Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Transformer for LLC converter?

Not open for further replies.


Member level 5
Feb 10, 2017
Reaction score
Trophy points
Activity points

Here in the discussion, I came across an LLC switched converter and I have no idea what a transformer with LL inductions looks like.

Here is a picture of a converter with details of a transformer and a resonant circuit.

The transformer is marked as TE65037, do you think it is the core of EE65?
I am interested in how a transformer with LL resonant coils on a common core is manufactured.

What can be found from the data revealed by the manufacturer?
a) n=9 The ratio of primary vs secondary winding is 9: 1
b) What is the resonant frequency? if C=54nF and Lr =20.32uH
f=1/(2*Pi*Sqrt(Cr*Lr)) about 152kHz, but manufcruter say 175kHz)
c) Ratio of total primary inductance to resonant inductance m
m=(Lr+Lm)Lr = 1
d) I assume that when all the coils are on the same core, the inductance ratio must match a quarter of the number of turns. And Np / Ns 9: 1
if Al=Lr/N^2 for Lr=20,32uH and N=12 is Al=151,9nH
Lr have 11 turn 20,32uH
Lm have 24 turn 96,7uH calculated
Lp have 27 turn 122,4uH calculated
Ls have 3 turn 1.5uH calculated

Is my reasoning correct?

A normal transformer would look something like this. The first primary winding 27 thread is either made of 0.3 mm CU tape or HF CU cable with 0.3 mm wire, current approx. 10A. Insulation barrier and 3 turns of Cu tape, current 63A. The winding orientation is identical
From what, how and where are Lr and Lm involved?
Lr is in series with Lp, so full current flows, so it must be from the same conductor as Lp, but how and where is it wound?
Lm has a lower end at the transformer terminal and the other must be connected between the end Lr and the beginning Lp, it is soldered to the transformer and from what, how and where is the winding Lm?
In short, what are the production instructions for the transformer with LL coils?

Thanks you

Hi Jadeit,
I am not quite sure I understood your exposition. However, I am going to try to describe the trafo based on the information you have.
In short, the transformer only has two windings.

Turns ratio between primary and secondary is 9. Assuming X turns on the secondary, the primary will have 9*X turns.
The core will be gapped to get the desired magnetization inductance. Longer gap will result on lower Lm. You can use a formula to estimate the necessary gap. To do it, you need to know the geometry of the core you are using.

The leakage inductance is achieved reducing the coupling factor between primary and secondary windings. A typical way to get it is using a coil former with two sections, therefore, the primary and secondary will be in different sections.

Primary inductance is just the addition of Lm+Lr.





Not open for further replies.

Part and Inventory Search

Welcome to