Connect with us

Chat_Ghosty's PSU

Discussion in 'Power Electronics' started by Chat_Ghosty, Jul 1, 2012.

  1. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    You can learn a lot from failing when part of your circuit doesn't work as you expected. But you won't learn anything from a circuit that doesn't work at all because a small fault completely prevents all of it from doing anything useful, or which blows MOSFETs constantly.

    You also need to learn a LOT before your circuit even approaches something you can actually MAKE. There are no component values indicated, except for the ICs. There are no details of the transformers and inductors. These things make or break a switching power supply.

    I very strongly recommend that you start with something more straightforward, where sections of the design can be diagnosed separately, and where each small mistake doesn't result in a shower of sparks and hours of rework, with no identifiable lesson learnt.
     
  2. Chat_Ghosty

    Chat_Ghosty

    49
    0
    Jun 30, 2012
    Lets start a bit simpler.

    [​IMG]

    The Cap Values should be 0.33uf and 0.1 uf.

    WIll this work?
     

    Attached Files:

    Last edited by a moderator: Jan 6, 2013
  3. davenn

    davenn Moderator

    13,315
    1,766
    Sep 5, 2009
    Conventional .... always think conventional, if you try swapping between the 2 all the time you will end up in strife as in that circuit
    There are only rare times you need to consider electron flow direction, this isnt one of them ;)

    Dave
     
  4. davenn

    davenn Moderator

    13,315
    1,766
    Sep 5, 2009
    ummm
    .... for a start your schematic shows far fewer components than the PCB layout
    the schematic and PCB layout must match

    you havent shown the fuse in your schematic
    what are those 2 other 3 terminal devices on the PCB that are not shown in the schematic ?

    why would say that ?
    the schematic clearly shows 470uF in the input to the regulator chip, but yet another mismatch the PCB layout shows 4700uF ??
    in reality it should be ~ 1000uF on the input since the regulator is capable of supplying up to 1 Amp

    Dave
     
  5. Chat_Ghosty

    Chat_Ghosty

    49
    0
    Jun 30, 2012
    I forgot to add the fuse in the PCB.

    The Data sheet said to use 0.33 and 0.1 for this VR.
    I did not add the Two Digital Voltage Displays in the Schematic.

    Why do I need a 1,000uf Cap when using a battery?
    I tought the 1,000uf : 1amp was for Smoothing when using a Bridge Rectifier.
    I did mess up on the cap values. Honestly I have no idea when to and how to calculate the values. This I took off the data sheets and added a few parts I needed.

    Any books I can read?
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    You're right that you don't need 1000 uF on the input if you're powering it from a source that's already DC. The actual value is not that important. You could just as easily use a 0.1 uF, the same as the capacitor on the output.

    Those capacitors are needed by the regulator, to ensure stability. They should be placed close to the regulator and connected to the regulator leads with connections that are as short as possible.

    You should be a lot more careful that what you post is correct. Mistakes are unavoidable, but when we see a schematic and a PCB that have more differences than similarities, with no explanation along with the posting (or even if there IS an explanation), it's hard to know where to start when writing a response!
     
  7. davenn

    davenn Moderator

    13,315
    1,766
    Sep 5, 2009
    Ahhh battery supply OK fair enough on those values :)
    Sorry was glossing over the battery on the input ... am so used to using them off a bridge rectifier ;)

    Dave
     
  8. Chat_Ghosty

    Chat_Ghosty

    49
    0
    Jun 30, 2012
    I was meaning for you to only look at the Schematic. My fault for not saying.
    The data sheet said to use a 0.33uf.
    Why does the caps need to be places as close as possible?

    Does the Schematic work?
    If so ill post a more complex one. And try and work up to SMPS if you guys have the time.
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,192
    2,694
    Jan 21, 2010
    To prevent instability (oscillation).

    The schematic doesn't do anything. You have ti build it (on a breadboard perhaps).

    Have you?
     
  10. davenn

    davenn Moderator

    13,315
    1,766
    Sep 5, 2009
    the caps are there, as Kris said, to stop oscillations within the regulator chip
    placing the bypass caps close insures that the legs of the chip dont start becoming inductors at certain frequencies

    normally in a rectifier supplied regulator, you would use a 0.1uF on input and output
    and you would also use a 1000uF on the input and a ~ 10uF on the output

    a
    that schematic will work
    working up to a SMPS will be a very long time down the track ;)
    you would be better off building a linear PSU using a mains transformer to a lower AC voltage and rectifying that

    a bit bulkier and heavier but a worthwhile learning experience and you will end up with a good PSU for workshop experimental use
    After that PSU is up and working, you could then up the learning/circuit complexity by adding current limiting etc

    Dave
     
    Last edited: Jan 6, 2013
  11. Chat_Ghosty

    Chat_Ghosty

    49
    0
    Jun 30, 2012
    I see, Ill try and get some of the parts and try and build it.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-