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Transformerless power supply

  1. Sep 21, 2016 #1
    I designed one transformerless power supply and did lots of calculations for that. can anyone answer me how to calculate value of capacitor using as a smoothing capacitor parallel to zener.


    and also tell me if the value of capacitor is larger than required then what changes may occur in the actual circuit.?
     
  2. jcsd
  3. Sep 21, 2016 #2
    As I know the higher UF of the capacitor the smoother your power supply will run at the expense of starting time, which means that your power supply will need a slightly longer ( one to two seconds ) time to start working properly, also the input and the output matter of the whole system matter.


    Always safety first
     
  4. Sep 21, 2016 #3
    If i use the higher UF capacitor then reactance of the capacitor becomes low and causes higher current to flow through it. Isn't that make any major change in the circuit? in that case is our circuit operate as per our requirement?
     
  5. Sep 21, 2016 #4

    NascentOxygen

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    The smoothing capacitance is determined by the maximum load current and the tolerable ripple voltage. There is a formula for this.
    A larger capacitance may cause a larger inrush current at switch-on. This can put a strain on the rectifiers, and the fuse—and also the on/off switch.
     
  6. Sep 21, 2016 #5
    Thanks dats what i'm expecting.
     
  7. Sep 21, 2016 #6

    berkeman

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    Can you post a copy of your schematic? That would help us to answer any questions that you have. There are lots of ways of making a transformerless power supply. Use the UPLOAD button to attach a copy of your schematic to a post. Thanks. :smile:
     
  8. Sep 21, 2016 #7
    Here is the schematic.. further circuit is not here. input supply is 230V AC 50Hz as per our country specifications.
    Simulation is done in ISIS Proteus 8.0
    Xmerless power supply.JPG
     
  9. Sep 21, 2016 #8

    NascentOxygen

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    That series 2kΩ resistor means you can disregard the caution I wrote earlier about capacitor inrush currents at switch-on.
     
  10. Sep 21, 2016 #9
    okay. so what should i do? remove it from series? actually this resister also has power loss in form of heat
     
  11. Sep 21, 2016 #10

    NascentOxygen

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    Well, what was your reason for placing it there?
     
  12. Sep 21, 2016 #11
    To limit the current. if voltage goes too high in that case it may protect capacitor by limiting the current
     
  13. Sep 21, 2016 #12

    berkeman

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    Yikes. I see several problems here. Where did you get this circuit? Can you link to the original source? Overall, this circuit makes no sense, IMO.

    For example, you have a 50Hz AC Mains source trying to charge a 20uF capacitor through a 470nF capacitor. Do you see any issue with this (and there is the series resistor problem adding to this problem)...?
     
  14. Sep 21, 2016 #13

    NascentOxygen

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    Oh, I see—you included it because I mentioned surge current? But you can't make it an arbitrary value—the current through that path becomes the current for the DC side of your power supply. Because you haven't shown what circuits this will be supplying, I can't guess how much DC current it needs to supply. Have you estimated the DC current your loads will draw?
     
  15. Sep 21, 2016 #14
    No I tried to design it by myself. i read from some source to add series resistance there http://www.designercircuits.com/DesignNote1a.pdf check this pdf u may get the answer.
    thankx for reply
     
  16. Sep 21, 2016 #15
    yes of course. my load is a relay of 12 Volts and have power ratings of 0.36Watts. that means load current is 30mAmps
     
  17. Sep 21, 2016 #16
    check this image. and look at the output waveform.

    Is it ok? or should i make some changes here also?
    power supply.JPG
     
  18. Sep 21, 2016 #17

    NascentOxygen

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    Before you go further, you do know that modules are available to do all this, more efficiently and probably much more cheaply than you can build it yourself. To wit, that AC capacitor needs mains voltage ratings (600V at least, but I would use 1000V because I know failure will be expensive), so that cap alone will be costly.
    Google search, or check out: http://www.digikey.com.au/product-detail/en/cui-inc/PBK-3-12/102-3108-ND/4332645
     
  19. Sep 22, 2016 #18
    Hmm, u r ryt. can u suggest any module den?
     
  20. Sep 22, 2016 #19
    You may not understood previous diagram as there was transistor and battery of 12Volt shown. the simplified diagram is here. you can check this. is that ok? or still have some problems?
    Xmerless power supply.JPG
     
    Last edited by a moderator: Sep 22, 2016
  21. Sep 22, 2016 #20

    NascentOxygen

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    I can't recommend a particular one. Does the one I linked to have suitable ratings? Or search on google, amazon, ebay, or mouser.
     
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