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I'm trying to simulate a simple full wave rectifier in LTSPICE. The output I am getting is not what I am expecting. In the picture below, the green line is the voltage output from the + terminal of the sine wave, the blue line is the - terminal of the sine wave and the red line is the output directly from the bridge rectifier (just prior to C1).

LTSPICE Circuit and Output

It looks to me as if there is a problem with the sine source, in that it's increasing. I've deleted the circuit several times and redrawn, and I've restarted the whole schematic file again several times. If I just place in a single sine source connected to ground and nothing, I get the expected output (cycling between +/- 34V) but as soon as I connect the - output to a circuit, it all goes crazy.

What am I doing wrong?

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  • \$\begingroup\$ There is a (possibly hidden) place to add series resistance in V1. Make sure that "Parasitic Properties" Series Resistance is set to 0, and I would suggest checking off "Make this information visible" \$\endgroup\$ – Spehro Pefhany Feb 6 '16 at 2:02
  • \$\begingroup\$ Thanks for the suggestion - I found the setting for series resistance and it was blank. I added a 0 to see if that would change anything, but same output unfortunately. \$\endgroup\$ – user3081739 Feb 6 '16 at 2:16
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    \$\begingroup\$ Hint: If you go to: LTspice \ Control Panel \ Waveforms and left-click on the "Plot data with thick lines" box, it'll make the plotted waveform very much more viewable here. \$\endgroup\$ – EM Fields Feb 6 '16 at 8:19
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I think you should be displaying the differential voltage across V1 since it isn't ground referenced. The output (which is ground referenced) is behaving as expected. I don't think that waveform you are seeing makes sense though..

BTW, there is a (possibly hidden) place to add series resistance in V1. Make sure that "Parasitic Properties" Series Resistance is set to 0, and I would suggest checking off "Make this information visible".

Edit: This simulation behaves similarly when I simulate it, and it's due to the bottom end of the source floating around. If you connect a 100K resistor from the bottom end of the source to ground it does not affect the output voltage but the top of the source looks more like what I think you would expect:

enter image description here

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    \$\begingroup\$ Thanks, this worked - I'm unsure how it produced the initial graphs but by right clicking the - terminal of the source and selecting "mark reference", I get the correct sine output. Thanks! \$\endgroup\$ – user3081739 Feb 6 '16 at 2:41

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