Equal to x peramps?? While resistance, capacitance, reactance and impedance have inverse units (conductance, elastance, susceptance and admittance), I don't know of any for inductance, voltage or current.

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Best wishes John Woodgate OOO-Own Opinions Only

Rayleigh, Essex UK

I hear, and I forget. I see, and I remember. I do, and I understand. Xunzi (340 - 245 BC)

On 2023-07-20 05:15, Richard Andrews via groups.io wrote:

Is there such a thing as x ohms/volt?

Is there such a thing as x ohms/volt?

?

Is there such a thing as x ohms/volt?

This is a suspended thread, but I am now able to look at the proposed tutorial The first question is, what sort(s) of transformer? While the basic theory is the same for all, the practical design methods vary considerably. There is no point in writing a tutorial that no-one is interested in.

I see the occasional query about a power supply having a mains transformer with inductances in the mH or less range, so there may be some interest in mains transformers.? I also see the occasional query about audio output transformers for tubes/valves.? I don't think anyone would try to wind their own toroidal, so we are talking 'E's and I's', maybe with the occasional 'T's and U's.

I'm not going to deal with transformers for SMPS, because they need a totally different approach, as do RF transformers with ferrite cores or no core.

======================================================================================
Best wishes John Woodgate OOO-Own Opinions Only

Rayleigh, Essex UK

I hear, and I forget. I see, and I remember. I do, and I understand. Xunzi (340 - 245 BC)

On 2023-04-29 19:50, Jim Wagner wrote:

BUT, what are those “easily measured or calculated parameters”? I am a circuit designer and have no idea what they are (or how to do the measurements)!. I strongly suspect that I am not alone. How about a tutorial for the wiki?

Jim

On Apr 29, 2023, at 11:06 AM, John Woodgate <jmw@...> wrote:

Many types of transformer do not need complicated models like Gummel-Poon for transistors, but of course complicated models like Chan can give more accurate results (often more accurate than is necessary, but that also apples to transistor models, which do not account for variations between samples). Simple models can use easily measured or calculated parameters, so it is easy to relate the model to the hardware.

Please note the new Subject line.

======================================================================================
Best wishes John Woodgate OOO-Own Opinions Only

Rayleigh, Essex UK

I hear, and I forget. I see, and I remember. I do, and I understand. Xunzi (340 - 245 BC)

On 2023-04-29 18:02, Jim Wagner wrote:

For me. the real transformer challenge is associating the physical parameters (dimensions, numbers of turns, core material, and such) into model parameters. One might reasonably assert that this is no different than, say, transistors. There is a big difference, though; I can build a transformer but I am not likely to build a transistor. I do not have the capability to measure transistors sufficiently to create models, so must rely on third-parties to do that. What third party do I use for that ferrite toroid transformer that i just built?

Perhaps the solution to this is a transformer model generator (like VDMOS tool). I can handle program writing but I do not know enough about magnetics to even think about something like that. To be useful, such a model generator should rely on measurements the most of us could do in a modestly equipped lab (say, with a signal generator and an oscilloscope).?

Jim Wagner

Oregon Research Electronics

On Apr 29, 2023, at 9:38 AM, Andy I <AI.egrps+io@...> wrote:

Susan wrote, "My big issue/stumbling-block when using 'spice simulators is transformer models; they all seem to be described in intractable terms making it difficult to translate something I have in my hand to an accurate simulation model."

That sounds like a topic for a separate subject (not this one).? The simplest transformer models are very simple.? It's the more complicated ones that can be challenging.

Andy

Jerry,

What causes a transformers inductance to decrease with increasing frequency?

It sounds like my model of how audio transformers work is too simple.

? --? Gavrik

On Wed, Jul 19, 2023 at 2:31?AM Jerry Lee Marcel <jerryleemarcel@...> wrote:

The only issue I see with that is that it doesn't take into account the fact taht inductance decreases as frequency increases.
The ratio is typically 4:1 between 20Hz and 20kHz.
So using the LF inductance all along results in using a too high coupling coefficient in order to agree with the HF response.
I routinely use 2 or 3 different values of Lnom depending on frequency.

Le 18/07/2023 à 18:31, ik.weide@... a écrit?:

For those who are interested in modelling tube amplifiers and the output transformers used:?I have a thread on DIYaudio? with easy to use LTspice transformer models.

There are currently 3 flavours: Push-Pull with ultra-linear taps, Ditto with extra cathode feedback windings and Single-ended. I am working on a Hammond 125A. Just enter the numbers from the transformer datasheet. All tedious calculations are done by LTspice in the model.
Something like [Rpp=8k Lpp=1220 UL=35 Cp=390p Rp=152 RS4=0.145 K=0.9999987] for an AMPLIMO Toroidal Output Transformer type 20PP8K0S.

Comments are welcome,

Ite

Jerry,

What causes a transformers inductance to decrease with increasing frequency?

It sounds like my model of how audio transformers work is too simple.

? --? Gavrik

On Wed, Jul 19, 2023 at 2:31?AM Jerry Lee Marcel <jerryleemarcel@...> wrote:

The only issue I see with that is that it doesn't take into account the fact taht inductance decreases as frequency increases.
The ratio is typically 4:1 between 20Hz and 20kHz.
So using the LF inductance all along results in using a too high coupling coefficient in order to agree with the HF response.
I routinely use 2 or 3 different values of Lnom depending on frequency.

Le 18/07/2023 à 18:31, ik.weide@... a écrit?:

For those who are interested in modelling tube amplifiers and the output transformers used:?I have a thread on DIYaudio? with easy to use LTspice transformer models.

There are currently 3 flavours: Push-Pull with ultra-linear taps, Ditto with extra cathode feedback windings and Single-ended. I am working on a Hammond 125A. Just enter the numbers from the transformer datasheet. All tedious calculations are done by LTspice in the model.
Something like [Rpp=8k Lpp=1220 UL=35 Cp=390p Rp=152 RS4=0.145 K=0.9999987] for an AMPLIMO Toroidal Output Transformer type 20PP8K0S.

Comments are welcome,

Ite

For those who are interested in modelling tube amplifiers and the output transformers used:?I have a thread on DIYaudio? with easy to use LTspice transformer models.

There are currently 3 flavours: Push-Pull with ultra-linear taps, Ditto with extra cathode feedback windings and Single-ended. I am working on a Hammond 125A. Just enter the numbers from the transformer datasheet. All tedious calculations are done by LTspice in the model.
Something like [Rpp=8k Lpp=1220 UL=35 Cp=390p Rp=152 RS4=0.145 K=0.9999987] for an AMPLIMO Toroidal Output Transformer type 20PP8K0S.

Comments are welcome,

Ite

I can answer my own question: editing the plot.defs file *immediately* has effect.
(I reran the simulation before trying but did not restart LTspice.)

Why don't they document these useful enhancements? Is it in any of the LTspice 
books or tutorials? I'm almost certain I tried this before with LTspiceIV and
it didn't work.