cheapo chineese 0-30v 3amp psu issues.

Discussion in 'Power Electronics' started by m3vuv1, Sep 10, 2019.

  1. m3vuv1

    Thread Starter New Member

    Dec 11, 2018
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    For what its worth if i lift one leg of R11 and one leg of C9,it still behaves the same,voltage adjusts to a max of about 9v and the current limit still works.
     
  2. panic mode

    AAC Fanatic!

    Oct 10, 2011
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    Do you understand what those parts do in this circuit? You should not just go around and disconnect things without at least trying to predict circuit behaviour.

    C9 is also in the feedback loop filtering any high freq noise. Should not have this disconnected.

    R11 is part of feedback that sets output voltage (R11/R12 is a voltage divider). if R11 is open, U2 would work as voltage follower so PSU output would match potential at wiper of P1.
    If disconnecting R11 does not make difference, R11 is either defective or you got there wrong values for some of components - either R11 is too large or R12 is too low or there are shorts (solder bridge etc.).

    you should show your construction method. There may be things that are obviously wrong or at least help narrow down possible issues.
    Also show parts list. Finally measure voltages at key points, and post the values.
     
  3. m3vuv1

    Thread Starter New Member

    Dec 11, 2018
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  4. panic mode

    AAC Fanatic!

    Oct 10, 2011
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    you should not put your own text into quote, makes it next to impossible to read. your content should be before or after quote.

    3mV is pretty darn close to "zero" as far as things go for a PSU outputs. that is margin for ripple, noise... that is 1/10000 of the PSU range.
     
    Last edited: Sep 13, 2019
  5. m3vuv1

    Thread Starter New Member

    Dec 11, 2018
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    i have 3 of these from an old gas analyzer,would they be a better replacement for the op amps?,see attached data sheet
     
  6. Audioguru

    Expert

    Dec 20, 2007
    11,249
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    The circuit is a Chinese copy of an old Greek kit that had many parts overloaded. It uses TL081 opamps that have the Opamp Phase Inversion problem where its output goes as high as it can when its input becomes within a few volts from its negative supply (when the power is turned on or off). Q1 detects that the negative supply drops first and clamps the output. But the value of the main filter capacitor C1 is much too small do allow it to work properly when there is a load. The voltage divider resistors feeding the base of Q1 might be wrong in the Chinese copy.
     
  7. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    Have you now got the correct type of transistors in Q2 and Q4 positions?
     
  8. SamR

    Well-Known Member

    Mar 19, 2019
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  9. m3vuv1

    Thread Starter New Member

    Dec 11, 2018
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    SamR likes this.
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