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Old 1st January 2013, 09:40 PM   #51
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Quote:
Originally Posted by nigelwright7557 View Post
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.
Since i have no idea about checking the resonant signal for tat chip, or as described in the AN,

If you let me know how they confirm the resonance in that SMPS, i will be able to help you save lot of time make it working



please show waves

regards
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Old 1st January 2013, 09:52 PM   #52
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I would assume that the capacitor and leakage inductance make a tuned circuit.
At resonance the circuit will pass much more signal than it would off resonance giving control of how much power is given out.

The primary inductance is 400uH and the leakage inductance is 365uH.

So the resonant frequency is:
1/ 2 pi sqr(lc)

Therefore:
c=1/4 pi pi l f f

Or c= 7nf for 100kHz
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Old 1st January 2013, 10:28 PM   #53
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Quote:
Originally Posted by clocktower View Post
it will be very complex to know exact value of the LLC without tuning the smps freq.
It is a PFM controller, so varies the frequency. There is no tuning to one frequency.
Since there are lot of input values, tere is always some degree of freedom at scaling.
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Old 1st January 2013, 10:30 PM   #54
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Quote:
Originally Posted by clocktower View Post
Since i have no idea about checking the resonant signal for tat chip, or as described in the AN,

If you let me know how they confirm the resonance in that SMPS, i will be able to help you save lot of time make it working



please show waves

regards
Scopeing the signal on the resoanant capacitors shows a sine from light to heavy loads (at idle or small loads its triangle like, due the magnetizing current), confirms the resonant operation.
Scopeing the half bridge voltage and gate signals confirms ZVS switching.

However by calculation ZVS switching can be guaranted over full load range.
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Old 1st January 2013, 10:32 PM   #55
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Quote:
Originally Posted by nigelwright7557 View Post
I would assume that the capacitor and leakage inductance make a tuned circuit.
At resonance the circuit will pass much more signal than it would off resonance giving control of how much power is given out.

The primary inductance is 400uH and the leakage inductance is 365uH.

So the resonant frequency is:
1/ 2 pi sqr(lc)

Therefore:
c=1/4 pi pi l f f

Or c= 7nf for 100kHz
I have just looked over that chip, its LLC.

I am still not sure where to measure, in order to make sure that the resonant is happening, and the circuit is running well.

Also the transformer you are using will waste your time making this circuit stable, even if you made it working.

You need the split type bobbin, side by side windings.
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Old 1st January 2013, 10:43 PM   #56
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Quote:
Originally Posted by nigelwright7557 View Post
I would assume that the capacitor and leakage inductance make a tuned circuit.
At resonance the circuit will pass much more signal than it would off resonance giving control of how much power is given out.

The primary inductance is 400uH and the leakage inductance is 365uH.

So the resonant frequency is:
1/ 2 pi sqr(lc)

Therefore:
c=1/4 pi pi l f f

Or c= 7nf for 100kHz
Read the application note again. There is NOT ONE, but two resonant frequencies.
Your induectance values are not good (your magnetizing inductance is smaller then the leakage). You need to rewind your transformer.
attached you will find tha half-translated excel calculator.
As you can see, I put in 300-330V input, 50V and 20A output. This is quite small from an ETD54 (please Nigel, tell the material of your ferrite, it is really important).
You can see, that 13 turns of primary is needed. This will take down your leakage inductance to a normal values. For 1kW the leakage inductance should be 18 uH (for this frequency range). (I must mention that your FETs will not take over 200W, due to the internal protection of the IRS IC)

Rewind the transformer primary for 13 turns. For 50V secondary you need 4 turns. Then measure the leakage inductance and the magnetizing inductance.
Then we can move forward.
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File Type: zip IRS27951_angol.zip (16.3 KB, 94 views)
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Old 2nd January 2013, 02:03 AM   #57
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Quote:
Originally Posted by clocktower View Post
your time making this circuit stable, even if you made it working.

You need the split type bobbin, side by side windings.
I have wound the primary next to the secondaries.
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Old 2nd January 2013, 02:05 AM   #58
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Quote:
Originally Posted by lorylaci View Post
Read the application note again. There is NOT ONE, but two resonant frequencies.
Your induectance values are not good (your magnetizing inductance is smaller then the leakage). You need to rewind your transformer.
attached you will find tha half-translated excel calculator.
As you can see, I put in 300-330V input, 50V and 20A output. This is quite small from an ETD54 (please Nigel, tell the material of your ferrite, it is really important).
You can see, that 13 turns of primary is needed. This will take down your leakage inductance to a normal values. For 1kW the leakage inductance should be 18 uH (for this frequency range). (I must mention that your FETs will not take over 200W, due to the internal protection of the IRS IC)

Rewind the transformer primary for 13 turns. For 50V secondary you need 4 turns. Then measure the leakage inductance and the magnetizing inductance.
Then we can move forward.
The leakage is definitely smaller it is 365uH.
The main inductance is 400uH.
This gives a k of slightly more than 1 which isn't brilliant.
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Old 2nd January 2013, 02:12 AM   #59
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Quote:
Originally Posted by lorylaci View Post
Rewind the transformer primary for 13 turns. For 50V secondary you need 4 turns. Then measure the leakage inductance and the magnetizing inductance.
Then we can move forward.
I wound the transformer primary -= 36 turns and secondary -= 4 turns.
From this I get 45 volts output.


If I have time Wednesday night I will rewind it.
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Old 2nd January 2013, 02:18 AM   #60
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On my previous SMPS which was a fly-back SMPS I had problems stopping the transformer whistling at high loads. I think the problem was the transformer being over wound and causing the switching frequency to be very low.

It looks like I have made the same mistake with the half bridge SMPS of over winding the transformer. I took the windings from the app notes of a example SMPS.
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