feedback compensation in SMPS.

[eem2am]

I would like to know if resistor R17 (120K) at the bottom of Figure 9, Page 3-17 is part of the feedback compensation components, or is it simply a potential divider resistor?

In other words, does R17 have an effect on the phase margin and the gain margin?

The document I refer to is slua124 ……….

“THE UC1901 SIMPLIFIES THE PROBLEM OF ISOLATED
FEEDBACK IN SWITCHING REGULATORS”

**broken link removed**

….a Unitrode Application Note

 

[berni80]

I would like to know if resistor R17 (120K) at the bottom of Figure 9, Page 3-17 is part of the feedback compensation components, or is it simply a potential divider resistor?

Of course is a potential divider but it also affect the static gain of your fb loop.

In other words, does R17 have an effect on the phase margin and the gain margin?

R17/R16 can "move up an down" your gain bode plot (in the output to control transfer function) and then this affects the phase margin and the gain margin (in the closed loop transfer function).

R17/R16 do not change your poles and zeros.

I hope this can help you.

 

[FvM]

R17/R16 do not change your poles and zeros.

I think it does, because it defines the discharge time constant of the demodulator C11. Unfortunately it's a non-linear circuit that can't be excatly represented by a pole. But R17 is effectively shorted by the OP's virtual ground node and the C11*R16 characteristic frequency is most likely above the frequency range of interest.