# Hi, can somebody help me with feedback circuit

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

1. ### 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.

2. ### kellys_eye

4,275
1,146
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

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

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

5. ### michael1978

388
2
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. ### davennModerator

13,730
1,914
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

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

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

388
2
Mar 17, 2012
HI thanks for help i understand now, so have nice wekend to everybody

10. ### LvW

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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

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

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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?

13. ### 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