Questions tagged [closed-loop]
75 questions
4
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1 answer
Closed loop vs. open loop system analysis and design
I have found questions similar to mine in the forum but none were quite answered to my full satisfaction. I have two questions:
1) Why is controller design is traditionally done with the open-loop system? Is it simply that if the system responds in…
Richard E
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4
votes
3 answers
Circuit stable in the Bode diagram, unstable in step-response
I am designing a simple current control circuit and trying to simulate it in LT Spice. The circuit is not optimized for some real-world application, it's more a learning method for me to get grip on stability analysis.
The circuit consists of a…
Roker Pivic
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4
votes
2 answers
Phase margin is 90° but transient step response shows overshoot
The Bode plot of the loop is as shown here:
The transient step response looks like this:
The block diagram looks something like this -
basically a single stage op-amp (OPAMP in figure) with high gain (cascode structure) biasing a FET (M1) such…
SBO
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4
votes
2 answers
Cannot predict closed-loop gain of this amplifier
This is the circuit I am currently analyzing: (link to LTSpice file)
I am trying to predict each stage closed loop gain and overall gain (with all loops closed).
First thing I did is calculate DC conditions in circuit for given parameters and then…
Keno
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3
votes
3 answers
Phase shift oscillator: what is reducing loop gain and how does changing feedback resistor affect things?
I have simulated the following circuit in LTSpice:
One can see that a stable sine wave with a peak of about 6.3 V is obtained, which has a frequency of 1 kHz (I calculated the RC network values to obtain 1kHz with the fromula which takes into…
Daniel Tork
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3
votes
1 answer
H-bridge class D amplfier
i am trying to make a closed-loop class D amplifier for a dissertation. I have the basics:
audio signal-->pwm modulator(LTC6992)-->gate drivers->H-bridge-->LC filter--> speaker
but i don't know what to do to make it a closed loop systems
any advice…
Frantisek Balaz
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3
votes
2 answers
Can an open loop system replace a close loop system
I'm thinking about a mathematical possibility how an open loop system can replace a close loop system so here is my explanation
Let's say I have a plant with transfer function as given in image (1)
But to achieve a desired output with minimum effect…
user215805
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3
votes
6 answers
How does opamp open-loop gain affect closed-loop gain in a circuit?
The gain of an opamp circuit is basically $$A_v=-\frac{R_f}{R_i}$$
But how come the gain of the opamp itself does not appear in the equation? How is the opamp amplifying anything in the circuit? What is the opamp doing in the circuit if it does not…
lateralus
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3
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1 answer
What is the difference between 'x' and 'plus' symbol in the block diagram
Generally speaking, what is the difference between the 'x' and the 'plus' symbol in a closed loop block diagram?
For example, in
(https://ieeexplore.ieee.org/document/6983570)
, what's the difference between the 'cross' sign and the 'plus' sign?
徐宇霆
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2
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3 answers
Why do we talk about system stability as a whole when Barkhausen criteria is valid only for one specific frequency?
The relationship AB=1 will be applicable only at a specific frequency. For instance, following is the bode plot for a circuit I have and as can be seen, the barkhausen criterion is met only at 6.3MEG radian/s. But at frequencies lower than that, the…
needbrainscratched
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2
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1 answer
Multi-Pole System - Why is there no bandwidth extension if loop gain is reduced?
[Design of Analog CMOS Integrated Circuits by Behzad Razavi]
The author explains that if the feedback (beta) is made weaker, the plot shifts down and hence, we hit the GX earlier now, thereby improving phase margin.
My question is, by decreasing…
AlfroJang80
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2
votes
2 answers
Ideal closed-loop gain derivation for negative feedback
Considering a negative feedback system, the closed-loop transfer function Af is given by:
where A is the open-loop transfer function and AB is the loop gain.
Every text I read says that if the magnitude of the loop gain is much larger than one,…
Stefanino
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2
votes
1 answer
How to deal with controling force by positioning oscillating magnet?
I am trying to code up a closed loop control system on force generated by the paring of strong rare earth magnets. I do not have much experience with PID logic but i have a weak grasp of the basics (ie controlling temp or something).
I am confused…
TheCodeNovice
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2
votes
1 answer
PID controller - should terms be completely independant?
I was under the impression that the P, I and D terms of a PID controller should be calculated independently of each other. That is, they would all use the same error information, but none of the three terms would be affected by either of the other…
John B
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2
votes
2 answers
Proportional Control Balance Beam
Bit of an unorthodox question I'm sure, but I'm making a balance beam (two rotors on either end of a see saw) with proportional control, and I can't seem to get it to balance at 0.
The proportional gain is controlled via a potentiometer, but there…
el16a2t
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