Electronic – DC power supply simulation trouble

acdcltspicepower supply

I'm trying to simulate a relatively simple AC->DC power supply in LTSpice, but it's not quite cooperating with me. I've followed this schematic:

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only replacing potentiometers with resistors due to my lack of LTSpice knowledge.

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Now, as you can see in the image above, I'm not exactly getting a clean DC signal out… What am I missing here?

Since my LM317 component isn't part of the schematic, I'll just upload a screenshot unless you really need the full file; however, it should be irrelevant as the same problem occurs even if I cut everything to the right of the 2200µF cap away!

Am I missing something in the design itself, or is this plainly a simulation problem? In either case, any suggestions on what is wrong?

Best Answer

You are not measuring the signals in relation to the circuits ground. Your (SPICE) ground point is on the output of the transformer before it goes through the rectifier. SPICE uses the ground symbol (node 0) as it's common reference.

You need to take a differential reading from your output to the circuit ground (e.g. bottom of C1)
To do this, click on the out node and drag the cursor to the circuit ground (you should see a red and black probe) and release.
You will see the signal labelled something like N001_N002 to signify it's not simply related to your SPICE ground point (wherever you put the ground symbol)

Alternatively you can move the ground symbol to the bottom of C1.

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