Author Topic: When to use a capacitor and when to use an inductor.  (Read 28854 times)

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Online blueskull

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Re: When to use a capacitor and when to use an inductor.
« Reply #25 on: September 29, 2016, 03:40:40 am »
Supply filtering can be performed using both.  Inductors are in series with the load and capacitors are in parallel.  Here is a classic example - the Pi filter:


I've been told since I was a kid (my nanny's husband is a retired technician) that PI filter is effective, which it is not.
Many believe LC tank can magically rough out ripple, which is only true if Q is low enough, in other words, load resistance is low enough or LC themselves are lossy.
Without dissipative or active components, an LC system always oscillate, 100% guaranteed.
99% of the time people won't notice it because either the load is significant to damp the oscillation, or ESR is good enough.
But in really high power kW range gears where Ohmic loss only contributes less than ~3% total power, naively think LC tank will magically rough out ripple will get things fried.
 

Offline Brumby

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Re: When to use a capacitor and when to use an inductor.
« Reply #26 on: September 29, 2016, 05:21:37 am »
While I don't disagree with what you have said, the question of stability - conditional or not - would seem to be somewhat outside the OP's understanding - and well beyond the question asked.

The fact is this: Inductors and capacitors can in some cases be used to achieve similar goals, but operate on completely different principles and, therefore, are not interchangeable in any way.
 

Offline T3sl4co1l

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Re: When to use a capacitor and when to use an inductor.
« Reply #27 on: September 29, 2016, 06:29:57 pm »
While I don't disagree with what you have said, the question of stability - conditional or not - would seem to be somewhat outside the OP's understanding - and well beyond the question asked.

The fact is this: Inductors and capacitors can in some cases be used to achieve similar goals, but operate on completely different principles and, therefore, are not interchangeable in any way.

Indeed, the space within which exchange is possible, is rather abstract compared to simply swapping out one component for another.

Namely, if you swap:
Voltage source <--> Current source
Series branch <--> Parallel nodes
Capacitor <--> Induuctor (value = 1/x)
Resistance <--> Conductance (G = 1/R)

You'll end up with the same RLC network, but with a series-parallel transformed equivalent.

Note this is not generally possible with nonlinear circuits, because we don't have every possible combination of device: a diode has a constant-voltage characteristic in forward bias (transform: current regulating diode -- a boutique item, though something which does exist); a transistor has a voltage sense input to current source output (a transconductance amplifier), where the input and output exhibit parallel capacitance.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
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