Topology with optocoupler

Posted by: Noir47 on 11/25/2014

Hello.

I want use LNK304 with optocoupler topology - Low-Side Buck-Boost Optocoupler Feedback, for getting 3.3V 0,1A non-isolated PSU.

Which zener diode and Rz should i use for it?
Also, what value of inductor L should be?

Thank for the answers.

Files

topology.png (63.71 KB)

scheme.png (3.15 MB)

Comments

Nobody doesn't know, huh?

Hi Noir,
Thanks for your posting your question into forum and we appreciate your time and patience.
The Inductor L Value you can design using our PIXLs Spread sheet. Please download PIXl's and enter your specification for LNK304 device Buck Boost, it will give the Optimal Value for your design specifications.
We did the design spreadsheet Calculation for your Output 3.3V and 0.1 A Output for Universal AC Range (85Vac-265 Vac), the Suggested Value is 680uH.
Since your output is to low 3.3V , Generally 3.3V Output is used for Powering Digital and RF Circuit,the tight regulation might not be possible with Zener Diode at the Output. LMV431 Feedback regulation circuit is recommended for 3.3V Output tight regulation.
However you can try 2V to 2.2V Zener and the Value of RZ is calculated by the test current that require for the zener diode. Since the RZ is Across the Output LED, the drop Across Rz is 1V . The RZ Value should be =(1V / Zener test Current(IZ). If you use the MMSZ4680T1G Zener diode part, the test current is 50uA. The RZ Value should be 20K.
Please let us know if you have any other questions.

Thanks,
PI-KSAN

Thank you for tips.

I change LNK304 to LNK306 to get a bit more of current.

I'm think that i can use TLV(LMV)431 feedback circuit OR zener diode + optocoupler for 5v and LDO linear stabilizer to get 3.3v.

I'm not sure what will more efficiently.

Thanks for posting question.
TLV(431)Feedback circuit works effectively and efficiently and you can avoid using LDO. LDO is an Extra Component and it might cost your BOM more as compared to TLV(431).

Regards,
PI-KSAN