Voltage mode, DCM Flyback, Small signal Power stage equation is incorrect?

[treez]

Hello,
Please check the Small Signal power stage transfer function of a Voltage mode, DCM Flyback as given on Equation 17, page 12, of AN-57 by Power Integrations...

AN-57:-
https://ac-dc.power.com/sites/default/files/product-docs/an57.pdf

This equation is very different from the one (equation 2A-20) given by Dr Basso on page 232 of his book “switch mode power supplies” (page attached below).
(Basso’s equation 2A-20 is for a buck-boost, but as you know, this is the equivalent to the flyback)

(Incidentally, “Vpeak” of equation 2A-20 refers to the peak of the voltage mode ramp generator)


When the above Equation 17 is used to calculate the open loop bode plots, it gives a nonsense crossover frequency value of 100khz (above the switching frequency). The excel document that I used to do the bode plots using Equation 17 is also attached.

 

[treez]

Page 13 shows transfer function of Voltage Mode, DCM Flyback:-
http://www.icbank.com/icbank_data/online_seminar_image/Flyback_CCMVsDCM_Rev1p2.pdf

Again, this confirms that the transfer function of Equation 17 (page 12) of document AN-57, is clearly incorrect. For one thing it doesn’t contain the Switching Period in it, whereas the other sources do have it in their equations. Do you agree? The Transfer function of Voltage mode DCM flyback must have the switching period in it.

 

[treez]

Table 2, page 6 (equation 17) of the below article shows the Voltage Mode, DCM Buck-boost control-to-output transfer function..


Hangseok Choi SMPS feedback loop article:
"Practical Feedback Loop Design Considerations for Switched Mode Power Supplies"
https://www.fairchildsemi.com/techn...erations-for-Switched-Mode-Power-Supplies.pdf


For some reason, Dr Choi totally omits the ESR zero in his expression. However, compared to the equation 17 in the AN-57 document (above), Choi’s equation again contains the “Vp” parameter, which is the peak to peak amplitude of the ramp signal of the voltage mode controller.
Equation 17 of AN-57 totally omits this and must therefore surely be wrong?