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LLC Converter Transformer Design

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Bjtpower

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Dear Friends.

We are designing the power supply of 12v/25 amp power supply.

we are having the application note of UCC29950.

But we are facing problem for Transfomer designs.

Can anyone help me out how to design a transfomer for LLC..??

http://www.ti.com/lit/an/slua733/slua733.pdf
 

BradtheRad

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You are more likely to get a reply if you give more information.
Do you wish to step up or down?
What is the power source?
What is intended switching frequency?
What waveshape feeds the transformer? Sine? Square?
 

Bjtpower

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input voltage is 400 volt from the pfc stage

it will step down converter.

About Waveshape, i exactly unaware of that,
Switching Frequency:MIN 65 KHZ
: Max 350 KHZ

Kindly help me out
 

BradtheRad

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I guess the series LC turns square waves into sinewaves. As for their amplitude at the transformer, it's hard to predict.

I'll take a guess at 400V peak... My simulation has 2A peaks in the primary, 40A in the secondary. Ratio is 20:1. This should allow for losses.

You also need to select the primary Henry value. For your frequency range, a suitable value is in the area of 1 to 5 mH. If it is much lower, my simulations show power factor error creeping into the picture.
 

FvM

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The UCC29950 application note has detailed instructions how to calculate a LLC converter, but it's no beginner's tutorial. It's probably more confusing than helpful if you hardly understand what LLC is about.

I believe that the design procedure described in the UCC29950 datasheet is better suited to get in touch with LLC.

Did you notice the initial comment in the datasheet design paragraph?

The LLC stage design procedure outlined here follows the one given in the TI publication “Designing an LLC Resonant Half-Bridge Power Converter” which is available at http://www.ti.com/lit/ml/slup263/slup263.pdf. The document contains a full explanation of the origin of each of the equations used. The equations given below are based on the First Harmonic Approximation (FHA) method commonly used to analyze the LLC topology. This method gives a good starting point for any design, but a final design requires an iterative approach combining the FHA results, circuit simulation and hardware testing. An alternative design approach is given in TI Application Note, LLC Design for UCC29950, Texas Instruments Literature Number SLUA733.
In other words, they suggest a different primary literature.

You may need other basic LLC literature to better understand the operation principles.
 

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