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Class D Switching Power Amplifiers and Power D/A conversion

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Old 17th August 2013, 12:43 PM   #3631
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another test irs3000 with atx ee core,
good sound with good weight,(bass)
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Old 17th August 2013, 08:20 PM   #3632
stewin is offline stewin  Kenya
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hi all can bus pumping cause class d to fail?
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Old 19th August 2013, 08:04 AM   #3633
stewin is offline stewin  Kenya
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Join Date: Jul 2007
thanks for the reply . i am facing serious issues with irs900 both thienchay and detex they work for a short time or a few days and fail i have had three different experiences .in all the above the voltage was
>>> +/- 70vlts about 6amps and filtering caps were 6800uf per rail.
>>>the load was 3ohms to 8 ohms
>>>all the output fets were one pair irfp250n
>>>all the inductor i used was etd 33 or ee 33 , 15turns and 1mm gap on both legs using a piece of CD or DVD disc
>>>switching frequency was 250khz normal on the thienchay and detex layout
two projects had two channels one project had four channels.

i am thinking maybe busspumping, slow fets ("but dismissing it because big proffesional companies powersoft use irfp250n") , non ucd topology or core saturation . please help i am really confused .

i have another irs900 three channels which has survived for one year plus without any issues except bowing fuse when one output of either channel ,a speaker or load is disconnected when the amp is on. all the specs are like the above except the voltage is +/-39vlts.
i will post photos later.
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Old 19th August 2013, 04:50 PM   #3634
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Location: Munich
Quote:
Originally Posted by stewin View Post
hi all can bus pumping cause class d to fail?
Basically it can, but with 200V MosFets running from +/-70V rails it is not likely.

Quote:
Originally Posted by stewin View Post
thanks for the reply . i am facing serious issues with irs900 both thienchay and detex they work for a short time or a few days and fail i have had three different experiences .in all the above the voltage was
>>> +/- 70vlts about 6amps and filtering caps were 6800uf per rail.
>>>the load was 3ohms to 8 ohms
>>>all the output fets were one pair irfp250n
......
i have another irs900 three channels which has survived for one year plus without any issues except bowing fuse when one output of either channel ,a speaker or load is disconnected when the amp is on. all the specs are like the above except the voltage is +/-39vlts.
i will post photos later.
Most short comings in layout, gate drive, snubbering and Qrr of the MosFets body diodes translate into pain for the MosFets. Detecting the most dominant short coming(s) is only possible with detailed measurements of the critical load situations using a fast oscilloscope.
Of course without any measurement you can be sure that the MosFet stress grows overproportional with the rail voltage.
So your observation that +/-39V is fine while +/-70V shows issues with reliability is nothing strange.

...sorry that I cannot offer a simple cure.
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Old 19th August 2013, 05:25 PM   #3635
stewin is offline stewin  Kenya
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thanks marcus but . i want to turn to ucd lorylaci schematic to try my luck. also i will use the only available good fet in my area which is the irfb4229 instead of irfp250.

what about output core 1mm gap and 15turns can it cause saturation and ruin the outputs?
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Old 19th August 2013, 07:15 PM   #3636
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Join Date: Dec 2003
Location: Munich
With 15 turns on an ETD34 and approx 1.1mm gap (CD) in all legs, I would expect an inductance somewhere in the range 10uH...15uH and saturation somewhere between 30A...45A.
Nothing to worry regarding saturation during realistic operating conditions.

For my personal couriosity:
Do you use solid wires, or stranded wires- which thickness?
How much self heating does the choke show during idle, when running from +/-70V at 250kHz?
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Old 19th August 2013, 07:52 PM   #3637
stewin is offline stewin  Kenya
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Join Date: Jul 2007
i use solid wires about 1.2mm - 1.8mm . and there is no core heating at all very cool.
>>>i think i should increase inductance about 30uh . i faced similar problems with ejtagle nonucd 200watts(" i was using t106-26 with 1mm cut by a hacksaw and 20turns") it used to fail at high spl if i used a 4 ohm subwoofer
>>>but after increasing the turns to 33turns every thing was o.k . i have used up to +/-47vlts with just one irf540n and one irf9540 and 4ohms load at high spl for a prolonged time and it did not have any issues at all. >>>also i have used 5channels with one powersupply +/-47vlts and in one body without any issues at all BTW the sub channel was bridged and had a load of 8ohms .

but because i need more power that is why i went the irs900 and aud600 way.

Last edited by stewin; 19th August 2013 at 07:56 PM.
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Old 23rd August 2013, 08:26 AM   #3638
stewin is offline stewin  Kenya
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Join Date: Jul 2007
Quote:
Originally Posted by paskal9 View Post
Click the image to open in full size.
managed to make them stable enough that i've decided to case them up and use them as the resident sub amp.

the output inductor goes too hot after 2 hours of movie run with huge bass so i've added an 80mm fan blowing to the pcb. gonna find another fan and do a permanent installation. the output mosfets are mounted to a heatsink underneath the pcb. the blue pcb on the top right is a 2x4 balanced minidsp to provide all the necessary dsp processing to the amp.

Click the image to open in full size.
they're quad channel irs900d bridged into 2 channel powering a 4 ohm sub. switching frequency are reduced to 250khz, output inductor are made from T106-2 iron toroid with 21uh inductance. output mosfet are irfb5615.

each of the bridged channel powers one of these 15" diy sub:
Click the image to open in full size.

in room frequency response of the subs powered by the amp:
Click the image to open in full size.
stopped at 102db before i could see any compression limit on the sub. don't wanna break the house.
hi paskal have you faced issues with the four channels you made or is it doing well?
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Old 23rd August 2013, 11:12 AM   #3639
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Location: chennai
Default hi stewin,

hi,,,
Greetings,
i face problem in irs3000, when i bridge the amplifier wont start oscillation,
are you have any solution for this problem,
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Old 25th August 2013, 05:15 AM   #3640
stewin is offline stewin  Kenya
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pls go back and visit pg 170 and 173>
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