copper foil width calculation of transformer regarding secondary side

Hi, Nizam

I cannot find the attachment. Please attach the picture so I can have a look, or share a link to your design on piexpert@power.com, attention to PI-Yoda.

Basically, the foil width should be equal to the coil former width minus the safety margin required for the particular design and winding stack conditions.

Best Regards

Hi,

Here I attach the PNG and PDF file for respective conversation. kindly Check the attachment.

And thanks again  

Hi, Nizam

Thank you for sharing the attachment with us. It confirms that the foil width text is scrambled for some reason.

In the same time it looks like you are using a old standalone version in PIExpert.

In the latest 10.3 version and the online one  for the secondary winding instructions for this design:

The formulas are:

FoilWidth = CoilFormerWidth - SafetyTape - 3TapeThickness

SafetyTape = 6.4mm - FoilCornersTrippleIsulatedLength - 3TapeThickness

3TapeThickness could be considered approximately = 0

Please check the drawing provided

Please update your standalone version of PIExpert and let me know if something is not clear.

Best Regards,

Dear Concerned,

Here I attach my design file with design consideration and specification that I have used in PI Expert. And I have been using PI Expert 10.3.

I am so pleased with your support.

I have some confusions on secondary side.. where you recommend " Start on pin(s) 7 and wind 3 turns of item [7]. Winding direction is clockwise. Finish this winding on pin(s) 6".

But PI Expert 10.3 that I have been using suggest me the following: 

"Secondary Winding

Use 3 mm margin (item [8]) on the top and 3 mm margin on the bottom (to meet safety). Start on pin(s) 12 and wind 5 turns of item [7]. Winding direction is clockwise. Finish this winding on pin(s) 10. Add 3 layers of tape, item [3], for insulation."

N.B Here I use Pin 12 and 10 as my secondary output for taking advantages during routing on PCB.

Basically My confusion now on calculation and  number of turns. I hope you understand what I mean. Please kindly check the attach project file. I need your kind support for finding the issues in this regard. As I am Noob using PI expert. 

And also for item 7 my consideration is below (is it ok?):

Copper Foil: 5 mil thick,  11mm wide, covered with 1 layer of lapped tape. Terminations to foil: 2 x 23 AWG magnet wire with sleeving..

I also try PI_Expert Online which Project file also included as 2nd attachment.

Thanks in advance

Hi, Nizam

To clear the confusion, my example of the secondary winding instruction - pins 3,7 and 3 turns is may creation of generic 24V/150W design. I have created it to check the winding instructions ONLY, without to know you particular specification. 

So, do not use the information from there. Use the information from your deign files.

About the foil width:

ETD34 coil former has a CoilFormerWidth = 20.9mm, Two times of  SafetyTape 3mm has been used, as per you file so,

FoilWidth = CoilFormerWidth - SafetyTape  = 20.9mm - 2x3mm = 14.9mm  could be used.

For safety:

It must have 3 layers of tape 20.9mm wide before and after the foil

Minimum of 3.4 mm length of each foil corners must be covered with 3 layers of tape. So, the tape used must be min 6.8mm wide and it must be used centered to the edge,

Internally, and externally both foil leads must be isolated with sleeves providing creepage and clearance as 6.4mm. So, the total single sleeve length is 12.8mm

Please see my picture above.

Regards,

Dear Concerned,

Now its clear and Thanks for your kind support.

Hi Pi-Yoda, 

I have a question about this setup for the copper foil. It is really necessary to add the 3mm margin on left and right side? 

Could be design in the way that there is no 3mm margin and the three insulation layer on  the foil corners covers unless 6.4mm in each side?

Thanks

Jesús

Hi,

I am not sure I understand the question. 

The 3mm margins are not mandatory. It is mandatory though, to maintain the minimum creepage and clearance as required by your safety standards.

If IEC60950 is considered, for the voltages in offline flyback converter this distance is min of 6.4mm. The actual actual safety margin implementation requirements are also explained in the standard.

Best Regards,

Hi PI-Yoda,

Thanks for your reply.

You wrote "The 3mm margins are not mandatory. It is mandatory though, to maintain the minimum creepage and clearance as required by your safety standards."

Assuming 6.4mm neccessary for creepage, I attached a picture that shows two different ways to get this requirement.

The second one without margins so the copper foil can be wider. Because a three layers insulation is used, no minimum distance through insulation is required and the creepage is kept over 6.4mm. Therefore, I think it is a valid setup regarding safety.

I would appreciate read your though about it.

Thanks

Jesús

Correct, it is a valid implementation without safety margin.

Best Regards,