[Prev][Next][Index][Thread]

RE: Series or Parallel resonant ? ( was: New pics and scope waveforms)

Hi Dale,

> Original Poster: Dale Hall <Dale.Hall-at-trw-dot-com> 
> 
> Hi Malcom,
> Thanks for your response.
> Please see my earlier reply to Richie's feedback.
> 
> I disagree with your response:

> >The truth is that both 
> >types exhibit a current maximum and a voltage maximum across 
> >their individual components at resonance. 
> 
> I believe the essence of whether LC parallel components
>  are series or parallel resonant depends upon where 
>  the source generator is in the circuit.

How one classifies the circuit depends on how one applies energy 
to it, that I agree with. However, any tuned circuit has a circulating 
current which is a maximum at resonance and byu Ohm's law, the 
voltage across each individual component in it is a maximum also.

 Series resonance: generator is part of the series LCR.
> All Rdc's are in series.
> 
> Parallel resonance: generator is across "Both" L and C physically parallel.
>   The generator sees L's resistance different than in the series model
>   in that C is across the generator, L+RdcL is across the generator.

The generator sees the shunt impedance of the circuit in this case 
whereas in series resonance, the generator sees the ESR. 

> In this context, I stand by my original statements.

I must differ on the contention that voltage is minimum across a 
parallel circuit at resonance.

> I agree this is all very confusing, I hoped to make it clear (?) sorry.
> 
> There appears to be easy confusion stemming from components in parallel
> contrasted to how they are driven,
>   generator in series with parallel components (Igen=max) or
>   a generator driving across parallel components (Igen=min).

Agree

> In your radio set front end example
>  assuming parallel resonance,
>  the incoming signal (a generator) appears across both L & C at same time,
>  the voltage must be minimum else the current couldn't be minimum
>  to represent minimum load to the incoming signal at Fo.

Aha!  Suppose the voltage was a minimum. The circuit would 
present a near short circuit to the aerial. Aerial current is a minimum 
as you say but the circulating current in the tuned circuit is a 
maximum.

 I agree with 
> >the secondary is more driven at Fr than by an impulse,
> sorry if I was misleading....
> 
> even the Primary simply and highly selectively at Fr extracts the
> fundamental
>  of the square impulse provided by a spark gap switch.
>  Current injected by the gap switch is accepted by the Pri LC sinusoidally,
>  not as rectangular impulse, due to the frequency selectivity of the LC
>  and that rectangular waves are composed of sinewaves which LC is able to
> isolate.
>  The LC actually highly rejects all energy outside the fundamental resonant
> freq.
>  High order harmonics see a very high impedance producing little current
>  due to their divergence from the highly selective resonant frequency. 
> 
> Experiment: set up a lowZ (simulating Rgap) square wave generator driving
>  a HI-Q toroid inductor and mica cap in series resonance.
>  The fundamental sinewave provides most of energy at resonance benefiting
> from 
>  Vpk_fund = 4/Pi*Vpk_squarewave peak {flat top] amplitude !
> 
>  Placing a high value load resistor across LC demonstrates
>   affects of De-Q'ing, equivalent series resistance, etc.
>   simulating Spark loading,  without sparking !

I think a resistor is a poor representation of an arc discharge as the 
characteristic is wrong.

Regards,
Malcolm
<snip>