Basic query on step down transformer output for regulated power supply

Discussion in 'General Electronics Chat' started by Shantanuonline, Aug 12, 2015.

  1. Shantanuonline

    Thread Starter New Member

    Aug 12, 2015
    9
    0
    Hi All,

    I am new into electronics and this is my 2nd post on this forum.
    I have a basic question on step down transformer. One of my DIY circuit need 12 volt regulated dc supply so i have purchased a 12-0-12 500 ma transformer and build the circuit as in the below URL.

    http://tinypic.com/view.php?pic=n1fs6v&s=8

    My question is what to do with the middle winding of the transformer highlighted in red. The transformer is marked as 12-0-12 and i need only 12 volt regulated supply. I read some post and it sounds like if i did not connect it properly then it may produce 24 volt and burn my connect circuit so i am worried.

    Thanks
    Shan
     
  2. Shantanuonline

    Thread Starter New Member

    Aug 12, 2015
    9
    0
  3. #12

    Expert

    Nov 30, 2010
    16,247
    6,743
    Use the bottom, left drawing.
     
    Hamlet and AnalogKid like this.
  4. Shantanuonline

    Thread Starter New Member

    Aug 12, 2015
    9
    0

    Thank you for your response.

    Can I use the same full wave bridge circuit which I have indicated in my initial post with 12 0 12 transformer?
    Actually I already solders all components and now just looking for correct wiring with transformer

    Thanks
    Shan
     
  5. #12

    Expert

    Nov 30, 2010
    16,247
    6,743
    If your initial post was correct, I would not have told you to use a different circuit. You have started out with 24 VAC into a bridge rectifier which will get you about 32 VDC. Do what I said and you will get about 16.3 VDC.
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Here is how to salvage your existing tranny and full-wave-bridge: Note the filtering required for a nominal 1A output current.

    127a.gif
     
  7. crutschow

    Expert

    Mar 14, 2008
    12,973
    3,219
    If you want a negative voltage for any reason, the unused output of the bridge labeled NC on Mike's circuit can be filtered to give -16.3Vdc.
     
  8. Shantanuonline

    Thread Starter New Member

    Aug 12, 2015
    9
    0
    Thank you all for your response. i will try #12 and mike suggestion this weekend.
    one more question, what if i use the first and middle winding of secondary coil of 12-0-12 transformer with full bridge rectifier with 7812 IC
    and leave the third winding as is without connected anywhere? will i get approx 12 v regulated output?

    i am not sure if this make sense but just my thought.

    Thank you
    Shan
     
  9. #12

    Expert

    Nov 30, 2010
    16,247
    6,743
    That will get you about 15.6 peak volts at the first capacitor. Allowing 2 volts for the regulator, you have 1.4 volts left for ripple voltage @ 1500uf. You will be able to use 0.31 amps because you are only using half the transformer. The way I told you to do it in the first response would get you 0.5 amps with 1300 uf.
     
  10. Shantanuonline

    Thread Starter New Member

    Aug 12, 2015
    9
    0
    #12, I have made the bridge with 2 diode as u mentioned earlier and the circuit works fine.
    Thanks for you help.
     
Loading...