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Class D Switching Power Amplifiers and Power D/A conversion

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Old 25th January 2013, 12:57 PM   #71
stewin is offline stewin  Kenya
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Originally Posted by IRSound View Post
Thanks Manoj ,

but why ? because I checked the value of filter with accurate LCR meter..it was about 70uH.
what should i do then ?
what you think about EER cores with 1~1.5mm air gap ?
and my last question...what is your recommendation for output filter @ 250KHz ?

Regards,
IRSound
with aud600 ir900 and ir4k5 with my experience is 20turns of etd 38 which is about 18uh and output fets are cool but with 70uh all the above amplifiers : the outputs heat even at low volume with an 8ohm load
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Old 25th January 2013, 05:34 PM   #72
IRSound is offline IRSound  Germany
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Hi Stewin ,

as I know , choosing the right value for inductor depends on your load.
for example if we want to connect 8 ohm loads to amp (C=470nF) , you will need a 120uH inductor. also for 4 ohm the value is about 30uH.
we can select middle of those value : 120+30/2 = 75uH ~ 70uH.
with 70uH , the best load should be around 6 Ohm. but i don't know what is the effect with other loads.

Regards,
IRSound
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Old 25th January 2013, 07:31 PM   #73
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I'm by far one of the least competent members here, but those values seem way off. 120uH + 470nF will be down like -10dB @ 20kHz with an 8R load.

47uH + 470nF will be flat to 30kHz and down almost -40dB @ fSW with an 8R load.
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Old 25th January 2013, 09:22 PM   #74
IRSound is offline IRSound  Germany
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Thanks for help..
i wasn't sure about that...but i saw this equation somewhere :
L=4*(R^2)*C
is it correct ?
could you please help us to find some ways for calculating part values for this LC LPF ?

Regards
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Old 25th January 2013, 10:57 PM   #75
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I will post my all class d amps here
all DIYs can use this

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MANOJ

before I die?
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Old 26th January 2013, 05:58 AM   #76
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Originally Posted by IRSound View Post
could you please help us to find some ways for calculating part values for this LC LPF ?
Math is for smart people... I just use the calculator here...

RLC Low-Pass Filter Design Tool
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Old 26th January 2013, 09:18 AM   #77
IRSound is offline IRSound  Germany
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wow ,..
really thanks about that.

so , what is the good value for Cut-off freq of LPF ? for example with 50uH/470nF its calculated about 32KHz. how should we find this is good with amp Fsw ?

Regards,
IRSound
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Old 26th January 2013, 10:25 AM   #78
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IMO, it just needs to start rolling off ABOVE 20kHz and be down around -40dB at fSW. Obviously you don't want any (or minimal) peaking at or below 20kHz.

Playing around with that calculator you will see it's difficult to get a filter that works ok with both 4R and 8R loads. You either end up with excessive peaking or roll-off at the cut-off frequency.
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Old 26th January 2013, 11:41 AM   #79
abetir is offline abetir  Philippines
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Originally Posted by manojtm View Post
Hi IR,
use T106-2 with 59 Turns 0.8mm wire

Regards
MANOJ
Hi Manoj!

does this applies to AUD600?

You have mentioned T106-2 iron powder, I have them and I wanted them to be of use on AUD600, but before that....a few question here..

Can I power this amp using a lowly -/+35vdc? Was there a needed adjustment on the circuit?
Can I also use an external 12vdc bias circuit? (not the one on your psu board)
Please guide.

Regards!
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Old 26th January 2013, 05:04 PM   #80
IRSound is offline IRSound  Germany
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Quote:
Playing around with that calculator you will see it's difficult to get a filter that works ok with both 4R and 8R loads. You either end up with excessive peaking or roll-off at the cut-off frequency.
Yes, you're right.
i found inductor should be around 38uH for C=470nF and R4~8Ohm. but with lower and higher impedance you will have a bad step response.

i have another question , is the DC resistance of inductor is important in Class-D LPF ? because with lower AL value cores (like micrometals -2 series) you will have higher number of turns and lower number of turns for higher AL value cores.

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