48 Volt Phantom Power Supply with Photo-Schematic. Transformer Question.

Discussion in 'The Projects Forum' started by alanbcooper, Jan 21, 2016.

  1. alanbcooper

    Thread Starter New Member

    Jan 21, 2016
    2
    0
    Hey guys,

    This is my first post and I am happy to have found this website. I am currently working on a project using a PCB and jumper wires to make a 48v Phantom Power supply to be used with multiple condenser microphones. To make a long story short, I found a "mostly" detailed post on another site of someone creating the power supply using a 120v to 25v step down transformer. My main concern is the amperage. The instructions call for a power supply with 1 Amp while the power supply I ordered and have received is 1.6 Amps. Will this cause any problems? Also I am confused as to what is going on in the middle of the picture of the photo-schematic. My transformer only has two contact points and a ground (on the step-down side). It appears as though there is a 3rd wire coming from the transformer traveling through the middle of the picture. Also just to be clear, whoever made the original supply used a turret-style board while I am using a PCB with jumpers like I mentioned earlier. Also I understand I could just buy a wall-wart power supply but I am making this so I can learn more about circuits and PCB's. Hopefully someone will be able to help.

    Link for details and parts list: http://www.tangible-technology.com/power/Phantom_frying.html

    Picture of "photo-schematic" power_v3a.JPG

    Thanks in advance,

    Alan
     
  2. #12

    Expert

    Nov 30, 2010
    16,257
    6,757
  3. alanbcooper

    Thread Starter New Member

    Jan 21, 2016
    2
    0
    Thanks for the link. It was a simple misunderstanding on my part as far as the amperage question. I am still confused however as to whether or not a center tapped transformer was used? If not, once again I am still confused as to what the pink line in the middle of the board is supposed to represent?

    Thanks again,

    Alan
     
  4. #12

    Expert

    Nov 30, 2010
    16,257
    6,757
    The transformer seems to not be center tapped, but the DC supply is center tapped. The pink line is the zero voltage line compared to the positive and negative DC voltages.
     
    MaxHeadRoom likes this.
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,772
    931
    It does appear that the PCB has two power rails (37 and -37) and the caps and zener connection indicate a 99.9% for certain center tapped arrangement.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,509
    2,369
    As per @#12 I think the transformer is drawn wrong it should have a centre tap for a +ve 0 -ve supply as shown.
    Max.
     
  7. #12

    Expert

    Nov 30, 2010
    16,257
    6,757
    Disagree. What I see is a single end of the secondary used as, "common" with one diode going each way from the other end to make a pair of half wave rectifiers. Like this:
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,509
    2,369
    Gotcha, As the wave forms show,
    I am not a fan of 1/2 wave supplies,
    Max.
     
    #12 likes this.
  9. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,772
    931
    There is a grounding lug for the center tap on the board. So you could use a center tapped one without any mods as far as I can see.

     
  10. BR-549

    Well-Known Member

    Sep 22, 2013
    1,981
    388
    I don't believe the transformer is center tapped. Ground is point B. Point C (the pink line) is +37 V.

    The top of C3 is 48 V reg.
     
  11. analogdude

    New Member

    Jul 14, 2015
    14
    2
    Yes, but the polarity of the lower capacitor inverted.
    Yes, but the polarity of the lower capacitor of your diagram should be inverted. Point C is the common of the +ve and -ve capacitor pins, and the transformer winding.
     
    Last edited: Jan 22, 2016
    #12 likes this.
  12. #12

    Expert

    Nov 30, 2010
    16,257
    6,757
    I disagree again. The board is arranged with the most positive DC at the top, the pink line being a center position, and the most negative voltage at the bottom. The capacitors are correctly oriented.
     
    MaxHeadRoom likes this.
  13. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    #12, the Negative 33V capacitor on your drawing is drawn with wrong polarity.
     
  14. bertus

    Administrator

    Apr 5, 2008
    15,645
    2,344
    Hello,

    In the link in the openings post, the schematic is also given:

    phantom1.JPG

    There are no values given in the schematic, but the two times single rectifying are used as voltage doubler.

    Bertus
     
  15. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,516
    1,246
    Agree with Dave. Caps on the original schematic and the photo are correct.

    Unless there is a lot of signal conditioning going on at the mic, 1 A is a ton of phantom power current.
     
    #12 likes this.
  16. #12

    Expert

    Nov 30, 2010
    16,257
    6,757
    Oh! He was talking about MY drawing.:eek: By golly, he's right!

    There. I fixed it.
     
    Dodgydave likes this.
  17. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,991
    3,736
    Why use 48V when the link on the first post says everything from 9 to 48V works and Never ever exceed 48 volts. I would use something between 9 and 35. 9 seems pretty easy.

    =========================

    upload_2016-1-22_17-40-18.png
     
Loading...