A tale of two simulators

LT spice, Curve Captor, PSUDII and whatever other sims you can think of.

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A tale of two simulators

Post by ampman1952 »

The attached file refers
I have put this schematic through LTSPice as well as the Duncan Amps PSU Simulator - and got very different results for the output voltage. The results from the Duncan Amps simulator are more believable with the resulting voltage being close to 1.414 * AC Voltage. The results using LTSpice project an output voltage of 1 * AC Voltage - no matter how I tweak the values of the inductors, the voltage at R2 on the diagram hovers stubburnly at 250 VDC.

The experts on this forum are free to send me to the back of the class for missing something obvious, :oops: but nevertheless I would be grateful for some advice on where I have made an error.

Cheers, and wishing you all a Happy New Year :)

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dave slagle
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Post by dave slagle »


I'm not sure about PSUD, but LT spice refers to AC in the peak form rather than RMS. So your 250V peak at your input is actually 175Vrms. I suspect if you change your input voltage to 350V in LT spice (representing a 250Vrms voltage) your results will make more sense.

happy new year!

Get Your Fix
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Post by sbench »

Dave is right, and something that trips up some people using LTSpice. The value that you enter in LTSpice for "amplitude" is peak, not peak to peak nor RMS. You can easily verify this by plotting that "250 volts" in LTSpice.

As entered, the rectified output should hover near 250 volts, not 350 volts as you observed.

PSUD lets you enter the value in RMS IIRC, and does the conversion internally. The results of the two programs are remarkably close in their results.

Happy New Year all!

Stephie <3
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Post by nl3prc »

If you want to enter 250vrms in LTspice you take 250*1.4141=353.525
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