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Inverter LC Filter Calculator

Let’s say we have a push-pull or full bridge inverter and its output goes to the primary of a transformer, and the secondary gives you high voltage AC like 220V square wave.

Now to make this AC waveform smooth and more like a sine wave we connect an LC low-pass filter just after this secondary, like this:

Connections Details of the LC Filter:

Inverter lc filter

Now to caalculate the values of the L and C, you can use the following calculator:

Calculator by homemade-circuits.com

Inverter Output LC Filter Calculator





How to Decide this fc Value?

We do not want to block 50Hz because that is our main signal. We want to block the switching frequency harmonics like:

So we choose fc just above 50Hz but much below the unwanted high frequencies.

Rule of Thumb:

You can select cut-off (fc) between:

3 × main frequency......... upto 10 × main frequency

Example:

If your inverter PWM has big amount of noise like around 1kHz to 3kHz, then you pick fc = 300Hz, so that:

Final Tip:

So just take 5 or 6 times the 50Hz, then:

fc ≈ 50 × 6 = 300Hz

It is a safe and effective choice for LC filter to clean inverter waveform.

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