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Old 31st December 2012, 11:40 AM   #41
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so basically you have to cycle powerto reset the converter. LLC converters is voltage mode so that figures .

One thought: as it is difficult to get an exact leakageinductance in the xformer and therefor Lr, how about adding an external inductor for the fine tuning of Lr? say 20-50% of total Lr? yes, more components, more board area but perhaps in the end less hassle. Only problem is that the.flux swing will be quite large and therefor demands low loss material or airgaps. (first thoght was a simple iron core but loss is probably to big) .

to bad I cant read hungarian...
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Old 31st December 2012, 11:51 AM   #42
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Quote:
Originally Posted by rikkitikkitavi View Post
so basically you have to cycle powerto reset the converter. LLC converters is voltage mode so that figures .

One thought: as it is difficult to get an exact leakageinductance in the xformer and therefor Lr, how about adding an external inductor for the fine tuning of Lr? say 20-50% of total Lr? yes, more components, more board area but perhaps in the end less hassle. Only problem is that the.flux swing will be quite large and therefor demands low loss material or airgaps. (first thoght was a simple iron core but loss is probably to big) .

to bad I cant read hungarian...
Yes for IRS2795x you need to reemoce it's supply and put back to restart.
For bigger power designs it is usual to have a standby supply (a quasiresonant flyback) to supply basic stuff at secodary, and the IRS2795x. If you put a switch to the IRS2795x suply then you can activate and daeactivate standby mode, and also reset after fault.

You can use extra inductor, but that costs more, takes more space.
If you have a bit expereince it is very easy to get the exact leakage inductance you want. Also you can change the controll elements for your resonant network
(you can change magnetizin inductance and resonant capacitance easily)

Also there is a special method of putting some magnetic shunt into the transformer to set exact leakage inductance. (google for 1MHz LLC converter)
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Old 31st December 2012, 12:31 PM   #43
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If I build a larger converter (personal use) would probably add a small PCB transformer for.onboard power to primary to simplify.design.

thanks for the input and happy new year
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Old 31st December 2012, 03:48 PM   #44
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Quote:
Originally Posted by rikkitikkitavi View Post
so basically you have to cycle powerto reset the converter. LLC converters is voltage mode so that figures .

One thought: as it is difficult to get an exact leakageinductance in the xformer and therefor Lr, how about adding an external inductor for the fine tuning of Lr? say 20-50% of total Lr? yes, more components, more board area but perhaps in the end less hassle. Only problem is that the.flux swing will be quite large and therefor demands low loss material or airgaps. (first thoght was a simple iron core but loss is probably to big) .

to bad I cant read hungarian...
Its quite difficult to get an exact leakage inductance.
I just wound the transformer then measured it.
With a secondary wound on top of primary I got quite a low leakage inductance. With the secondary wound next to the primary it became very high. I guess the compromise is to wind the secondary partly on the primary.

I also found I was getting a high primary inductance I guess due to using an ETD54 core. I had to gap the transformer to bring the inductance down.
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Old 31st December 2012, 07:55 PM   #45
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But does not gapping ruin the low EMI from soft switching?
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Old 31st December 2012, 07:59 PM   #46
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Originally Posted by rikkitikkitavi View Post
But does not gapping ruin the low EMI from soft switching?
It just needed a very small gap.

I am open to suggestions for getting the right primary and leakage inductance using an ET54 transformer.

I guess I could partly overlap the windings to lose a bit of leakage inductance.
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Old 1st January 2013, 03:52 PM   #47
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Quote:
Originally Posted by nigelwright7557 View Post
It just needed a very small gap.

I am open to suggestions for getting the right primary and leakage inductance using an ET54 transformer.

I guess I could partly overlap the windings to lose a bit of leakage inductance.
What is the material of your ferrite? Epcos N87?
At the frequency range of the application note (60-150 kHz), you will find it hard to deisgn it to a low power level of 240W.

Nigel, you are not deisgning, just quessing. Do calculations, use math.
I am working on the translation of my excel spreadsheet to English for you.
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Old 1st January 2013, 09:19 PM   #48
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What is the material of your ferrite? Epcos N87?
At the frequency range of the application note (60-150 kHz), you will find it hard to deisgn it to a low power level of 240W.

Nigel, you are not deisgning, just quessing. Do calculations, use math.
I am working on the translation of my excel spreadsheet to English for you.
I built the transformer as suggested in the app notes so I am not guessing.

It should be pretty easy just matching Lr, Lm and Cr.
I have Lr and Lm so just need to match Cr.

The control components have already been given to me by the app note.
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Old 1st January 2013, 09:31 PM   #49
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it will be very complex to know exact value of the LLC without tuning the smps freq.
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Old 1st January 2013, 09:36 PM   #50
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it will be very complex to know exact value of the LLC without tuning the smps freq.
I used open circuit secondaries to measure primary inductance.
I used short circuit secondaries to measure leakage inductance.
This method is in the application notes.
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