SystemD_2kW, any interest for an open design? - Page 7 - diyAudio
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Class D Switching Power Amplifiers and Power D/A conversion

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Old 28th November 2012, 04:21 PM   #61
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A few minutes ago an advertisement killed my posting.
I strongly ask the mods to think about the concept of advertising.
Often it happens, when I klick on attachments of postings that another window/tab opens and forces me to shop web pages etc.
My reaction is not at all that I would buy things there, it is more that I blacklist these companies.
Today it was worse. When sending my post - an advertisement page popped up.
I closed it, at least I intended to close it, but instead of getting rid of that advertisement my posting was killed. I do not care whether I might have missed the closing button by 1mm, but this sort of advertising is unacceptable to me!
Unfortunately I cannot do much more than blacklisting also this company....
I learned to live with floods of advertisement, but this newer sort of harassment and duress is really killing the fun on DIYaudio.
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Old 28th November 2012, 05:20 PM   #62
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The over voltage protection is still an open topic.
Desireable shut down window: 92V...100V

OVP1
My high end proposal with a dual OP and two precision references would end up
in the following additional components and solder joints for the OVP:
17 components
43 solder joints
Precision OK.

OVP2
Pergo's proposal with zener diodes:
9 components
21 solder joints
Tolerances and thermal drift of zeners, availability of the right zeners and the soft+slow discharging
of the 4u7 will make it hard to hit a reasonable shut down window.

OVP3
Another approach:
It is not necessary to check both rails in seperate, but the sum is relevant.
Furtheron the IRS20957 has a reference on board.
By measuring VREF and the real values of 330k and 10k it is easy to calculate the
necessary Rx. Of course for mass production such approach is unpleasant, but for DIY it is easy.
Both 2N5551 should be glued together in order to keep thermal errors acceptable.
11 components
25 solder joints
Precision: Adjustment needed.

Votes?
Further proposals?
If yes, please prepare in a comparable way.
Attached Images
File Type: jpg OVP1.JPG (56.7 KB, 540 views)
File Type: jpg OVP2.JPG (53.4 KB, 519 views)
File Type: jpg OVP3.JPG (57.5 KB, 508 views)
File Type: jpg OVP3updated.JPG (57.9 KB, 500 views)

Last edited by ChocoHolic; 28th November 2012 at 05:33 PM. Reason: Updated schematic with Rx for OVP3
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Old 28th November 2012, 05:41 PM   #63
pergo is offline pergo  Italy
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in OVP2 you don't need series 5k6 resistor with zener.
Let the zener going directly to the bjt base.
Better accuracy

ps: you can add a diode in series with zener for better stability over temp.

Last edited by pergo; 28th November 2012 at 05:45 PM.
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Old 28th November 2012, 05:59 PM   #64
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Better accuracy?
You mean better burning! It is not likely that a small zener and the base-emitter path can handle the currents that you would get by this clamping of the high power PSU.
I think it will need the series resistor.
Please note that this shut down disables the class D amp,
but supply voltage can still increase.
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Old 28th November 2012, 06:39 PM   #65
pergo is offline pergo  Italy
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ahh ok
I was thinking that the power supply will shutdown, not only the IRS.

But you cannot reach +-100V in any case.

Last edited by pergo; 28th November 2012 at 06:45 PM.
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Old 28th November 2012, 08:09 PM   #66
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Depending on the used PSU, there might be the option to shut down the PSU as well, but some folks might even use a monster transformer with rectifier and caps....
The shut down has to be set below a sum of 200V, definitely yes.
In case of good snubbering you do not need excessive margin there.
Setting it to 185V...190V should be OK.
For experiments with the intended choke for SystemD_2kW, I used SystemD_MD, which uses 150V-MosFets and ran this amp with +/-74V rails for pretty some time (first thermal considerations for the intended 2kW choke...). The amp acted like this would be normal. At room temperature typically the real avalanche happens not earlier than 10% above the specified voltage rating. Furtheron the avalanche voltage slightly increases with temperature and last but not least some amount of avalanche energy is allowed without destruction.

I think stopping the IRS should cover even serious overvoltage as long as the 100V rail caps do not lift their heads.
Closer look: As soon as the IRS stops, the output will be pulled towards GND by the feedback resistor and/or speaker. With this the Mosfets and the IRS will not see the full voltage any more but just the difference between rail and output.
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Old 29th November 2012, 05:15 AM   #67
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Choco,

I think somewhere in between we can implement the OTA LM13700 in order to facilitate several functions required in hysteresis control. I have seen a similar thing somewhere in IEEE article "Hysteretic PWM control method for all types of DC-to-DC converters"


Kanwar
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Old 29th November 2012, 05:20 AM   #68
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Quote:
Originally Posted by ChocoHolic View Post
An upgrade with much more comparator gain could be the second schematic, still I am not convinced that the extra efforts are worth it. But it simulates nice. Sloping with the concerned input signals takes 30ns, delay just a few ns (hard to believe).
Please also note the inspiration from Workhorse combined with my improvement to move the mirror to a neg voltage and clamping which avoids saturation of the BJTs.
Nice improvement Choco,

Clamping them with low reverse current schottky's will add further to improvement.
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Old 29th November 2012, 05:27 AM   #69
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Quote:
Originally Posted by phase_accurate View Post
For the impatient ones:
If driven to around 10% of max output voltage the influence on THD (which is low in this situation anyway) is benign, at 90% drive it means a THD improvement of about tenfold. But these are simulations and have to be taken with the usual grain of salt of course.

Regards

Charles
Hi Master,

I shall assume by 90% drive you mean during the large signal response[close to high voltage output swing near/close to rails] the hysteresis control is most worthy of its implementation. If this is the case then i think its good to explore more into this. Simulation looks extremely promising.

regards,
Kanwar
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Old 29th November 2012, 06:24 AM   #70
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Quote:
I shall assume by 90% drive you mean during the large signal response[close to high voltage output swing near/close to rails] the hysteresis control is most worthy of its implementation.
Yes, exactly. Because this isn't my mother-tongue I sometimes express myself in a little (?) unclear way.
It is also a problem with carrier-based amps that distortion increases with drive due to carrier aliasing (other factors conme into play as well but this is an often diregarded one). Some principles used to fight it are the carrier pre-distortion proposed by Candy or the MAE loops used by TI.

Regards

Charles
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