"The voltage and current of the cap and coil is always equal and inverted."

This is totally incorrect.
How can the voltage across the cap be of one polarity and the voltage across the coil be of opposite polarity?

 

"the inductor current is at a maximum and the capacitor voltage is zero"

How can the current in the inductor be a maximum when the voltage across the inductor is zero??????

Do you understand what you are saying ?????

Perfectly.....
Do you?????
Those two parameters are not in any way in conflict.
If you short an inductor, then there is zero volts across the inductor for any value of inductor current (which is being maintained by inductive energy), so certainly the voltage across an inductor can be at a maximum with its voltage being zero.

Edit: The underlined statement is obviously a typo.
I meant to say "so certainly the current through an inductor can be at a maximum with its voltage (across it) being zero."

At near the peak current of the inductor in a parallel resonant circuit, the capacitor will change polarity as the voltage approaches zero.
At the instant of the polarity change, the inductor current is at maximum and the capacitor voltage is zero.
That's why the phase between voltage and current is 90° in a parallel resonant circuit.
Take another look at my simulation.

Before you jump to criticise someone else's explanation of a circuit operation you need to be sure you understand it yourself.

 

At near the peak current of the inductor in a parallel resonant circuit, the capacitor will change polarity

This is totally incorrect.
Read my description of how the capacitor gets discharged initially by the inductor and then the inductor continues to deliver its energy and starts to charge the capacitor in the opposite direction.

 

At near the peak current of the inductor in a parallel resonant circuit, the capacitor will change polarity

This is totally incorrect.
Read my description of how the capacitor gets discharged initially by the inductor and then the inductor continues to deliver its energy and starts to charge the capacitor in the opposite direction.

No it's totally correct.
It's yours that is not.
So my simulation and description is in error and your description is correct??
Sorry, but you'll pardon me if I don't believe that.
Note that I am talking about a resonant circuit this is freely oscillating with no external input after the initial starting pulse.

 

At near the peak current of the inductor in a parallel resonant circuit, the capacitor will change polarity

This is totally incorrect.
Read my description of how the capacitor gets discharged initially by the inductor and then the inductor continues to deliver its energy and starts to charge the capacitor in the opposite direction.

It is pointless to argue if you are referring two different circuits. Are you referring to the same circuit that @crutschow posted with the LTspice sim? Asserting that it is 'totally incorrect' adds little to the discussion. Showing where the LTspice sim is incorrect while reconciling descriptive differences in analyzing the two circuits will go a long way towards keeping this thread going. Keep in mind that the object here is to answer the TS's question.

 

A simulator is trying to present a result from your input. It does not necessarily represent what is actually happening in the circuit.
To be making some of the comments above is totally inaccurate in electronics terms.

 

If you short an inductor, then there is zero volts across the inductor for any value of inductor current (which is being maintained by inductive energy), so certainly the voltage across an inductor can be at a maximum with its voltage being zero.

Do you mean current through the inductor can be max when shorted?

 

If you short an inductor, then there is zero volts across the inductor for any value of inductor current (which is being maintained by inductive energy), so certainly the voltage across an inductor can be at a maximum with its voltage being zero.
Do you mean current through the inductor can be max when shorted?


The comments above are totally irrelevant to the discussion on a tank circuit. Don't bring in "red herrings. "

 

A simulator is trying to present a result from your input. It does not necessarily represent what is actually happening in the circuit.
To be making some of the comments above is totally inaccurate in electronics terms.

You are wrong again.
The simulator show precisely what is happening in a parallel resonant circuit when oscillating.
And my comments are totally accurate.
You saying otherwise doesn't make it so.

Do you mean current through the inductor can be max when shorted?

Exactly.
An ideal (superconductor) inductor would maintain it's current indefinitely (max or otherwise) when shorted.

The comments above are totally irrelevant to the discussion on a tank circuit. Don't bring in "red herrings. "

They are perfectly relevant.
They answered the statements you made.
But I'm about through trying to talk through your ignorance and insults.
If you can't explain why my tank circuit simulation is incorrect then please stop the crap.

As my old 8th grade teacher use to say: "You can lead a horse to water but you can't make him drink".

 

Let's hear from the OP and see if he understands anything you are saying. I have had 22 million visitors through my website with comments saying my descriptions are the first time they have understood anything.

 

Exactly.
An ideal (superconductor) inductor would maintain it's current indefinitely (max or otherwise) when shorted.

Indeed. I think you want to edit this line to 'current through the inductor' yes?
'If you short an inductor, then there is zero volts across the inductor for any value of inductor current (which is being maintained by inductive energy), so certainly the voltage across an inductor can be at a maximum with its voltage being zero.'

Let's hear from the OP and see if he understands anything you are saying

Yeah. How about we do that?

 

Indeed. I think you want to edit this line to 'current through the inductor' yes?

Yes of course. That was a typo.

Let's hear from the OP and see if he understands anything you are saying.

As this point he's probably sorry he asked.

I have had 22 million visitors through my website with comments saying my descriptions are the first time they have understood anything.

Amazing!
And all 22 million have made that comment?

 

What is the voltage of a cap or coil or resistor? Is it the external voltage expressed across them.......or does it only depend on the current thru them?

What is the polarity of the voltage drop (due to current) of a resistor, cap and coil?

It can get confusing because of the different possible references. Some people reference the source. Some reference current and some try to reference the resonance itself.

And so I will let you guys to it.

 

Hi,

What happens when we short out a constant current source? The current flows through the short indefinitely even though the voltage is zero.

If an inductor has current through it to start with that is called the initial current. The initial current can be replaced by a very very simple CONSTANT current source. We then have an inductor (now with zero energy) in parallel with a constant current source.

If we then SHORT out the inductor we also short out the current source because the current source is part of the real inductor now. Thus, the voltage goes to zero, but the constant current source CONTINUES to provide current, and this current not only exists when we first short out the inductor, it will exist indefinitely because it is a constant current source with a short across it.
The only reason with a real life inductor we would see the current start to decrease is because of the imperfections in the inductor, especially the series resistance (ESR) which eats up energy. In the ideal case with no ESR and no other loss effects, the current will continue forever. That's just how the indcutor itself works.

So certainly it is valid to have much current through the inductor when it is shorted out. Even a real life inductor would show current for a while anyway. In theory we could have a million amps and zero volts.

But back to the main point of the thread.
The simplest explanation of the parallel circuit is that the energy that is contained within the inductor and capacitor is continuously recycled from one form (voltage) to another form (current) and everything in between. This means that no new energy can be absorbed from the external circuit and thus the signal will pass through. In the simulation if we look at the energy levels in both cap and inductor we will see that the total energy is always the same, once it starts up.
The total energy tells the whole story. If we have an isolated circuit that contains 3 units of energy and we add 1 more unit of energy and get out 1 unit of energy, then the circuit neither absorbed nor lost any energy. Thus whatever energy we put in we got back out.

It might also be interesting to note that it does not take a resonant circuit to get this to happen. In the real circuit we also have at least one loss element, like a series resistor, that will absorb energy at times when we are not at the resonant frequency. Without that loss element (which is in nearly every circuit somewhere) there would never be a loss of energy. That would mean the circuit would not work as we intended it to work. To get it to work, we use the resonant part of the circuit to work with the loss part of the circuit and together they make up a filter.

 

To start with, your parameters with the TANK CIRCUIT are wrong.
The pulse must be applied and then removed. Your indication shows the rail voltage going to zero.
That's why I have shown a circuit that has correct timing and automatic timing, controlled by the value of the components in the TANK CIRCUIT.

 

Hello,

You other thread has virtual the same question:
A simple question on radio tuner

Did you see my post there?

Bertus