How to wind a custom flyback transformer properly?

Power Power Supplies (board mount)
1

Hey everyone, I’m working on designing a custom flyback transformer and I’m trying to make sure I wind it properly according to my design specs. I have the following details and a few questions about the winding process.

Transformer Details:

Core: ETD29/16/10-3C97 (Bsat = 330mT, Ae = 76mm², Al = 72mm²)

Turns Ratio: 6:1 (Np : Ns)

Primary Turns (Np): 68 turns

Secondary Turns (Ns): 11 turns

Switching Frequency: 70 kHz

Peak Primary Current: 3.16A

Reflected Voltage (Vr): 120V (due to the synchronous rectifier)

Duty Cycle: 57.1%

Efficiency: 93%, Output Power: 65W, Input Power: 70W

My Winding Components:

Bobbin: B66359B1013T001 (13 pins)

Transformer Specification: Similar to RLTI-1464 in the UCG28826EVM-093 schematic

Wire Gauges:

Primary: 0.4 mm wire (2 parallel strands)

Secondary: 0.8 mm wire

Insulation: Polyimide BGA tape for proper layer isolation.

my question is : In the schematic, pins 10, 11, and 12 seem to be connected to the HV DC bus, while secondary winding not having numbered pins. How do I correctly assign these pins to the secondary winding? I’m also assuming pin 13 is not used ?

also the videos i have seen don’t use the mounting clip like the B66359S2000X000, where does it go ?

I’ve done the necessary calculations for the transformer, including the turns ratio, reflected voltage, and peak current. However, I’m a bit unclear on the mechanical and electrical details of how to physically wind it. Any advice or resources would be greatly appreciated!

TL;DR: I need help with winding a custom flyback transformer with a 6-pin bobbin (B66359B1013T001), following the UCG28826EVM-093 schematic, and ensuring safe separation and proper primary and secondary winding on the core. Any tips or detailed guides would be awesome!

schematic link https://www.ti.com/lit/ug/sluud60b/sluud60b.pdf?ts=1773981061462&ref_url=https%253A%252F%252Fchatgpt.com%252F

B66359B1013T001- https://www.digikey.com/en/products/detail/tdk/B66359B1013T001/3914795

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2

Hello @msuleman,

The good news is that you have landed deep into the domain of applied electronics. The bad news is that transformers are part science and part craft requiring highly specialized techniques and refined intuition.

I’m afraid you will find little direct assistance for this specialized application on forums. The best I can do is encourage you to keep reading. Also, take every opportunity to perform a teardown of similar power supplies. Carefully disassemble and document how the transformers were constructed.

DANGER: The isolation between windings is an essential requirement for isolation of line voltage from the user. For example, the TI schematic does not include the third prong safety ground. Failure of T1 is especially dangerous as it would expose the user directly to the line voltage.

Sincerely,

APDahlen

P.S. Be mindful of certifications and see if you can correlate transformer design to specific safety requirements.