How can u distinguish positive and negative feedback.?

[desperado1]

positive and negative feedback

How can u distinguish positive and negative feedback.?

 

[yxo]

how to reply of positive feedback

1. You have to suppose that whether current or voltage is go up or go down at any branch (call it (1))
2. Picture to yourself the path around a loop. When you return to the branch from which you started look at the changing of current or voltage(depends on what you chose). If the direction is changed the feedback is negative, otherwise it positive. Look in example

 

[LvW]

distingusih between positie and negatice feedback

How can u distinguish positive and negative feedback.?

Hi desperado1,

there is a clear definition of pos/neg feedback.
However, it is more involved as you probably expect since - for each real circuitry - EACH neg. feedback will turn into a positive one at higher frequencies.
Therefore, your question has a good and theoretical background.

The denumerator N(s) of each transfer function - when written in "normalized form" - is N(s)=1-Lo(s). Lo(s) is the loop gain which for low frequencies is negative in case of negative feedback.
Now, its simple:
a) In the frequency range where the magnitude of N(s) is >1 there is negative feedback;
b) In the frequ. range where the magnitude of N(s) is <1 there is pos. feedback.

More than that, in the NYQUIST diagram the transition from neg. to pos. feedback is at that point (frequency) where the Nyquist curve crosses a unit circle around the critical point "-1".

Was that your question ?
Regards

 

[santom]

how can feedback be positively given?

Very Good Explanation LvW..! It is very useful..!!

 

[yxo]

how to identify loop-gain positive or negative

It useful only at DC. The loop -gain at particular frequency is often not obvious and dificult to calcuclate.

 

[LvW]

distinguish positive and negative feedback

It useful only at DC. The loop -gain at particular frequency is often not obvious and dificult to calcuclate.

See my contribution from Nov. 10th.
LvW

 

[desperado1]

definition of positive and negative feedback

1. You have to suppose that whether current or voltage is go up or go down at any branch (call it (1))
2. Picture to yourself the path around a loop. When you return to the branch from which you started look at the changing of current or voltage(depends on what you chose). If the direction is changed the feedback is negative, otherwise it positive. Look in example

Thx for the reply......... can u explain and elaborate this concept for transistor.........

thanks in advance..................

 

[yxo]

example of positive and negative feedback

Thx for the reply......... can u explain and elaborate this concept for transistor.........

thanks in advance..................

What do you mean? It was an example of circuit in the my first post Are you about to see the circuit with more than one trans?

 

[xdy83]

positive and negative feedback definition

about simple circuits, the simple methord is to count how many transistors in the signal transport loop, which leads the signal to change phase like a amp of common source.

 

[desperado1]

examples of positive and negative feedback

Thx for the reply......... can u explain and elaborate this concept for transistor.........

thanks in advance..................

What do you mean? It was an example of circuit in the my first post Are you about to see the circuit with more than one trans?

i m new to electronics field........to be very honest i didnt understand what u mean of voltage positive and negative.............can u explain in a more understandable manner......please dont mind...........coz i m new to this field............

thanks in advance....

 

[yxo]

reply negative feedback

There are a lot of book about feedback and my advice you to pick up and read something because this subject is very difficult and complcated. Anyway, we call feedback negative when an output signal(for example from the block "A") is substrated from the input and result is given to the "A" again, where as positive feedback imply that the output signal is added to an input.

 

[LvW]

best negative feedback

There are a lot of book about feedback and my advice you to pick up and read something because this subject is very difficult and complcated. Anyway, we call feedback negative when an output signal(for example from the block "A") is substrated from the input and result is given to the "A" again, where as positive feedback imply that the output signal is added to an input.

This a very simplified description of the feedback effect.
What are you doing when both signals which are combined are out of phase by - let´s say - 100 deg ? Negative or positive feedback ?
In this case, the general definition as cited in my reply from Nov. 10th applies.

 

[edaoj]

negative feedback odd number of inversions

The best way is to identify the feedback loop and then traverse through it and check for number of inversions. You can have more detail in J.Baker book but its only in 2nd edition.

 

[anatta]

positive & negative feedback simple explanation

i want to read about feedback control system which books is good to read for beginner.

 

[LvW]

what do u mean by positive and negative feedback?

The best way is to identify the feedback loop and then traverse through it and check for number of inversions. You can have more detail in J.Baker book but its only in 2nd edition.

An odd number of inversions only tells you something about neg. feedback for dc (0 Hz). That´s not sufficient ! See my earlier reply.