making usb mobile charger help

Discussion in 'The Projects Forum' started by Asad ahmed1, Jun 12, 2016.

  1. Asad ahmed1

    Thread Starter Member

    Feb 10, 2016
    68
    0
    First I put the step down transformer to get 5.7 volts then I put a diode and bunch of capacitors after that I put 7805 ic to get constant 5 volts but my out is 4.95 ...will it works ..is my circuit is correct for charging and giving constant supply..
    I made bridge rectifier but it reduces my output ....
     
  2. bushrat

    Member

    Nov 29, 2014
    97
    22
    Asad ahmed1 likes this.
  3. Asad ahmed1

    Thread Starter Member

    Feb 10, 2016
    68
    0
  4. bushrat

    Member

    Nov 29, 2014
    97
    22
    should be no problem..provided that is does not draw too much current.
     
  5. Asad ahmed1

    Thread Starter Member

    Feb 10, 2016
    68
    0
    why we have bridge circuit if only one diode can do the work ?
     
  6. bushrat

    Member

    Nov 29, 2014
    97
    22
    Post a schematic of what you have completed so far, it will help everyone see what you are doing.

    Using one diode, you are only getting half of sine wave, capacitor will discharge lower, and you will see ripples on your 7805, see this link
    Using full bridge rectifier, capacitor will remain charged (close to full charge) and it will have less ripples on your 7805, see this link
     
  7. Asad ahmed1

    Thread Starter Member

    Feb 10, 2016
    68
    0
    my circuit is same as this the difference is that I stepped the ac voltage down to 5.7 V and in place of 3300nf I placed 3 4 capcitors .after that i placed the 7805 ic and placed 0.1 uf there ...the output came 4.95
     
  8. bushrat

    Member

    Nov 29, 2014
    97
    22
    ..so are you using AC to convert into DC or are you using a battery of higher voltage and a transformer to step it down to lower voltage?..
     
  9. Asad ahmed1

    Thread Starter Member

    Feb 10, 2016
    68
    0
    Iam using Ac to convert into Dc
     
  10. bushrat

    Member

    Nov 29, 2014
    97
    22
    Ok, so using 2 or 4 diode rectifier will give you less ripples on input of 7805.
     
  11. Asad ahmed1

    Thread Starter Member

    Feb 10, 2016
    68
    0
    how would I get 5 volts if i use more diodes ..where do i put diode how would I able to product working charger help me please
     
  12. bushrat

    Member

    Nov 29, 2014
    97
    22
    Be careful when working with high voltage AC, it hurts.
    Stepping voltage down to 5.7 v can cause problems on your voltage regulator. Can you set it at somewhere between 9-24 V?

    [​IMG]
     
  13. Asad ahmed1

    Thread Starter Member

    Feb 10, 2016
    68
    0
    I got the Transformer from an old charger i measured the output and it was 5.7 ac volts..
     
  14. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    With 5.7 volts from the transformer and a bridge rectifier with e decent capacitor, you will get about 6.66 Volts at the input of the regulator.
    As the regulator needs at least 2 Volts higher input voltage as the output voltage, you will have troubles with the regulation.
    Either use a transformer with a higher output voltage or use a Low Drop Out regulator.

    Bertus
     
  15. bushrat

    Member

    Nov 29, 2014
    97
    22
    For 7805 to work properly, it needs minimum 7 V to operate. If you look on the datasheet, it says that 7805 has 2V dropout, and maximum input voltage is 35V.
    5.7V will not work properly for you. If may work if you hvae no load, but once you connect something, the voltage will drop even lower, below 5 V.
     
  16. Asad ahmed1

    Thread Starter Member

    Feb 10, 2016
    68
    0
    thanks for your reply Going to get my self a new transformer ..
     
  17. dannyf

    Well-Known Member

    Sep 13, 2015
    1,824
    364
    with some assumptions, your circuit is likely working.
     
  18. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,998
    745
  19. Asad ahmed1

    Thread Starter Member

    Feb 10, 2016
    68
    0
    wow Trying this huge thanks ...
     
  20. Asad ahmed1

    Thread Starter Member

    Feb 10, 2016
    68
    0
Loading...