car/truck drivers that seem to make the place look like a different planet!
                              LOL
                              Muh-soggy-knee

                                Comment

                                • stj
                                  Great Sage 齊天大聖
                                  • Dec 2009
                                  • 30941
                                  • Albion
                                  #9
                                  Re: OMG... I sure hope I NEVER see this in a circuit I buy...

                                  https://www.youtube.com/watch?v=6syBu8KjcIQ

                                    Comment

                                    • stj
                                      Great Sage 齊天大聖
                                      • Dec 2009
                                      • 30941
                                      • Albion
                                      #10
                                      Re: OMG... I sure hope I NEVER see this in a circuit I buy...

                                      https://www.youtube.com/watch?v=BAh6KoPfMkQ

                                        Comment

                                        • ben7
                                          Capaholic
                                          • Jan 2011
                                          • 4059
                                          • USA
                                          #11
                                          Re: OMG... I sure hope I NEVER see this in a circuit I buy...

                                          Originally posted by Th3_uN1Qu3
                                          Due to the lack of mains isolation, this circuit will never make it in a wall wart type supply.

                                          However, it's not like cheapo Chinese wallwarts are any better - if you took apart a transformer from one of those, what's keeping the mains away from your 5V-powered device is literally ONE LAYER of ridiculously thin yellow tape on the transformer, plus the enamel coating on the wires. Yet they work fine... for the most part. Occasionally they blow up, taking your device with them, and sometimes they even electrocute somebody. But as long as dumb, uninformed penny pinchers will keep buying them, the Chinese will keep making them.

                                          The wall warts that have (real) safety markings on them use much thicker insulation on the transformer, and have all the required input and output filtering components, making the supplies intrinsically safe under all operating conditions specified in the manual.
                                          I have a cheap one that won't output it's full rated load, the output voltage just drops. The transformer looks like it barely has any windings. Must not have insulation...! I'm thinking about putting some voltage (500V for starters, then maybe 1000V?) across it and testing the insulation. Might even put it across a MOT (Microwave Oven Transformer, outputs about 2000V at around 1000W) for a finale! xD

                                          Originally posted by stj
                                          https://www.youtube.com/watch?v=BAh6KoPfMkQ
                                          Not to keep this thread off topic, but this is a LOT funnier...
                                          https://www.youtube.com/watch?v=gi-CgXWxO8M
                                          Muh-soggy-knee

                                            Comment

                                            • stj
                                              Great Sage 齊天大聖
                                              • Dec 2009
                                              • 30941
                                              • Albion
                                              #12
                                              Re: OMG... I sure hope I NEVER see this in a circuit I buy...

                                              fake, the bag normally inflates a hell of a lot faster and that car has something like 5 of them.

                                                Comment

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