Opto-coupler pole in isolated SMPS

[eem2am]

isolated smps

Hello,

On page 12, 13 and 14 of AN1059 application note they do the feedback compensation for the L6561 flyback power factor corrector circuit.

However, considering the equation at the bottom of page 13 (H(s)), or any other transfer functions listed, -None of them include the effect of the opto-coupler pole.

****AN1059 Flyback PFC application note.
http://www.datasheetcatalog.org/datasheet/SGSThomsonMicroelectronics/mXyytxs.pdf

In relation to this, -pease may I quote from Basso’s book, page 322………

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“Compensating the power supply without keeping in mind the opto-coupler pole position is useless. Always measure or compute the pole position and include it in the loop design process to avoid last-minute bad surprises”
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The AN1059 application note clearly has taken no account of the opto-coupler pole.

Do you know how this can be so?

Thankyou very much for reading.

 

[erikl]

...
The AN1059 application note clearly has taken no account of the opto-coupler pole.

Do you know how this can be so?

Thank you very much for reading.

I guess the opto-coupler's frequency bandwidth is so far beyond the rest of the PFC circuit's bandwidth that it doesn't have to be taken into consideration (i.e. is negligible).