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Author Topic: Conventional (non-OU, but related) electronic circuit problem  (Read 8051 times)

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Itsu,

You have reduced the error by reducing the hysteresis, but with the different Vfwd's on D5 an D6 due to the assymetrical rails, this error will vary as you vary the amount of hysterisis.

My suggestion would be to operate the comparators on just the 6 volt rail, generate a mid-rail reference (buffered voltage divider) to use for signal ground connections, and AC couple the inputs.  Your waveforms will be symmetrical and that symmetry will not change as you adjust hysteresis.     

Regarding the noise issue, I would add some analog signal conditioning in front of the comparators.  Consider adding an AC coupled variable gain stage and a LP filter in front of the comparators.  What order of filter you will need is dependent on the amount and type of noise you are dealing with (a 4th to 8th order filter comes to mind).  With a sufficiently slow loop filter at the PLL, truly random noise (i.e., white noise) will average out to a zero phase error.  Non-random noise (i.e., spurious or synchronous signals) can be a bit more problematic, but with a LP filter of sufficient order, adjustment of comparator hysteresis, and a slow PLL loop filter, their contribution to phase errors will be reduced significantly.

Using identical analog front ends (i.e., the same gain, filter, and comparator circuits) will null out the phase shifts caused by these stages.

Fixed frequency analog filters will need to be modified for operation at each of the various frequencies you mentioned.  If you need truly variable frequency capability, there are some switched capacitor options available to use as tracking filters, but at frequencies greater than 100KHz, these options become limited and more complex.  However, I would think variable frequency operation over a large bandwidth would be unnecessary unless you plan to somehow vary L1 or C1 by large amounts during operation.  Modifying the passband of fixed filters for each of the desired frequencies of operation would be a simpler solution.

Using diff amps at the front-end would allow detection of I and V with a non-ground referenced L1/C1 (i.e., using a sense coil and a matched pair of voltage dividers for I and V detection).

I would also consider adding an adjustable mono stable between one of the comparator outputs and its PLL input to allow for adjustment of I/V phase.

You mention Ruslan type circuits.  However, can you provide more details as to why L1 and C1 are being driven by an opamp in the OP schematic?
 
PW


PW,

thanks for these elaborate set of suggestions which sounds to me like a significant overhaul of the front-end part.

I am sure verpies will be commenting on them.


Quote
You mention Ruslan type circuits.  However, can you provide more details as to why L1 and C1 are being driven by an opamp in the OP schematic?
 
Concerning this question, the objective was to drive the Series LC (inductor / Wima cap) with a PLL system to have a stable frequency.

As the originally used PWM was a TL494, verpies designed a PLL system around this PWM so it can be used in a PLL system.
So we have this PLL locked TL494 to drive the Yoke and thus the Inductor / Grenade in the normal way (TL494 output to MOSFET drivers / MOSFETs to Yoke etc.) with the feedback of the voltage and current phases into the 74H4046 driving this TL494.

To test if this would work (the PLL 4046 / TL494) we tried the diagram as presented in post #1, where we use 1 output of the TL494 (square wave), convert it to sine wave, add some gain to it and feed it back to a series LC under test (C1/L1).

But again, it could be verpies had a more universal concept in mind, so adaptations to a specific "Ruslan type of environment" needs to be straightened out.

Itsu
   

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My suggestion would be to operate the comparators on just the 6 volt rail, generate a mid-rail reference (buffered voltage divider) to use for signal ground connections, and AC couple the inputs.  Your waveforms will be symmetrical and that symmetry will not change as you adjust hysteresis.     
I think this is a good idea.  Alone, it will not help with the noise, though.

Regarding the noise issue, I would add some analog signal conditioning in front of the comparators.  Consider adding an AC coupled variable gain stage and a LP filter in front of the comparators.
That filter would need to be retuned below specific PLL capture frequencies for each particular application.

Fixed frequency analog filters will need to be modified for operation at each of the various frequencies you mentioned.
Oh, you just essentially wrote the same thing.

What order of filter you will need is dependent on the amount and type of noise you are dealing with (a 4th to 8th order filter comes to mind).
What filter topology would you suggest for the least variability of phase delay vs. frequency (grp dly), in the passband ?

Using identical analog front ends (i.e., the same gain, filter, and comparator circuits) will null out the phase shifts caused by these stages.
Yes, but only if the noise characteristics on both channels are identical.  In Itsu's experience the signal from the CSR is much more noiser than the voltage signal.

However, I would think variable frequency operation over a large bandwidth would be unnecessary unless you plan to somehow vary L1 or C1 by large amounts during operation. 
I agree.  The large bandwidth is only for the universality of the circuit in multiple applications.

Using diff amps at the front-end would allow detection of I and V with a non-ground referenced L1/C1 (i.e., using a sense coil and a matched pair of voltage dividers for I and V detection).
An advanced yet inexpensive idea to minimize the common mode noise ingress at the input.  I forgot about it.  Thanks for the reminder.

I would also consider adding an adjustable mono stable between one of the comparator outputs and its PLL input to allow for adjustment of I/V phase.
Wouldn't manipulation of the phase detector in the PLL chip accomplish the same result?

You mention Ruslan type circuits.  However, can you provide more details as to why L1 and C1 are being driven by an opamp in the OP schematic?
I know the answer to this one:
That was just a proof of concept with the op-amp Itsu had on the breadboard. He knows well that the AD8032 is not suitable for driving high power loads. In a real application, such as the one you mentioned, the LC circuit would be driven by power MOSFETs driven by the PWM Controller (the TL494 in the first version of this circuit or a faster one in future versions).
   

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thanks for these elaborate set of suggestions which sounds to me like a significant overhaul of the front-end part.
Definitely - prepare yourself for it mentally.
   
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What filter topology would you suggest for the least variability of phase delay vs. frequency (grp dly), in the passband ?

I'd consider an 8th order lowpass using a quad opamp with four unity gain Sallen Key filters (depending on the type of noise and the S/N ratio, a lower order filter may suffice).  Group delay will indeed be ugly, but if the two filters are well matched, a phase trim somewhere in the system should allow mismatches to be trimmed out.  The type of filter selected will depend on the makeup of the noise to be rejected.

The Bessel filter produces a milder slope with regard to group delay versus frequency as the cutoff frequency is approached.  However, an 8th order Bessel will only give you about 30dB of rejection at the nearest harmonic.  The 8th order Butterworth has a much steeper group delay slope as cutoff is approached, but will provide more like 60dB of rejection of the nearest harmonic.

Because both inputs will see the same frequency, the phase errors should be consistent and, as above, able to be trimmed somewhere else in the system.

The advantage to using analog filters is that they are low noise and relatively easy to implement.  The disadvantage is that components will need to be low tolerance with low Tc and in order to change the frequency, components will need to be changed for each desired frequency of operation.

From a hardware standpoint, a much simpler solution is to use a switched cap filter. One that comes to mind is the 10th order lowpass filter LTC1569-7 (they are a bit pricey @$15 each, but if you are willing to wait for shipment from China, I have seen them go for $5 or so).  The advantage of using this filter is that they are easily tuned to the desired frequency via an external clock, with no hardware changes required, and are usable up to just over 300KHz.  They have a nearly constant group delay at around 18us that only changes to 17us around the cutoff frequency (and with excellent chip to chip matching).  They have a very steep rolloff above the cutoff frequency and could, with relative ease, be incorporated as a tracking filter.

They do require a clock (32X) and will need an anti-alias filter on the front-end and a LP at the output to remove residual clock noise.  However, because the clock is 32X the cutoff frequency, these can typically be low order RC filters.     

Quote
Yes, but only if the noise characteristics on both channels are identical.  In Itsu's experience the signal from the CSR is much more noiser than the voltage signal.

Regardless of which filter type is used, I do not believe that the "flavor" or amount of noise will have an influence on the phase error through the two filters.  The frequency of interest will be the same for both filters and group delay will be somewhat matched between the filters.  As long as low Tc components are used, any phase error difference between the filters should be rather static and able to be trimmed out somewhere in the system.

Regarding Itsu's greater noise at the Isense leg, this is why I suggest a proper low noise amplifier in front of the filters.  Not only will this reduce noise, but it will allow Rsense to be reduced to more realistic values.

Quote
An advanced yet inexpensive idea to minimize the common mode noise ingress at the input.  I forgot about it.  Thanks for the reminder.

I would consider a three opamp IA configuration at the front-end (yes Itsu, even more complexity...).  The advantage is the ease with which gain can be adjusted without messing with the CMRR.  There are some low cost resistor arrays available with 0.1% matching and low Tc that are great for this application that will allow for excellent CMRR without trimming.  Use of low noise opamps and low impedances will also keep noise to a minimum.  And, as mentioned in my previous post, broadband random noise (i.e., thermal noise) will average out to zero phase error given sufficiently slow PLL time constants.

Quote
Wouldn't manipulation of the phase detector in the PLL chip accomplish the same result?

Yes, I suppose it would, but how would you do that?  I don't see how you could actually manipulate the edge sensitive PC2 in the 4046, particularly if not using the VCO as one of the PC inputs.  The use of a monostable on one sense leg, as I mentioned, was just a quick thought with regard to nulling out any filter induced phase errors.   

Regarding the 4046, does adjusting RV4 (OP schematic) provide some degree of phase trim?  I had considered using the VCO output to feed an edge detector with those edges used to reset an integrator to provide the 2X sawtooth for the 494.  Doing so would, however, require modifying/adjusting the integrator or current source for wide ranges of frequencies.  As I said, your solution was rather unique.  Tip of the hat to ya'...

Quote
I know the answer to this one:
That was just a proof of concept with the op-amp Itsu had on the breadboard. He knows well that the AD8032 is not suitable for driving high power loads. In a real application, such as the one you mentioned, the LC circuit would be driven by power MOSFETs driven by the PWM Controller (the TL494 in the first version of this circuit or a faster one in future versions).

Seeing how the Ruslan type threads began to decompose about the time people thought copper was being transmuted to steel based on a YT video, and have pretty much gone silent since, are there active threads on this forum where this continues to be pursued in private or closed to the public threads?

For example, the apparently limited access to the "New Developments" thread you linked to?

Just wondering...

PW
« Last Edit: 2022-02-08, 01:45:05 by picowatt »
   

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Hi PW,

impressive post, thanks  O0



Concerning the Ruslan thread: as far as i know there are no "private or closed to the public threads" on this forum for this item at the moment.

I was hoping for someone to pick it up and continue with another owner / moderator, but that is not the case.


Itsu
   
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Itsu,

Before settling on a front end design, it might be useful to discuss the measurement environment. 

In your OP schematic L1/C1 are ground referenced.  If I recall, of the many circuits presented, some did have the inductor leg ground referenced, some did not.  As your desire is for a somewhat universal method to maintain resonance, will all desired applications have a ground referenced L1/C1?

If L1/C1 are not ground referenced, additional issues will need to be addressed.

PW
   

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PW,

good question, the Stalker device did not have the Inductor / Wima cap series LC ground referenced / connected see 2nd diagram:
https://www.overunityresearch.com/index.php?topic=3926.msg91690#msg91690

and if i remember correctly neither did the ones i had build before because there was always the problem with ground loops to deal with for scoping signals.

But i know i have done some testing with the series LC connected to ground without seeing much difference in the signals and there are diagrams showing it ground connected.

So what are these "additional issues which will need to be addressed"  if L1/C1 are not ground referenced?  If not very massive then i suggest to incorporate them.

By the way, i have asked Peter to add you that "new developments" thread verpies was referring to.

 
Itsu
 
« Last Edit: 2022-02-08, 20:11:12 by Itsu »
   
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So what are these "additional issues which will need to be addressed"  if L1/C1 are not ground referenced?  If not very massive then i suggest to incorporate them.

Itsu,

With L1/C1 ground referenced, I and V sensing should be a rather trivial matter.  You'll want a gain stage driving a filter which then drives your comparator.

I'd start with a simple AC coupled gain stage that has a low resistance connected across the input with simple first (or second) order LP filtering for anti-aliasing.  For the Isense leg, the input resistor would be a low value CSR, for the Vsense leg, that resistor would be the low value portion of a resistive divider, with the higher resistance leg being connected to the Vsense point.  The voltage seen at the inputs will be very low, and ground referenced, so minimal input protection and bandwidth limiting will be required for the input amplifiers.  The only component that will require special attention with regard to the operating environment (HV, corona, etc.) would be the resistor used for the high resistance side of the Vsense voltage divider.  That resistor can be a high voltage resistor or a string of lower voltage resistors in series to achieve the required holdoff voltage and low capacitance.

Regarding the gain stage, I'd want the value of the input resistors low enough to require some amount of adjustable gain to drive the filters at a level sufficient for good S/N performance from the filter, while avoiding any clipping from either the center frequency or any noise/HF components present at the input.  As well, the frequency response of the input amplifier can be tailored to produce a LF roll-off to provide LF rejection of the mains frequency, etc.

For the filter, I'd go with the aforementioned switched cap filter (LTC1569-7).  The VCO output from a single 4046 can be used to clock both filters (one filter each for the I and V sense legs).  This allows simple DC control of the filter cutoff frequency via a trimpot at the 4046 VCO input (this is a separate 4046 for filter clocking, not the PLL).

The output of the filter should drive a buffered RC low pass for removal of clock feed-through.  The buffer output then drives the comparator.

This may sound complicated but its really not.  Hardware wise its just two opamp stages and one small filter package per sense leg (plus one 4046 for its VCO to drive the filter IC's).  As with anything being clocked at high frequencies, attention to layout, grounding and decoupling is required.  With attention to those details, I have obtained excellent performance from these filters even on the likes of a protoboard.

With a non ground referenced L1/C1, things become a bit more complicated.  Isense can be easily performed using an isolated winding on a small core, however, Vsense becomes quite problematic.  I have considered several options with regard to this over the past months, but I have yet to settle on a solution I feel comfortable with.  I can discuss those considerations in greater detail if you desire, however, most options use some form of the above discussed circuits with additions/modifications to the Vsense leg, making the amplifier and filter circuitry discussed above a good staring point for consideration.

A control method I am considering requires control of the phase and resonant frequency of both the grenade and inductor loops, as well as amplitude control of at least the inductor loop (relative to the grenade).  This requires I and V sense of both the grenade and inductor loops.  To simplify initial experiments, I plan to ground reference both grenade and inductor (there was at least one schematic presented on the past threads that did show both inductor and grenade ground referenced). 

PW
« Last Edit: 2022-02-10, 01:03:17 by picowatt »
   

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Thanks PW,

so it is doable, both grounded as un-grounded.

I see the LTC1569-7 is not available at the moment, probable due to the chip shortage, a problem which goes for more advanced chips lately.

I will see if i can transform my setup to a grounded one using one of those mentioned schematics and what influence this has on the signals.

Itsu.
   
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Thanks PW,

so it is doable, both grounded as un-grounded.

For the un-grounded systems, all I have are a few concepts that need to be investigated.  Watching videos with corona being drawn to screwdrivers makes me think that common mode voltage and noise is going to be a significant issue.  I have considered several solutions that range from use of a basic diff amp at the front-end to more isolated systems using opto or galvanic isolation.  However, having looked at the specs for a few "off the shelf" isolated solutions, I have doubts as to whether their hold-off capability is sufficient in this operating environment.

I have considered sensing only the current flowing in the loop using an isolated pickup and having the circuit adjust for max current in that loop as a way to stay in resonance.  I even made a few proof of concept tests on such a system.  However, not only do I want to be able to monitor and maintain a given I/V phase relationship in the individual grenade and inductor loops, I want to be able to select and maintain a given phase relationship between the I and/or V of those two loops.  This will require four sense inputs (2 Isense and 2 Vsense).  I decided first attempts would be with both the grenade and inductor ground referenced, which allows empirical I and V values to be collected, prior to considering lifting the grounding on one or both loops.  But, when crossing that bridge, a diff amp input would be a first consideration.

Quote
I see the LTC1569-7 is not available at the moment, probable due to the chip shortage, a problem which goes for more advanced chips lately.

Digikey and Mouser have them in stock (as do a few Ebay sellers from China).  Search using only "LTC1569" or with the full monty such as "LTC1569CS8-7".  Just make sure you get the "-7" version, not the "-6" (-6 is only good to 64Khz).

The reason I am considering using these in my initial experiments is that I need four filters with good filter to filter thermal stability/tracking and I already have a few of these on hand.  For your initial tests, you could use a dual or quad opamp configured as a 4th or 8th order LP.  If you go the analog route, be sure to use low tolerance resistors and capacitors with a low Tc (NPO, etc).  Good thermal stability would be my primary concern because static phase errors between filters can be trimmed out elsewhere in the system.

In the system you are proposing, inductor resonance will determine your P-P frequency.  Will you then be required to adjust the cap or inductance in the grenade loop to chase its resonance?   

Quote
I will see if i can transform my setup to a grounded one using one of those mentioned schematics and what influence this has on the signals.

Itsu.

Please let us know how grounding affects your circuit. 

I hope Verpies will comment on all of this as well, particularly with regard to Vsense in this environment.

PW

« Last Edit: 2022-02-10, 13:47:29 by picowatt »
   

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I hope Verpies will comment on all of this as well, particularly with regard to Vsense in this environment.
Whatever the solution, it needs to avoid capacitive coupling and that means differential sensing (preferably isolated from ground) with short connections.
I have an original solution to this problem for ~$20 if you can come up with an equally cheap yet fast PWM modulator (~10MHz with sub nanosecond jitter)  8)

P.S.
Yes, "PWM modulator" is a redundant phrasing but I was afraid that "PW modulator" would not be understood by everyone reading it.
   

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For the un-grounded systems, all I have are a few concepts that need to be investigated.  Watching videos with corona being drawn to screwdrivers makes me think that common mode voltage and noise is going to be a significant issue.  I have considered several solutions that range from use of a basic diff amp at the front-end to more isolated systems using opto or galvanic isolation.  However, having looked at the specs for a few "off the shelf" isolated solutions, I have doubts as to whether their hold-off capability is sufficient in this operating environment.

I have considered sensing only the current flowing in the loop using an isolated pickup and having the circuit adjust for max current in that loop as a way to stay in resonance.  I even made a few proof of concept tests on such a system.  However, not only do I want to be able to monitor and maintain a given I/V phase relationship in the individual grenade and inductor loops, I want to be able to select and maintain a given phase relationship between the I and/or V of those two loops.  This will require four sense inputs (2 Isense and 2 Vsense).  I decided first attempts would be with both the grenade and inductor ground referenced, which allows empirical I and V values to be collected, prior to considering lifting the grounding on one or both loops.  But, when crossing that bridge, a diff amp input would be a first consideration.

Digikey and Mouser have them in stock (as do a few Ebay sellers from China).  Search using only "LTC1569" or with the full monty such as "LTC1569CS8-7".  Just make sure you get the "-7" version, not the "-6" (-6 is only good to 64Khz).

The reason I am considering using these in my initial experiments is that I need four filters with good filter to filter thermal stability/tracking and I already have a few of these on hand.  For your initial tests, you could use a dual or quad opamp configured as a 4th or 8th order LP.  If you go the analog route, be sure to use low tolerance resistors and capacitors with a low Tc (NPO, etc).  Good thermal stability would be my primary concern because static phase errors between filters can be trimmed out elsewhere in the system.

In the system you are proposing, inductor resonance will determine your P-P frequency.  Will you then be required to adjust the cap or inductance in the grenade loop to chase its resonance?   


Please let us know how grounding affects your circuit. 

I hope Verpies will comment on all of this as well, particularly with regard to Vsense in this environment.

PW


PW,


Quote
In the system you are proposing, inductor resonance will determine your P-P frequency.  Will you then be required to adjust the cap or inductance in the grenade loop to chase its resonance?   

In the original Ruslan setup, there was as i understood it no resonance on the Grenade coil and i have to recheck the Stalker circuit to see it is needed there.

Itsu
   

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Whatever the solution, it needs to avoid capacitive coupling and that means differential sensing (preferably isolated from ground) with short connections.
I have an original solution to this problem for ~$20 if you can come up with an equally cheap yet fast PWM modulator (~10MHz with sub nanosecond jitter)  8)

P.S.
Yes, "PWM modulator" is a redundant phrasing but I was afraid that "PW modulator" would not be understood by everyone reading it.





Quote
Yes, "PWM modulator" is a redundant phrasing but I was afraid that "PW modulator" would not be understood by everyone reading it.

 :)



   
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PW,
In the original Ruslan setup, there was as i understood it no resonance on the Grenade coil and i have to recheck the Stalker circuit to see it is needed there.

Itsu

Itsu,

With regard to the Stalker schematic, I understood all items marked with an asterisk as needing to be "adjusted" or "tuned".  In that schematic, there is a HV cap across the grenade, just prior to the "output choke", and it is marked with an asterisk. 

What method did you use to select the value of the cap across the grenade winding?

PW

   

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Yes, the Grenade needs to be tuned, but not necessarily for the same resonance as the inductor as in my experience, it is(?) impossible to have both the Inductor and the Grenade tuned to the same resonance frequency.

Vasik mentioned that a 2:1 resonance was used also to overcome that dual resonance problem, i tried both a single resonance point (24Khz), but did not succeed, as the 2:1 relation.

But all in  all, my Grenade output was to low overall (should be 300 to 400V DC after rectification).

Itsu
   
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Yes, the Grenade needs to be tuned, but not necessarily for the same resonance as the inductor as in my experience, it is(?) impossible to have both the Inductor and the Grenade tuned to the same resonance frequency.

Vasik mentioned that a 2:1 resonance was used also to overcome that dual resonance problem, i tried both a single resonance point (24Khz), but did not succeed, as the 2:1 relation.

But all in  all, my Grenade output was to low overall (should be 300 to 400V DC after rectification).

Itsu
Hi Itsu I don't want to faff about here so here goes if the Katcher is running at 1.8 mhz how on EARTH are you going to shuve that through the grenade ? it's impossible to de modulate it with the push pull running at 24 khz!

you need the missing link perhaps   O0 O0
   
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