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Q&A Meaning of some components around voltage reference in SMPS

I have generated flyback convertor schematic by TI's Webench Power Designer. Parameters: universal AC input (85-265V AC) 5V, 2A output isolated UC3843A controller Basically I understand f...

2 answers · posted 3y ago by Chupacabras‭ · last activity 3y ago by a concerned citizen‭

Question component SMPS

#2: Post edited by

Chupacabras‭ · 2021-06-09T19:33:23Z (over 3 years ago)

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I have generated flyback convertor schematic by TI's [Webench Power Designer](https://webench.ti.com/power-designer/switching-regulator).
Parameters:
- universal AC input (85-265V AC)
- 5V, 2A output
- isolated
- UC3843A controller
Basically I understand flyback topology, but I do not understand the function of some components around voltage reference (LMV431 used there).
~~What are R21, C21, D21 for?~~
~~What are R22, C22, C23 for?~~
Just cut-out of the schematic:
![Just cut-out of the schematic](https://electrical.codidact.com/uploads/aHPGmdFeLPXFB4WijXcypunK)
Full schematic:
![Full schematic](https://electrical.codidact.com/uploads/VZaBxUDq4diBqVyUwwnL4zb8)

I have generated flyback convertor schematic by TI's [Webench Power Designer](https://webench.ti.com/power-designer/switching-regulator).
Parameters:
- universal AC input (85-265V AC)
- 5V, 2A output
- isolated
- UC3843A controller
Basically I understand flyback topology, but I do not understand the function of some components around voltage reference (LMV431 used there).
What are R21, C21, D21 for? How to calculate values?
What are R22, C22, C23 for? How to calculate values?
Just cut-out of the schematic:
![Just cut-out of the schematic](https://electrical.codidact.com/uploads/aHPGmdFeLPXFB4WijXcypunK)
Full schematic:
![Full schematic](https://electrical.codidact.com/uploads/VZaBxUDq4diBqVyUwwnL4zb8)

#1: Initial revision by

Chupacabras‭ · 2021-06-09T19:25:34Z (over 3 years ago)

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Meaning of some components around voltage reference in SMPS

I have generated flyback convertor schematic by TI's [Webench Power Designer](https://webench.ti.com/power-designer/switching-regulator).  
Parameters:
- universal AC input (85-265V AC)
- 5V, 2A output
- isolated
- UC3843A controller

Basically I understand flyback topology, but I do not understand the function of some components around voltage reference (LMV431 used there).  
  
What are R21, C21, D21 for?  
What are R22, C22, C23 for?

Just cut-out of the schematic:
![Just cut-out of the schematic](https://electrical.codidact.com/uploads/aHPGmdFeLPXFB4WijXcypunK)

Full schematic:
![Full schematic](https://electrical.codidact.com/uploads/VZaBxUDq4diBqVyUwwnL4zb8)

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