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Class D Switching Power Amplifiers and Power D/A conversion

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Old 11th September 2017, 08:09 PM   #681
Cresnet is offline Cresnet  Jordan
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In the BOM +-80V, I cannot find the value for D7 & D8.
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Old 12th September 2017, 05:17 PM   #682
ChocoHolic is offline ChocoHolic  Germany
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That's correct. The +/-80V version is designed without D7 & D8.
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Old 12th September 2017, 11:33 PM   #683
00940 is offline 00940  Belgium
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Had some fun with the soic package... Plenty of room left on a 100*55mm board for an input stage and its supply (with only one mosfet package obviously). That's work for tomorrow.

No smd parts under 1206... should be easy to solder. All caps but the output filter's ones are smd NP0.
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Old 13th September 2017, 04:48 PM   #684
ChocoHolic is offline ChocoHolic  Germany
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Quote:
Originally Posted by 00940 View Post
...(with only one mosfet package obviously)...
I see you also skipped D7, D8, R30, R31.
Basically that is possible, however you might have to readjust R32 and R33.
Or alternatively you might need to enlarge the dead time. For dead time adjustment you will need R26, so better keep this in the layout.

No need to be afraid of immediate defects, but if you notice that during idle the MosFet is generating unpleasant heat, then will have to readjust.
And of course you can spend some months on retweaking the last 0.000000000% THD.

If you also intend to use the layout for +/-80V then you should increase various distances between tracks with rail voltage or halfbridge levels.

Last edited by ChocoHolic; 13th September 2017 at 04:56 PM. Reason: Typo
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Old 13th September 2017, 06:47 PM   #685
00940 is offline 00940  Belgium
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Once again, thanks for the warnings/comments/suggestions.

Quote:
Originally Posted by ChocoHolic View Post
I see you also skipped D7, D8, R30, R31.
Basically that is possible, however you might have to readjust R32 and R33.
Or alternatively you might need to enlarge the dead time. For dead time adjustment you will need R26, so better keep this in the layout.
Without much thinking, I indeed remove those resistors to ease routing. I intended to simply add 6r8+15 and use a 22r resistor. A bit naive maybe... D7 and D8 were skipped according to your suggestions (post 223).

I'll find a way to fit r26 back in.

Btw, since we're speaking layout do you think I need another pair of 1uF caps near the mosfet under the board ? I've got a pair next to the mosfets pins on the groundplane side.

Quote:
If you also intend to use the layout for +/-80V then you should increase various distances between tracks with rail voltage or halfbridge levels.
With one mosfet package, I'm doing this as a strictly home-hifi affair. I wouldn't feel at ease without the second pair of mosfets at those voltages.

Thus clearances are just like we discussed a few months back :
- the ground plane has an isolate rule set to 12mil,
- the power planes have isolate rules set to 16mil (I corrected the two tracks going to the left of the board, they were too close as there is 80v between them),
- the drc check is set at 12mil for the rest.
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Old 13th September 2017, 09:12 PM   #686
ChocoHolic is offline ChocoHolic  Germany
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Quote:
Originally Posted by 00940 View Post
Without much thinking, I indeed remove those resistors to ease routing. I intended to simply add 6r8+15 and use a 22r resistor. A bit naive maybe... D7 and D8 were skipped according to your suggestions (post 223).
I think keeping the 15R resistors unchanged would fit better, also fitting to post 223. (Higher drive impedance leads to shorter effective dead time.)
But in fact I did not go for a real life optimization of the single
MosFet version. With respect to this it is good that you will 'find a way to fit R26 in'.


Quote:
Originally Posted by 00940 View Post
... do you think I need another pair of 1uF caps near the mosfet under the board ?
Personally I would place it, even when in standard home use the stress is low - with a second pair of 1uF the design will fit for full power use at 4R load.
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Old 13th September 2017, 11:16 PM   #687
Eva is offline Eva  Spain
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A single SMD capacitor (or more) between +V and -V main power rails, as close as possible to switching transistors, keeps the highest frequency portion of switching current away from ground plane. A second SMD capacitor between -V and GND moves the highest frequency portion of voltage ripple due to switching currents to +V rail, which is not connected to any sensitive electronics. There are 220nF 250V 1210 X7R caps for 1st purpose, and even 2.2uF 100V X7R 1210 for 2nd. This makes possible brute-force turn-off with gate diodes and buffers, at di/dt over 1000A/us with modest EMI, which makes a cooler amplifier and removes the need for dead time.

Choco you are a good teacher, but remember that received knowledge remains connected to the master as long as the master has developed deeper knowledge or has more proof of concept.
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Old 14th September 2017, 07:48 PM   #688
ChocoHolic is offline ChocoHolic  Germany
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It is not about masters and pupils. It is about learning from each other.
More than ten years ago you gave me a good hint regarding resonances in the halfbridge and I took this hint as a highly valuable starting point for own examinations.
Of course over the years tons of insights came from my scope, combined with simulations/calculations and own fundamental considerations.
But it is not only the autodidactic process - many other hints on various topics came from various different sources (forums, colleagues, friends, books, papers, conventions...).

Why can't you accept to learn from others? I bet in April 2016 you were aware of the LiteAmp. Most likely you also were aware of my short overview about possible variations / evolutions of post filter feedback designs with the IRS2092, which I listed in posting #79 in this thread:
Tips and suggestions on IRS2092 implementation?
But completely ignoring all this you still posted:
'By design IRS2092 only supports pre-filter feedback...'
PA AMP 4 x IRS 2092 Full bridged 2 x 1000W RMS 4 OHM - 200 USD - real power or Fake ?
..and ignored my asking mail about the technical considerations why you insist on this outdated view.
I really beg: Please come back to a normal exchange of thougts.

P.S.
Regarding shortest dead times, or even overlap, or what you call no dead time:
In this region of timing I clearly refuse the wording dead time. In this region it's not about dead time, because here the model of dead time is simply insufficient. Any reasonable model for this is about the details of the transitions. The model has to take into account multiple types of transitions which happen partially in parallel, partially overlapping, partially in sequence. Transitions of voltages, transitions of currents and transitions of complex impedances. No matter how much brute force you will apply in order to speed up the switching - the switching is not an ideal step, but a transition. Dive into this and you will notice that brute force with 'no dead' time will lead to higher idle losses, but in turn it can reduce switching losses at medium and higher loads, because it allows to avoid or reduce the Qrr related switching losses and also reduces the commutation time for the load current. Both obviously leads to a smaller integral(Vds(t) x Id(t) dt).
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Old 14th September 2017, 08:36 PM   #689
Cresnet is offline Cresnet  Jordan
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Just finished the assembly of the 80V version, I noticed at that the Mosfets heats much more that those in the 40V version, at the same load.
28V 8A @ 4Ohms for example

Any advice?
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Old 14th September 2017, 09:03 PM   #690
ChocoHolic is offline ChocoHolic  Germany
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Without any detailed measurements it is impossible to see whether you are talking about the normal amount of higher losses in this operating point or if your build is still suffering from an error.


In any case please also be aware that the 2x80V is not intended to drive 4R.
Reference from posting #400:
Quote:
Originally Posted by ChocoHolic View Post
2x80V_IRFI4020:
Possible operating range: 2x50V...2x84V
Max. power at stabilized 2x84V: 400W / 8R
Power with realistically sagging supplies, idling at 2x80V:
250W/8R (not suited for 4R and 2R !)
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