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Power Transformer Model Inductance

Posted by deafbykhorns (A) on August 11, 2015 at 17:19:39

This is a spawn from the "Don't trust schematics" thread. First schematic is Dave's example.
Dave Slagle clarified how to model a power transformer in LT Spice.
"The inductance is simply the square of the voltage ratio so a 120:240+240 transformer would be a 1:2+2 voltage ratio or a 1:4+4 inductance ratio."
That being said, I modeled a power supply with a little higher inductance using his ratio above which gives me the same results (I believe it has a higher series resistance and poorer regulation?). If I zoom in on ripple voltage and show .7v ripple peak to peak (as an example). That would be less than .5v rms, correct? Can I apply that ratio to the OPT to calculate hum with given ripple (considering the gain also)? I hope I worded that correctly....
BTW, I had to play with the data label expression to correctly show the output voltage as text. Don't understand whats up with that, here's the formula to get the data- "round($*10)/-1". Weird, I normally don't have to do this with this in tube gain stages. Not sure how to express AC volts at the first label that shows 0V.

Also, does this inductance ratio apply to OPT's? If so, how would I calculate inductance on a 5000K:8ohm OPT? Do I assume secondary is .1H and calculate from there to model OPT's? Or am I over thinking this and simply call the OPT manufacturer for spec? I know some might like a certain (custom) transformer for a given design.

I think this method of power supply simulation has many advantages over the traditional PSUD program DIY'ers have been using. Although, the PSUD warns you when exceeding the limits of the device. I don't have an engineering background and have learned how to use the program quite well in a few months (about couple hours a week). I would recommend DIY'ers to give it a try, it's also cheaper to blow something up in a SIM ;-)

• Dave Slagle transformer inductance clarification   (Open in New Window)

Edits: 08/11/15 08/11/15 08/11/15

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