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Hi, can somebody help me with feedback circuit

Discussion in 'General Electronics Discussion' started by michael1978, Jun 28, 2018.

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  1. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    Hello to everbody,

    can somebody expain how work and what they form feedback capacitor inductor resistor,
    if it was only resistor feedback i understand, but this make me dificult to understand with capacator and inductor....
    and also L2...thnx.
    FEEDBACKANALYSIS.png
     
  2. kellys_eye

    kellys_eye

    4,275
    1,147
    Jun 25, 2010
    The resistor and inductor associated with C1 are representative values (parameters) for the losses in C1 and allow you to make a more accurate calculation for resonance and/or Q. Same applies for the resistance associated with L2.
     
  3. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    Hi, Kelly, so that is tuned circuit, C1 and Inductor,, they resonace at 11.25Mhz, but i dont understand, what happen when is lower frequency or higher frequency than 11.25Mhz
     
  4. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    It will not work. Q1 has no power.
     
  5. michael1978

    michael1978

    388
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    Mar 17, 2012
    GoodMorning Duke, so you mean only at that frequency will work Q1, otherwise there is no feedback?, because i have one software feedback analysis, is very easy to design the circuits, after i build the circuit in multisim and i make experiment andi i dont see anything change in voltage of current, when i change the frequency still is working?
     
  6. davenn

    davenn Moderator

    13,798
    1,939
    Sep 5, 2009

    No, it wont work at all ... the circuit shows no power supply ... you cannot sim a circuit that has no power
     
  7. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    Yes of course that not work, let take example that RC is resistor is connected for example to 12V power supply, a 1V peak input, now i dont understand what they do lc, you can use one resistor feedback...……..
     
  8. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    If you draw a horizontal ground line and a horizontal power line, clangers like this will be less likely.
    I hate lumps of 'earth' floating through the air.
     
    davenn and kellys_eye like this.
  9. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    HI thanks for help i understand now, so have nice wekend to everybody;)
     
  10. LvW

    LvW

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    146
    Apr 12, 2014
    Michael...so you now really understand the meaning, the task and the characteristics of the two feedback loops in the circuit? (I hope you know that R3-L2 also provides feedback). I would be surprised...
     
  11. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    I think feedback is thrugh tuned circuit and resitor
    I think feedback is thrught tuned circuit and R1 of rc circuits,...……..the emitter resistor is to bias and also gain, and l2 the same but he deopends from frequency low or high imedance and also gain…….
     
  12. LvW

    LvW

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    146
    Apr 12, 2014
    Regarding DC bias: The circuit has no biasing voltages at all.
    And - as mentioned - the emitter resistor provides negative DC feedback (and - yes- contributes to bias) and R3-L2 provide negative ac feedback!!
    What is the purpose of R1-L1-C1 feedback path? Does it always work as a feedback loop?
    Why a series resonant circuit?

    Michael - I am asking these questions because your answer was "....I understand now...!-
     
  13. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    Ohhh Realy i am sorry, that i did not open the forum, realy i am sorry, i thougt is finish i understand, and i thought i understand, for that i did not open the forum,
    Is a resonance at specified frequency, the LCR is series impedance, at lowest value, this means the negative feedback is at a maximum, so the circuit gain is at a minimum. at LC and i am still learning
     
    Last edited: Jul 4, 2018
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