# How to filter transformer output

• posted

Could some electronics guru please help ? I have a SPICE simulation of a simple inverter(DC-> AC). The output of the transformer is a square wave within some rails. If I pass it through a smoothing filter (e.g., RC with cutoff at 60.0Hz), the output is in the mV. In this case, what is the best way to remove higher harmonics from the square wave output ?

• posted

Makes no sense to use an energy dissipating RC to filter a /power/ inverter output. See the advanced techniques section on harmonic elimination through PWM techniques

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• posted

On a sunny day (Sat, 15 Oct 2011 07:54:38 -0700 (PDT)) it happened Daku wrote in :

Tune it.

• posted

Sounds like your spice simulation is broken. If you posted it in LTspice someone might look at it. But as Fred B. said, "Makes no sense..."

George H.

• posted

A square wave contains lots of odd harmonics. Build your filter's cutoff to be after the 2nd harmonic. But remember that there's significant energy in the harmonics, so the filter will be absorbing lots of energy. Efficiency will be in the tank. Better to look into a PWM or stepped square wave solution.

```--
David
dgminala at mediacombb dot net```
• posted

reduce saturation of the primary or increase the frequency.

Something along those lines.

Jamie

• posted

A series inductor and parallel capacitor will do fine. But, be careful of SPICE simulations. You can get great filters by optimizing just one parameter like voltage, and then discover that the currents are 1E12 Amps. In other words, the simulation is entirely mathematical, and not necessarily bound to the real world.

Jon

• posted

1) Select how much power you want to lose. 5% 10% 20%? You are stripping off power harmonics 3,5,7,9 etc and wasting it away as heat. See power contributions of the harmonics of a square wave. 2) Then you can select your cut off frequency and filter order. 3) Then select your filter topology. LC or RC sections.

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