SMPS feedback compensation

smps feedback compensation

Hello all,

I am reading into pole zero analysis etc for compansating an smps.

it is difficult for me and i am wondering of this easier analysis to be applied.....

The feedback divider voltage is going to be delayed by the feedback components......that is, the feedback compensation components will filter the feedback voltage.......the amount of filtration depends on the loop gain and phase.......i am thinking...

is the following postulation correct...?....

If SMPS output is oscillating...then that means that more filtration needs to be applied to the feedback divider voltage ? (ie caps need increasing in value...resistors need decreasing in value)?

If SMPS transient response is too slow...then that means that less filtration of the feedback divider voltage is needed (ie resistors need increasing in value..and caps need decreasing in value)?

smps feedback

here a simple circuit of smps

analysis feedback smps

grittinjames,

not sure how that circuit helps the OP.

eem2am, you can find good information for feedback on some of ST's Flyback converters with 6561 application notes. They go into pole analysis in some detail.

If you've got severe oscillating problems I would be looking at the resistive biasing of the feedback network to begin with - if the gain is too high this can cause the smps ic to restart causing oscillation (depends somewhat on the ic you are using).

oddbudman

smps resistors

Hi,

If you start adding more caps it will delay more your feedback, and leads to heavy oscilattions.
there is no caps required in feedback path. if it is there shuld be in not more than some pf

simple smps feedback

Thankyou grittinjames..

though i believe caps are often put in to speed up the feedback...not delay it....thinking of a cap across the upper divider resistor...that atually sppeeds up the feedback voltage getting to the error amplifier.

smps transient response

i agree caps across upper divider will speed up.
but all the high freqency noise will reach to yr error amp directly.
if frequency compensation option is there in your error amp
i think you can have some correction there

smps oscillating

thankyou grittinjames...i take exactly your good point...

and of course we may stop some of that high frequency noise form getting to the error amplifier directly by not just putting Cap across upper divider resistor...but putting an RC series across the upper divider resistor.