#65: Understanding Toroid Cores

[@tomthompson6911]

This was an excellent video, Larry. I think more videos of this type will appeal to a wide audience of builders.

[@chuckcrizer]

Fantastic video about toroids and real life issues. Very interesting and worthwhile. Thanks for the in-depth analysis and explanation.

[@michaelhunter3690]

Thank you for doing all the leg work, and explaining what should be done.

[@OzzieBenzC300]

I’ve been looking for info about this for about an hour on the web. Thanks for making this vid. Appreciated. 73 KY4DA

[@w0qe]

You are welcome! Larry, W0QE

[@joesitter20101]

Thanks so much for publishing this easy to watch video. Although I've worked with these devices I've never really had a good understanding of them but now I've gained some very useful knowledge.

[@victorreppeto7050]

I love it when you drown me in the details like this!! Awesome video!!

[@tommiller1710]

This is good stuff Larry! I have had similar problems and was not able to figure out what was happening. Keep up these kind of topics. I especially enjoyed the RF sampler videos too!

[@w0qe]

Thanks Tom.

[@youneshamache3314]

I designed lately a sine wave inverter in which i had to design a toroid inductor to filter the output voltage signal, and i noticed that other inverters had a 3mH toroid with up to 100 winding turns, so i bought a toroid with the same dimensions and surprisingly i reached the same value but only after 17 turns ! And i didn't know why untill i came across this video ! The explanation was amazing and it helped me alot ! Thank you

[@w0qe]

Glad you found the video useful! Larry

[@markusberg2770]

Thank you for posting your research and findings.

[@k7iq]

Yes, topics like this are very good ! Similar to Lloyd Dixon's old seminars but different enough to help a lot ! Enjoyed the one SIm Smith video I just watched, too. Please keep this up as time and ideas allow ! Thank you for these. K7IQ

[@w0qe]

Hang around Bob as I have a lot more planned. Glad you enjoyed the video. Larry, W0QE

[@Stovetopcookie]

10:00 oh wow I get it. If you go to lower perm you need more turns which keeps flux density lower. So there is no one perfect way you have to play with the values until you get something that satisfies all parameters. This is a great walkthrough

[@Stovetopcookie]

This was so helpful and well explained thank you

[@w0qe]

Ernest, Glad you are enjoying the videos. Larry, W0QE

[@mohamedlanjri]

Great video, thanks for sharing experience and knowledge. It helps a lot when you're trying to get into this components. If I'm allowed to make a suggestion/request... It will be great if you can explain the core materials, it's nomenclature, what they mean, what should we have into consideration when you say for example this is material 30

[@QUIX4U]

That's all well and good (sent me to sleep it did with the drone sounds, never mind the missus put it in pause before tapping me on the shoulder.. sleeping dear she said..?? Nah was listening I said (and then spotted hw much I had missed). Oh buggah well it hadn't woken me up with what I wanted to know.. So, how do I use a toroid then? I want a 1:1 audio toroid, to accept 20hz to 20 kilo hertz, at approx. 150 watts? Which toroid core should I buy and hiw much of what sized enamelled wire will I need?

[@W1RMD]

Watching this again was a huge help. If you don't mind me asking, what's your background to have such knowledge on the subject? Thanks again for taking the time to make the video as it seems that you've done a ton of research on the subject.

[@w0qe]

Ryan, Ryan, I come from a family of engineers. My grandfather taught EE at the University of Pittsburgh, my dad was an EE designing megawatt power grid transformers, and I followed suit but mostly designed analog and digital circuitry in the70s through the 90s. Later I did RF and cellular work. Finally I spent about 10 years as a consultant doing RF work. My interest in amateur radio from 1964 through today was also an influence. 73, Larry, W0QE

[@Yorumcu63]

Great video Thank you

[@paulmanhart4481]

Hi. I find this stuff fascinating but conflicting. Maybe you can help me. There’s a guy on KZbin (Dazecars), who has a nice design for a variable speed controller for a 130 vdc treadmill motor using a SCR. After the SCR, he goes to a toroidal inductor to reduce noise (it’s still AC then). My question is 1. What type and size toroid do I use? 2. How many wraps for hot and common wires? 3. Does it matter if the wraps are equal spaced? 4. Does it matter how each wire starts it’s wrap? Above or under? Both the same etc.? I really appreciate your help here. Thanks, Paul

[@VanFlicke]

Thank you Thank You Thank you for this video!

[@DonzLockz]

Great info, very helpful in understanding these black magic products. :)

[@W1RMD]

Thanks for this. A LOT of counterfeit components these days! Is there quick easy sure fire way to get an exact value component? Great video! 73's W1RMD

[@w0qe]

"Exact value component" is what? You can wind some number of turns of wire and then measure the inductance and Q. Inductance is easy to measure but if you really want the correct it needs to be measured at the frequency you are going to use it at as inductance will change slightly with frequency and will change significantly when you are within 25% or the parallel resonant frequency. Q is much harder to measure if you expect it to be high. Often if you just want to know what type you have put 5 to 10 turns and measure the inductance and then compare to published inductance vs number of turns tables. Larry, W0QE

[@victoryfirst2878]

I TIP MY HAT TO YOU SIR. I WISH I HAD YOUR VIDEOS WHEN I WAS IN HIGHSCHOOL. I REALLY MISSED OUT IF YOU KNOW WHAT I MEAN.

[@ErnestGWilsonII]

Thank you for making this video Larry! I am of course subscribed with notifications turned on and thumbs up! 73 W3GUY Side note on this one, even this might be too advanced for a beginner like me, I'd really like to see a video that talks about each of the specific properties of a toroid.

[@shoreguyeast]

Question for you. I'm interested in constructing a inverter for a old BC611 hand held. I need a 88mh toroid. Can you give me a rough idea of physical size of the core?

[@blacksmock445]

I know it's not your fault, but why do toroid and ferrite manufacturers persist in using the c.g.s system of units? I was taught this at school in the UK 60 years ago, but when I left school and attended technical college at 16 years of age, we had to adapt to the MKS or SI system of units, so no Gauss, lines, Oersteds , Gilberts or Maxwells for us. Webers per square metre (flux density) became Teslas while I was at college. So, most of the rest of the world uses metres not centimetres. Like Doug de Maw's book on the subject, your video was very informative on a practical level. Much appreciated.

[@w0qe]

I really have no idea of the early history for the system of units involved. I'm not able to affect changes upon the world so I just "go with the flow". Larry, W0QE

[@blacksmock445]

@@w0qe Thanks for your reply. I've done a little research on this and my son, who works with magnets in a US National Laboratory, tells me that he had to get used to using cgs units when dealing with some outside suppliers. There were two different systems of cgs electrical units, one for magnets and inductors, the other for electric fields and capacitors. They "rationalised" the system and produced a third cgs system which I believe is what they still use. The mks system is also rationalised and fits in with the wider field of units used in science and engineering. Back in the 50s when I first became interested in radio, neighbours gave me many old radios which used 2-volt valves, lead-acid accumulators and HT Batteries, some even had grid-bias batteries (C-Batteries). One set always puzzled me, because its capacitors were labelled in centimetres instead of microfarads. This was apparently part of the old "electrstatic" system of units.

[@SuburbanDon]

Great job My first look at this magnetic stuff.

[@sean8286]

Excellent...You should be teaching at MIT

[@randydireen3566]

Thanks so much for another great video!

[@w0qe]

Randy, Thanks again. Larry, W0QE

[@WestCoastMole]

Hi Larry Two questions for you. The first regards the Fair-rite Data sheets for the ferrite cores. Under the Material Tab The first graph displays 2 Curves for Complex Permeability. One curve is labelled u' the second curve is u". I can't find a legend table that specifies what these curves are plotting. I want to determine what the performance difference is between 67 & 68 material in the application for a resistance transformer in the HF to VHF range. From the overall description it seems like u" is more significant and needs to stay as low as possible. The Application also is a critical factor. While material types of 67 & 68 are best for transformer applications at HF 43 material is needed for EMI Suppression in the same frequency range. How did they come up with that ? ? ? It's very confusing. AA6XE Bob

[@w0qe]

Bob, u' defines the inductance and u" defines the loss for inductive materials. John, KN5L has done a lot of work characterizing Fair-Rite cores. Look at www.kn5l.net to see how he analyzes the cores in SimSmith/SimNEC using the Fair-Rite published data and how closely the simulations match VNA measurements. Larry, W0QE

[@WestCoastMole]

@@w0qe Thanks Larry your answer is on target and fits the bill. I've done a quick scan of the KN5L Website and come away impressed. There is a plethora of links and I have viewed only a few. This one is getting bookmarked. Lots of Signal, very little noise. Thanks again B

[@addaemichael4683]

sir i have seen many videos on youtube where ferrite core were used in class D amplifier.in Ghana the red cores are hard to find.so can i use ferrite coer ?.if yes the which size and how will i do that.thanks

[@clems6989]

Please do a video on using toroids in transmission line transformers. Such as BALUN's and UNUN's etc...I am struggling with these...

[@w0qe]

Matt, I have a couple of videos planned that are on this topic. Let me know if you are looking for anything specific.

[@clems6989]

I have been reading and studying toroid impedance transformers for weeks now. Read everything I can find including the works by Sevic. And still it's just not clicking. Your means of explaining things really makes sense to me.

[@Stovetopcookie]

Agree. Looking forward to seeing a video with baluns. Also I want to toss out there. I have seen Balun cores with a piece of coax through the holes where one end of the ground shield is not connected to anything. What is going on?

[@twong689]

The torroids just look beautiful.

[@photocanonn]

Greate job! more comfortable video for learning! thanks... i want to understanding what Q means, and which magnetic conductance mor comfortable for inductors.

[@w0qe]

Thanks! Q is defined for a reactive component as the ratio of reactance to resistance and is a measure of how "good" the component is . A perfect capacitor or inductor would have infinite Q. Generally high Q is desired but there are circuits such as for common mode reduction where low Q is preferable. Entire circuits such as filters can also have Q which indicates the ratio of reactive power to dissipative power. There are excellent descriptions on places like Wikipedia. Larry

[@JimPBarber]

Great video, how are you coming up with the RMS?

[@w0qe]

Jim, Explain your question in a little more detail please. Larry

[@JimPBarber]

@@w0qe In the spread sheet CoreParams.xls The last column, 400Vrms @ 2mhz. and the note to the side Desired 10uH @2Mhz 400vRMS how do we get 400. I have seen similar calculations with anything from 50 to 500Vrms but have no idea how that number is come by. I have the ARRL antenna books and have turned the pages until they are dogeared, but have yet to have anyone explain.

[@w0qe]

Jim, I was just doing an FYI calculation showing that if I wanted to design a 10uH inductor that would have a flux level of

[@byronwatkins2565]

Beads are designed with more hysteresis to absorb transient energy. They do also increase inductance but that is not their primary purpose.

[@philipacovington]

Great video! Is your spreadsheet available for download? Thanks!

[@w0qe]

I did not upload files for the earlier videos but if you give me an email address I will send it to you. Larry, W0QE

[@jmcguckin]

Why does flux density matter? Why impose a 100 flux limit?

[@addaemichael4683]

thanks a lot sir.am most grateful

[@SiddarthHudedamani]

Sir i am making a DC DC Buck converter with input voltage of 120 v and output of 15v with 20 amps and frquency is 100khz for this i need to design a inductor so how to choose a core for this or can u suggest any core i can used for this application

[@w0qe]

Companies such as Micrometals, Fair-Rite, and TDK who make cores have inductor selection guides on their web pages which should help. Larry

[@josepeixoto3715]

did not get it, not yet, don't know what is inductance, flux, cores materials for 60hz or for 20 khz, nothing...

[@Stovetopcookie]

Hi Larry. Where do you find the maximum safe flux in the core? You mentioned 50 Gauss at 10 MHz. Is this for all cores or does it change by material? Is there a formula for it? 7:20

[@Stovetopcookie]

8:40 At 2 MHz I assume I can have a flux max of 100 gauss. How did you get that?

[@w0qe]

Ernest, Unless your modulation mode is very low duty cycle where the peak power can be extremely high you do not run into issues of core saturation before you have core heating limits. I'm not really sure how much the maximum allowable flux level changes with frequency but it is lower at higher frequencies. If you did run into core saturation the effects would be in linearity of the circuit. For amateur radio modes such as CW and SSB are not really low duty cycle. Larry, W0QE

[@jeanyves5380]

Hi, thank's for your video. Is there a relation between the tore color and his permeability? I found several of them i'd like to recover. Actually some are bright yellow and other are green. Thank's.

[@w0qe]

Jean, Some manufacterers color the cores so that color implies the permeability but there are others that follow their own coloring scheme and ferrite cores are usually not colored at all. Consequently I just measure the core by winding about 5 to 8 turns on it and measuring the inductance vs frequency on a VNA. Larry. W0QE

[@jeanyves5380]

​@@w0qe Hi and thank you very much (don't know your name). I knew what you say for example Amidon follow his own colors but they have grids describing them. But there are some let's say kindoff "standards one" and i did not know the colors. I did not see your other video into which you explain all the colors vs permeability. Sorry for my english from france. Thank you!

[@w0qe]

Jean, My name is Larry. Amidon is not a manufacturer of ferrite and powdered iron cores. They spec the parts to be specific colors. Manufacturers such as TDK, Laird, Fair-Rite, Micro Metals, National Magnetics etc.either have colors for certain parts or can coat them according to the customer requirements. Larry, W0QE

[@jeanyves5380]

​@@w0qe Hi Larry and thanks for your explanations , i just saw Amidon Mark, did not buy them. Here's my problems: I'm making a pwm synchronous buck which runs at 500 khz. This is quite fast. The ouput current can rise to 20 Amps. The problems i got are : I calculated a 2.2 µH which is very small (it is what is required on the schematic) All the cores i tried are heating a lot. I need to have between 6 and 2 turns only meaning the permeability is too high and i don't wana buy them for the need for now. I could not found 4 or 5 permeability values. I'm wondering if a non looped simple pen should do the trick? Without heating, i mean the small ferrit baton could even heat a lot. I have formulas to calculate them. I'd thing even only the air could do the trick but it need 3 times more wiring which is quite a lot i think. I do not know if the parasitall emiting if you a a core on air is worse? I know some materials do not support high frequencies : it may be the problem. The current being high, we can have iron losses if the powders are not isolated. The second problem is that : passing 5 Amps the buck stop to work in regulation mode and passes in security mode : cutting/restarting at a lower frequency. This means that there is something going wrong in the currents or voltage somewhere and is probably due to the 1st issue of heating. Until this limit : the regulation and everything is correct. Here's the circuit i'm using: My input voltage is 30 volts, my output is variable : 3 to 24. I cannot pass 21v output with a 6.8 Ohms load and 14 v with a 3.4 Ohms. www.analog.com/media/en/technical-documentation/data-sheets/37411fg.pdf I do not ask you to resolv the problem of course it's mine. I just share what i'm actually doing and may be you could have some advices. Regards Larry.

[@kyks6771]

My kinda guy🤘

[@lamhewithkunal]

Can you please suggest what tests are to be performed for comparing two different cores for their equivalency.

[@w0qe]

Krishna, If you really want the 2 cores to be equivalent they would need to be the same physical size, have the same permeability at the frequencies you are using them at, and would need to have the same loss again at the frequencies you are using them at. Cores are NOT very precise and 2 cores from the same manufacturer can vary by about 15%. The difference between manufacturers can even be more even if they are advertised as the same nominal permeability. If I had 2 cores that were identically sized or very close I would wind something like about 8 to 10 turns over about 80% of the core and sweep the inductance over the frequency range you are interested in. If possible using a calibrated VNA and plot the complex impedance for both cores. If you used the same wire size for both windings the difference in the resistive part of the impedance will show the loss from the core. Larry, W0QE

[@rchn9953]

For optimum common mode EMI suppression on power lines, by winding paired cable, what are the best material and construction criteria - ex. thickness, annular volume - for the same number of turns? Thanks.

[@w0qe]

I am working on a video that hopefully will address some of your common mode questions. Nevertheless EMI suppression is easier to do than building a balun to go into a line used to transmit high power. There is no such thing as "optimum common mode suppression" but you can certainly reduce the CM current by a lot. I would definitely use #31 material for this application resulting in common mode impedances that are primarily resistive which allows you to use a couple of chokes in series without the reactances cancelling each other out. You must use wire that is heavy enough to handle the differential current and I usually would use a core that is large enough get 7-10 turns on it without the ends getting too close to each other. Jim Brown, K9YC has a lot of info on impedances vs frequency for various number of turns and core sizes. Search for his on Google. Larry, W0QE

[@trentdix7509]

Where might I find how to create/utilize the toroidal field for building applications, say, working with foamcrete? I have a project in mind for this though I'm not sure how to approach this yet.

[@w0qe]

Trent, I do not understand your question. Please explain what "building applications" means. Larry, W0QE

[@trentdix7509]

@@w0qe Larry, thanks for your reply. By building applications I mean my friend and I are working to build a dome made of foamcrete. And I'm wondering if there isn't some way to apply the toroidal field to our building design. Like maybe there's a way to have the toroidal field imact the foamcrete, in a way, to the end that when or as it's drying that field will cause the foamcrete to form an intetesting structure. Supposedly, people of ancient times incorporated the toroidal field into their architecture.

[@w0qe]

Trent, The toroidal shape is very good at minimizing external RF fields. This is why you often see them mounted very closely together on printed circuit boards. All "closed loop" structures with reasonable permeabilities keep the RF field closely contained to the core. If you want an external RF field to be present you want an air core or rod core inductor or just an antenna where the purpose is to create an external RF field. Larry, W0QE

[@trentdix7509]

@@w0qe Larry, Thank you for this answer!

[@wb6csh]

Good video for learning! Thank you Larry! 73 Michael - wb6csh

[@w0qe]

Thanks Michael. 73, Larry W0QE

[@rickhunt3183]

All ican say is wow. Perhaps seeing some real world applications would help with the understanding of what and why. Maybe building inductors for specific applications. What effect does wire diameter have? This is old school radio stuff that people aren’t bothing to learn. I think it’s important to know how to build a filter or a tuner or linear from scratch. KN9QNI

[@addaemichael4683]

this a great video but i want to make 22uh inductance for class D amplifier but i dont have the red core for best inductance so what should i do?

[@w0qe]

The red cores I used were #2 mix with a permeability of 10. There are many ways to make a 22uH inductor but you might just look at an air core inductor. Using the Wheeler formula (Google "Wheeler inductance formula") it is easy to make a 22uH inductor and wind it with stiff enough wire that it becomes self supporting. Larry, W0QE

[@shyamsundarjena4585]

Hello Sir, I was making a toroidal transformer using T106-2 core.Primary has one turn,secondary has 90 turns.The voltage across secondary is around 140-150 volt.The core is getting heated up within 15 min.in case of toroid transformer, how to calculate peak flux ( i mean which voltage is need to be considered whether primary or secondary or both).In my case I hv considered higher voltage of two wingdings (i.e. secondary,140-150 V), and peak flux is around 3-4 Gauss.So the core should not be heated up as you mentioned in your video but i am not getting the same.so please give some suggestions..

[@w0qe]

There are many possibilities why your core is heating up but these are just guesses based on what you have written. 1.) 3 to 4 Gauss should not heat up the core unless your frequency is well above the HF region. 2.) Is your core really a T106-2? There are many manufacturers and not all use the same coloring. Try winding about 10 turns on a core and measure the inductance to see if it is as expected for a T106-2 which should be 1.0 to 1.5uH. 3.) Recheck your calculations just to be sure. 4.) Is the heating due to the current in the windings and not core loss? If so then the wire size needs to be increased. Hope this gives some ideas. Larry, W0QE

[@shyamsundarjena4585]

@@w0qe Thanks for the reply..I will check and get back to you..can you share your mail id,i wl send the photograph the board..thanks

[@w0qe]

Add the 2 letters xx in front of the channel name (w0qe) at gmail dot com

[@J.T323]

I'm not an electrical engineering and need some help please...can I use a ferrite core to make a low frequency (50Hz) transformer or is silica steel my only option...thanks

[@w0qe]

Johann, You can make a 50Hz transformer with a ferrite core but I wouldn't suggest you do it because the number of turns you would need to use would be huge. Ferrite cores have permeabilities from about 40 to 1500 while cores for 50/60Hz transformers have permeabilities of more than 20,000. Larry

[@w0qe]

Johann, You can definitely use the microwave transformer as a step down transformer. However the transformer will have about 10 times more turns on each winding than is needed. These extra turns will result in a lower core loss which is good but will have more voltage drop with load than a properly transformer would have but you might not care. Larry

[@J.T323]

@@w0qe Thanks alot for all the info,I really appreciate it...thanks

[@fernandohood5542]

Where would I find info on maximum flux verses frequency?

[@w0qe]

Fernando, For "normal" uses the issue becomes the core temperature rise vs frequency and not the maximum flux. However if you have a use where the duty cycle is very low (think high power pulse applications) saturation might become the primary concern. Obviously the core manufacturer is the best source for the information you want. Larry, W0QE

[@fernandohood5542]

@@w0qe In your calculations you used a value which you used as a limit. I was just trying to understand how you determine this limit.

[@w0qe]

@@fernandohood5542 The limits I used were conservative flux values that would not cause heating based on my experience over time. I have many seemingly identical cores from different manufacturers and made between about 1980 to the present and they perform quite differently. When I have done designs that I believe will have significant core temperature rise I build a test circuit so that I can drive the core with the voltage, current and at the frequency I will be operating it at and then measure the temperature rise. This may not sound like a very scientific way to do a design but it is fairly quick and easy to do and I know for sure that the core temperature will not be too high. Larry, W0QE

[@kayurananthgirish2480]

How to check Al value toroid core

[@fernandohood5542]

Hi I want to create toroidal transformer to step a voltage from 40khz at 12 volts to about 100 volts. What material would you recommend.

[@w0qe]

Fernando, 40kHz is really quite low in frequency so I would suggest you look at ferrite materials with permeabilities of 2000 or more. Typically these materials come in shapes like pot cores which usually come with a plastic bobbin to make winding easy. Cores like these are common as they are used in switch mode power supplies. Larry, W0QE

[@fernandohood5542]

@@w0qe Thanks.

[@fernandohood5542]

@@w0qe Okay so I created the transformer with primary center tap. I am seeing + 100volts pulse when I pulse one half of the primary and - 100volts when I pulse the other half. When I alternate the pulsing the output signal dies. I was expecting +100 and -100 pulses. I am using a t38 core. Digikey 495-3867-ND.

[@w0qe]

@@fernandohood5542 I'm sure there an good explanation as to what is happening but I don't understand what your circuit is. Can you send me a link to your schematic with more information. Larry, W0QE

[@fernandohood5542]

3:42

[@OpeyemiAdelusi]

Question though: where do you buy the cores??

[@w0qe]

I have powdered iron cores from Micrometals, KitsandParts, Amidon, and various distributors such as Kreger. I have bought ferrite cores from Arrow, Mouser, and directly from FairRite. Also I have scored some really good buys at flea markets but then I have to go home and measure them to be sure what I have. I only buy these if the price is really good and the quantity is reasonably large. Sometimes you end up throwing them out. The previous names were all USA based companies. Larry, W0QE

[@OpeyemiAdelusi]

@@w0qe holy crap that was fast! Thanks man!!

[@w0qe]

@@OpeyemiAdelusi Just caught me at the right time! :) Larry, W0QE

[@OpeyemiAdelusi]

@@w0qe wow lucky break! I'm a subscriber now!

[@joiedevelos212]

can i use metal plate for toroid core sir ?

[@w0qe]

Joie, I do not understand the term "metal plate for toroid". If you are asking whether a toroid van be mounted on a metal plate the answer is maybe. A toroid that is standing up with the wires away from the metal plate would be ok but if the turns are against the metal plate the turns would have a lot of capacitance across then and the performance would be poor. Larry

[@joiedevelos212]

@@w0qe what i mean sir is we have metal plate here in our shop, 3" thickness , i plan to cut this to a circle to make a toroid core for my diy amplifier supply, my question, is this kind of metal is applicable for toroid core transformer ?

[@w0qe]

Joie, I think the performance you will get by machining a toroid out of solid steel will be very poor. Conventional transformer cores are laminated and made with special steel alloys to minimize eddy current losses. Toroid cores are not laminated but made with metal particles of nickel, steel, and manganese and other materials to control the core losses. The manufacturers of cores put a lot of research into minimizing loses for the intended frequency ranges that the cores are to operated at. Larry

[@hermanfrans9169]

🙋‍♂️👍👍👍🤝

[@hankhamner3671]

What is your formula for Ae?

[@w0qe]

Hank, At 4:00 in the video the core is shown with OD = outside diameter, ID = inside diameter, and H = core thickness. If the units are in cm then Ae = ((OD - ID)*H and has units cm^2. This of course is slightly exaggerated since the small effect of the rounded corners was not included but these effects are small. I might add that with the formula for inductance having Ae in the numerator means that stacking 2 identical cores will double the inductance. Larry, W0QE

[@AlejandroFedorov]

I doN'T understand why inductance is linear and not square dependence

[@w0qe]

In an inductor there is flux produced by current flowing in all the turns. If you have an inductor that is wound around a core with a very high permeability the flux produced in a single turn is seen by all the turns resulting in an inductance that rises as the square of the turns. However if you wind the inductor with no core (air) the flux produced by a single turn will diminishingly be seen by a few adjacent turns. This results in the inductance of an air core inductor rising more than just linearly for the first few turns and then linearly after that. Winding the inductor on a core with a permeability of about 10 will result in inductance that increases by the number of turns somewhere between linearly and squared. Does this make sense? Larry, W0QE

[@AlejandroFedorov]

@@w0qe yes, thank you very much

[@vivekneha15]

Can you send me the excel used in the vedio

[@w0qe]

Where should I send it to? Larry, W0QE

[@fernandohood5542]

frequency?

[@w0qe]

What do you mean?

[@fernandohood5542]

I am trying to step up I mhz voltage at 30v to 60v p-p at 200ma. My secondary is in parallel with a transducer(capacitor) and I calculated I need 25uh to make it resonate at that frequency. Which type of core is suitable for such frequency . There seems to be a parameter called volt time do I need to worry about this? What would you suggest to accomplish my objective. I am not skilled in this area so your assistance would be greatly appreciated.

[@w0qe]

Fernando, If you want the secondary of your transformer to be 25uH and to have 42.4Vrms (60Vpk) across it at 1 MHz I would probably use #61 (u=125) material. An FT-140-61 core would need 13 turns for 25uH but you might need to squish or spread the turns if you need exactly 25uH. The flux with 42.4Vrms across the 13 turns would be 88 Gauss which is comfortably below the 150 Gauss maximum that is generally used at 1MHz. You could also use a T106-2 core (u=10) with 43 turns which would have a flux of 32 Gauss which is below the 150 max. Gauss for iron powder cores at 1 MHz. Both these cores would produce nice high Q transformers and I would probably wind the primary on top of the secondary. The circuit with have peaking due to the resonance so I can't say how many turns you would need on the primary but SimSmith can easily calculate this given the transducer capacitance and resistance. If you are new to the channel and haven't watched many videos please look at the videos in the "Basics series" starting with video #75. Larry

[@fernandohood5542]

@@w0qe much appreciated. trying to find those cores on digikey. ui or ue is the same as u? -

[@w0qe]

Something like Digikey part #1934-1595-ND would be fine. This part is the same as a FT-140-61. Larry

[@ekiskaliburnirvana9047]

The problem is that nobody sells toroids anymore..

[@w0qe]

I either sample cores or buy them from distributors but in order to get decent prices I buy many more than I need. Over time I have collected a large assortment of materials and sizes. Most of the cores I have purchased come from FairRite or Micro Metals. Larry

[@richarde735]

I have four new 240-31’s arriving today, just searched for ferrite core and the type. they were $11 or $12 each.

[@stevenbliss989]

Sendust? Are they same acros the industry?

[@w0qe]

What is Sendust? Larry