Hello

I really need help in this. i know how open loop buck converter works,
but i don't know how does closed loop buck converter works.. pls help

 

Hello,

What do you need to know about this? There are various aspects of the circuit.
Also, do you already know how a linear (non switching) regulator works?

 

Hello

I really need help in this. i know how open loop buck converter works,
but i don't know how does closed loop buck converter works.. pls help

Maybe the first thing you need to decide - is PWM or burst mode.

 

Well in a closed loop system the output voltage is monitored and some aspect of the control is altered to raise or lower the output voltage ass appropriate.

 

@ian field is PWM mode...

 

@ian field is PWM mode...

One of the simplest PWM buck designs is the hysteretic.

There are some reference designs incorporating linear type regulators as voltage sensing devices incorporated within a hysteretic design.

IIRC; the TL431 application notes include such a circuit example - most of the main manufacturers include pretty much the same examples in their appnotes, but the hysteretic design isn't in every manufacturers offering.

 

In general a closed-loop buck converter feeds back voltage from the output, compares it to a desired reference voltage, and adjusts the PWM duty-cycle to keep the output voltage at the reference voltage (negative feedback).
If you use linear feedback, the loop will generally require some frequency compensation circuits to stabilize the loop and prevent it from oscillating.
If it's a hysteretic (bang-bang) converter than you don't need compensation.

 

@crutschow thanks the tips. i roughly know what is going..
do you have any website link regard of get the transfer function of buck converter???