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What is FL1 pin in transformer??

Posted by: nscw2011 on

Hello.

 

I try to design flyback converter with PI expert.

My flyback converter have 3 floating output. So each output need 2 pin from transformer.

Two 15V 0.5A and one 5V 1A.

 

As checking out the output, I found something weird thing at transformer construction tab.

I selected EF20 bobbin which have only 5 secondary pin.

But PI expert used 6 secondary pin for output and that pin named FL1.

 

I have question about transformer pin named 'FL1'.

What is that FL1 pin is?

I have no idea that pin is came from.

Can anyone tell me what is that pin and where is that pin located in actual transformer? or any clue? so i can google it.

I'll try to attach every pdf file that PI expert showed me.

 

Thanks in advance.

Files

Attachment Size
TinySwitch-III_PIDesign3.pdf 2.33 MB
asdf.png 7.4 KB

Comments

Submitted by karim19 on 07/28/2021

Hi,

There is no pin, FL1 means flying lead, as EF20 is only 5 pins and you need 6 pins on the secondary side, you will connect straight to the PCB one of the secondary winding "FL1" otherwise you will need to look after a bobbin with 6 pins on the secondary side (you might need to switch to a bigger transformer or use a custom bobbin, you don't want it if too expensive)

 

 

 

Thanks karim19 :)

Thanks for help me!!

hope you have great day!!

I guess i'll just connect that flying lead pin to unused primary pin and connect to PCB.

Submitted by PI-Yoda on 07/28/2021

FL1 stays for Flying Lead1 and is used as automatic assignment when PIExpert cannot accommodate the required winding's ends to the pins available.

Yes, you can connect it to an empty primary pin but you have to be aware of three possible issues.

  1. Safety violation. Check the creepage and clearance to make sure that your design is safe.
  2. If the lead is transferred to the primary side internally, that is another half transformer turn.
  3. If the lead is transferred to the primary side externally, it must be as short as possible. Any long secondary lead creates leakage inductance. It may look small, but it ‘transfers’ to primary side by the turns ratio squared.

No you cannot do that, You must keep a creepage distance between the primary and the secondary!!!! Something around 6 mm. You might use Triple insulated wires for your secondary windings then the pin pads must be located on the secondary side. 

Submitted by karim19 on 07/29/2021

Or maybe follow PI's advise but be careful of the safety violation. Best regards