Phase vs frequency graph of type 3 error amplifier?

[grizedale]

Hi,

Page 292 of the Basso book on smps gives the small signal transfer function for the TL431/Opto feedback network as a type 3 compensator.

When i work it through it in excel, i get the following phase vs frequency graph....

https://i56.tinypic.com/o5xcm1.jpg


....do you know if it looks right?

Why is there a big discontinuity at around 7KHz?

 

[mtwieg]

You should see -90 degrees at low and high frequencies, with a rise near +90 degrees in the middle, near your loop crossover frequency. Try doing a log frequency scale, starting at a lower frequency (like 100Hz) and it might take the right shape.

Also the discontinuity is apparently a jump from -90 to +90. Must be the specific math functions you used to calculate phase. Sometimes weird rollover like that occurs.