What stuff matches basic ideal, or near ideal equations, the most/least ?

Thread Starter

DarthVolta

Joined Jan 27, 2015
521
So far I'm just using the most BASIC models for RLC circuits, so they are just purely R-L-C. And for BJT's, I haven't learned very much atomic level semi-conductor phyisic's, yet (I will) so I'm not using models with junction capacitance yet.

I've been learning the 2ndODE's for basic RLC transient analysis. I suspect that that will get applied to mesh/nodal analysis by way of systems of ODE's, and so into vector spaces and matrices, of ODE's.

For back of the envolpe calulations of BJT's, in discrete/through-hole parts, when do the simple ideal models, drift from reality ? A hard driven BJT switch, for instance, I don't know how to calculate how they act in transistion. I guess I need the RLC model of a BJT
 
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Papabravo

Joined Feb 24, 2006
16,086
As you move higher in the frequency spectrum models have to be adjusted accordingly. Capacitors start behaving like inductors and inductors start behaving like capacitors. Circuit elements are connected with waveguides instead of wires. Is that enough to make your head spin?
 

dl324

Joined Mar 30, 2015
12,871
For back of the envolpe calulations of BJT's, in discrete/through-hole parts, when do the simple ideal models, drift from reality ?
There is no definitive point where ideal models become useless. We use them to simplify calculations. If that doesn't give a solution that's accurate enough, we introduce non-ideal parameters and recalculate.

You may think that resistors, capacitors, and inductors are simple, but they aren't.

A resistor has inductance from the leads and/or how it's constructed and capacitance. Capacitors have inductance from the leads.

Whether we need to consider parasitics depends on the circuit. The key is to know when they're significant enough to matter.
 

Delta Prime

Joined Nov 15, 2019
988
Hello there :) There are two types of electrical devices, real and ideal. Real devices can be measured. They are the only things that physically exist. They are the actual interconnects or components that make up the hardware of a real system. Real devices are traces on a board, leads in a package, or discrete decoupling capacitors mounted to a board.

Ideal devices are mathematical descriptions of specialized circuit elements that have precise, specific definitions. Simulators can only simulate the performance of ideal devices. The formalism and power of circuit theory apply only to ideal devices. Models are composed of combinations of ideal devices.
The impedance of any real, physical interconnect or passive component can be measured. However, when impedance is calculated, it is only the impedance of four very-well-defined, ideal circuit elements that can be considered. We cannot measure ideal circuit elements, nor can we calculate the impedance of any circuit elements other than ideal ones. This is why it is important to make the distinction between real components and ideal circuit elements
 

Thread Starter

DarthVolta

Joined Jan 27, 2015
521
I guess I should just do more AC analysis in LTspice and compare to basic calc's. I was quite happy the other day when I made an RLC series curcuit and it barely oscillated and I could calculate how it decayed over time.

IDK, I keep expecting there to be something else I never heard of, besides, RLC/the 4 EM equations...IDK...I guess it's just active elements.

I suppose then there's super conductor's, plasma's, spin-electronics, and a lot more, so yeah, of course IDK. I have study harder, not be lazy.
 
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Papabravo

Joined Feb 24, 2006
16,086
I guess I should just do more AC analysis in LTspice and compare to basic calc's. I was quite happy the other day when I made an RLC series curcuit and it barely oscilatted and I could calculate how it decayed over time.

IDK, I keep expecting there to be something elese I never heard of, besides, RLC/the 4 EM equations...IDK...I guess it's just active elements.

I suppose then there's super conductor's, plasma's, spin-elctronics, and lot more, so yeah, IDK
Have you dug into the various types of passive filters? That is a pretty rich area of inquiry.
 

Thread Starter

DarthVolta

Joined Jan 27, 2015
521
I know a few op-amp eqn's, but they are still more like a black box to me, especially with the output limits, maybe I just missed that.

I use phasor's, but I'm not into true frequency analysis yet, but I'm just about there with ODE's and Laplace trasform to s=jw
 

Delta Prime

Joined Nov 15, 2019
988
Hello there :) Allow me to introduce myself "Ideally" .
I only can suggest to look into the advanced models of transistors as well as operational amplifiers
My gratitude for your response in correcting my stated false fact, too which I am not entitled to .... Your keen attention and dedicated effort conveying knowledge bring laurels to AAC.
 
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