SystemD_2kW, any interest for an open design? - Page 12 - diyAudio
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Class D Switching Power Amplifiers and Power D/A conversion

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Old 5th December 2012, 10:36 AM   #111
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"P.S. To bad that you stopped your SOCD." -> Very little time and nobody there to help with layout software...

BTW.: From this project, I still have some unused 4668 at home. Choco, my contribution to your project could be that I could send them over to you for free if you want. Also, I think I can help you getting some schottkies at no cost. The IRS2011S would also be found in my desk's drawer...
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Old 5th December 2012, 10:45 AM   #112
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You mean the cascode which is often also called emitter switched BJT?
I remember ST has a strong portfolio where they have integrated both in one device.
Could be an option, but still you will have to provide the large base current consumption of the BJT - possible, but ugly on the high side.
And live with a higher overall voltage drop - not the typical solution for 200V.
IMHO more typical for >500V.
Nevertheless I will have a look to that, thanks for reminding me.
Did not consider these devices for classD up to now.
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Old 5th December 2012, 10:46 AM   #113
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" ....simply accepted that the speaker terminals are at +78V DC vs GND."

My intended PSU is single +178VDC (actually 3 PSUs of 59VDC secondary in series). The secondary side of the PSUs is isolated against PE (500V isolation), so I could just build a high-ohmic voltage divider to get a center voltage of +88V5 and connect this center point to PE -> speaker terminals free of DC. Not really an issue.
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Old 5th December 2012, 10:50 AM   #114
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Yes. Also I think discrete LV Mosfet+common gate IGBT may be worth trying.
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Old 5th December 2012, 10:55 AM   #115
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Quote:
Originally Posted by darkfenriz View Post
Yes. Also I think discrete LV Mosfet+common gate IGBT may be worth trying.
Hmmmm, tempting
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Old 5th December 2012, 10:59 AM   #116
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@Tom
That's a great offer!
The schottky's I could definitely need. Also freewheeling diodes.
IRFP4668: I have 14pcs, hoping that I will not fry more, but in case the project gets popular and enthusiast who want to build, then there will for sure happen a shortage in this forum...
IRS2011: I think I will stick with the IRS20957, accepted this chip as a friend during designing SystemD_MD and still have 16pcs available.

Let's check for further details by PM.
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Old 5th December 2012, 11:13 AM   #117
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"The schottky's I could definitely need. Also freewheeling diodes."
For freewheeling I recommend V30200C, also a schottky. A very good diode from Vishay, I don't think there is any better one for this applicaion.
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Old 5th December 2012, 11:47 AM   #118
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I have not digged for best freewheeling diodes so far.
V30200C is giving me sorrows regarding dv/dt rating. 10kV/us.
Already in SystemD_MD there are dv/dt slightly above that under hard switching close to current protection.
And this typically goes up with increasing currents....

The fat series shottkys are cool. 60CTTN015.
IMHO, the massive capacitance will not be a problem in the planned application.

Any real life experience on both topics above?
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Old 5th December 2012, 12:00 PM   #119
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We use the V30200C as a rectification diode for a forward converter. I do not think dv/dt in a diode is critical, they do not tend to fail due to excessive dv/dt - there is simply no mechanism that causes a diode to fail of dv/dt. Diodes fail of thermal runaway or too high cathode voltage 99% of the time. Most times it is the MOSFETs failing due to to high dv/dt (parasitic BJT starts to conduct or gate gets charged via miller cap). Still, I agree, that a reliable design should not exceed specified max rating - true.
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Old 5th December 2012, 12:01 PM   #120
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To me for freewheeling this one is also looking promising,
but max. dv/dt is not specified at all...
HFB35HB20
https://ec.irf.com/v6/en/US/adirect/...ctID=HFB35HB20
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