Ideal conditions in which circuit analysis is done

[student-engineer]

What are the ideal conditions in which circuit analysis or analysis of an electrical system is done?I know that the air friction,friction between materials is ignored in ideal systems, such as for ohms law applications.What else is ignored in analysis of ideal electrical systems?

 

[Svein]

Stray capacitance, wire inductance, transmission line theory for short wire lengths,...

 

[student-engineer]

Stray capacitance, wire inductance, transmission line theory for short wire lengths,...

Can you provide a link to some relevant pdf,research paper or any blog/article regarding this?I was googling about it but could not find anything relevant.

 

[Svein]

No, sorry. All those factors are dependent on the physical layout of the circuit and therefore they cannot easily be simulated. I remember a competent analog engineer changing the layout a couple of millimeters, ordering a new PCB, measuring the results and adjusting the layout once more. I think he went through four or five iterations before he was satisfied.

 

[student-engineer]

No, sorry. All those factors are dependent on the physical layout of the circuit and therefore they cannot easily be simulated. I remember a competent analog engineer changing the layout a couple of millimeters, ordering a new PCB, measuring the results and adjusting the layout once more. I think he went through four or five iterations before he was satisfied.

I am not that much competent though .I wanted to know just for the sake of information as I think I should be just knowing about these too.As no system is truly linear,the non-ideal practical conditions lead to non-linear real time behavior of practical linear systems.Thank you anyways for your contribution to this thread.

 

[unix101os]

Electrical components whether a resistor, capacitor, inductor, or solid state device like a transistor all exhibit a combination of resistance, capacitance, and inductance. Also every components has some tolerance. So for example a 1kohm resistor may have a 5% tolerance. so that means the resistor could be anywhere between 950ohm and 1050ohms. This is why on older radios you see things like trim potentiometers (variable resistor) to help tune the radio. today we have resistors which much tighter tolerances as much as 0.1%. So a 1kohm 0.1% resistor could be 999ohm or 1001ohm. The same goes for capacitors and inductors. Other things to consider is that wire's are also a combination of resistance, capacitance, and inductance. Sometimes you have to pay attention to this when dealing with signals or anything periodic. Temperature also plays a role as it can cause variations in resistance, capacitance and inductance. So when doing electrical design the datasheet for the component is usually referenced to account for change in temperature so there are no undesired effects.

For example:
you have a 3.3v device. the data sheet says it can be operated from 3.0 to 3.6V but you have a 5V supply. You can convert the 5V to 3.3V by using an adjustable linear voltage regulator. To adjust the voltage you use a voltage divider (two resistors in series). you want to make sure that given temperature and resistor tolerances that you voltage will not drop below 3.0V or go higher than 3.6V or else you risk your device shutting down or blowing up.

 

[berkeman]

What are the ideal conditions in which circuit analysis or analysis of an electrical system is done?I know that the air friction,friction between materials is ignored in ideal systems, such as for ohms law applications.What else is ignored in analysis of ideal electrical systems?

Well I certainly ignore air friction in most of my SPICE simulations , but everything else is modeled. You can't get good agreement between simulation and the real circuit behaviors without including parasitics and tolerances. Are you familiar with how Monte Carlo simulations help to model tolerances in real world circuits?

 

[Windadct]

I would think more about IDEAL components, and not ideal conditions.

A simple way to think of an ideal component, is that it has only ONE or TWO parameters... A resistor only ohms, Capacitor only capacitance. A transformer - "ideally" only a ratio, but inductances could be needed for many analysis.

Other than temperature, even in more detailed analysis do we consider the "conditions".

 

[Ronald Channing]

I would think more about IDEAL components, and not ideal conditions.

A simple way to think of an ideal component, is that it has only ONE or TWO parameters... A resistor only ohms, Capacitor only capacitance. A transformer - "ideally" only a ratio, but inductances could be needed for many analysis.
Other than temperature, even in more detailed analysis do we consider the "conditions".

excellent answer.

Ideal elements and other elements used in basic circuit analysis follow the lumped matter discipline. These allow people like me who don't know a thing about maxwells equations to use them in algebraic fashion. Elements are "Discrete" and "lumped" among other things..3 simplifications/assumptions which he explains in the video below.
In this answer, Anant Agarwal (of MIT) explains below what "lumped matter discipline" is:



In his book:

includes a derivation of KVL, KCL from maxwells equations.

There was also another constraint, that is the length of the circuit is less than the operating wavelength of the signal. and thus frequency also matters as wavelength is inversely related with frequency.
https://en.wikipedia.org/wiki/Lumped_element_model