buck converter design; selecting the input capacitance ripple voltage

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Thread Starter


Joined Jun 14, 2016
Hey everyone

So, I'm looking forward to building a buck converter circuit based on this schematic right here.

the transistor will be controlled by an MCu, furthermore the AC input is from the power line which in my case is 220V 50Hz. My final output is to be 3.3V DC.
Coming to determine a value for the capacitor labelled Cr in the schematic, I know the that the formula of the ripple voltage is : Vr = Vm / 2fRC
Where Vm is the peak voltage of the AC voltage source, f is the frequency of the input signal, R is the resistance seen by the capacitor Cr basically and C is the capacitance of the Cr.
I'm guessing the R in this case will be of the transistor right? thing is how can I determine the resistance of the transistor in such a case, given that my signal is pretty much DC.
Any help would be highly appreciated.

Thank you!
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