Feedback point for flyback smps
Hi,
I have flyback topology for utility meter. I use LNK362GN and TL431 for switching and feedback. In your application notes and PI expert, I have noticed that feedback point is before inductor or ferrite bead. What would be happened if I select feedback point after the inductor? I mean, as seen in the attachment, what would be happened if I select the feedback point 'B' instead of 'A'?
Best regards,
Mehmet.
Comments
When I select 'A' point, my RFID card works worse because it is near my transformer. But when I select 'B' point, my RFID card is not affected. Therefore, I want to select 'B' point. Is it change smps function or emc performance badly?
Hi mkilicaslan,
Thank you for using PI product on your design. It is better to sense the feedback from point A. The inductor (L2) and capacitor (C5) will introduce POLE in the system if you select point B. The pole might worsen your ripple and might also worsen the dynamic response. Check your ripple and transient response. If it passes your requirement, then there is no problem to sense at point B.
Best Regards,
PI-SvenofNine
Hi mkilicaslan,
Thank you for using PI product on your design. It is better to sense the feedback from point A. The inductor (L2) and capacitor (C5) will introduce POLE in the system if you select point B. The pole might worsen your ripple and might also worsen the dynamic response. Check your ripple and transient response. If it passes your requirement, then there is no problem to sense at point B.
Best Regards,
PI-SvenofNine
The feedback is made using R58 and R62. Your selection is only relating the current supply through the LED of the Optocoupler. The TL431 sets up the current value;so it is stable even it is connected at point A