Re: LCLR Resonance...

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Rajesh Seenivasan" <rajeshkvs@xxxxxxxxxxx>

Hello everybody,

Thanks for guiding me.

Sory for not including my circuit with my earlier mail. Here is the 
ASCII circuit:
(use fixed width font like "Courier New" font to view the circuit)

  --------R--------L1----
  |   (0.1ohm)  (100uH)  |
  |                      |
  |                  ---------
  |                  |       |
  |                  |       |
  |                  |       |
 AC          (333nF) C       L2 (20uH)
 src                 |       |
  |                  |       |
  |                  |       |
  |                  ---------
  |                      |
  |                      |
  -----------------------

At (or very close to) resonant frequency:
1. the magnitude of currents thro C and L2 (tank circuit) were same 
and were IN PHASE with each other (probably 180 degrees phase difference?).
2. the current thro C was IN PHASE (or 180 deg phase diff?) with AC src.
3. But, the current through L1 was not in phase with the AC source. 
The phase diff was approximately 90 deg (by looking at the two 
waveforms using oscilloscope).

In my auto-tuning circuit, I would like to use the current through L1 
for feedback. If it is not in phase with the AC source voltage, how 
do I use it as a feedback for auto-tuning?

Thanks in advance,
Raj.

> From: "Tesla list" <tesla@xxxxxxxxxx>
> To: tesla@xxxxxxxxxx
> Subject: Re: LCLR Resonance...
> Date: Fri, 29 Sep 2006 10:31:28 -0600
>
> Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
>
> Hi Raj and Jan,
>
> Most likely Raj is not exactly at resonance.  The phase on one side 
> of resonance will be +90 and on the other side will be -90.  The 
> switch from one phase to the other can be quite sudden depending on 
> the Q  (if the parallel LC is driven with a series resistance).  In 
> his case, I think he has a second L in series with the parallel LC 
> circuit and I'm not certain if there is any resistance other than 
> the signal generator's source impedance, so he may in effect have a 
> series RLC circuit (thevenize the L's and drive the C).  One would 
> need to compute the transfer function for phase in this case.
>
> Gerry R.
>
>
>
> > Original poster: Jan Wagner <jwagner@xxxxxxxxx>
> >
> > Hi,
> >
> > > At 09:21 PM 9/26/2006, Raj wrote:
> > > Dear forum members,
> > > Yesterday, I tried to simulating the behavior of a LCLR circuit 
> > > using PSPice. I connected a LCLR circuit to an AC source (sine 
> > > wave generator). The analysis type was 'AC sweep'.
> > > Using PSpice, I plotted various graphs with Frequency on the 
> > > x-axis and the following three parameters in Y-axis:
> > > 1. Current through Parallel Inductor (inductor in tank circuit)
> > > 2. Current through Parallel Capacitor (capacitor in tank circuit)
> > > 3. Current through Series inductor.
> > > My understanding is that at resonance:
> > > 1. The current through the tank circuit's L and C will be same.
> > > 2. The tank circuit's (either through L or C) will be IN PHASE 
> > > with the input sine wave source.
> >
> > Depends on the schematic, but if you don't see 0deg phase then 
> > maybe you have wired it up as a double resonant converter? E.g. the 
> > R is in series with the tank circuit?
> >
> > regards,
> >  - Jan