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Old 8th January 2013, 11:08 AM   #81
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Quote:
Originally Posted by lorylaci View Post
Again I can offer you to send my controller's PCB design. Its pretty easiy, does not use compontents smaller than 1206, so can be soldered by hand easily. Also its on a separate board, so you can check the controller working separately, which is pretty useful.
Do you need my PCB design?
I will see how I get on with my current pcb.
It should work with one cut and one link to sort out the star grounding.
Thanks for the offer.
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Old 8th January 2013, 04:56 PM   #82
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Quote:
Originally Posted by nigelwright7557 View Post
I will see how I get on with my current pcb.
It should work with one cut and one link to sort out the star grounding.
Thanks for the offer.
Befora checking the whole circuit just check the controller.
Use an external 12V supply to supply it. Be sure to use a <10 ohm resistor insted of the lower FET drain and source connection (otherwise the IC's OC protection turns on). Apply some dummy cpaactiros (4,7nF ceramic) instead of the FET gates, and check the capacitor votlage with scope probes.
Make a screen capture (for digital scope) or photo the bildschirm (analog scope).
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Old 8th January 2013, 09:22 PM   #83
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Quote:
Originally Posted by lorylaci View Post
Befora checking the whole circuit just check the controller.
Use an external 12V supply to supply it. Be sure to use a <10 ohm resistor insted of the lower FET drain and source connection (otherwise the IC's OC protection turns on). Apply some dummy cpaactiros (4,7nF ceramic) instead of the FET gates, and check the capacitor votlage with scope probes.
Make a screen capture (for digital scope) or photo the bildschirm (analog scope).
I did that previously using 30 volts to supply the mosfets and 18 volts to supply the 27952. I got a square wave out on HO and LO.
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Old 10th January 2013, 08:48 PM   #84
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I got my smd rework gun today.
I soldered in a new chip.
I checked it on 30 volts to mosfets and 18 volts to 27951 and it outputs a square wave on LO and also a signal on HO.

I now have a transformer with 200uH primary inductance and 75uH leakage inductance.
The resonant capacitor is 22nf.
This works out at resonant frequencies of 60KHz and 100KHz the same as the app note project.

I get a brief voltage on the output on power up then the 27951 goes into power down mode.

What should I try next ?
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Old 10th January 2013, 09:21 PM   #85
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I have also ordered a etd49 transformer bobbin and cores to try to get he correct inductance. The etd49 is used in the app note.

Here is the LO output of the 27951

Click the image to open in full size.

Last edited by nigelwright7557; 10th January 2013 at 09:38 PM.
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Old 11th January 2013, 05:45 PM   #86
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Quote:
Originally Posted by nigelwright7557 View Post
I got my smd rework gun today.
I soldered in a new chip.
I checked it on 30 volts to mosfets and 18 volts to 27951 and it outputs a square wave on LO and also a signal on HO.

I now have a transformer with 200uH primary inductance and 75uH leakage inductance.
The resonant capacitor is 22nf.
This works out at resonant frequencies of 60KHz and 100KHz the same as the app note project.

I get a brief voltage on the output on power up then the 27951 goes into power down mode.

What should I try next ?
You have a primary inductance of 200uH without gap? If you have gap, try to decrease the gap to get an inductance of 4-500uH. Then you will have a k about 5, so a resonant capacitor of 33nF will match to 250W.

Can you measure the parasitic capacitances of the transformer primary? (use the LC meter as a capacitor meter on the primary) It would be helpful to set the maximal switching frequency. Your minimal switching frequency (with 75uH 500uH and 33nF) combo will be about 70kHz.
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Old 11th January 2013, 08:36 PM   #87
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Originally Posted by lorylaci View Post
You have a primary inductance of 200uH without gap? If you have gap, try to decrease the gap to get an inductance of 4-500uH. Then you will have a k about 5, so a resonant capacitor of 33nF will match to 250W.

Can you measure the parasitic capacitances of the transformer primary? (use the LC meter as a capacitor meter on the primary) It would be helpful to set the maximal switching frequency. Your minimal switching frequency (with 75uH 500uH and 33nF) combo will be about 70kHz.
It is 250uH without a gap. and 95uH leakage inductance.

With my meter cross the primary I get 70pf.

My new transformer transformer will be here on Monday, I will try the etd49 with 13 primary turns as you suggested earlier.
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Old 11th January 2013, 08:46 PM   #88
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How did you get 13 for primary turns ?

I worked out 33 from the app note.

So if I work out 33/13 * 250uH I get 636uH which sounds about right.
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Old 11th January 2013, 09:36 PM   #89
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I rewound my etd54 with 33 turns primary and 9 turns secondaries.
With a small gap I get 600uH primary and 85uH leakage.

Last edited by nigelwright7557; 11th January 2013 at 09:43 PM.
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Old 11th January 2013, 10:29 PM   #90
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I now have two resonant frequencies from 600uH and 685uH.
With a 10nF Cr this gives me 60800 and 65000.

Last edited by nigelwright7557; 11th January 2013 at 10:34 PM.
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