TNY280 SMPS feedback design, step response testing and compensation

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I am using TL431 and optocoupler for feedback purpose. I have below given queries about feedback system
1 What is operation mode of optocoupler in feedback circuit- Linear or saturated ?
2 I need to understand how to design feedback system using tl431 and optocoupler and its response to step change in load
3. How feed back affect load and line regulation?
4. How to test stability of feedback circuit and what is compensation circuit?
5.Suggest design note for the same

Thanks and Regards,

Good day!

The TL431 should be operating in linear mode, since the varying voltage should be the basis for feedback, If it is operating in saturation mode, it would be difficult to design a feedback system because it would either be high or low. A TL431 may be used for tighter output voltage regulation.

Feedback system and loop compensation is not needed in using the TinySwitch family; it uses a simple ON/OFF control scheme. Feedback does affect line and load regulation, however, the IC responds rapidly, and should be able to meet line and load regulation requirements.

For further design references, you may check out the following link: