Author Topic: In AC analysis, do people replace large inductors  (Read 460 times)

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Offline MathWizardTopic starter

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In AC analysis, do people replace large inductors
« on: November 02, 2022, 02:42:47 am »
For small signal AC analysis with phasors, and caps, people routinely ignore the low value impedance of bypass caps, and just pretend they are a short. But with a large blocking inductors, I guess I've never worked out those circuits circuits enough, so I'm wondering if people would replace a relatively large impedance inductor with an open circuit ?

So like in an AC small signal analysis of some RF amp with an RF blocking inductor, if it's impedance is way bigger than anything else, do people replace it with an open circuit in the models for a given frequency?
« Last Edit: November 02, 2022, 02:45:05 am by MathWizard »
 

Offline TimFox

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Re: In AC analysis, do people replace large inductors
« Reply #1 on: November 02, 2022, 03:31:51 am »
You can replace a large "choke" with an open-circuit for an early analysis, but it is not a good idea to ignore the finite reactance for a detailed analysis.
In RF, they are usually called "RFCs", for radio-frequency choke.
In a typical RF circuit, you may find the reactances of an RFC and a bypass capacitor in parallel, and you could get an unwanted resonance if you ignore them.
In Spice, the DC operating point is found by open-circuiting all capacitors and short-circuiting all inductors, but that's a different calculation.
 
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Offline EPAIII

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Re: In AC analysis, do people replace large inductors
« Reply #2 on: November 02, 2022, 04:20:57 am »
I fear the answers to such a question are both Yes and No. The trick is knowing when each of those applies.
Paul A.  -   SE Texas
And if you look REAL close at an analog signal,
You will find that it has discrete steps.
 
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