Author Topic: Mr. Feedback circuit  (Read 5398 times)

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Mr. Feedback circuit
« on: August 18, 2015, 17:09:34 pm »
Hello i would like to ask if anyone had succeed in working with the feedback circuit...

i use an ic called lm318 which is an differential amplifiuer and it even have into it antiparallel diodes...

http://www.ti.com/lit/ds/snosbs8c/snosbs8c.pdf

I managed to make it work at the self resonant frequency of the vic but there are other lower resonant frequencies it is not able to lock to because the self resonance noise mess around with the waveform...

 Filtering mess around with phase.. so it won't lock at the peak of resonance...
« Last Edit: August 18, 2015, 22:18:16 pm by sebosfato »

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Re: Mr. Feedback circuit
« Reply #1 on: August 19, 2015, 01:58:10 am »
Same here, the thing locked in all over the place. What bothered me was that the thing has to re-scan every time it gates and the scan frequency is very low. Tells me something major is being missed on our part and not revealed on his part. Apparently when that signal does happen there can be no mistaking it, that would take care of the false lock in's.

I have been able to obtain a classical capacitor charging signal from the toroid setup of meyers. That signal only happens at a specific resonance. To obtain that signal the circuit has to be gated just at the peak of the step charge.
It forms a single arcing line out of the pulses.

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Re: Mr. Feedback circuit
« Reply #2 on: August 19, 2015, 14:33:51 pm »
My frequency in the scanner is 0,7Hz so its little faster than stan...... its a triangle wave...

I also had it to lock at some unpredictable places... but i notice they are all sub harmonics..

i wonder if the pll wasn't mean to generate subharmonics since there were those frequency dividers... well actually it could be working as a multiplier...

i also wonder if my feedback is working as should since its following that one frequency...
« Last Edit: August 19, 2015, 17:11:17 pm by sebosfato »

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Re: Mr. Feedback circuit
« Reply #3 on: August 22, 2015, 21:47:44 pm »
i believe my feedback circuit is working but the frequency mixer is creating a delay which cause the pll to lock little over the resonant frequency...  i will remove that add...

its very nice to have all waveforms going and all 3 led's light! the feed back pulse indicator, the lock in indicator and pulse on

the pll can maintain the frequency stable and follow as i move the wiper arm...


ps (i took the frequency mixer out of the system, but still it would not lock to the exact frequency... )

i start to think that or the uf4007 antiparallel diodes at the inputs of the opamp are creating unnecessary capacitance.. i mean unnecessary because it already have build in antiparallel diodes .. lm318
3

or the igbt + driver are not fast enough

or the waveform of the feedback circuit...

ohh i;m tired...
« Last Edit: August 22, 2015, 23:23:15 pm by sebosfato »

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Re: Mr. Feedback circuit
« Reply #4 on: August 22, 2015, 23:55:21 pm »
take a break, my young friend..
Clear yr mind...Party a bit  :)

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Re: Mr. Feedback circuit
« Reply #5 on: August 23, 2015, 00:11:07 am »
take a break, my young friend..
Clear yr mind...Party a bit  :)

i will do just that after i get this working ;D 

i'm doing some tests on amp restriction... it seems my secondary is maybe too big.. its the same as the chokes size...

another thing i did today i connected some electrodes in series.. no result .. i'm getting only up to 20kv on this vic because above at this voltage the ends of the chokes becomes blue and will certainly break up soon... this is in air for  this first tests..


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Re: Mr. Feedback circuit
« Reply #6 on: August 25, 2015, 16:38:44 pm »
my feedback circuit is ot locking at resonance i just figured why...

when we pulse the vic while its operating also when the primary sends a pulse on the coils on resonance are exctly at maximum negative voltage so when you apply the pulse it takes 90degre to the output of the feedback windings to start sending a pulse... so it will never lock to resonance in this way..

i´m figuring a way to make the feedback electromagnetic now...

i know that the opamp used have high comom mode rejection...

it just ocuured to me that when i hooked my pll with current feedback it detected the correct frequency... also when i used a simple antena coil.... that probably was working because of the electromagnetic field generated from the cell...

so the only way left is to make the feedback coil a biifilar winding and make dc current to pass thru it...

this makes a balanced circuit... where when the inductance of the core is changing there is a voltage, and if i remember well it should be just in quadrature... it was from a old book i had but left it in italy... i guess i have a pdf of it somewhere it was called practical transformers with a 3phase transfoermer in the front.. yelow pages..

actually it was not bifilar it was a kind of two cores that are arranged to not close flux between the two where the first core flux density induce a permeability change of the other core so changing the inductance of a coil wound arond it... if it has a constant current applied to it it will develop a voltage in quadrature..


just found this http://worldwide.espacenet.com/publicationDetails/originalDocument?CC=WO&NR=2010015025A1&KC=A1&FT=D&ND=&date=20100211&DB=&&locale=en_EP

the problem with current feedback is theres no where to get it since in my circuit suposedly at resonance no current should flow... it is a kind of series resonance to ground too .. though

« Last Edit: August 25, 2015, 17:57:46 pm by sebosfato »

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Re: Mr. Feedback circuit
« Reply #7 on: August 31, 2015, 09:25:42 am »
well i think meyer feedback circuit was another part that was wrong placed to fool people about how should really operate...

although it seems a differential amplifier as i posted in the last post it generates a  90degrees dephased square wave relative to the input... this mean that the resonance takes on and it rules when the energy can be supplied or not by the primary..

this 90 degrees come from the fact that its acting as a zero crossing detector.. but its detecting the zero voltage crossing across the coil..

could be possible to make it detect only half wave after the zero crossing? or to detect the edge?

would be in phase?

well i will make sure of that!