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Old 10th September 2011, 08:06 AM   #1291
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Quote:
Originally Posted by CPX View Post
Thanks lorylaci for helping me.

Now the level shifter is okay, i knew about the needed logic level voltages and i tried increasing dead time because of residual spikes.. now r2 is 90ohm, R3,R4 2,2 k...anyway ir2110 accepts up to Vdd+25 for logic 1.

Some rf noise gets into lm311 negativ input throught feedback wire..shielding it has helped somewhat. but white noise still increases with output voltage.

I still have a lot of feedback errors :no load/1.5 ohm load results in up to 5 volt rms drop and shape distorsion.Strangely enough this efect is reduced if i increase switching frequency..but at 600khz the power transitors are frying

At 20khz input signal and no load i have peak output greater than supply rails..is this what you called bus pumping?

Tested up to +-42(full load),2 ohm load and ~ 9 amp rms output..after that point output transitors have blown..audible output distorsions are starting after 2 amp ...

I will try shielding output coil and see if that helps..i am starging to run out of ideas..
I suggest to stop experimenting with test board. It won't be so much better!
Test board is good to show that the circuit works, but for details not.
Make a good pcb layout, almost everything depends on that.

The experiment with 20kHz is not bus pumping (bus pumping effect rises at low freq and low impedance loads), it is just simply resonance.

What are your FETs? IRF540 or IRF540N? Even IRF540N is not so suitable for 2Ohm at +-42V, and it has a bad body diode (505nC, a good 200V FET has that). Try some IRF540Z, much better (41nC body diode). The spikes will greatly reduce!

1cm gap is too much (normal gaps are 1-2 mm for this application). What is the inductance of your otuput coil?
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Old 10th September 2011, 09:10 AM   #1292
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If I have to use it. Unless let it switch frequency can reach 500 K.

Or I still put the throw in a cupboard, until someone told me this can work at 400 K HZ ac above.
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Old 10th September 2011, 10:23 AM   #1293
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I used irf540... the first pair worked up to 9A as said before but the second exploded very fast taking ir2110 with it..on further testing i found out that the ramaining irf540 that i have are fake..(0.3 ohm rds on) so i will continue after buying irf540z.

I also used aditional Schottky diodes(B20100) so irf body diode shouldn't count...but i observed only a small spike reduction after conecting them.

Inductance of output coil was 32 uH..but the last power tests were done on 20 uH(i removed some windings in order to increase frequency).

ljm_ljm i do not understand what you are trying to say..please try rephrasing a little.
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Old 10th September 2011, 10:52 AM   #1294
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Quote:
Originally Posted by CPX View Post
I used irf540... the first pair worked up to 9A as said before but the second exploded very fast taking ir2110 with it..on further testing i found out that the ramaining irf540 that i have are fake..(0.3 ohm rds on) so i will continue after buying irf540z.

I also used aditional Schottky diodes(B20100) so irf body diode shouldn't count...but i observed only a small spike reduction after conecting them.

Inductance of output coil was 32 uH..but the last power tests were done on 20 uH(i removed some windings in order to increase frequency).

ljm_ljm i do not understand what you are trying to say..please try rephrasing a little.
IRF540 has a much worse body diode than IRF540N even. (1uC body diode OMG) If you use very old FETs don't complain you have bad results.

Output inductor inductance normally has small effect on switching freq, because phase lead network and propagatation delay sets normaly the freq.

Use newer components, 100V modern FETs are easy to get. And use a PCB!
The test board has lots of parasitics. Adding a schottky on test board does not count so much.
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Old 10th September 2011, 02:25 PM   #1295
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For now i can only make hand pcbs(my laser printer is broken) so i do not know if they will be any better than test board
I will write gain after getting better parts...
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Old 10th September 2011, 07:40 PM   #1296
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It seems i have omitted r8.With r7=82 kohm and r8=10 kohm and C1=1nF much of the signal modulated white noise has disappeared....

Last edited by CPX; 10th September 2011 at 07:44 PM.
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Old 10th September 2011, 08:37 PM   #1297
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Lorylaci, did you build the amp using a well designed PCB ?
If so, could you please post measurement results ? Also listening impressions would be useful.
The invitation extends to anyone else who built this amp.
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Old 10th September 2011, 08:46 PM   #1298
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. You can take apart transformers from SMPSs by cooking them in water, they are usually gapped, with increased gap, you could build a good inductor. Last weekend I cooked "transformer-soup" for an hour, the reward was a dosen of ETD cores.
Could you please give more details about how to "cook" SMPSs ?
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Old 11th September 2011, 12:02 AM   #1299
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Remove any tape that is over the transformer. Put transformer into water. Boil for an half hour or more. Remove transformer from boiling water. Wrap your hands in kitchen towels or something and pull it apart. Or you can use a sharp knife or cutter where the halves meet, but do it carefully, if the glue isn't totally softened you'll end up cracking the core. Cracked cores can be superglued back together, they will still work fine.
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Old 11th September 2011, 04:59 PM   #1300
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Remove any tape that is over the transformer. Put transformer into water. Boil for an half hour or more. Remove transformer from boiling water. Wrap your hands in kitchen towels or something and pull it apart. Or you can use a sharp knife or cutter where the halves meet, but do it carefully, if the glue isn't totally softened you'll end up cracking the core. Cracked cores can be superglued back together, they will still work fine.

Ok, most of P3 PC smps has EI 33. I cook it and take apart

One think I dont understand. When I increase a gap to 2mm on example with paper or peace of plastic on central leg of letter E, foreign sides ( 2 legs od letter E) are gaped too. I cant fastened core like before, I use strong glue tape but all the kicking. And when I wind the core, some of winding must go over the gap, I dont know what can i do!?

Can I wind it like on the picture? On example is needed 20 turns, 10 turns up and 10 turns down?

How much turn of wire is needed for inductance of 20 and of 30uH, with this core?
Thanks
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