Power limitations for LLC-smps for amplifier

Jump to Latest
#21
search for
"Topology Investigation for Front End DC/DC
Power Conversion for Distributed Power System
Bo Yang
Dissertation submitted to the Faculty of the
Virginia Polytechnic Institute and State University"

These are very comprehensive papers

read chapter 5
 
#24
I have been thinking about an way to use off-set winding and also making the windings "taper off" as shown in the sketch. A quick test reveals that it should be possible to hit 45primary windings, and 100uH+300uH primary inductance with a approx 0,5mm gap in the center.

An externally hosted image should be here but it was not working when we last tested it.
 
Last edited:
#26
@voltvide: From what I can read in the differenr pdf's it appears that the x-former-window (the space to wind the pri and sec) is somewhat tailored to the application. So a transformer from an typical ATX-psu have a long and narrow window to allow best possible coupling and a x-former suitable for side-by-side (two-chambers) wil have a more square-ish window.

TroelsM
 
#27
I do not see llc-xformers with square-like windows, because
they use the same core shapes as flyback or other converters.
The loose coupling is achieved with 2-chamber bobbins.
Have a look at one of my prototypes attached here:
 

Attachments

  • P7020007.JPG
    P7020007.JPG
    278.2 KB · Views: 236
#29
I forget to mention that this xformer is readyly wound available from Wuerth Electronics, part No WE-760895651. Works nice here and could be a good starter for you as well. (Normally I do wind my own xformers, but I got hold of 3 free samples)
 
#30
I am pretty certain when I did LLC transformer the two windings were next to each other and not on top of each other.
This is how you get a leaky inductive system.

I used a PIC micro to generate 3 frequencies.
1/ On power up a very high frequency to cope with virtual short on output.
2/ Frequency slightly above resonance to give full power out.
3/ Frequency quite a bit above resonance to regulate output when feedback signal said output voltage was slightly above required voltage.

I built the transformer then connected it to a sig gen through a resistor so I could calculate resonant frequency. From that I got the frequencies for PIC micro to generate.

There is a happy medium with the applied frequency.
Not so high that little power is output and not so low that capacitive mode cause mosfets to destruct.

I also put a small ohm resistor in the lower leg of the low side mosfet to monitor current.
I monitored it with the PIC and if a high current event occurred the PIC tripped out.
This must have saved loads of blown mosfets while testing.
 
Last edited:
#31
nigelwright7557 said:
I am pretty certain when I did LLC transformer the two windings were next to each other and not on top of each other.
This is how you get a leaky inductive system.

I used a PIC micro to generate 3 frequencies.
1/ On power up a very high frequency to cope with virtual short on output.
2/ Frequency slightly above resonance to give full power out.
3/ Frequency quite a bit above resonance to regulate output when feedback signal said output voltage was slightly above required voltage.

I built the transformer then connected it to a sig gen through a resistor so I could calculate resonant frequency. From that I got the frequencies for PIC micro to generate.
Click to expand...

Thank you for the input. I see that most (if not all?) of the LLC constructions a side-by-side winding. With the stuff I have I cannot get a inductance-ratio of more than 1:2 and according to the literature you want the ratio to be between 1:3 and 1:10.

I just measured a " partly overlapping" transformer that measures around 360uH with sec open and 60uH with sec shorted. One problem is that the exposed part of the primary gets a little hot, maybe because the exposed part is the primary cause of the leakage?

It sounds clever with the PIC solution, but the LLC controllers are so cheap that the controller is not my main problem.

Did you make the transformer from scratch? did you measure Lp and Lm?

Kind regards TroelsM
 
#33
I have used multiple strands and I'm pretty sure that the skin effect is not my biggest problem. It looks like the fringe flux around the center-leg-gap is a serious problem for the closest wires, - especially if they are thick.
 
You must log in or register to reply here.
Top Bottom