LM2575: I want to separate parts of 3V3 Power.

Hello

You should be able to connect the 3.3V regulator input to the 24V.

Depending on your load current and device package, you will need to check the

power dissipation.  

You can also try to use an input filter on the input of the 3.3V supply.

Depending on what kink of noise you are seeing you will need to experiment to find the best solution.

Thanks

Dear Frank,

Thanks for your answer.

above circuits is parts of audio device under development.

Audio noise is generated by parts using 3v3 power.
(I checked that there is no audio noise by applying 3v3 power to external power.)

So, I would like to design the 3v3 power circuit so that it does not affect the 18V power circuit and the 5V power circuit.

Please, Inform me tips modify that circuits.

Thank you.

Best Regards,

Inho Jeon

Hello

Please provide a 'scope shot of the "out"

node and the output voltage of the design.

I will re-assign this post to Sam, who can help you 

going forward.

Thanks

Dear Frank,

I attached files. That is  'scope shot of the "out"  about 3v3 power output.

Thank you.

Best Regards,

Inho Jeon

Dear Frank,

I attached files. That is node and the 3v3 output voltage of the design.

Audio_Devices.pdf

Thank you.

Best Regards,

Inho Jeon

Dear Sam,

Thank you for reply.

I probed 'L1'(part no.) near 3.3V output.

And, Please inform me inductor you said to 18VOUT to the input of the 3.3V and 5V power.

Thank you.

Best Regards,

Inho Jeon

Dear Sam,

You mean add serial 1~10uH Inductor with parallel 1~10uF caps
on 3.3V & 5V input DcDcConv, is that right?

Please, inform me specifically.
Best Regards,
Inho Jeon