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Benchtop Power Supply Question

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    #81
    Re: Benchtop Power Supply Question

    Well, the CMOS TLC555 can go down to 2v or so, if needed?

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      #82
      Re: Benchtop Power Supply Question

      You need a reference voltage for the comparators, not sure what he's using for that. Hitachi 555's are pretty ooollldddd

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        #83
        Re: Benchtop Power Supply Question

        I have almost finished a diagram's prototype for the laptops PSU project . So far , my choice went for a parallel series of LM338 , backed up by parallel diodes as illustrated in an image previously , while leaving a chance for additional ones , as necessary . Right now , I estimate LM338 power at 5A maximum , to stay on safe side , and for each another 5A , I'll add another one ..

        When the project is finished , although the delays and distractions were more than to count , It will be available only for some particular friends , and through PM's .

        In the meantime and for the people who liked my backups parts , my Sony Cam is back on line after some repairs , so I may re-post the previous images which were very bad , and yet , you know there are some size limits for uploads , so I'll resize them in PS as necessary .
        Here's a sample of my vintage capacitors .
        Attached Files

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          #84
          Re: Benchtop Power Supply Question

          that picture looks like my dustbin after a repair

          parallel high current diodes doesnt work btw,
          the one with the lowest voltdrop takes more of the current - then fails leaving the remaining ones overloaded.
          then they fail.

          happens all the time in some cheap tv psu's that try to do it.
          also kills a lot of early Ryobo battery chargers

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            #85
            Re: Benchtop Power Supply Question

            Originally posted by stj View Post
            that picture looks like my dustbin after a repair
            Come on stj; I'm in the middle of hundreds of projects , including a 30 km FM transmitter , and the picture's background initially should look vintage


            Originally posted by stj View Post
            parallel high current diodes doesnt work btw,
            the one with the lowest voltdrop takes more of the current - then fails leaving the remaining ones overloaded.
            then they fail.
            I really doubt that when they're each rated 6A. and fyi , they'll be equipped with special heatsinks similar to old CRT monitors ...
            So you deserve another ...lol

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              #86
              Re: Benchtop Power Supply Question

              @stj;

              That's how my dust bins look like ,
              Attached Files

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                #87
                Re: Benchtop Power Supply Question

                Originally posted by jiroy View Post
                Come on stj; (...) and the picture's background initially should look vintage



                Originally posted by stj View Post
                parallel high current diodes doesnt work btw,
                the one with the lowest voltdrop takes more of the current - then fails leaving the remaining ones overloaded.
                then they fail.
                happens all the time in some cheap tv psu's that try to do it.
                also kills a lot of early Ryobo battery chargers
                Originally posted by jiroy View Post
                I really doubt that when they're each rated 6A. and fyi , they'll be equipped with special heatsinks similar to old CRT monitors ...
                So you deserve another ...lol
                In practice what @stj claims is TRUE! You'll watch this behavior when the overall current exceeds the maximum rate per diode (plus a unknown value).

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                  #88
                  Re: Benchtop Power Supply Question

                  Originally posted by megaraider View Post






                  In practice what @stj claims is TRUE! You'll watch this behavior when the overall current exceeds the maximum rate per diode (plus a unknown value).
                  It's like pushing me to reveal more secrets I would prefer to keep it hidden!! Well fine megaraider ... How the overall current would know which one is the first when the special heatsink is making them symetric with high precision ? .
                  Yet , I do agree that if something is arranged chaotically , of course it will rise many different problems ..

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                    #89
                    Re: Benchtop Power Supply Question

                    The trick is to either go ahead and match them else current limit them, just like bjts.

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                      #90
                      Re: Benchtop Power Supply Question

                      Originally posted by jiroy View Post
                      It's like pushing me to reveal more secrets I would prefer to keep it hidden!! (...) the special heatsink is making them symetric with high precision ? .
                      No secret ... IMO a great mistake.
                      The heatsink, no matter how 'special' it is, only works to keep the diodes under temperature limits, and if common to keep them all at about the same temperature.
                      Nothing else, sorry!

                      Originally posted by eccerr0r View Post
                      The trick is to either go ahead and match them else current limit them, just like bjts.
                      Yes!

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                        #91
                        Re: Benchtop Power Supply Question

                        why not just use a 25A rectifier from an old pc psu?

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                          #92
                          Re: Benchtop Power Supply Question

                          Originally posted by megaraider View Post
                          No secret ... IMO a great mistake.
                          The heatsink, no matter how 'special' it is, only works to keep the diodes under temperature limits, and if common to keep them all at about the same temperature.
                          Nothing else, sorry!



                          Yes!
                          Leave the how matter it is special , for me , and try to answer my question ... Though I won't tell you when you're right or wrong .

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                            #93
                            Re: Benchtop Power Supply Question

                            Originally posted by stj View Post
                            why not just use a 25A rectifier from an old pc psu?
                            It's because I'm leaving the always possibility to add more Diodes/LMs in case I want to put more laptops on the table . When I'll draw the circuit , I'll leave that possibility for lot of other parts too . So nothing against rectifiers basically other than that ..
                            I left the core calculations for the last touch for such reasons .

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                              #94
                              Re: Benchtop Power Supply Question

                              Originally posted by jiroy View Post
                              Leave the how matter it is special , for me , and try to answer my question ... Though I won't tell you when you're right or wrong .
                              Really No question to answer
                              Wishing you good luck exceeding individual max rated current using parallel diodes with you're special heatsink…

                              Originally posted by stj View Post
                              why not just use a 25a rectifier from an old pc psu?
                              Originally posted by jiroy View Post
                              it's because i'm leaving the always possibility to add more diodes/lms in case i want to put more laptops on the table.
                              Not a problem... add more rectifiers in parallel
                              Last edited by megaraider; 02-20-2023, 08:01 PM.

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