How to reduce the leakage inductance in a transformer?

[zyrixx]

how do you reduce the leakage inductance i a transformer, specifically for SEPIC or Flyback where the needed magnetizing inductance is too large.


thnks!

 

[v_c]

reducing leakage inductance

Reduction of leakage inductance is equivalent to maximizing the coupling
between the windings so (in theory) all of the flux generated from one winding
is coupled to the other winding, or windings.

In general there are some points to note:
1. Leakage inductance energy must be absorbed by snubbers or clamps.
2. Leakage inductance is usually the culprit of cross regulation effects observed on multiple output transformer based systems.
3. You can reduce leakage inductance by using a winding shape that maximizes the window breadth of the chosen transformer.
4. You can also reduce leakage inductance by interleaving the windings. However, when you interleave windings, you will increase the interwinding capacitance.
5. The physical distance between the windings required for high-voltage isolation increases the leakage inductance. One way to reduce this is to use highly insulated wire for the windings.

I suggest that you look at thes articles by Lloyd Dixon on Inductor and Flyback Transformer Design https://focus.ti.com/lit/ml/slup127/slup127.pdf.
and on Windings https://focus.ti.com/lit/ml/slup125/slup125.pdf. After you read these two articles, you should get some ideas on how to reduce the leakage inductance.

In fact, you should look at the entire Magnetics Design Handbook from TI (Unitrode) at https://focus.ti.com/docs/training/catalog/events/event.jhtml?sku=SEM401014

The following are the topics that are presented in the Handbook. Each is a downloadable PDF file.

1-Introduction and Basic Magnetics (Magnetics Design for Sw. Power Supplies)
2-Magnetic Core Characteristics
3-Windings
4-Power Transformer Design
5-Inductor and Flyback Transformer Design
Ref. Design Sect. R1-1: Magnetic Core Properties
Ref. Design Sect. R2-1: Eddy Current Losses in X-former Windings
Ref. Design Sect. R3-1: Deriving the Equivalent Electrical Circuit
Ref. Design Sect. R4-1: The Effect of Leakage Inductance on Performance
Ref. Design Sect. R5-1: Coupled Filter Inductors Yield Improved Performance
Ref. Design Sect. R6-1: How to Design a Transformer with Fractional Turns
Ref. Design Sect. R7-1: Winding Data

Best regards,
v_c

 

[Meridian]

reduce leakage inductance

how do you reduce the leakage inductance i a transformer, specifically for SEPIC or Flyback where the needed magnetizing inductance is too large.
thnks!

Leakage usually occurs via the windings. At some place or places the insulation or coating may be thinner or "defective" during the manufacturing process.