Im building an ac/dc converter for a battery charger, it takes in 120V AC in and outputs 90V DC at 20A max. To further improve the output performance of the buck converter, i decided to build a pi filter containing 2 capacitors and an inductor..it is essentially used to filter harmonics at at 100 kHz. What do you think of the schematic?

 

If that ground shown is an earth ground, this will have problems, due to lack of an isolation transformer. The full line current will flow through a diode at one point in the cycle. I'm not sure if it's still against policy to discuss non-isolated off-line power here - it was at one time.

 

As long as your input AC is from an isolation transformer, your ok, if your thinking of using a transformerless mains input, forget it, Too Dangerous
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To what use will you put this power supply? -Will the load be floating?

 

Why are you concerned about harmonics in a battery charger?

 

On second thought, this is exactly the kind of mains powered project that is prohibited by the User Agreement.
http://www.allaboutcircuits.com/user-agreement/

Excerpt:

Restricted topics. The following topics are regularly raised however are considered "off-topic" at all times and will result in Your thread being closed without question:

• Any kind of over-unity devices and systems
• Devices designed to electrocute or shock another person
• LEDs to mains
• Phone jammers
• Rail guns and high-energy projectile devices
• Transformer-less power supplies