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Old 10th March 2012, 01:46 PM   #1771
Dimonis is offline Dimonis  Russian Federation
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Quote:
Originally Posted by norazmi View Post
Btw what exactly cause filter caps become hot? Too high freq?
Only bad quality caps ,never had such problem , maybe smth wrong with the inductor?
What amplitude of ocsil.frequency is at output ? And what frequency?

Last edited by Dimonis; 10th March 2012 at 01:48 PM.
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Old 10th March 2012, 03:53 PM   #1772
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inductor is T106-2, idk in real life because i dont have osc, in simulation its normal, output freq 500Khz before inductor. i`ll try change filter caps maybe its broken or bad.
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Old 10th March 2012, 04:28 PM   #1773
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Quote:
Originally Posted by norazmi View Post
inductor is T106-2, idk in real life because i dont have osc, in simulation its normal, output freq 500Khz before inductor. i`ll try change filter caps maybe its broken or bad.
What about the winding? How much turns?
To bad without oscil , you can't realy confirm that it's 500kHz .
Simulation is good , but the practical realisation differ a lot.
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Old 10th March 2012, 04:33 PM   #1774
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yup ur right Dimonis, i do measure with amprobe freq meter in real life. and i have inductor meter too, measure it 30 uh. I`ll try to find out and try to change with another filter caps. inductor remain cool, that filter caps hot when play loud, and at idle it remain cool. Trying to google too maybe i can find out what may cause the filter caps heat.
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Old 10th March 2012, 04:40 PM   #1775
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i`ve found this something interesting: by John Widder and Yun Tao Zhao, STMicroelectronics.

Class D amplifiers generally use a low-pass filter to attenuate the switching noise in the output waveform while passing the audio signal to the loudspeaker, but many engineers are not familiar with the functions performed by the various components in a Class-D amplifier filter or how to calculate the proper values. This article explains the purpose of the filter components and how to calculate their values.
The heart of a Class-D amplifier filter is a L-C low-pass filter. The corner frequency of the filter is chosen so that the filter will have minimal effect on the desired output frequency range while attenuating the switching noise as much as possible.

Low-Pass Filter
The optimum value for the filter inductor is
L = RL/2πfC
where fC is the desired corner frequency of the filter and RL is the load (speaker) resistance. Note that the inductor value is dependent on both the desired corner frequency and the speaker impedance so the inductor value will changes if the speaker impedance changes.
Practical designs require the use of standard component values so small adjustments usually have to be made to the ideal inductor and capacitor values. Rather than calculating the inductor and capacitor values independently and then adjusting their values, it's better to calculate the inductor value, select the closest standard inductance value, and then calculate the required capacitance using the selected inductor.
C = 1/((2πfC)2 • L)
The quality factor (Q) of a filter is the ratio of the center frequency to the filter bandwidth.
Q = RL√(C/2L)
A high Q produces an underdamped curve and a low Q produces an overdamped curve. The Q of the filter should be in the range 0.6 > Q > 0.8 to avoid underdamped or overdamped behavior. If you use the equations above the filter should have a Q of about 0.7, which provides good performance and allows for impedance variation in the speakers. Note that the Q of the filter will change if the speaker impedance is changed without adjusting the filter component values, which can result in an underdamped or overdamped response.
Component Selection
Not only is it important to choose the correct L-C filter values, it is also important to choose the correct types of components for the class-D amplifier in order to avoid losses and minimize harmonic distortion.

The DC current rating of filter inductors must be greater than or equal to the maximum current that it will see. The change in inductance versus load current should not be more than 10%. The core material can affect the amplifier's harmonic distortion and should have very low hysteresis losses.

The capacitor should be a multilayer polyester, polypropylene or polycarbonate film capacitor. Avoid using ceramic capacitors in the low-pass filter. Ceramic capacitors experience large changes in capacitance as the voltage across them changes, which can result in distortion.
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Old 10th March 2012, 05:37 PM   #1776
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Here's a simple program for calculating LC filter , which considers the above features.
R in Ohm F in Herz L in uH C in uF
Attached Files
File Type: zip Filter calc D.zip (239.6 KB, 324 views)

Last edited by Dimonis; 10th March 2012 at 05:46 PM.
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Old 11th March 2012, 03:16 AM   #1777
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solved, bad caps, all run good now
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Old 12th March 2012, 02:56 AM   #1778
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Domonis can i ask is it possible to replace 74HC00 to 74AC00 do they have same pin configuration, any parts to be replace?
does ir2110/2113 can drive 4 irf4227
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Last edited by irvynejay; 12th March 2012 at 03:02 AM.
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Old 12th March 2012, 07:22 AM   #1779
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Quote:
Originally Posted by irvynejay View Post
Domonis can i ask is it possible to replace 74HC00 to 74AC00 do they have same pin configuration, any parts to be replace?
does ir2110/2113 can drive 4 irf4227
1.Yes they have the same layout , the 74AC... serial is prefered , it's faster.
2. It depends on the working frequency of the amp , if above 250-300kHz - only one! If you try to drive more , the ir2110 will just simply overheat.

Look at the curve (it's from datasheet of the 2110)
It's not for 4227 , but find some approximately matching.
Attached Images
File Type: jpg 2110.JPG (52.0 KB, 736 views)
Attached Files
File Type: pdf ir2110.pdf (188.0 KB, 165 views)
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Old 12th March 2012, 07:35 AM   #1780
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ok i just replace the 74hc00 to 74ac00 and it work thanx
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