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I am trying to make a model of a diode bridge rectifier in LTspice (it has to be connected to a transformer as it's part of a larger project).

I have tested the transformer and the rectifier independently and they seem to work. However, when I put them together, they don't work as expected (images attached).

The problem I'm facing seems to be the placement of the ground: when I place it near the transformer, so its AC ground, I am getting some waveforms, though not very clean. A little digging around suggested that I should have placed the ground at the DC side, but this does not give me any output at all. Any help would be appreciated.

When Ground is placed near the transformer: When Ground is placed near the transformer

The green waveform in the first image is the output of the transformer; the blue and red waveforms are at the top and bottom of the resistor respectively.

When Ground is placed near the resistor: When Ground is placed near the resistor

Scale is only upto 33 microseconds, there is a statement at the bottom which says that the analysis is 0% done.

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    \$\begingroup\$ You're using the ST model for the rectifiers? Maybe that's the issue. Also, please label your nodes with human-readable names. Things like n007 not only cannot be easily read, they can change if you modify the circuit. \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Feb 1, 2023 at 18:26
  • \$\begingroup\$ @SpehroPefhany I'm not using the ST models actually. That's the model I'm supposed to use for the project, which wasn't working, so I wanted to test it out with the default diode provide by LTSPICE. Apologies for not naming the nodes, I'm just getting started with the software. \$\endgroup\$
    – Aryan
    Commented Feb 1, 2023 at 18:36
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    \$\begingroup\$ The first image looks correct to me - this really is how your waveforms look when you use a diode bridge - both the + and - side are live and you shouldn't touch either one (if using dangerous voltages). In the second one I guess the simulator is having some trouble running the simulation even though the circuit is okay. Simulators using ideal diode models (are you?) it can run into similar issues because the transformer secondary has no voltage reference. What if you add some high resistance such as 10M ohms between one side of the transformer and ground - then does the simulation run? \$\endgroup\$
    – Criticizing Israel not allowed
    Commented Feb 1, 2023 at 18:45
  • \$\begingroup\$ @user253751 it does run, thank you! Added a 10M ohm resistor on secondary side. \$\endgroup\$
    – Aryan
    Commented Feb 1, 2023 at 19:07
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    \$\begingroup\$ @user253751 LTSpice does not follow that convention, so 1M = 1m = 0.001 ohm \$\endgroup\$
    – PStechPaul
    Commented Feb 2, 2023 at 2:17

1 Answer 1

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Try replacing the diode models with real diodes of adequate rating for the situation (right click on the diode, pick new diode).

Or put a resistor (maybe 20kΩ) across the input to the bridge rectifier.

You've got something there that's too ideal and likely causing some issue with the solver. It's nothing directly to do with the placement of the ground.

Here it is working with a real diode model (with the default diode model it has issues)

enter image description here

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