is isolation really needed in low power converters?!

Discussion in 'The Projects Forum' started by chaosmc, Mar 4, 2016.

  1. chaosmc

    Thread Starter New Member

    May 21, 2012
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    I would like to make a dc/dc buck converter. Having few resources I am limited on testing it on breadboard. So as you can understand we are talking about low power levels. For example I want to use the output voltage as a feedback and then do my stuff with opamps so I can produce the desired PWM. My question is about the isolation of the output voltage measurement. I know that in high power we have to use it (for example by using a current transducer or by an isolation transformer etc.)


    However I see on various textbooks that they put parallel to the load another resistance so that they can make a voltage divider and they use that voltage (which is of course a fraction of the output voltage) as their input to their control. Do I really have to worry about isolation problems when I am considering power levels of 10Watts? If I just put a 10kOhm load and I use a 100kOhm as a voltage divider to limit even more the power level for my control, will that be enough? I guess I could try by trial and error and in the worst case scenario I will burn some opamps but I would like your input if possible!


    Finally do you have any suggestions for “typical robust” Mosfets for such applications? I am interested on testing various generic control schemes such as PID control. Have in mind that I would like to use them on breadboard so a through hole solution would be perfect for me. I know that even just a transistor perhaps could work just fine but I am interested on n-Mosfets specifically. input voltage around 10V, output load 0.1-1A.
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,779
    1,103
    If you're talking about isolation from mains voltage then the power level isn't generally the issue. More important is preventing someone being electrocuted by touching something at high voltage.
     
  3. crutschow

    Expert

    Mar 14, 2008
    12,995
    3,229
    Isolation has nothing to do with the power level.
    It has to do with safety (if the input is from the mains for example) or isolating grounds to minimize ground loop noise in the circuits.
     
  4. chaosmc

    Thread Starter New Member

    May 21, 2012
    17
    0
    Thanks guys for your input.
    So for example in the attached circuit there is no problem if the output power is 10W or 10KW!? The amplifier will be OK in both situations?

    (The input mains is indeed isolated...I am considering about my feedback in this post)
     
  5. crutschow

    Expert

    Mar 14, 2008
    12,995
    3,229
    The resistors you refer to in you original post are there to reduce the voltage, not for isolation.
     
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