Theoretical understanding of XL 1509

[anso-engineer]

Hello,
I am trying to wire this IC to my circtuit for reducing voltages from 12V, so good to understand the purposes of those elements. And the nominals for them choosed, because for 3,3V option there is bigger Cout capactior and more less L1.

Also I am not sure about needance of D1, is it for reverse current protection?

 

[MrAl]

Hello,
I am trying to wire this IC to my circtuit for reducing voltages from 12V, so good to understand the purposes of those elements. And the nominals for them choosed, because for 3,3V option there is bigger Cout capactior and more less L1.

Also I am not sure about needance of D1, is it for reverse current protection?

View attachment 148548

Hi,

D1 is sometimes called a "catch diode" in that it conducts when the voltage on the left side of that inductor tries to go negative and thus still allows the inductor to provide a positive output during that time. This is the time then the internal transistor turns off.
This is typical for the usual buck circuit. It does have to be a high speed diode like a Schottky though.

 

[Les Jones]

D1 is needed to provide a path for the current when the switching device in the XL1509 switche off. During the time that the switching element is off the stored energy in the inductor powers the load. I suggest that you google "how switching regulators work."
Les.