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Old 26th May 2011, 02:38 AM   #1151
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Default hi guys

Quote:
Originally Posted by lorylaci View Post
Air coils are big, ineffective, and radiate noise.
Because they are big they were able to dissipate the loss because of the high current (because of low switching freq).

Since this is an UcD amp, the feedback is after inductor, so every non-linearitiy of the inductor is compensated by the feedback. Gapped ferrites also very linear until 80% of saturation. Iron-powder cores are less linear.

So chosing air-core inductor for linearity is stupid. I think they chose it because any other could not dissipate, mainly because the low switching freq. A bad solution for a bad choice.
hi lory
the air core inductors are good choice for most fans of this project, and you answered that the air core inductors is a stupid idea is stupid that is all for you ?????
fuses to prevent fire as no current limit according to your own is a stupid idea??
I should not comment with bad words
that will make you look stupid
best regards
peter
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Old 26th May 2011, 03:24 AM   #1152
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I think it is wrong to call someone stupid if someone expressed his opinion, after all we are all here because of communication, build an amplifiers and a kind of coming together.

In conjunction with air coils, theory and practice show better performance for amplifiers who use a inductor with core of specialized materials for class D, and many comercial amps use them. Air cores are more linear and good for small inductors in serial with output at class AB, radio technic and speakers passive crossover.

Otherwise, my JBL and Yamaha 15" (hi class) speakres for crossover dont use air cores, but use some material cores (i dont know what is it, ferrite or micormetals..)
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Old 29th May 2011, 05:32 AM   #1153
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lori
do not confuse people all know that the best inductor is the air core, 30 turns of 12 awg wire cal has a very low dc resistance, and diameter of over an inch capacitance is minimal, I remember that it is a international forum and not everyone can get Micrometals inductors or similar
and use in tests of air core inductor is ideal.
the best option is this http://www.sagami-elec.co.jp/file/7g31a.pdf if it inductors
Like a couple of STW34NB20 work more than 650 kHz for high fidelity fans that if the dead time less than 25 ns
saludos desde Mexico
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Old 29th May 2011, 09:06 AM   #1154
Pafi is offline Pafi  Hungary
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Pedro!

A core is not an inductor. Air core can be good, if you want to build an induction heater, or antenne.

Forget about low DC resistance, it's not really important! Any resistance below 0.01*Rload (40 mohm at 4 ohms load) is perfect!

What is more important is Q factor at switching freq, and this is quite low for a multilayer air core inductor made of solid wire. The reason: magnetic field doesn't stay inside the "core", it penetrates into the wires as well, causing eddy currents. The density of this eddy current can be (and will be) much higher than the idle ripple current density, because it is induced by many turns.

And of course the opened inductor radiates very much EMI.

Capacitance can be low or high depending on the winding scheme and insulator type/thickness. (This also applies to any other cores.)

You wrote too many sentences I cannot understand:

Quote:
and use in tests of air core inductor is ideal.
Besides inproper grammar I still cannot understand:
In what tests? In what aspects? Compared to what other inductors?

Quote:
the best option is this
Best? You said air core is ideal! This is a shielded inductor!
Quote:
...if it inductors
Does anybody understands this?

Quote:
Like a couple of STW34NB20 work more than 650 kHz for high fidelity fans that if the dead time less than 25 ns
I can't decode this. What is the connection between these things?

But you are right, saying some idea is stupid is not a polite/clever behaviour.

Last edited by Pafi; 29th May 2011 at 09:29 AM.
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Old 2nd June 2011, 08:29 PM   #1155
NMOS is offline NMOS  Germany
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Hi, need help


look PCB,.... jave finished my first Class D project, amp works but

oscillating at high frequencies, i hear it in the tweeter

C17 or C5 in original schematic is hot after 4 minutes

mosfets IRFP250n

any idea to solve problem
Attached Files
File Type: pdf Class D UCD PDF PCB.pdf (99.1 KB, 764 views)
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Old 3rd June 2011, 06:02 PM   #1156
NMOS is offline NMOS  Germany
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Hi my first class D amp is working


1. but Inductor is very very hot and cooking
have make some test with different inductors

30 uh und 50 uh all the same ...cooking very heat and some high frequency noise

Does somebody have solution to remove noise ( its like noise from FM radio staion if signal is very bad) and cooking inductors heat

mosfets are warm.

2. today evening have test with inductor from defective PA class D amp, but with this inductor Mosfets cooking and inductor is only warm, noise is about 80 % gone but now I have another noise, it sounds like 19 KHZ Stereo carrier signal from FM radio station and Im surprised, 1,5 uf polyester capacitor after inductor is very warm with this inductor, ir 2110 is much more warm with this inductor too


I have add in my design all improvements from this forum like 1 NF in input stage and 100 uf to remove dc

and.... 100 pf with 22k to increase switching frequency compare to 330 pf in original design

have no idea to solve my problems

Last edited by NMOS; 3rd June 2011 at 06:07 PM.
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Old 3rd June 2011, 08:25 PM   #1157
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Quote:
Originally Posted by NMOS View Post
Hi my first class D amp is working


1. but Inductor is very very hot and cooking
have make some test with different inductors

30 uh und 50 uh all the same ...cooking very heat and some high frequency noise
You need to use a micrometals core.
t106-2 with a couple of meters of 18swg enamelled copper wire.
Ebay sells them in one offs.
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Old 3rd June 2011, 08:39 PM   #1158
luka is offline luka  Slovenia
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Old 4th June 2011, 06:57 AM   #1159
NMOS is offline NMOS  Germany
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Quote:
Originally Posted by paul14 View Post
For 2 cores i don`t know how to, but with 1 core you 15 turns
Click the image to open in full size.
where can i get this induction calculator soft...google nothings find v1.03a
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Old 4th June 2011, 09:04 AM   #1160
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Quote:
Originally Posted by NMOS View Post
Hi my first class D amp is working


1. but Inductor is very very hot and cooking
have make some test with different inductors

30 uh und 50 uh all the same ...cooking very heat and some high frequency noise

Does somebody have solution to remove noise ( its like noise from FM radio staion if signal is very bad) and cooking inductors heat

mosfets are warm.

2. today evening have test with inductor from defective PA class D amp, but with this inductor Mosfets cooking and inductor is only warm, noise is about 80 % gone but now I have another noise, it sounds like 19 KHZ Stereo carrier signal from FM radio station and Im surprised, 1,5 uf polyester capacitor after inductor is very warm with this inductor, ir 2110 is much more warm with this inductor too


I have add in my design all improvements from this forum like 1 NF in input stage and 100 uf to remove dc

and.... 100 pf with 22k to increase switching frequency compare to 330 pf in original design

have no idea to solve my problems
The inductor from class d amp may be a good choice.
Polyester capacitor is not suitable for this application. You should see its datasheet. Check for dissiaption factor. In a WIMA catalog PET (poly(ethyleneterephtalate) a polyester type) has 3% dissipation factor at 100kHz (increasing at higher freqs), while a polypropylene has 0,25% at 100kHz. So you should get some PP capacatior intended for high-frequency use, read the datasheet first carefully.
What is your switching freq? Scope pictures?
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