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Class D Switching Power Amplifiers and Power D/A conversion

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Old 25th April 2013, 06:12 PM   #11
godfrey is online now godfrey  South Africa
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No, I didn't post any class D amp schematic.

Where did you see the schematic with the mistakes?
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Old 25th April 2013, 10:32 PM   #12
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Here on forum.....but i forgot in which thread.
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Old 25th April 2013, 11:39 PM   #13
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Quote:
Originally Posted by Mikelandjelo View Post
I can tell u that this is good design and very powerful,easy to make,try and play with.Point is that somebody posted this here and posted it with mistakes which r now corrected,so u r welcome .
I can tell you from building something very similar that it will have hum problems with no input signal.
Any hum on the power supplies will modulate the output signal.

It can also have problems when overdriven like the VS power supply dropping out and possibly blowing up the output mosfets.

Been there and done it.

You are better sticking to something like an IRS2092 with its built in fault tolerance.
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Last edited by nigelwright7557; 25th April 2013 at 11:45 PM.
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Old 26th April 2013, 11:27 AM   #14
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I will not agree ..... srry .... this design is good one .... i didnt say best ever ...... This is single supply design if u didnt notice ..... On 24V to 50V it gives great power.....hum is discutable here ..... u can have hum becouse u made bad input regulation....Volume pot should be at the inputs on the sch and in front of them u should put fixed fg. x10 opamp.When pot is on max only hum which come to it will appear on output......if u short inoput on schematic there is no way that u can have anything on output.
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Old 26th April 2013, 08:19 PM   #15
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Despite my favor for postfilter feedback designs instead of no feedback at all...

I think this amp will not have much of hum with shorted inputs.
It is a full bridge. Without signal both halves will run at 50% duty cycle and generate identical hum vs. GND. But the speaker is not vs GND, it is differential between both ends of the bridge and hum cancels out. That's one of the inherent advantages of full bridges.
Hum will enter the speaker signal at larger modulations, but in that situation most people won't care, because then the music signal is by far larger than the hum.
It is likely to become visibile in detailed measurements with fourier analysis, but I can easily believe that it is no headache under normal use conditions.
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Old 26th April 2013, 09:14 PM   #16
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Hence why fullbridge is suitable for openloop designs wheres halfbridge is not.
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Old 26th April 2013, 09:47 PM   #17
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Quote:
Originally Posted by Tekko View Post
Hence why fullbridge is suitable for openloop designs wheres halfbridge is not.
Because:
Without signal both halves will run at 50% duty cycle and generate identical hum vs. GND. But the speaker is not vs GND, it is differential between both ends of the bridge and hum cancels out.

In a half bridge the speaker is between half bridge and GND ==> no differential connection of the speaker between of two identical hums ==> no canceling of the hum.
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Old 27th April 2013, 01:02 AM   #18
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I will try to explain how i see hum ....

First of all i will not agree that full bridge create less hum than half bridge.As audio signals r amplified by 2 times or more in full bridge topolgy also is hum.Couse hums of the chanels r in oposite phases.

Second , and most important......hum is modulation which is transfered to speakers.....Modulation can exist only if it happens on input comparator.It can happen in normal conditions on few ways.

1. If triangle voltage has floating while input is zero......
2. If voltage which is setting the 50% duty cycle is not super stabilised
3. If comparator has ulta super small input current (most of the cases).Then even smallest variations can make hum (which is high frequency modulation)
4. If input audio pre amp is not well compensated
5. If voltage for triangle generator and comparators (read PWM section) is not well regulated.
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Old 27th April 2013, 02:03 PM   #19
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Quote:
Originally Posted by Mikelandjelo View Post
Second , and most important......hum is modulation which is transfered to speakers.....Modulation can exist only if it happens on input comparator.It can happen in normal conditions on few ways.
Definitely no.
The concerns in this thread are not about hum which enters the speaker signal through the modulator.
People are trying to point to the hum which enters the signal through the switches directly from the power rail.

Just do the most basic calculations:
1. Set a constant and perfect idle duty cycle of 50%.
2. Assume some portion of AC voltage on the power rail.
3. Apply Kirchhoff's voltage law to calculate the voltage across the speaker.
==> You will see the advantage of the full bridge.
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Old 27th April 2013, 09:37 PM   #20
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O yes , (I like this conversation) ..... We r discussing about most important things here....not related to the schematic that i posted.....And i like the discussion.I am sure that we all will learn.

Full bridge is doubling output voltage and making 4 times higher power on output.....mathematicaly.....in real world that is power boost of 2.If power is boosted then hum and noise r boosted too.U didnt read slowly what i wrote in my post.If u have AC on power rail.....and this is real case......then if u alow to that AC to be present on your DC which is on low side of amp u will have triangle signal floating and most important thing DC voltage which is setting 50% will float too.Full bridge is huge advantage to get super high power boost but only if DC on low side is perfect.Also any input preamp stage should be low impedance input (audio side) and not high imepdance (that combined with gain of 10 fg. will create hum all the time.

This tehnique (D-Class) is state of art of progressing in electronics,possibilities r unlimited.I am looking forward to hear what u guys think about this.
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