Filter calculation for dc-ac converter

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jean12

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Hello there,can anyone help me to make calculation for dc-ac converter and determine the frequency with which I have to switch the Power MOSFET?
See the circuit herein attachment,I am repairing a dc-ac converter whith the following characteristics:

Power:750VA
Output Voltage:220V
Frequency:50Hz
That circuit in attachment is the one which were used but the controlling circuit was burnt so I want to design a new one but I thing I have to refer to the filtering circuit,

Please help on this.

Thanks.!!!
 

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  • diagram.bmp
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This simulation portrays my guess at what's happening.

AC square waves come from the H-bridge, then through a filter. The load sees a sinewave.



The coils have a 'choke' effect on AC going through them. The higher the carrier frequency, the less current they allow.

It's a question what frequency will cause a lot of current to go through C2 and C1.

As a guess I used 15mH for the coils, and a carrier frequency of 1.9 kHz.

C2 is exposed to large current spikes. Either 4.7 uF is too large a value, or something is wrong with my concept.
 

C2 is exposed to large current spikes. Either 4.7 uF is too large a value, or something is wrong with my concept.
Click to expand...
Just a stupid idea. Any capacitance value connected directly to the H-bridge output is unwanted or in other words "too large".

It will cause excessive switching losses and generate interferences. A large value like 4.7 uF is likely to kill the H-bridge. RC snubbers may be O.K. to compensate for a poor circuit layout.
 

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