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Idea about Flyback circuit

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nikhillife11

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Hii all,

I need a bit of help with Flyback PSU circuit. In the image below I have marked a series resistor and capacitor in RED colour. I want to know why are they used and why the connection is from the I/p of primary of transformer to the ground of secondary winding.
Please help me to understand it better.

Thanks all.

Regards
Nikhil
 

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mtwieg

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My guess is that it is there to protect the isolation barrier across the transformer and optocoupler. At least the high voltage rating of the capacitor implies that.

My question is what's all that other crap on the secondary side...
 

Orson Cart

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THe RC is to reduce common mode noise propagation and help meet EMC standards, the total circuit is a forward converter - it's not a flyback - and all the other "crap" is the synchronous rectifiers using 2 mosfets instead of diodes, Regards, Orson Cart.
 

nikhillife11

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Yup Orson Cart

Your right,But can u help me with a bit of explanation that how theses capacitor and resistor in series works.. Can you give me a details knowlegde for the same please

thanks and regards
Nikhil
 

FvM

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Most SMPS, e.g. off-mains power supplies are using a single small capacitor to drain RF currents injected in the transformer between primary and secondary. I guess, that the designer faced an EMI resonance peak and found the series resistor helpful to reduce it. some SMPS have a small ferrite tube at a capacitor pin to supress resonances, but it's a compomrise, also reducing the capacitor effect.
 

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