DIY Transformer for use with Bode Plots. - Page 1
Forum section: electronics / testgear

author: mawyatt
author_rank: Super Contributor
timestamp: May 18, 2022, 06:23:11 pm
content: This is an extension of the previous thread:https://www.eevblog.com/forum/testgear/injection-transformers-bode-plots-application/Awhile back when ordering parts from LCSC we picked up a couple Common Mode Filters C2832691 and C2924780 with the idea to attempt to convert into a Bode Injection Transformer.Finally got around to fooling around with the smaller filter, and decided to unwind the windings. After removing the center shield and yanking the wires from the black epoxy we were able to remove the windings. Since we didn't have any twisted pair wire, decided to use the wire from the filter and after straightening we used a hand drill to twist the wires in a light twist. This twisted pair was sewn into the core and the ends swapped and mounted onto a fixture we had created with a 3D print. Know our 3D print skills suck, and we need to get better adhesion, but that's another topic!!Anyway, after printing a lid and base, we mounted some BNC and Banana connectors as shown below. Decided to terminate the transformer with either 100 or 50 ohms, so used 4 2W 100 resistors, and soldered one set of resistors and clamp the other set with the Banana terminal nuts as shown. This allows the remove of a resistor pair for a 100 ohms termination, and 2W were used just in case we provided too much voltageHere's a plot of the Transformer using a 50 ohm source @ 0.2Vpp (SDG2042) and Siglent SDS2104X Plus under Bode mode.Note IL at 100Hz is ~ 0.06dBV and at 1MHz 0.12dBVNot bad for a ~1$ reconfigured CM Filter using same wire, four 100 ohm 2W resistors, couple BNC connectors and 4 Banana terminals, total cost <$10Edit: Added another plot out to 100MHz.Best,

author: mawyatt
author_rank: Super Contributor
timestamp: May 19, 2022, 03:31:01 am
content: Was able to unwind the larger CM Filter and rewind with twisted pair made from the unwind wire. This is a larger core ($3), and larger wire so should be able to handle more DC current in applications where that's required. Performance looks good as does the smaller core. 3D Printed another front cover (Grey), and waiting on a deeper bottom, 12 hr print timeBest,

author: RoGeorge
author_rank: Super Contributor
timestamp: May 19, 2022, 07:01:08 am
content: I wouldn't have expected it to be so linear.Nice touch 3D-writing on the lid!About getting bigger ferrite cores, the biggest yet easy to source (from scraped electronics) would be the magnet from (defective) audio speakers.Many audio speakers have the magnet made from something that looks like ferrite. Some can have a very large magnet, much bigger than the usual OTS ferrite cores. Not to say big ferrite cores tend to be very expensive. Magnets have a Curie point low enough so they should be easy to demagnetize by slowly heating them with a common stove/oven.Never tried, but it should work!

author: jonpaul
author_rank: Super Contributor
timestamp: May 19, 2022, 07:31:27 am
content: Bonjour, BRAVO! nice job,in 1960s we used the ESI bode plotter with electrostatic paper.In 1980s we used the fine open loop stability plot system from Deane Venable.Speaker magnets material will be unsuitable, and strong BH curve bias due to the magnetization.The professional units have much lower LF cutoff than 100 Hz, 1..10 Hz.Bon chance!JonPS: I might have old core larger sizes, better material, contact me by PM if interested in better cores

author: RoGeorge
author_rank: Super Contributor
timestamp: May 19, 2022, 08:13:48 am
content: Quote from: jonpaul on May 19, 2022, 07:31:27 amEven after de-magnetising the ferrite by heating the magnet above the Curie point in an oven?

author: jonpaul
author_rank: Super Contributor
timestamp: May 19, 2022, 08:27:08 am
content: Hello again RoGeorge...I have been designing and manufacturing WB trafos for decades....The ferrite or metallic NiCo speaker magnets are designed to hold the remnant magnetism and not for AC use let alone wideband transformers.Even after heating above curie the materials properties like u, Bmax, BH curve characteristic is not much changed.It depends more on the type of ferrite eg MnZn eg and the Ferrite mix, compression, etc.Recommend the 1980s..1990s TDK and Ferroxcube books notes on ferrite core material properties and selections.Core material of WB trafos is generally high perm (u 10,000) and optimized for freq resp, linearity and not for remnant mag nor power handling. We used H5C2 TDK, N27 Siemens, etc.Another alternate to ferrite is powdered iron, eg from MicroMetals.What you suggest is an interesting experiment, but AFIK the shapes of the speaker magnets are not suitable.As toroid's and various split cores shapes are readily available at low cost, I think its not worth the effort.Just the ramblings of an old retired EEBon ChanceJon

author: RoGeorge
author_rank: Super Contributor
timestamp: May 19, 2022, 09:18:52 am
content: Thank you for the extra info. Not trying to argue about that, but you know how wishful thinking is. I'm still curious how good (or bad) such a demagnetized speaker magnet will work in practice.The signal levels for an injection transformer are usually very small (needed to be so in order to keep the amplifier under test to behave linearly with the injected signal). My hope is the signal would be low enough so the BH curve will stay close enough to the origin, so the magnetic hysteresis will remain negligible.Aside from the ferrite selection, I've clicked the posted links and read more about injection transformers. Never used one, so I might be asking wrong questions, but why the secondary is still made of many turns?If I inject signal in a feedback loop, I'll want minimum perturbation of the feedback loop, with minimum parasitic C or L from the transformer's turns. Why not having the secondary turn as a single piece of wire passing through the hole of the core (so more like a current transformer)?- this will give a minimal impedance to the secondary, making it to appear closer to the Ri=0 of an ideal voltage source- if the induced voltage in a single turn secondary is too small, then we can still get good measurements by synchronous averaging (we have a clean and synchronous reference signal coming from the generator)- in theory, even a two-halfs core clamped around an existing wire in the DUT should work. We do not care much about the absolute levels, we only care for the ratio between the input and output signal to remain the same across all the measuring bandwidth- in fact, having a small gap in the core might be an advantage, by adding the "magnetic resistance" of the gap in series with the (otherwise closed) magnetic circuit of the (former closed) core. My intuition tells this will reducing the hysteresis even more, and linearize the transformer's response.I wonder why all these are not the norm for injection transformers. Most probably because none of these improvements matter/work/can be applied in practice.

author: mawyatt
author_rank: Super Contributor
timestamp: May 19, 2022, 01:26:04 pm
content: @RoGeorgeYou bring up an interesting thought about reduced windings in the secondary. With the drive coming from a AWG then the drive level can be much higher, maybe a 2, 4 or even 10X secondary reduction. Maybe an experiment is in orderThanks for the complement, sometime we'll try and use a different color filament for the 3D printed text. Beginning to understand 3D printing a little better, but still a ways to go. Some folks on here are really good at this!! Certainly fun to watch the 3D object "grow", and highly recommended to any serious DIYer!!@jonpaulThese DIY injection type transformers have a lower 3dB corner below 10Hz and above 1MHz, even tho we conservatively stated 100Hz to 1MHz.Best,

author: 2N3055
author_rank: Super Contributor
timestamp: May 19, 2022, 02:56:58 pm
content: Quote from: RoGeorge on May 19, 2022, 09:18:52 amI agree with Jon, those ferrites in loudspeakers are made of hard remanence materials- They might work to some point as you correctly say, but I would be curious about it just for an experiment.

author: 2N3055
author_rank: Super Contributor
timestamp: May 19, 2022, 03:02:17 pm
content: Quote from: mawyatt on May 19, 2022, 01:26:04 pmSomeone else had an idea before (can't remember who, maybe Tim?) to make a single braid pentafilar winding, and connect 3 windings in series and 2 in parallel for secondary.Usually trafos are terminated into something like 10-20ohms for injection in control loop (not to make big difference in feedback resistors value).I also have some CoolMu coressomewherethat I wanted to try....I had best intention to try it but life had other plans...

author: jonpaul
author_rank: Super Contributor
timestamp: May 19, 2022, 06:05:43 pm
content: Rebonjour...wideband transformer design is a compromise and tradeoff, LF ..HF BW, ratio, # turns Lp, Llkg, Cp-s, Cshunt.See many fine refs on WB trafo design, one example is /Magnetic Components from our old friend Steve SMITH,https://www.amazon.com/Magnetic-Components-Applications-Steve-Smith/dp/0442203977RE stability/bode polts/injection trafos, i suggest original papers and hardware from Deane VENABLE in 1980shttps://www.venableinstruments.com/loop-stabilitythe excellent modern systems and transformers from Omicron Labshttps://www.omicron-lab.com/fileadmin/assets/Training_and_Events/Webinar/2014-11_Webinar_LoopGain.pdfhttps://www.omicron-lab.comBon chance!Jon

author: mawyatt
author_rank: Super Contributor
timestamp: May 21, 2022, 05:02:45 pm
content: We decided to make another transformer out of the last CM Filter we have, and removed the windings then twisted the pair together as before. This time we cut the twisted pair in the middle and created two twisted pair windings on the core. The two windings were arranged as primary in series and secondary in parallel. This should yield a Vo/Vi transfer of 1/2 or -6dBv, and we measured -6.85dBv.For sanity checks on all 3 transformers used as Injection Bode types, we setup a simple circuit for Closed Loop Bode evaluation. The circuit is a simple Op-Amp (LM358) non-inverting gain of 21 with the feedback resistor of 20K and the shunt to ground resistor of 1K. The + Op-Amp input was grounded thru a 1K resistor and the transformers were connected from the 20K and 1K junction to the Op-Amp - input. The Op-Amp was power by +-10V.A Siglent SDG2042X AWG was used as the input (we could have used the scope built-in AWG). This was on a LAN with the Siglent SDS2104X Plus scope. Amplitude was set to 0.05Vpp so as not to saturate the small trasnfomers, and confirmed by monitoring the transformer output waveforms.Thanks to tautech for helping us in the past to get familiar with LAN use (and earlier the SDS2104X Plus), as we didn't know "Diddley Squat" about LANs. BTW Dave used this old redneck engineering term "Diddley Squat" meaning "not much", in his latest How a LCR Meter Works video! Guess this term found it's way to the Land Down-UnderHere's what the latest transformer rendition looks like with the series/parallel windings.The Bode plots are shown for the mentioned Op-Amp circuit above, measuring the Open-Loop Gain and Phase of a Close-Loop-System. The plots are for the 1st & 2nd transformers with the different cores, and the last is with the split winding transformer. Please note the indicated Gain and Phase Margin indicated by P1 and P2, you see the frequencies at Markers X1 and X2.Not sure what's going on around 100~200Hz on the left, likely some interaction with the transformer, this should be a smooth plot coming away from 100Hz.Note the use of the 10 bit mode in the scope, big help with the large dynamic range involved, and with the dynamic channel input scaling the scope performs in Bode Mode, extending the DR even further.Anyway, this simple, cheap Isolation Transformer seems to work quite well with the SDS2104X Plus and the built in Bode Plot capability. Very powerful feature being able to do Open-Loop measurements on Closed Loop systems without any additional equipment (you can use the scope built-in AWG) other than a DIY low cost Isolation TransformerBest,

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 21, 2022, 05:44:24 pm
content: Yeh specifically they're strontium ferrite, a magnetically hard material (wide BH loop); you need MnZn (LF/broad) or NiZn (high freq), soft materials with small loop.Also amorphous/nanocrystalline, which show up from time to time in pulse transformers, CMCs, etc.Tim

author: mawyatt
author_rank: Super Contributor
timestamp: May 21, 2022, 11:50:58 pm
content: Have no idea what these CM Filter cores are made of, actually surprised they worked as well as they did. Noted on the other thread linked in first post that some folks had used Vacuumschmelze Nanocrystal Core type toroidal cores, only cores I recall using were from Micrometals and TDK, and that was eons ago, never heard of these!! Digikey has a few in stock that run from $10~20 per core.Has anyone had success with these Vacuumschmeize cores, or other types?One thing that Jay_Diddy touched on in some of the other threads is that in very high open-loop gain circuits (like op-amps) the negative feedback return signal creates an almost null voltage at one of the transformer terminals. This gives the scope input a difficult time with accurate amplitude and phase measurements, which contributes to the uncertainty at lower frequencies, and may be more of an issue than the transformer core material.Open Loop response shown below with a OP-07 (Closed-Loop non-inverting gain of ~17.7dBv) and the region between 100 and 1KHz is chaotic, thus showing from 1KHz to 1MHz which looks good considering it's just plug-in on a board with jumpers. Just for fun swapped the transformer leads and you should see the inverted response (negative in dB & phase response) which is shown in 2nd image.BTW whether you like the Siglent or not, that's pretty impressive on screen dynamic range for a mid-level DSO that's based upon a core 8 bit ADC, can't wait to see how well the 12 bit version behaves!!Best,

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 22, 2022, 02:38:14 am
content: Yes, they live up to the hype -- check datasheets, they're pretty solid. The best example is the appnote comparing CMCs with equivalent size ferrite parts, the Am./NC are a fair cut above at low frequencies, and remain above even into the skin effect and capacitive cutoff regions. (As laminated metal, they do exhibit skin effect starting around 20kHz or so.) Likewise, keep in mind that the A_L figure varies with frequency -- for the same reason, it goes quite lossy at that point (R = X) and so L is decreasing with frequency in that range. So keep that in mind. You're just designing for impedance, and they're great for pulse transformers and CMCs because that impedance is just so high, even as it drops off through the capacitive region.An important but now-archaic application was ISDN transformers, something like DSL but shifted lower I think? Very wide. Not sure what's commercially available now, or if it's basically going to be homemade, but anyway for stuff like this, homemade is fine.Tim

author: TopQuark
author_rank: Frequent Contributor
timestamp: May 22, 2022, 07:45:04 am
content: I have been down this path of building wide BW transformers before as well.I tried the Vacuumschmeize cores, while they are good, it likely won't improve things beyond what you have now. My only issue with them is they are quite fragile, I believe my Vacuumschmeize core shattered after living on my bench for a while.My current build uses a ~ 3 USD high permeability core from Taobao (https://item.taobao.com/item.htm?id=561000102517), works quite well as shown in measurements.

author: mawyatt
author_rank: Super Contributor
timestamp: May 22, 2022, 01:23:23 pm
content: Thanks, but that link doesn't work! Do you have another in English, or the part number and OEM, and what size is the core, looks large?Performance looks good, have you done any open-loop measurements with an op-amp in a closed loop amplifier?The limiting factor maybe not be the core, but the ability of the DSO to "pull out" the response where the overall loop gain is very high a low frequencies. However, the larger core may have a benefit of allowing a larger DC thru current while still remaining somewhat linear.Thanks for the response.Best,

author: mawyatt
author_rank: Super Contributor
timestamp: May 22, 2022, 02:41:13 pm
content: Quote from: TopQuark on May 22, 2022, 07:45:04 amPlease explain the core shattering, do you mean actually cracking while overheating, or physical stress (dropped)?Best,

author: TopQuark
author_rank: Frequent Contributor
timestamp: May 22, 2022, 02:42:43 pm
content: Yea Taobao is a pain to work with, I've attached a screenshot of the item listing.It is quoted as a nanocrystalline core with 50mm OD, 32mm ID, 15mm Height.No mention of who"AT&M" makes it or any part number, as per usual for stuff listed on Taobao.I haven't used it for opamp open loop measurements, but have used it in SMPS loop response measurements and it works well, can't find the screenshot at the moment, might run a test and post the loop measurement later.TBH as long as enough signal goes through the transformer, the actual response of the transformer does not matter that much to me, as the measurement of the loop response is always done after the injection signal goes through the transformer, not before it.Cheers

author: TopQuark
author_rank: Frequent Contributor
timestamp: May 22, 2022, 02:46:55 pm
content: Quote from: mawyatt on May 22, 2022, 02:41:13 pmIt was working fine when I built the transformer, but measuring the transformer response after a few months yielded very poor results. I could hear something loose shaking the core, but the core looks fine externally, as there's a plastic casing around the core material.I am not 100% certain it was shattered, but re-winding the transformer did not improve things. Most likely it shattered internally when I bumped it around / dropped it off my shelf etc.

author: _Wim_
author_rank: Super Contributor
timestamp: May 22, 2022, 07:18:48 pm
content: Quote from: jonpaul on May 19, 2022, 07:31:27 amThat quite achievable DIY also. Quite a while ago I made these following these excellent instructions: (http://www.simprojects.nl/images/DIY_signal_injection_transformer.pdf)My results were posted here:https://www.eevblog.com/forum/testgear/looking-for-a-low-cost-way-of-measuring-dc-dc-converter-control-loop-response/msg1738013/#msg1738013

author: joeqsmith
author_rank: Super Contributor
timestamp: May 23, 2022, 12:55:41 pm
content: Looking at the Jay link, I can't understand why he was showing 10dB/div. Interesting is he shows a // resistor with the secondary. I wonder if he was driving a 1M source.Quote from: mawyatt on May 18, 2022, 06:23:11 pmYour source is 50ohms and you are driving your transformer that has a 50ohm in // with the primary? Then the secondary is also in // with a 50ohm which drives a 50ohm input?When you built the second transformer (series parallel) you did not use the // resistors and you also changed how you measured it. Could you go back and measure it the same way as the first?Quote from: TopQuark on May 22, 2022, 07:45:04 amCould you change the vertical scale to 0.2dB/div and repost?

author: mawyatt
author_rank: Super Contributor
timestamp: May 23, 2022, 03:54:36 pm
content: Quote from: joeqsmith on May 23, 2022, 12:55:41 pmWe actually removed the all termination resistors on all the transformers, these were originally included to save from having an external termination for some other tests. The series/parallel version would require a termination of 12.5 ohms from proper termination with a 50 ohm source drive.Here's what I think you are asking for, these are with 50 ohm source drive, transformer input measured with DSO Hi Z (1M) and output terminated with 50 ohms (DSO). First plot is larger core mentioned, second is smaller core and third is with series/parallel transformer externally terminated with 50 ohms (DSO) and a pair of 33 ohm shunt resistors, for a combo of 12.41 ohms (close to ideal 12.5 ohms for series/parallel transformer).I'll post the primary and leakage inductance of the transform later.Edit: Here's the transformer measured details measured @ 10KHz.Large Core in Grey Box Lp 8.2mH, Ll 4.5uH, Cc 122pFSmall Core in Blue Box Lp 8.0mH, Ll 8uH, Cc 71pFSeries/Parallel with Small Core in small Grey Box Lp 5.4mH, Ll 3.6uH, Cc 48pFAnyway, hope this helps and what you are looking for.Best,

author: joeqsmith
author_rank: Super Contributor
timestamp: May 23, 2022, 04:44:37 pm
content: Thank you. This was very helpful and makes much more sense. Could you display them with 0.2dB/div rather than 1 like you show with your first plots. Maybe 2deg/div. I'm not sure what the Siglent can show.It sounds like the Siglent can't route these signals internally so you have some output that is 50 ohms that you connect to a T. One leg of the T goes to one channel of the scope set to 1M. The other leg of the T goes to the transformer primary. The secondary goes to a second channel of the scope set to 50 ohms. Is that correct?When you run these tests, how do you calibrate the system? Do you just use a section of coax for the thru and normalize to that?***Sorry, but I had one other question. Assuming the circuit you are testing applies some DC bias, are you testing this effect? What sort of breakdown voltage do you need between the two windings? Things go wrong, seems like it could go really bad.

author: mawyatt
author_rank: Super Contributor
timestamp: May 23, 2022, 06:04:11 pm
content: There's no way to calibrate the system we know of other that taking cal measurements and then creating plots from collected data with cal corrections. These Siglent DSOs are relatively new to our lab, so maybe someone with more experience with these can chime in.I would not place much emphasis in the plots supplied beyond 1MHz, since this is the area of our interest resides. We made no special attempts to minimize or equalize cable lengths, or even include cables effects, or low loss cables....just some stuff we had laying around, even had scope inputs set on 20MHz BW! Likely much of the "artifacts" past 1MHz are due to the scope BW, crude setup, cabling and such. For a more thorough test one would use full scope BW, controlled setup, quality short cables, connectors & such as you would expect for proper RF measurements...which this thread wasn't intended for!!Our intent was to show the CM Filter cores in a DIY configuration utilizing the wire from the CM Filter can be useful for Bode type Closed Loop Measurements within a 1MHz frequency range, thus frequency range note on case covers. I would not use the CM Filter wire if the use entailed a large voltage across the transformer, this would require a proper insulated twisted pair with thick insulation, again our usable is for Closed Loop measurements for Op Amps and such, not high voltage circuits like SMPS.DC bias is a concern and why we got the larger core, thinking a larger core should have a higher DC saturation capability vs. the smaller core, even though we don't know what the core details are. Likely we'll get a proper core and windings later if need be, thus questions to others that have utilized proper cores.This effort was just a quick DIYer to "see" if these cores would work and get familiar with the Closed Loop capability using the SDS2104X Plus and especially to "see" if this capability could be applied to high loop gain circuits such as Op Amp based circuits.The setup has been torn down, but if we get some time will try and rerun with the tighter dB and phase scales.Anyway, hope this helps explain the DIY effort behind these CM Filters, reconfigured as Isolation Transformers for Bode Injection use.Edit: Added finer resolution plots for a Thru, Large Core, Small Core and Series/Parallel with Small Core and scope BW is 100MHz.Best,

author: joeqsmith
author_rank: Super Contributor
timestamp: May 24, 2022, 01:11:11 am
content: I have no problem with the DIY toss something together. I'm just trying to make sure I understand what you are presenting. I am surprised how well things appear to work at lower frequencies and thought I could attempt to repeat your tests with some other configurations.

author: mawyatt
author_rank: Super Contributor
timestamp: May 24, 2022, 02:38:54 am
content: Surprised as well!! Did not expect the low frequency, or flatness performance, quite nice for a couple $ CM Filter reconfiguredThe low frequency impedance to the transformer is low, however the input sampling is across the transformer primary so this compensates some for the transformer low frequency characteristics.Also quite pleased with how well the Siglent DSO behavesBest,

author: joeqsmith
author_rank: Super Contributor
timestamp: May 24, 2022, 02:51:17 am
content: I tried wrapping 30 turns bifilar on two tape cores I had. The performance was very poor.Primary inductance was 109.4mHLeakage inductance was 4.1uHCoupling capacitance was 119.8pFResistance 4-wire was 0.589 ohmsI didn't check the leakage as the freq response was so poor.0.2dB 225Hz - 2.51MHzPhase over this range is 21 degreesTo get below 100Hz, I would need to hunt down some better cores or start adding turns.... Interesting problem.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 24, 2022, 04:02:19 am
content: Why -0.2dB? The cutoff is arbitrary, and easily calibrated out.Tim

author: joeqsmith
author_rank: Super Contributor
timestamp: May 24, 2022, 09:59:42 am
content: Quote from: T3sl4co1l on May 24, 2022, 04:02:19 amI wanted to provide metrics with numbers. Why specifically -0.2, I followed the link the OP provided which then took me to other links. I assumed that the OP read all of this as well which is why they had shown their first screen shot at 0.2dB/div. In the one reference they mention the 0.1dB, for example:QuoteThey provide some constraints for their design:QuoteI had asked the OP about calibration and assumed it was somehow normalized but it made no sense to me that the phase would be zero as it would have to match the thru standard. Maybe the Siglent has a way to compensate for the delay. I would have started by showing an open and maybe a couple of attenuators to give people some confidence in their data but as they said,QuoteQuoteSimilar to the last post about the UnUn, it's nothing I have any use for and just thought I would play along to add to the discussion. My interest stems from the first data the OP presents where the show 0.2dB at 10Hz. I have no idea if that's a problem with the setup or if its real. Seemed very impressive. As I posted, my first attempt was around 252Hz. Hardly in the ball park.

author: mawyatt
author_rank: Super Contributor
timestamp: May 24, 2022, 02:57:52 pm
content: Quote from: joeqsmith on May 24, 2022, 09:59:42 amNo worries, the setup is fineMeasured the DSO input Ch2 as 50.07 ohms with input cable and connector and added a 100.08 ohm series resistor as a Thru, both measured with a KS34465A. The DSO Ch1 is High Z and reads Vin, Ch2 is 50 ohms and reads Vo, and DSO set to Bode Mode.The results should show 20*log{50.07/(50.07+100.08)} or -9.539dBV, and shows -9.56dBV @ 100Hz, -9.59dBV @ 100KHz and -9.61dBV @ 1MHz. Certainly fits within our present needs for this capabilityThis is with the DSO at the highest resolution available on Bode Mode and using 10Bit Mode yielding 0.1dBV/div and 1 degree/div. Hopefully the new true 12bit ADC version (the present SDS2104X + uses an 8bit ADC and extends performance to 10 bits with DSP but limits scope BW to 100MHz) will allow higher resolution. Keep in mind this DSO does range scale the inputs to allow much larger Dynamic Range than possible with 8 or 10 bits digitation, basically dynamically scaling to fit the input within the "sweet spot" of the base core ADC.Best,

author: joeqsmith
author_rank: Super Contributor
timestamp: May 24, 2022, 10:38:34 pm
content: Thanks. For the phase, is the reference a manual offset you can add?

author: mawyatt
author_rank: Super Contributor
timestamp: May 25, 2022, 12:06:38 am
content: The phase, amplitude reference & scaling is just settings for the display.Best,Mike

author: joeqsmith
author_rank: Super Contributor
timestamp: May 25, 2022, 12:43:39 pm
content: Makes sense. Thanks. I'm still not sure about your test setup. Assuming you had followed the threads you had linked (what a rabbit hole), what your thoughts are about the following comment and the three that follow:https://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/msg3038468/#msg3038468

author: mawyatt
author_rank: Super Contributor
timestamp: May 25, 2022, 01:58:48 pm
content: We're using the transformer as an injection device for Closed Loop measurements and the built-in Bode function of the SDS2104X + measures the input across the transformer primary with Ch1 and the output is Ch2 which can be set to 50 or 1M ohms. The absolute amplitude and phase of the injection signal isn't critical for Closed Loop measurements as long as the amplitude is not high enough to cause issues with the system under test or saturate the transformer, and not low enough for the DSO to have trouble digitizing. The later becomes an issue with high loop gain systems where the feedback attempts to cancel the injected signal, this can be seen in some of the Close Loop plots shown earlier at the low frequency ends of the plots.Edit: With Closed Loop Bode the transformer secondary is placed in series with the feedback loop and DSO channels are connected across the secondary. Here's a video showing how the setup is configured for this Bode Mode and also shows how the Isolation Transformer for Bode use is built and connected.Another link.http://www.simprojects.nl/images/Gain_Phase_measurements.pdfAs mentioned a couple times, the DSO samples the Ch1 input {Vin} and Ch2 output {Vout}.Since the Bode plot is Vout/Vin and Vo = T(f)* Vin, where T(f) is the Transfer Function as a function of frequency of the DUT,then Bode Plot = Vout/Vin = (T(f)*Vin)/Vin or simply T(f)Note the Bode Plot is independent (ideally) of input signal level as it should be for an ideal linear system transfer function.This is the way the Siglent DSO computes the Bode Plot I believe.Note: On measuring equivalent magnetizing and leakage inductance of the transformer, one must be careful not to saturate the transformer core. It's a good idea to monitor the excitation current, as just a few milliamps can cause issues with these small cores. Also, the pair of equivalent inductances need to be measured close to the intended equivalent model use frequency for the estimation of transformer performance, this means at low frequencies for the magnetizing inductance and higher frequencies for the leakage inductance. Using an LCR meter with variable amplitude and selectable test frequency is helpful here. For a detailed model one should also include the effects of distributed winding capacitance, core loss, wiring loss and so on.Anyway, hope this helps to understand how these cores and transformers are used and behave as Injection devices for Bode Plot usage.Best,

author: tautech
author_rank: Super Contributor
timestamp: May 25, 2022, 08:41:02 pm
content: Nice thread Mike.FYI here's some good info on FRA and finding its limits albeit with the little X-E scopes not the 2kX Plus models.https://www.eevblog.com/forum/testgear/siglent-sds1x04x-e-bodeplot-ii-(sfra)-features-and-testing-(coming)/

author: mawyatt
author_rank: Super Contributor
timestamp: May 26, 2022, 02:06:15 am
content: That's a must read thread tautech! rf-loop did a great job with the Bode Function. I need to spend some time reading thru all the posts in the thread, lots of good quality informationBest,

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2022, 02:34:51 am
content: My last attempt25Turn Bifilar, single core 31mm od, 16.5mm id, 12.9mm thick.Ccoupling @ 10kHz 43pFLp @ 10kHz 8.97mHLl @ 10kHz 0.863uHR 0.116 ohmsCalcuated -3dB Lf should be 442 Hz. I measure 421. The 0.2dB Lf measures 2.7 kHz.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2022, 02:40:02 am
content: While that last core was much worse than the initial attempt, my goal was to get something a little closer to OPs setup. Again, I am only questioning that 0.2dB cutoff. It's why I kept asking about the setup. Not how the transformer is used.I had made another attempt to make something that would run a bit lower than the first core. 0.2db was 60Hz to a MHz.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2022, 11:55:03 pm
content: I marked up Jay_Diddy_B's drawing I linked above. Obviously in the first two circuits changing the location of CH1 is going to have a major effect what the low frequency response looks like when we measure our transformer. Consider as we approach DC the primary will start to load the output. Because we are looking at a ratio of ch1 to 2, it can make the response seem flat.I'm not a fan of the added resistor he shows but at DC, hey.. Anyway, the third circuit, I change the scopes inputs to 50 ohms on both channels and include a splitter.I suspect the initial setup is wrong as Jay pointed out. Calculating the rolloff we won't be anywhere near 10Hz as expected. Maybe it adds to the confusion.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 29, 2022, 01:59:31 am
content: Attempted to use the LiteVNA to looking at the last transformers gain. The LiteVNA is spec'ed to work down to 50kHz. Things really fall apart below 10kHz.

author: mawyatt
author_rank: Super Contributor
timestamp: May 29, 2022, 02:40:20 pm
content: Quote from: joeqsmith on May 28, 2022, 11:55:03 pmThe original setup is not wrong, it's exactly as stated multiple times and illustrated in the Bode Plot video shown above. The Bode measurement with the Siglent DSO Ch1 isAcross the Transformer Primaryand Ch2 across the secondary with input impedance set to 50 ohms. Since the intended use and thread title of the transformer as stated is for Bode use, and mostly as an Injection Transformer for Closed Loop measurements, this method as stated and used partially removes the transformer (and source) characteristics from the measurement and revels the effective use of the transformer for Bode use.This is NOT directly intended (although can be used) for a controlled impedance type use like 50 ohm RF, but generic Bode use where the effects of the input source are partially removed by the input sampling location. The intended case is for Closed Loop measurements the input sampling is actually moved to the transformer secondary side, the transformer is for isolation with the DUT, and one secondary winding wire goes to Ch1 as Input and the other secondary winding wire as Output goes to Ch2, the secondary creates a "floating injection source" inserted in series with the negative feedback (with restrictions) for the DUT. Since the Bode plots are of complex type (Magnitude and phase) the result loop response of the DUT is simply Vout/Vin in magnitude and phase. Note the effects of the signal source, transformer, cables are completely removed (ideally) from the result and why this technique is so powerful when applied properly!!Here's some previous quotes in this thread answering your questions regarding the transformer intended use, and what the plots show.Our intent was to show the CM Filter cores in a DIY configuration utilizing the wire from the CM Filtercan be useful for Bode type Closed Loop Measurementswithin a 1MHz frequency range,Here's what I think you are asking for, these are with 50 ohm source drive,transformer input measured with DSO Hi Z (1M)and output terminated with 50 ohms (DSO)The low frequency impedance to the transformer is low, howeverthe input sampling is across the transformer primary so this compensates some for the transformer low frequency characteristics.Of course the intrinsic transformer doesn't have a basic 10Hz 3dB corner, just look at the primary inductance measurements of ~8mH which implies an impedance of 1/2 ohm at 10Hz!!! This is not to say the core transformer low end isn't important for Close Loop Injection use, the transformer must inject a signal into the DUT and this injection level falls off at the high and low frequency end due to transformer and source characteristics, as well as other effects. In the Closed Loop Bode measurement the loop gain of the DUT comes into play, and usually the loop gain has a general low pass type charteristic. So a rising DUT loop gain as frequency decreases causes the DSO Ch1 signal to be small as the negative feedback attempts to "null out" the injected signal which appears to the Closed Loop System as an error signal. The DSO will increase the input sensitivity to help compensate for such, but eventually reaches a sensitivity which can no longer "pull out" the signal from the noise, and the Bode response degrades. The same happens at the high end where the transformer rolls off, thus the injected signal rolls off. However, the DUT loop gain is also falling off which partially helps with DSO detecting the signals since less of the injected signal is "nulled out" by the negative feedback loop gain.We realize this is a rather complex subject and likely difficult to get ones "arms around", especially with all the nuances involved in proper setup, use, and measurement understanding. Please spend some time studying the mentioned video (and other related papers on Bode Plots and Close Loop Measurement Techniques), this is an excellent resource for getting an understanding of Closed Loop Bode measurements, and even illustrates how this method can be utilized to measure the very complex non-linear nature of SMPS even tho Bode is a linear type function.Awhile back, well before this thread, some folks downplayed the Bode capability of these DSOs. Likely from a lack of knowledge and/or understanding just how useful this technique is when properly applied with the DSO. PicoScope, Siglent have this capability (we know and use both), Keysight and others also.Anyway, hope this helps clarify what this thread was intended to illustrate, and how useful these DSOs are for Closed Loop Bode measurements with the simple addition of a repurposed inexpensive Common Mode Filter core for Bode Injection Transformer usage.Best,

author: mawyatt
author_rank: Super Contributor
timestamp: May 29, 2022, 02:50:32 pm
content: Quote from: joeqsmith on May 29, 2022, 01:59:31 amNot surprised at this result at lower frequencies! Pretty much useless at frequencies where Closed Loop Bode plots are useful, not to mention dealing with 50 ohm inputs where the DUT must not be perturbed by the measurement sensing probes.This is where these newer DSO really shine, not long ago to do these types of Bode measurements one required a dedicated instrument, now it's built-inBest,

author: joeqsmith
author_rank: Super Contributor
timestamp: May 29, 2022, 05:16:25 pm
content: Indeed it does help. You're looking at it from an application view where I am just comparing the performance of two transformers in a 50 ohm system. I thought the goal of your first post was to show the transfer function of the transformer in a 50 ohm system which was partly why you initially had added these 50 ohm parts. Indeed we can calculate the low roll off. As your link to Jay's talks about, what you showed seemed too good to be true. Of course, we can't see see the low response with how you are measuring it. It's just my misunderstanding of what you were trying to present.The data I have shown is with the transformers in a 50 ohm system. I was curious how flat I could get the low frequency response. I assumed that the person Jay linked to wanted that 0.1dB flatness because they have no way to compensate for the error and would not know what was being injected.Shown is the same core on the original NanoVNA. These VNAs have better performance at lower frequencies but they are not going to get you near 10Hz. Agree that its not useful for your application and more an FYI.I haven't spent much time looking into Siglent products. After there was that whole thread about them going after eBay customers, I never considered them. Eventually we procured an arb from them where I work just to try get a feel of the quality. That was my first experience with the brand. Interesting to see the built in Bode plot. To do this today, I would use a separate scope, generator and PC.

author: mawyatt
author_rank: Super Contributor
timestamp: May 29, 2022, 06:21:56 pm
content: Quote from: joeqsmith on May 29, 2022, 05:16:25 pmDon't know about the eBay issue with Siglent? What happened?Frankly, we never expected the Siglent SDS2104X Plus to be as good as has demonstrated over and over in our use. This was our 1st venture into the new DSO/MSO arena with our personal $ funds, before retiring everything was HPAK Tek, LeCroy and R&S, so very selective and cautious!!After much review here, learning and "selective listening" to those in the know, we pulled the trigger and acquired one (have 2 now). Even after 2 years of use it still amazes in performance and overall capability. May sound like a Siglent fanboy, but that's not the case as Siglent has some products that we're not particularly fond of, but generally their stuff is pretty good and good value, the SDS2104X Plus being an absolute outstanding value for serious use IMO. The front end design, noise level, offset DC range, waveform accuracy, computational accuracy, Display, FFT, Bode, Lan & Web interface and so on are all really good, and using a wireless mouse is icing on the cakeThe PicoScope is good, we needed this for the 16bit ADC precision waveform evaluation and it served the purpose well. It's also quite capable as a low frequency DSO, but never been a fan of laptop instruments, so not used very often.Best,

author: joeqsmith
author_rank: Super Contributor
timestamp: May 29, 2022, 07:07:48 pm
content: Quote from: mawyatt on May 29, 2022, 06:21:56 pmYou can read about it here:https://www.eevblog.com/forum/testgear/siglent-they-filed-a-_wrongful-trademark-claim_/msg783231/#msg783231In the end they put together a story of what had happened and did an interview with Dave.

author: mawyatt
author_rank: Super Contributor
timestamp: May 29, 2022, 09:26:11 pm
content: Interesting, didn't know about that!Thanks!Best,

author: tautech
author_rank: Super Contributor
timestamp: May 29, 2022, 09:43:23 pm
content: Quote from: mawyatt on May 29, 2022, 09:26:11 pmAncient irrelevant history never to be repeated.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 29, 2022, 10:28:15 pm
content: Quote from: tautech on May 29, 2022, 09:43:23 pmOf course that's going to be your response!

author: tautech
author_rank: Super Contributor
timestamp: May 29, 2022, 10:47:50 pm
content: Quote from: joeqsmith on May 29, 2022, 10:28:15 pmWell really Joe why did you even dig out that old storm in a teacup ?You seem to think that no TE manufacturer can be excused of ever making a mistake.....yet all your vids on DMM robustness prove they certainly can and when an AC+DC measurement fails to show one might be lethal you fail to call that manufacturer out forever more.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 29, 2022, 11:08:09 pm
content: Quote from: mawyatt on May 29, 2022, 02:40:20 pmYour point about the impedance at such low frequency is certainly valid. In the video you link, he tests his transformer manually with a 10 ohm load, 50 ohm source and from 300kHz to 4Hz. I suspect he has higher inductance. He drops the drive to 100mVp to avoid saturation at 4Hz then seems he stays with that drive level.While the video was talking about SMPS and it sounds like that is also your area of use. I don't see why it couldn't be used for testing other control systems stability.If I attempt to look at the last core I made using his technique, probes set to 1X, 200mVp-p drive. Shown is the difference from 10kHz to 4Hz. I understand your comment about the DUTs loop response.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 29, 2022, 11:10:39 pm
content: Quote from: tautech on May 29, 2022, 10:47:50 pmBecause OP asked for the data.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 29, 2022, 11:19:19 pm
content: If I run a similar test with the other transformer (much higher inductance) we can see that the lower frequency coupling is much better. Phase isn't great. Again, what we expect. For testing SMPSs, again I agree that it may not be useful to have such a transformer.Should mention this was taken with 10X probes rather than 1X. Same drive levels.

author: mawyatt
author_rank: Super Contributor
timestamp: May 29, 2022, 11:43:08 pm
content: Quote from: joeqsmith on May 29, 2022, 11:08:09 pmWe just used the magnet type wire that came with the CM Filter and twisted the 2 wires together and wound this back onto the core. If we had more wire then we could have increased the primary inductance with more turns, but didn't, so used what we had. Need to find some old Cat 5 cable to strip!!In the video, he uses more wire and turns, thus greater primary inductance. This is why we were asking about the various core types, especially the large core shown by TopQuark but have no idea how to order from Taobao!! Wanted to use a larger core with more windings to create a larger primary inductance. Your core looks to have more windings and should yield a higher primary inductance than the ones we made.Actually our use is more inline with op-amp type circuits as well as SMPS, both are difficult but the op-amp types usually have lots of loop gain which creates problems with accurately sensing small signals and the reason for the low frequency somewhat randomness in the plots, and keeping the signal low so the core doesn't saturate is important for good results. This is the type of area where synchronous sampling pays big dividends, but that's another complex topic best served in a separate thread.Edit: This method is certainly valid for testing all sorts of feedback control systems, from op-amps, SMPS circuits, optically coupled systems, electromechanical systems and so on. Very powerful technique and why we were amazed this is essentially a scope built-in feature, and with the excellent front end with low noise, high dynamic range, and accurate scaling factors, can cover quite a range of uses. By far the best value electronic instrument we haveAnyway, hope this helps.Best,

author: joeqsmith
author_rank: Super Contributor
timestamp: May 30, 2022, 12:11:10 am
content: Quote from: mawyatt on May 29, 2022, 11:43:08 pmHe talked about 7 meters of wire in the video you linked. He backs that up with his comment about his DC resistance. Yours appeared closer to 25 turns so yes, I wasn't too surprised. Again, I started out with 30 turns on tape as it seemed it had not been considered.QuoteMaybe "tape" was glossed over or the assumption was my inductance was off by a decimal point (typo). Anyway, just something to keep in mind.https://www.magneticmetals.com/products-materials/tape-wound-toroidal-coresAlso, for the wire I am using Teflon insulated single strand silver coated. I used the hand drill to for the tight twisted pairs. Just an FYI. Good luck with your project and thanks for the all the additional information.

author: mawyatt
author_rank: Super Contributor
timestamp: May 30, 2022, 12:30:24 am
content: Yes our smaller core has 25 turns, and noted in the video the long ~7M wire, ours was only ~2 meters. Did note your larger inductance and assumed you had a much higher permeability core, so a metal tape core seems reasonable. Have no idea about the core we used since it was part of the CM Filter. One could do tests and figure out some core parameters, but no time budget for that at the moment.Best,

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 30, 2022, 11:48:39 am
content: Hi,I am late to the party. I missed the start of this thread. Do you have any questions for me?Jay_Diddy_B

author: mawyatt
author_rank: Super Contributor
timestamp: June 01, 2022, 10:25:17 pm
content: We used the PicoScope Frequency Response Analysis tool with a PicoScope 4262 (16 Bit ADC) to see if we could improve the Bode Plot results with the Closed Loop measurements with a OP-07 in a non-inverting 11X Gain configuration. Using the Noise Reject Mode with a Sample Rate of 500KHz and Noise Rejection Bandwidth of 1Hz (64X oversampling) we attempted to improve the Close Loop Bode Plot results hoping the PicoScope 16bit ADC and the FRA DSP Noise Reduction effects would pull out Ch1 signal and smooth out the randomness below 100Hz. As you can see that was not the case.Conclusion is that the Isolation transformer needs to have a much higher Primary inductance to keep the low frequency signal level reasonable for the scope to capture accurately since the high gain feedback loop is effectively nulling the scope Ch1 Vin signal, so we'll be getting a larger core and winding another transformer with larger primary inductance for these low frequency Closed Loop Bode measurements with high gain Op-amps like the OP-07.Others with larger primary inductance Isolation transformers might want to give this Close Loop Bode Plot a try, very interesting and useful technique.Best,

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: June 02, 2022, 04:04:39 am
content: Hi,Let me use LTspice to illustrate some of the features of the measuring the open loop gain of an op-amp. I have used the universal op-amp in LTspice so that I have a known answer. I have configured the op-amp to have an open loop gain of 1E6 and and a GBW product of 500K.AC domain ModelIn SPICE I can have a floating source so I do not need to include the transformer. The open loop gain is obtained by plotting V(a)/V(b).The results show that I have an amplifier with a single pole slope, a gain of 1E6 and a GBW of 500kHz. This is the correct answer for the universal op-amp used in the model.The gain is 94dB at 10Hz.Time Domain ModelSwitching to the time domain, transient analysis, and using a 10Hz 2V p-p signal the signals at nodes A and B can be examined.The voltage between nodes A and B is 2V p-p, as defined by the source. The voltage from A to ground is 2V p-p. The voltage on node B with respect to ground is only 40uV p-p. This is the inject signal divided by the loop gain at the injection frequency.The signal on Node B is very small. It is -94dB, 50000 times smaller than the injection signal.Coupling Transformer LF bandwidthThe coupling transformer LF -3dB point is given by:F = (Rsource // Rload) / 2 x Pi x LmagI have chosen Lmag = 68mHThis gives a LF (-3dB) point at 58.5 HzAdding the Transformer to the open loop measurementAdding the transformer with a -3dB point of 60Hz does not impact the open loop response at all as shown in this model. It does reduce the signal amplitude at 10Hz by 16dB.It is the signal to noise ratio and the noise floor of the FRA that impacts the measurement, not the bandwidth of the isolation transformer directly.Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: June 02, 2022, 04:20:01 am
content: Hi,Here is a very simple test to circuit to determine if your FRA is capable of making the measurement:It is a 100dB attenuator.Jay_Diddy_B

author: RoGeorge
author_rank: Super Contributor
timestamp: June 02, 2022, 06:26:33 am
content: Quote from: mawyatt on June 01, 2022, 10:25:17 pmAbout achieving less than 100Hz lower frequencies, are they really needed?Asking that because (in my understanding) the instability of a feedback loop is expected to happen at the frequency where the amplitude of the feedback loop bode plot crosses the open loop amplifier's bode plot. Usually this intersection of the two plots happens at a frequency in the kHz range, at least, so why bother testing at 10Hz?A feedback network designed to work up to only 10Hz will have a bode plot that will not intersect the amplifier's open loop bode plot at all (thinking here the casual opamps with gain bandwidth ~1MHz).Is the sub 100Hz injection useful for "just in case", is it for something else than testing loop stability, or am I missing/misunderstanding something else entirely?

author: 2N3055
author_rank: Super Contributor
timestamp: June 02, 2022, 07:16:13 am
content: Quote from: RoGeorge on June 02, 2022, 06:26:33 amOne area I know that needs it are PFC controllers... sometimes you need to look at frequencies even less than 5-10 Hz...EDIT: My bad I misunderstood the question.... In context of measuring open loop gain of opamp very low frequencies are not very interesting..

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: June 02, 2022, 09:52:55 am
content: Hi,Measuring a control loop is different than measuring the open loop bandwidth of an op-amp. When measuring a control loop the main frequency of interest, as pointed out by RoGeorge, is when the gain is 0dB. By definition the amplitudes of the signals at nodes A and B are equal in amplitude and there is no concern about the signal to noise ratio.When measuring an op-amp open loop gain, the low frequency gain is very high, 1E6 typical, 120dB. The signal on Node B is 1 million times smaller the signal on Node A.Low crossover frequencyI have created a model of an amplifier with a dc gain of 10,000 and a Gain Bandwidth of 5Hz. This is G1 and E1 in the model.In the AC analysis the 0db point is 5Hz as designed. The gain at 1Hz is 14dB.In the time domain, at 1 Hz, the signal at node B is only 5x smaller, -14dB, with respect to the signal at node A.With the relatively large signals, there are no SNR challenges.At the 0dB frequencyFor completeness, at the 0dB frequency, the signals at Nodes A and B are equal in amplitude, and phase shifted by 90 degrees.Jay_Diddy_B

author: mawyatt
author_rank: Super Contributor
timestamp: June 02, 2022, 01:17:31 pm
content: Lots of interesting discussionsAccessing gain and phase margin in op-amp based circuits generally are not a problem for the DSO because the signal levels are sufficient to resolve. However trying to determine overall loop gain and phase at lower frequencies becomes increasingly difficult as the frequency decreases because the signal amplitude decreases due the negative feedback and the isolation transformer lower frequency response. Increasing the signal level available at lower frequencies from the isolation tansformer may help and why we're looking into a higher primary inductance transformer.In a way we are asking a general purpose DSO to perform as a dedicated high input impedance & sensitivity network analyzer and it does a nice job within reason. However, dealing with high loop gain such as op-amp circuits, the available signal level becomes so low at lower frequencies the DSO can't resolve such and the results show. Here's where a dedicated instrument shines, and likely using techniques such as synchronous sampling to help "pull out" the signal from the noise and produce accurate and repeatable results.Most of the time the lower frequency performance can be easily estimated and the lack of performance here isn't a problem, however there are certain case where one needs this lower frequency performance. We ran into one such case a number of years ago when developing a closed loop piezo electric nanometer positioner utilizing "Flexures" as bearings, the control loop for this device was quite complex even at lower frequencies.Anyway, quite pleased that a general purpose DSO can actually perform these type of measurements and produce respectable results within a reasonable range of operating parameters.Now to see if a larger transformer can slightly expand that operating rangeBest,

author: TopQuark
author_rank: Frequent Contributor
timestamp: June 03, 2022, 03:07:30 am
content: QuoteApologies for the delayed response, I've attached the results as per requested. Love your videos btw, keep up the good work.I have received questions regarding the core I used and its availability. I got mine from Taobao which is not very accessible to the rest of the world. If purchasing from Aliexpress is an option to you, you can find cores similar to mine by searching for "nanocrystalline core" at the site.https://www.aliexpress.com/item/4000447631159.html<- This core looks to be the same as the one I have used, although I didn't purchase mine from them. The seller also offer similar cores with other sizes.Quote from: RoGeorge on June 02, 2022, 06:26:33 amI echo the same thoughts, usually I only look at crossover frequency, gain slope at crossover, gain and phase margin for SMPS control loops. I don't deal with PFC much, so if crossover is <100Hz, I probably don't need to run a FRAI also agree the bode plot performance issues <100Hz has more to do with the instrument than the transformer. Looking at the videos showing the Bode 100 at work, it is obvious that whatever hardware/software they are using is way faster, has high dynamic range and noise rejection capabilities than the Siglent scope even at <100Hz, using transformers with similar sizes compared to ours.Looking at the whole picture, I think what the industry can really benefit from is something with Bode 100 speed and accuracy, Cleverscope style isolated DAC/DDS (so no isolation transformer needed), NanoVNA design philosophy and price. Although that's just me daydreaming.

author: mawyatt
author_rank: Super Contributor
timestamp: June 04, 2022, 02:12:50 pm
content: Here's an example from 2019 where we could have used these Closed Loop techniques. Please read through the entire thread to get an idea of what's involved, one of the more complex analog feedback systems we've encountered in our career.https://www.photomacrography.net/forum/viewtopic.php?f=25&t=40510&hilit=PIezo+ElectricNote the positioning graph with 200nm (0.2um) total range in 8~10nm (yes nanometers!!) stepsThe technique developed to make these nanometer measurements is another interesting topicHaving this Closed Loop capability back when developing this project would have certainly helped, we knew about the technique and had used such as early as <1990 but with dedicated HP equipment, and didn't consider a mid-level MSO for this in 2019.Best,

author: bicycleguy
author_rank: Frequent Contributor
timestamp: June 04, 2022, 05:06:31 pm
content: @mawyattVery interesting posts. Slightly off topic as far as the bode response but you might find this pdf about the actuators that align the mirrors on the Jame Webb Space telescope interesting. Quoting from the first page:'This linear actuator is capable of 10 nanometer position resolution over a range of 20 mm and can operate under cryogenic conditions'

author: mawyatt
author_rank: Super Contributor
timestamp: June 04, 2022, 07:17:27 pm
content: Quote from: bicycleguy on June 04, 2022, 05:06:31 pmThanks, that's a very interesting article and quite an amazing device. Figures 12 & 14 show very good linearity and amazing repeatability.Our efforts pale in comparison, but in defense we did this at home and within a few $K out of pocket.We've been asked at other places how one measures sub-micron position, and since we're the OP guess it's Ok to go a little "off topic".The technique utilized to measure position levels down to the nanometer region (and at home) employs optical alignment of a target. The target is a simple piece of quality print paper laser printed with a medium grey patch. Detailed observation of the paper under high magnification revels a totally random pattern of carbon black "dots" of laser powder (which is low temperature plastic impregneted carbon) and fused to the white paper under thermal and pressure, which give a medium grey appearance from afar.The paper is cut and glued to a glass microscope slide and the slide placed on the piezo electric positioned almost normal to the optical axis to be viewed. A rigid fixed custom lens/camera fixture is arranged to view the slide and focused with a high quality (Mitutoyo 20X) stable lens & assembly on the slide center. Because the slide is almost normal optical axis the area above and below the center will be out of focus and a band of in focus will show with the DoF of the lens assembly (usually a few microns, a little trig will show how wide the band will be). The piezo element is commanded over the measurement range and at each position an image is captured with the hi res camera (Nikon D850). This small movement causes the DoF band to move across the image as the target moves under the piezo electric actuator.After the images are captured, they are feed into a software stacking routine like Zerene. This is setup to attempt to align each image in-focus band to the first image in-focus band. The software uses high contrast areas like the white paper and random carbon black dots to use as alignment guides, and uses algorithms to define in-focus areas. These tiny random carbon black deposits fused onto the paper actually work better as alignment points than the usual alignment guides, and there's plenty of them!!The amount of movement the image requires to realign with the first image is the movement the target imposed and is recorded. This recorded data shows the relative image shift required by each image in the stacking routine and used to evaluate the piezo electric positioning when compared to the total range involved. All this is done at the image pixel level and this is then converted to actual physical movement by the pixel dimensions.This is a relatively complex task and takes time, but in the end can resolve target position movements in the nanometer region as shown......and it doesn't require an expensive lab, or complex expensive setupAnyway, hope some folks find this interesting.Best,

author: mawyatt
author_rank: Super Contributor
timestamp: July 31, 2022, 08:23:55 pm
content: Just for fun we just did an open loop gain/phase measurement with the popular TL-431 shunt regulator. The setup was with the SDS2104X+ and a DIY Isolation transformer, with the primary driven by a AWG and unterminated. The secondary was placed between the Cathode and Reference in the feedback loop. The TO-92 package was plugged into a Photo-Board with jumpers, so lots of parasitic capacitance and contact resistance.Also did an output impedance plot by driving the TL-431 Cathode with a signal thru a 1K resistor and plotting the response across the 1K resistor. The results are shown in dB K Ohms, so 0dB is 1000, -20 is 100, -40 is 10, -60 is 1 and -80dB is 0.1 ohms.#19 is the Bode Plot of the TL-431 Open Loop Response with bias at 10ma, with Data Sheet from UMW (actual device OEM).#17 is with TL-431 Output Impedance biased at 10ma, with Data Sheet plot from TI (UMW doesn't have a 10ma plot)#18 TL-431 Output Impedance biased at 100ma, with Data Sheet plot from UMW.Edit: Added another plot (#23) showing a TL-431 with a shunt 101.4nF ESR 1.72 ohm cheap ceramic load capacitor. This is in the "Forbidden Zone" as shown in the data sheet graph and the Open Loop Bode plots shows the Phase Margin as ~8 degrees at ~310KHz, or just on the verge of oscillations, and somewhat confirms the Data Sheet zone!!Best,Best,