Feedback compensation on the primary or secondary side (SMPS)

[azadfalah]

Hi friends,


TL431 is usually used in the feedback section of the switching power supply

What is the difference between the two?
if TL431 is in follower mode and compensation is done on the primary side
Or the internal OPAMP of the IC switching is in the follower mode and the secondary compensation is done by TL431 ( Usually this is seen )

Which mode is better?


compensation is done by TL431 in secondary side

 

[Easy peasy]

please show example of TL431 in follower mode ?

 

[cupoftea]

Yes i am also interested in what you mean by "TL431 in follower mode".
But i will stick my neck out and say that the TL431 must act as error amplifier, (and the primary side IC as "follower"), since only the TL431 can "see" the output voltage. The controller on the primary side, has no way of knowing what is the output voltage.
Unless you are speaking of non isolated SMPS?...but then you probably wouldnt be using an opto

 

[Easy peasy]

@cupoftea, correct, the only output follower is by linear opto, e.g. IL300

 

[crutschow]

The TL431 cannot operate in a "follower mode", whatever that is.