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Old 24th August 2011, 11:36 AM   #1
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Default Hard clipping classD

I have one interesting problem with all my prototypes of classD, they donot clip cleanely, like classAB, instead they clip like this (one photo finded on this forum).
I have tryied many feedback schematics, including self-osc or clocked designs, comparators LM311-LM319-AD8561, dead time with CD4070-74HC02-74HC14, drivers IR2110-6N137 and TC429, the same results. Even a Behringer PMH5000 distorts like this, unmoddified.
I have developed one clipper schematic, sensing supply voltages and preventing this clipping, but i think this is a band aid.
I want to know if this clipping is a normal thing in a full range classD, without any tricks (clipper, limiter).

Even my sims (Philips Ucd, discrete design) indicates problems with recovery from clipping.
Attached Images
File Type: jpg 800w 8ohm b.jpg (83.4 KB, 359 views)
File Type: jpg before clip.jpg (186.8 KB, 348 views)
File Type: jpg right before crack.jpg (200.0 KB, 334 views)
File Type: jpg clip.jpg (194.8 KB, 329 views)
File Type: jpg sim ga ucd.jpg (174.6 KB, 319 views)

Last edited by ionutgaga; 24th August 2011 at 11:47 AM.
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Old 24th August 2011, 11:50 AM   #2
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Is your bootstrap cap running out of juice?

Warm regards
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Old 24th August 2011, 11:53 AM   #3
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They clip on both positive and negative, meaninig this is not a problem regarding bootstrap circuit. Offcourse, i have tryiet with floating small smps, the same result.
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Old 24th August 2011, 11:58 AM   #4
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Photos take it from Ucd based feedback, 370khz at idle, AD8561, 74HC02, IR2110, IRFB4332, +/-100v, T130-2, 40uH and 2uF.
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Old 24th August 2011, 01:14 PM   #5
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I'm not sure I understand the problem. Why do you want your amp to clip in the first place?
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Old 24th August 2011, 02:23 PM   #6
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This is normal
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Old 24th August 2011, 02:35 PM   #7
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A self-oscillating design will always stop oscillation when driven into clipping, and the reduction in switching frequency just before (and after) clipping is normal. The reasons for this are fairly well documented on the web. A well laid-out UCD design will exhibit a somewhat cleaner entry and exit of the clipping region than is shown in the photos, but what you show is fairly normal.

Don't forget that the bootstrap capacitor will be slowly discharging when the circuit is not switching, so make sure it has eenough capacitance.
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Old 24th August 2011, 08:44 PM   #8
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I have had problems with clipping on the IRS2092.
Driving it hard is fine but if I hard clip it then the chip will sometimes gets upset and resets. IR just said dont overdrive it into hard clipping, useful reply lol They said if I apply more than 10 v pk to pk then it will upset the input and cause the chip to reset.
Murton-Pike Systems PCBCAD51 pcb design software. http://www.murtonpikesystems.co.uk
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Old 25th August 2011, 08:05 AM   #9
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In this topic ucd 25 watts to 1200 watts using 2 mosfets Eva says:

Originally Posted by Eva View Post
Additionally, a minimum pulse width circuit with a quad NAND gate prevents the IR2110 from malfunctioning due to too narrow pulses at the inputs. This is a known failure mode of IR2xxx chips.
It is applicable with self-osc schematics?
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