Questions about Buck converter

Thread Starter

BLUE_FLAVOR

Joined Apr 3, 2024
4
What is the role and purpose of the 470uf capacitor?
Is it simply disconnected because it's connected in parallel with 330uF?

And 5 pin out is 15V pulse or low pulse?

What is the expected transformer ratio?

1712309208935.png1712309251882.png
 
Last edited by a moderator:

BobTPH

Joined Jun 5, 2013
9,137
What is the role and purpose of the 470uf capacitor?
Is it simply disconnected because it's connected in parallel with 330uF?
Its purpose is to supply transient current when the buck regulator switches on.

It is not in parallel with the 330uF capacitor. They are only in parallel if both terminals are connected together.
 

MrAl

Joined Jun 17, 2014
11,565
What is the role and purpose of the 470uf capacitor?
Is it simply disconnected because it's connected in parallel with 330uF?

And 5 pin out is 15V pulse or low pulse?

What is the expected transformer ratio?

View attachment 319177View attachment 319178
Hi,

Batteries usually have some series resistance and wires have both that and series inductance. These two factors cause a voltage drop expecially for fast rise times. This means it is worthwhile to have some energy storage close to the power switch transistor so the energy from input to output can be transferred faster. That's more important as the switching frequency goes up.
Typically those caps are also of the low ESR type so they can supply a lot of energy very quickly without too much voltage sag.

Amazingly, that capacitor placement also has the side effect of allowing the battery to last longer in real life circuits.
 
Top