+/- 9V supply

Discussion in 'The Projects Forum' started by liam, Mar 31, 2015.

  1. liam

    Thread Starter New Member

    Apr 22, 2008
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    0
    Hi,

    I am trying to build a +/- 9V supply. The problem i am having is tat the transformer is getting very hot, can some one confirm that the circuit should work? the transformer i am using is a pt/13/2/15. the transformer has 2 off 15v outputs for which i have commend together to form +/- is this correct?

    psu.png
     
  2. MCU88

    Member

    Mar 12, 2015
    360
    35
    Your schematic looks correct.
     
  3. crutschow

    Expert

    Mar 14, 2008
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    3,221
    Are you sure the output polarity on the two windings is correct?
    What is the measured output voltage?
     
    Roderick Young likes this.
  4. liam

    Thread Starter New Member

    Apr 22, 2008
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    From ground to the the anode of D6 i get 3.66v and from the cathode of d5 i get -4.8V . with these measurements i have de soldered the 2 voltage regulators.

    the polarity for the two windings is shown in the picture attached. i have joined the two center pins together. is this correct?

    upload_2015-3-31_20-28-26.png upload_2015-3-31_20-28-26.png
     
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
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    Something is fishy. Gnd to anode of D6 should be ~15Vac.

    1N4003s are a bit light for this application. I think you have one or more blown 1N4003s

    15V-0-15V is high for this application. You will be making a lot of heat in the regulators. It would have been better to use a 10V-0-10V or 12V-0-12V tranny.
     
  6. Roderick Young

    Member

    Feb 22, 2015
    408
    168
    Try setting your voltmeter to AC, and measuring the voltage across each secondary, then the voltage across the two secondary pins on the outside that you did not connect together. I'm with Crutschow, sounds like you have the transformer wired with the wrong phase. Also, I noticed on your schematic that pins 5 and 6 of the transformer are wired together. Are you sure those are the center pins?
     
  7. liam

    Thread Starter New Member

    Apr 22, 2008
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    Thanks for the reply guys, i should say that the diodes i have used are different to the ones in the schematic, the ones i could find at uni are 1n5817 and these are the ones fitted.
    i have measured across the 2 non joined pins of the secondary and when i turned the power on the volatge was about 12V then it kept reducing to about 2V in about 5 seconds.

    as for the voltage for each secondary output- the top output as per the data sheet picture i got about 4.6 volts and it slowly starts dropping and for the other secondary i get 8V and that slow starts dropping.

    i am not sure about pin numburs but the way it has been wired is to join the dot of the top secondary to the non dot of the second secondary and used this as ground.
     
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
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  9. liam

    Thread Starter New Member

    Apr 22, 2008
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    guessing if i remove them off the pcb and measure the output of the transofrmer i should get rough 15V or is there a way to test if i have blown them? could you recommend a diode i could use?
     
  10. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Digikey has 726 different through-hole parts (292 if we limit it between 2A and 3A) that would work in your application. Choose one :)

    Lift all four anodes from the transformer pins, and measure again.

    Hope you learned this lesson: (never substitute a part unless you look at the data sheet of proposed substitute.)
     
    liam likes this.
  11. liam

    Thread Starter New Member

    Apr 22, 2008
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    i have de soldered the didoes and the transformer is buzzing away nice and happily at about 14V . like you said it must have blown the didoes. once again thank you all for your help and advice . it has been greatly appreciated
     
  12. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    (Hey Dodgy), another satisfied customer...

    Going QRT for a few days...
     
  13. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    C32 and C3 are not recommended. Check the datasheet examples.

    Ken
     
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