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Class D Switching Power Amplifiers and Power D/A conversion

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Old 15th March 2012, 02:46 PM   #1811
CPX is offline CPX  Romania
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Quote:
Originally Posted by Dimonis View Post
Hi CPX
My soundcard (built-in on motherboard Intel DP35) has such results (measured line-in-line-out) . I think they are not good enough for measurement?
And my netbook has awful noise ~56dB and IMD ~0.5%
Can't find Acoustic Analyzing System 5E , can you share it with me?
Yes..your results are pretty bad.Try decreasing output level a little(2,3 db) even if the software says volume to low in calibration windows .If the results are the same you can still test your amplifier by using substraction.
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Old 15th March 2012, 02:52 PM   #1812
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Originally Posted by manojtm View Post
Hi dimonis
Self osc. UCD is not good for Higher WATT (above 200W).It will create lot of problems
ie. Heat,Noise & high Start up Current
Why do you say that?A bad design will generate these problems not self osc ucd topology.
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Old 15th March 2012, 03:00 PM   #1813
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Why? The only reason you will get all those things is because of bad schematic or pcb design. Using an IRS20957 instead of a 2110 will get rid of those nasty level shifters, and allow a proper high-speed comparator running off +/-5v supplies. I have designed bridged self-oscillating amps, with fully-balanced input and modulator stages at significantly higher outputs than 200W.
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Old 15th March 2012, 03:02 PM   #1814
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BTW, my response was to the rather foolish statement by 'manojtm', not the sensible comment by 'CPX'!
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Old 15th March 2012, 03:06 PM   #1815
manojtm is offline manojtm  India
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Quote:
increasing the switching frequency will reduce the THD but also decreases the efficiency
and maximum output power level before clipping. Increasing
the switching frequency increases the amount of loss because switching currents lower the efficiency across the output power range. A higher switching frequency also lowers
the maximum output power before clipping or the 1% THD
point occur.
from LM4651 & 4652 Notes .their test App. notes fsw=125KHz
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Old 15th March 2012, 03:16 PM   #1816
manojtm is offline manojtm  India
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Quote:
BTW, my response was to the rather foolish statement by 'manojtm', not the sensible comment by 'CPX'!
This is not a foolish!!!!!!!!!!!!!!!!!!
you just tell me the Efficiency of your AMP
output imp. change your fsw
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Old 15th March 2012, 03:21 PM   #1817
manojtm is offline manojtm  India
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companies CROWN & Crest Audio they are not supporting self osc UCD for PA application

RGDS
Manoj
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Old 15th March 2012, 03:25 PM   #1818
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Output impedance doesn't change sw frequency much in mydesign(max 20 khz form no load to short).
My amp has between 10% and 90% efficiency

500 hz test:
1 ohm load: 9A 74%; 14A 81%;17A 85%
3 ohm load: 1A 41 %; 4A 77%; 8A 90%
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Old 15th March 2012, 03:30 PM   #1819
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Including the fully-isolated dc-dc conversion stage to allow operation of the amplifer from a 24V dc supply (converts 24V to +/-85V together with the associated low-voltage supplies), I get over 82% efficiency at 120W out. Tested this morning at half-power on a 240W amplifier. (This is a low power amp, but it is one I'm working on at the moment).
So perhaps 94% eff for the amp stage and 87% for the isolated dc-dc stage. I'm sure that someone like Eva can do even better.
I design class-D amplifiers as my main work for a very well known international engineering corporation, so I don't expect to be lectured at by someone who thinks an LM311 is a good modulator comparator!
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Old 15th March 2012, 03:32 PM   #1820
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Just in case anyone wonders why a 240W bridged amp requires +/-85V rails, that's because it has a directly-driven 100V output, so doesn't require the normal step-up transformer normally used on 100V PA amplifiers.
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