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Class D Switching Power Amplifiers and Power D/A conversion

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Old 7th May 2004, 05:13 PM   #1
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Arrow Class-D amplifier R&D

Everyone's invited in this thread , who wishes to apply some of their valuable knowledge on the class-D amp project which is considered as a revolution in audio amplifier development.
Unlike Class-AB amps this class-D amp must have some advantages over other types, such as
1 Less heat dissipiation
2 High-Fidelity
3 Ease of construction
4 Technological edge.

Now some good assumptions or say Standards[maybe]

1 Carrier must be A near perfect Triangular Wave @250KHz rather than a ramp.Which must be generated by fast opamp.
2 Must avoid use of CMOS IC's.
3 Natural sampling must be done.
4 Quad opamps such as TL074 may be used for avoiding long PCB track connections to prevent stray inductances as well as capacitances.
5 Full Bridge Configuration must be used to eliminate power supply pumping effect.
6 Air-Core inductor filters must be used to avoid saturation effect.
7 Good supply decoupling must be ensured.
8 Dual supply must be used for solidstate grounding w.r.t. positive as well negative bifurcation.
9 PCB track layout must be efficient and proper in R.F. respect.
10 Deadtime must not be greater than 200nS to reduce THD
11 Negative feedback maybe used to reduce THD levels.
12 Noise floor must be isolated by providing seperate grounding for signal path as well as power ground.

Here is the proposed frontend circuit of Class-D amp

DIYERS are requested to support this projects by constructive criticism and by their valuable suggestions.
Any Queries are most welcomed.
AT last correct me If i were wrong!
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Old 7th May 2004, 06:22 PM   #2
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Arrow Commentable Thoughts

Ampman eagerly awaits for comments!
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Old 8th May 2004, 05:16 AM   #3
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Arrow Commentable Thoughts

A question arises in my mind about the typical values of level shift resistors.
1 Type of opamp for Triangle generator [100MHz type fast opamp].
2 Can we use quad opamp TL074 for difference amp, error amp, complementary comparators.Will it give better resutls.
3 Howabout using tantalum capacitors for decoupling of supply rails of Gate driver IC IR2110 as well as opamps.
4 Can we fed single triangular wave to multiple comparators in multichannel amp for synchronisation.
5 How much of deadtime will be optimal for avoiding shoot- through in mosfets , while still maintaining sonic linearity i.e. low THD levels.
6 Max level of triangular signal.
7 How much of NFB must be applied.
8 Output filter design such as 2nd order butterwoth.
9 Snubbing Networks as well as Reverse recovery diodes.

EXPERT DIYERS such as
SIR "PHASE_ACCURATE" [CHARLES]
IVX[IVAN]
JAKA RACMAN
SSANMOR[SERGIO]
SUBWO1

Must contribute their valuable suggestions in this Group Project .
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Old 8th May 2004, 05:25 AM   #4
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Arrow Commentable Thoughts

A little bit of query regarding damping factor in class-D amps.

What are the factors effecting damping factors in class-D amps.

In what way it can be increased to get good low end response.


With R&D regards
amp+man=????
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Old 8th May 2004, 08:12 AM   #5
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If you were going to use a Mosfet driver like IR2110 (this would apply to most drivers anyway), couldn't you eliminate the level shifting by taking the negative rail as the ground and regulating the Centre tap down to the required levels. I assume your initial layout was for a floating supply for the modulation?
I'm not the best on Class D theory but i was under the impression the output inductors were the major factor in determining the damping value, a lower resistance inductor equals a lower damping factor i thought. I'm probably wrong but it was worth a shot.

Also, just out of interest, what is an class D amplifier fabricator doing asking questions on how to make them?
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Old 8th May 2004, 09:54 AM   #6
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http://pdfserv.maxim-ic.com/en/ds/MAX9700.pdf
Have a look under its spread spectrum feature. I'm not sure whether it will works at lower frequencies and higher power levels but I thought it may be a worth mentioning.
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Old 8th May 2004, 10:11 AM   #7
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Quote:
Originally posted by fr0st

Also, just out of interest, what is an class D amplifier fabricator doing asking questions on how to make them?
Mr. Frost We have only manufactured Class-AB N-channel MOSFET/IGBT amplifiers for professional market TILL NOW.
but we are engaged continously in Class-D R&D To start its production for betterment in amplification arena.


Again Thanks For ur comments.
With Regards
Ampman
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Old 8th May 2004, 10:19 AM   #8
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Arrow Commentable Thoughts

Quote:
Originally posted by fr0st
If you were going to use a Mosfet driver like IR2110 (this would apply to most drivers anyway), couldn't you eliminate the level shifting by taking the negative rail as the ground and regulating the Centre tap down to the required levels. I assume your initial layout was for a floating supply for the modulation?
Yeah u can be rite , then how we can reference the feedback from the out put of H- Bridge totem pole to the input of difference amp.

With regards
Ampman
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Old 8th May 2004, 10:57 AM   #9
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Arrow Re: Commentable Thoughts

Quote:
Originally posted by amp_man_1


Yeah u can be rite , then how we can reference the feedback from the out put of H- Bridge totem pole to the input of difference amp.

With regards
Ampman
Well , I remember that their is no need to reference the feedback to the center tap of transformer in case of feedback taken from H-bridge and fed to difference amp.
Secondly, only single supply will do the entire job for the amp, Thats why No level shifter, no Dual Supplies.

With Regards
Ampman
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Old 8th May 2004, 01:14 PM   #10
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Opamps are opamps and comparators are comparators. I wouldn't mix them up. I'm almost sure you could use the same opamp for the error amp, difference amp, and triangle generator, but I wouldn't use the same thing for the comparator to make the PWM signal.

With full bridge, the feedback path is necessary, but it is nice for lowering THD.

The level of the triangular wave depends on the input amplitude. General rule of thumb is to have about 80-90% modulation. 100% causes distortion, and its not good to have it too low.

If you're going to do full bridge (I would suggest it), then I would consider a full bridge driver such as the Hip4080 or 4081. This will probably make the output signal more accurate.

Just as a small suggestion, depending on what voltages the rails are, you might want to step down the voltage from the high and low side before the output filters. I don't think the difference amp wants to see a possible +/- 50 volts
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