LM2576 output filter L & C values

[manishanand14]

Hello Guys!

Please tell me how they have calculated the values of L & C in the output filter[as given in the datasheet].
I guess it has something to do with 52 kHz fixed frequency internal oscillator.
This is the diagram taken from the datasheet.


Also tell me how one can CALCULATE the output filter component values for LC filter in general for a switching type regulator.

 

[goldsmith]

Hello Guys!

Please tell me how they have calculated the values of L & C in the output filter[as given in the datasheet].
I guess it has something to do with 52 kHz fixed frequency internal oscillator.
This is the diagram taken from the datasheet.
untitled.png

Also tell me how one can CALCULATE the output filter component values for LC filter in general for a switching type regulator.

Hi manishanand14

It is so simple ! for a buck converter Lout = [5(vi-vo)/In]*(Vo*t/Vi) where In is nominal out put current .
And for out put capacitor there are many ways to calculate , but one of the simplest ways is : C=In/Fpwm*vrpp

Best Wishes
Goldsmith

 

[manishanand14]

What about the changes in input voltage supply.

Also output voltage can be changed.

Also how you have calculated the values .I need the fundamental concepts.Some theory to refer to.

 

[goldsmith]

Re: LM2576 output filter L & C values

What about the changes in input voltage supply.

Also output voltage can be changed.

And you tell me what is the duty of feedback network in an SMPS ? and also how a buck converter does work ? of course a feedback system will try to keep the out put constant ! and if you try to understand art of buck converter you'll get how it will do it and why out put is constant .

Also how you have calculated the values .I need the fundamental concepts.Some theory to refer to.

You need to refer to the pressman's book ( switching power supply design ) - page 26 . it demonstrated that how to obtain that formula by equation of inductor current and some approximations , as well .
Best Wishes
Goldsmith

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In addition , when you want make a variable PSU , you need to design your filter for maximum out put variations .