Bipolar DCDC Problems

Discussion in 'The Projects Forum' started by Kierip Sab, Apr 5, 2016.

  1. Kierip Sab

    Thread Starter New Member

    Mar 11, 2016
    Hello tinkerers,

    I am having a technical problem, which did not occur during the breadboard phase, which I expected that It should have happened.
    the first board img 1790.JPG
    contains a
    ac to dc TMPS 05-112 AC to DC convertor which is cosy.
    lm7806 for 6V regulation.
    and a NMXD0512S0 with a 7V max input and a +-12V 235mA which is enough for driving the next board.

    second board contains
    non inverted OPAMP LTC1354 with dual termination 49,9 ohm and 5K for RG.
    I connected the ground of the secondboard with the BNC termination over to the first board. the 230V ground is not connected to the NMXD0512S0, because it has its own ground.

    I noticed during testing that the signal from the function generator was interfering with the DCDC NMXD0512S0 creating very high pitched unsual sounds. and I was wondering how to solve this? If I do not connect the BNC to the ground I get a Antenna effect that doesnt help at all. evenso using an 49,9 ohms.

    Should I use some Inductors? between the lines?
  2. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
    The TMPS is rated for 416 mA out at 5 V, or 2.08 W. At +/- 12 V this equates to 86.7 mA minus the converter efficiency. At 80% that leaves about +/-70 mA. If that is enough for your circuit, then ok.

    All signals must have some reference relationship for the circuit to work. Your schematic shows the inverting input floating, no ground connection to the BNC connector, and no connections to the external signal source. And there is nothing marked 230V, so I have no idea how that figures in. Plus, 230 V is a very high voltage to be running around in a 12 V circuit.

    Your schematic does not match your description, and your description is not clear. Please post a more complete and more accurate schematic of the overall signal system, including all power supplies and grounds.

    Kierip Sab likes this.
  3. Picbuster

    Active Member

    Dec 2, 2013
    We need the complete schematic to allow us to help you.
    One of the important parts is: decoupling cap's 100nF between +12V and gnd and -12V and gnd as close as possible to opamp.
    The supply voltage chips need a minimum load ( see data sheet it is 1 or 2 mA I think) 1k between +12 and gnd and -12 abd GND will do the job (expand this with a led as indicator) If load and capacitors are not installed oscillation may occur. ( see attached to explain)

    But again this is an assumption based at the limited information provided.