Need help with ×-Device Transformer parameters

QSPICE
1

I have a transformer I am trying to model using the X-device in Qspice. I “think” the three most important parameters for my circuit are…

L - Primary zero-current inductance (I am assuming this is the inductance of the primary winding with no current flowing?) However, I am told that inductance varies with frequency, so I’m not sure what to make of this. I believe the inductance is 26H.

RSER - Primary Series Resistance. (I think this is the static resistance of the primary winding?) According to the datasheet this is 50ohms.

RPAR - Primary Parallel Resistance. (If my resistance of primary is 50 ohms, and secondary is 50 ohms. How do I find this RPAR?

Here is datasheet pic of static resistances
static

2

Could you please provide the link to the datasheet of the transformer you are trying to model? I presume you are working with a signal transformer in the audio application.

There are two primary reasons why inductance varies with frequency:

  1. The permeability of the magnetic core is always frequency-dependent.
  2. Parasitic elements such as winding capacitance can alter the equivalent inductance. In modeling, sometimes the simplified version of an inductor/transformer only includes inductance and resistance, while in reality, it also involves parasitic capacitance. At higher frequencies, the effects of this capacitance can become dominant and the modeling needs including that.

In general, you would only need to consider a complex model if your goal is to model the transformer beyond its typical application frequency.

3

Here is the link to the transformer. It’s the 1570, not the 1570XL

https://www.lundahltransformers.com/wp-content/uploads/datasheets/1570_0xl.pdf

I am not operating this transformer beyond it’s frequency range. So you’re right, Im probably worrying for nothing. I am getting a little worried about the windings acting like a hidden resistor, or inductor. Causing a corner frequency that I am not aware off. I worry about my bode plot being affected by it.

As you can tell, I have no idea what I’m doing half the time. But thank you Kelvin.

4

In this datasheet, it only provides static resistance of each winding, but without inductance. Static resistance is refer to series resistance of each winding. Possibly this part is constructed with a very thin wire with many turns. From this datasheet, winding inductance (i.e. primary or secondary inductance) is not provided, but can be expected as a very large number as its frequency response claimed that 10Hz to 200kHz with +/- 0.5dB change of gain. This transformer can still act as an effective transformer at 10Hz, its inductance has to be large!
Parallel resistance is not given, and in inductor/transformer model, parallel resistance is in general modeling the loss of core; may be can be ignored in this transformer modeling.

image
image701×343 60.9 KB

In short, with limited information from datasheet, it is a challenge in getting its model. But I still want to show you, how the frequency response in this datasheet can be simulated.

Frequency response states that, between 10Hz to 200kHz, gain is +/-0.5dB.
Test condition is that, source with 600ohms, this represents signal source with source resistance 600ohms; serial-serial connections, which represents two primary windings are connected in series. And the load is same as above, where secondary windings are connected in series, and with a load = 2.8kohms in series 0.7nF

As a results, we can setup a model likes this to verify if the gain can within +/-0.5dB.
You can see value are double as two winding are in series. Gain is refer to measurable output and input voltage relationship of LL1570.
In this setup, you can change Lwinding and can alter the frequency response.

You can use coupled inductor model or ×-Device. I don’t use Rser in ×-Device, as instance parameter of ×-Device only model primary side but not secondary, and in your case, for schematic to visually looks more understandable, I use external resistance to model both primary and secondary resistance.

LL1570 (coupled inductor model).qsch (5.5 KB)
LL1570 (×-Device).qsch (5.7 KB)

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image1309×459 41.1 KB

5

If I wanted to wire this in parallel instead of series, I could input 50/2 instead of 50*2. Would I also need to do Lwinding/2?

This is very good stuff here. Thank you.