I need to design a DC to AC inverter circuit that will take a regulated DC voltage (likely in the 10V to 12V range) and convert it to 120VAC at 400Hz, with an AC current draw of 0.3A.

I have looked at several web pages that detail the design of such a circuit, but I have yet to find one that describes how to choose the transformer (how to pick the correct part on say Digikey). enter image description here

Here's one example design: https://www.electronicshub.org/12v-dc-220v-ac-converter-circuit/

How do I choose the correct transformer on digikey?

If I have a 12V DC square wave, I think I need a 10:1 windings ratio in my transformer. But digikey does not list the windings ratio as part of its specs for power transformers. What am I missing here?


  • \$\begingroup\$ Surely it specifies input and output voltages. These will get you within 5% or 10% of the winding ratio (thanks to transformer losses). You will have to deal with the same losses in the reverse direction. \$\endgroup\$
    – user16324
    Sep 24, 2020 at 20:35
  • \$\begingroup\$ I'd strongly recommend learning how to draw standard schematics (and at least as importantly, reading them): This is unnecessarily hard to interpret for someone who's got an education in electronics. Anyway, you're planning to output 36 W, so your low-voltage side needs to feed the same power through the transformer. That inherently defines the average current your transformer's primary will have to withstand, and the power your transformer core will have to be able to work with without saturation – go from there. This project is liable to killing people, by the way, so be extra careful! \$\endgroup\$ Sep 24, 2020 at 20:48
  • \$\begingroup\$ (to be a little more specific: this cartoonish version of a schematic suggests you might not be at a point where you can fully understand how this works, and that means you'll have a hard time understanding why you need a transformer with specific properties. Also, it worries me that you'd be doing a project with such a high level of lethal danger at this level of understanding. Maybe start with an inverter that doesn't try to kill you with its voltage?) \$\endgroup\$ Sep 24, 2020 at 20:50
  • \$\begingroup\$ I just copy/pasted this image from the tutorial webpage linked above. I didn't draw it myself. \$\endgroup\$ Sep 24, 2020 at 21:08
  • \$\begingroup\$ Note the 2N2222 is rated C-E vmax of 40v. If this is for an automotive application, it won't survive. Well it will, until one day it catches fire for "no good reason." \$\endgroup\$
    – rdtsc
    Sep 24, 2020 at 21:16

1 Answer 1


The turns ratio kind of implied on Digikey. They instead list the input voltage and the output voltage which you can then use to calculate the turns ratio if want to. Generally it's useful to know what the voltage ratings are because if you apply a higher voltage than what it's rated for, the transformer will saturate a lot quicker, or the insulation winding may not be able to handle it. I found this transformer that may suit your needs. It's slightly oversized, but that helps lessen any potential voltage sag.



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