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Old 23rd January 2004, 01:54 PM   #1
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Arrow TRIANGULAR or SAWTOOTH which is best for CLASS-D

What typer of carrier switching waveform is best suited to class-d amps
Triangular or Sawtooth and why???
PLZ suggest
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Old 23rd January 2004, 04:00 PM   #2
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Default Re: TRIANGULAR or SAWTOOTH which is best for CLASS-D

Quote:
What typer of carrier switching waveform is best suited to class-d amps
Triangular or Sawtooth and why???
PLZ suggest[/B]
Triangular carrier waveform is the best due to:
1) Effectively doubling resolution due to two edges for the comparison
2) Because of 1) less high frequency components in the output spectrum
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Old 23rd January 2004, 04:03 PM   #3
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A Triangular waveform compleetly defeets the point of a class D amp. As with this sort of amp the output devices are supposed to be in their on or off state, where they dissipate littel power (due to either no curent flowing, or only a very small voltage drop when fully turned on). If you but anything other than a sqare wave through them, you will be not fully on or off very much at all, so there will be a lot of power dissipated in the transistors and the amps efficienct will fall quite a lot.
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Old 23rd January 2004, 04:11 PM   #4
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You misunderstand, bigparsnip

The triangle/sawtooth wave is what you use in a class-d amp as a reference to produce the PWM wave. amp_man_1 has no intention of trying to force a triangle wave through the output!

And for amp_man_1, triangle is best as soren has mentioned.

I designed a class-d amp on paper a couple of years ago and am now thinking of implementing it It was spookily similar to the one you posted recently. However, the NE5532 you used is too slow IMO. I am currently looking into very fast op-amps to try.

edit: Triangle is also best because you can make it symetrical about 0V very easily. With a sawtooth you have to align exactly to the mid-point (not easy) to have 'zero' output from the PWM, i.e. 50:50 mark:space ratio.
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Old 23rd January 2004, 05:18 PM   #5
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Ok, your are right here I suppose if you are talking about the signal into the PWM, I just thought when I saw switching signal that is was the signal being used to switch the output that was being talked about, not between the control parts.

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Old 23rd January 2004, 07:40 PM   #6
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Asymmetry in the triangle wave can be a slight help, depending
on the character of the comparator and asymmetries elsewhere.
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Old 24th January 2004, 05:01 AM   #7
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Arrow Commentable Thoughts

The reason for this question is that I want to use SG3525 as PWM instead of OPAMPS , but as far as SG3525 is concerned it has Sawtooth carrier wave not a Triangular waveform.
Does it seems a reasonable substitute?
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Old 26th January 2004, 11:37 PM   #8
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Default Op-Amps

Here's a hint. Yes Op-Amps are too slow. The really good Class D amplifiers use the LM319 precision comparitor. Two of them with the audio signal applied to each in cophase but the same triangle applied to each. You get cophase PWM signals and if you apply those in bridge mode to a bridge output stage, a lot of the grunge disappears.
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Old 27th January 2004, 08:44 AM   #9
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Hello Mr. DMFRASER
I think ur talking about Crest audio's LT series Schematics, aren't u.
Regards
ampman
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Old 27th January 2004, 04:41 PM   #10
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Default Dual Comparitor

Actually I'm talking ICEPower. I find the ICEPower are the best class D amplifiers available in terms of cost and sound quality. I am paying inder $100 (OEM 500 lot price) for the ICE1000A amplifier module, 1000W RMS and they sound great.
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