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Old 22nd January 2013, 09:26 PM   #151
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Quote:
Originally Posted by nigelwright7557 View Post
Any suggestions where to go to next ?
Nigel, You were talking about using a sigal generator to drive the LC network.
Could you do two measurements:
- Normal measurement, you did prevously (you have got a peak at 23kHz) (you don't need to repeat this, if you havent change anything in the LC network)
- A measurement with secondaries shorted. Short the secondaries, then run the signal generator. Check where is the peak!

I am waiting for your measurement!
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Old 22nd January 2013, 09:37 PM   #152
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I can see where I have made a mistake.
I have made my inductor to 625uH and 120uH and the spread-sheet wants to tell me what their values should be. So I currently have far too much inductance for the output values given for the control components.,
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Old 22nd January 2013, 10:16 PM   #153
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Quote:
Originally Posted by lorylaci View Post
Nigel, You were talking about using a sigal generator to drive the LC network.
Could you do two measurements:
- Normal measurement, you did prevously (you have got a peak at 23kHz) (you don't need to repeat this, if you havent change anything in the LC network)
- A measurement with secondaries shorted. Short the secondaries, then run the signal generator. Check where is the peak!

I am waiting for your measurement!
With 47nF and my transformer secondary shorted I get a resonant frequency of 200KHz

With 47nF and secondaries open I get 28KHz.
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Old 22nd January 2013, 10:30 PM   #154
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Quote:
Originally Posted by nigelwright7557 View Post
With 47nF and my transformer secondary shorted I get a resonant frequency of 200KHz

With 47nF and secondaries open I get 28KHz.
THAT IS INTERESTING!

From 47nF and 200kHz (thomsone-equation) we get: 13,5uH
Your transformer according to these measurements has a leakage inductance of 13,5uH

From 47nF and 28kHz we get: 688uH
Your transfromer has a total primary inductance of 688uH.

I said previously that your inductance measurements can be bad. From this measurement we got a totally differnt leakage inductnce. Since this values is mslaler, your maximal currents are much larger (and this correlates with that your circuit don't start).

Now which measruement should be believe? 120uH or 13,5uH. Could you make a photo of the actual transformer? From the photo I can make an approximation, of which value couldbe true.

(of course the best is to do an other measurement, with an other inductance meter)
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Old 22nd January 2013, 10:44 PM   #155
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I couldn't get enough leakage inductance so I had to wind the secondary on top of the primary.

My handheld meter said 125uH and my USB inductance meter said 10uH, so it looks like my USB one is closer by miles after all. I didn't believe it at first.

I will rewind the transformer and see what the USB meter says.

Click the image to open in full size.
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Old 22nd January 2013, 11:26 PM   #156
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I rewound the transformer and ignored my multi-meters and just measured the resonant frequencies on the scope.

I get 120uH leakage and 700uH main inductance.

I powered it up and it doesn't reset anymore.
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Old 23rd January 2013, 11:51 AM   #157
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So you have taken a huge step towards a working LLC resonant converter!

Congrats!

Please continue with the thread as you see fit.
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Old 23rd January 2013, 08:16 PM   #158
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Quote:
Originally Posted by nigelwright7557 View Post
I rewound the transformer and ignored my multi-meters and just measured the resonant frequencies on the scope.
What is the type of your handheld meter?
It seems that your USB inductance meter is more acurate measureing the leakage inductance. Of course using a signal generator is the best method.

Quote:
Originally Posted by nigelwright7557 View Post
I powered it up and it doesn't reset anymore.
Grats, Nigel.

Now it is time to fine-tune your circuit.
So you have 120uH leakage, 700uH total primary inductance and your resonant capacitor is 47nF.

What frequencies have set?

Could you make some scopepictures about the following:
- low side FET gate voltage (with no load - max frequency, and with about 50-100W load)
- half bridge output (drainof low side FGET) (with no load - max frequency, and with about 50-100W load)
With this pictures I can tell if the dead-time is good (enoguh, too much, too less).
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Old 23rd January 2013, 08:26 PM   #159
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Quote:
Originally Posted by lorylaci View Post
What frequencies have set?

Could you make some scopepictures about the following:
- low side FET gate voltage (with no load - max frequency, and with about 50-100W load)
- half bridge output (drainof low side FGET) (with no load - max frequency, and with about 50-100W load)
With this pictures I can tell if the dead-time is good (enoguh, too much, too less).
My low frequency is 27,777Hz which gives 120uH
My Fr1 is 66,666Hz which gives 700uH

I used a large dead-time so I could be sure that wasn't the problem. I have 1000pf as the timing capacitor. 10k as Rmin and 2k2 as Rmax.

My inductance and capacitor are a bit off from the spread-sheet so there is still a bit of work to do yet.

My LC meter was £27 so isn't the best one.
The LC USB meter I made myself using a PIC micro and oscillator circuits based around comparators.
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Last edited by nigelwright7557; 23rd January 2013 at 08:29 PM.
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Old 24th January 2013, 01:04 AM   #160
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Quote:
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I used a large dead-time so I could be sure that wasn't the problem. I have 1000pf as the timing capacitor.
I found 390pf caused the transformer to vibrate a little.
With 1000pf it is dead quiet.
I obviously recalculated Rmin and Rmax to suit from the spread sheet.
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