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Old 27th November 2010, 04:25 AM   #591
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Hello Dzony988,output inductance is too big i use 20uH with very good results
do not forget that this is selfoscilating amp and its oscilation is dependent off the output filter! iff you have a scope please check the oscillation frequency you'll see that the amp dos not run at 250Khz not even close iff you want 20hz-20Khz band is required to determine the oscillation frequency (the amp with 1,5uF+30uH oscilate at 150Khz)
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Old 27th November 2010, 04:33 AM   #592
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IRFP240 they may work
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Old 27th November 2010, 07:19 PM   #593
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IONUTZXPO, thank you for replay. Its means I can use 20uH output coil and 1.5uF or smaller???

Is something else changes of componets to reduce the noice, like c10 of 100pF to 2.2nF, 4.7nF form pin 3 of LM311 to GND.....?

Can I use for output coil yellow core from PC ATX supplay. That coil have 20uH as I recall, since there are several different wires, use thickest I guess.

Thanks again, and please tell me about output capacitor that goes with 20uH, can I use PC coil and other changes to schematic to reduce the noice.

Thanks and Regards, Nikola
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Old 27th November 2010, 09:17 PM   #594
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hi Nikola,you can use 15-20uH +1uF for output filter ,i added 4.7nF over the 100pF (C10)and the noise is allmost gone
you can use pc coil but with gap otherwise the core will saturate and will heat up fast
i use Micrometals IronPowder cores T130-2 and litzwire
they are the best for output filter in class d amps

Last edited by ionutzxpo; 27th November 2010 at 09:19 PM. Reason: editing
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Old 27th November 2010, 11:41 PM   #595
stewin is offline stewin  Kenya
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hi guys i've just found irfp260 in my country . and they do have a lower rds than irfp250 will they work better than irfp250 in this circuit i've heard about the 4227 but are not available . btw irfp360 are available too steve
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Old 28th November 2010, 12:06 AM   #596
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Quote:
Originally Posted by stewin View Post
hi guys i've just found irfp260 in my country . and they do have a lower rds than irfp250 will they work better than irfp250 in this circuit i've heard about the 4227 but are not available . btw irfp360 are available too steve
IRFP240 is lower than IRFP250.

I quite often use IRFB4019, low capacitance but can still manage 17 amps.
One bad side is it is to220 package so cant dissipate as much heat as the IRFP240.
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Old 28th November 2010, 11:58 AM   #597
qsa is offline qsa  Germany
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Is it possibile parralleling 2 x IRFP 250 mosfets on high and low side Rails ?

IR 2110 with 2 A peak current should be enough power to drive 2 mosfets parallel for maximum ouput power with low impedance speaker

Could this work ?

Last edited by qsa; 28th November 2010 at 12:00 PM.
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Old 28th November 2010, 03:56 PM   #598
stewin is offline stewin  Kenya
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Unhappy which fet can fit

hi guys the available fets are (irfp 240,250,260,360,450,460). irfb series or igbts are currently unavaillable here even the parts shop have no clue what they are. my question is which of the above fets can be used and is effecient . i thought that rds was the one that matters in class d. but thanks to this forum i learned that irf640 with a higher rds was superior compared to the irf540.
both irf540,irf640 are available but i wanted the TO247 package because of their voltage and current ability. stewin
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Old 28th November 2010, 05:24 PM   #599
Pafi is offline Pafi  Hungary
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thanks to this forum i learned that irf640 with a higher rds was superior compared to the irf540
I strongly disagree. And my burned IRF640s too.

You have to search for the smallest voltage rating which exceeds the summed supply voltage by 15 % at least.
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Old 28th November 2010, 06:34 PM   #600
stewin is offline stewin  Kenya
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so for a powersupply of +/- 85vlts it is safe to use the irfp360 instead of irfp260 with this circuit
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