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Class D Switching Power Amplifiers and Power D/A conversion

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Old 24th February 2013, 08:44 AM   #291
Cresnet is offline Cresnet  Germany
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Thanks for the valuable informations, but I would like to know the power supply voltage!

Thanks!!!
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Old 24th February 2013, 09:20 AM   #292
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All shown measurements were done with the Hypex SMPS1200A700.
It is delivering +/- 83V during idle situation and is stiff enough to allow the amp to deliver about 1200W sinewaves into 2R.

Edit:
When you drive the amp into heavy clipping with 2R load, then the SMPS is shutting down at about 1.5kW.
IMHO for professional applications this SMPS is only making sense if you use a limiter, which avoids heavy clipping.

Last edited by ChocoHolic; 24th February 2013 at 09:28 AM. Reason: see Edit
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Old 24th February 2013, 09:41 AM   #293
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Quote:
Originally Posted by ChocoHolic View Post
All shown measurements were done with the Hypex SMPS1200A700.
It is delivering +/- 83V during idle situation and is stiff enough to allow the amp to deliver about 1200W sinewaves into 2R.

Edit:
When you drive the amp into heavy clipping with 2R load, then the SMPS is shutting down at about 1.5kW.
IMHO for professional applications this SMPS is only making sense if you use a limiter, which avoids heavy clipping.
You using a Hypex SMPS1200A700 nice.. do you use this as your bench powersupply.

JSP Page

sigh its like 150 Euro Thats = 150 * 11.67 = R1750.5

anyone here know of a cheaper type sypply with the same quality and specification ?
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Old 24th February 2013, 10:49 AM   #294
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...yes, the Hypex supplies are not cheap.
But to me they appear to be well designed.
Not regulated, no PFC, but still overall good.
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Old 24th February 2013, 10:55 AM   #295
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Edit:
And they are designed with synchronous rectifiers, so they are not suffering from supply rail pumping in unbridged applications.
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Old 24th February 2013, 12:33 PM   #296
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-Overvoltage protection is fine.
-Over current protection is shutting down at 40A, here still a lot of work ahead to verify the worst case situation in detail and adjust to 50A and verify that...

-With respect to Tom's question, here the measurements regarding the damping factor.
I used a traditional solid state amp and a low inductive resistor to feed sine waves with 20App into the output of the class D amp and kept the input of the class D amp shorted.

@20App
20Hz: Voltage impact on D amp = 27mVpp, Ri= 1.35mOhms, ==> 2R damping factor = 1481
50Hz: Voltage impact on D amp = 28mVpp, Ri= 1.4mOhms, ==> 2R damping factor = 1429
100Hz: Voltage impact on D amp = 28mVpp, Ri= 1.4mOhms, ==> 2R damping factor = 1429
200Hz: Voltage impact on D amp = 28mVpp, Ri= 1.4mOhms, ==> 2R damping factor = 1429
500Hz: Voltage impact on D amp = 27mVpp, Ri= 1.4mOhms, ==> 2R damping factor = 1481
1kHz: Voltage impact on D amp = 20mVpp, Ri= 1mOhms, ==> 2R damping factor = 2000
2kHz: Voltage impact on D amp = 40mVpp, Ri= 2mOhms, ==> 2R damping factor = 1000
5kHz: Voltage impact on D amp = 97mVpp, Ri= 4.85mOhms, ==> 2R damping factor = 412
10kHz: Voltage impact on D amp = 206mVpp, Ri= 10.3mOhms, ==> 2R damping factor =194
20kHz: Voltage impact on D amp = 533mVpp, Ri= 26.7mOhms, ==> 2R damping factor =75
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Old 24th February 2013, 06:48 PM   #297
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Strange that you have less output impedance at 1kHz than at 50Hz.
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Old 24th February 2013, 08:26 PM   #298
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...right - I also wondered about that and double checked the measurements and got identical readings.
But we have to consider that the output impedance is extremely low.
On purpose I showed the 2R damping factors, while normal marketing strategy would be to show the 8R damping factor only at 1kHz - which is 8000
Cool number, but perfectly meaningless.
Anyway, when measuring such low output impedances already the magnetic field of the load wires can easily induce signals to the input of the amp which lead to output signals larger than the signal you want to measure.
Even with optimized wire geometries there will be fields which induce into the amp input. Also fields from its internal layout tracks and voltage drops in the GND plane influence the damping factor.
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Old 25th February 2013, 03:54 PM   #299
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nice done Choco ,great thread!
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Old 26th February 2013, 06:52 PM   #300
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Quote:
I also wondered about that and double checked the measurements and got identical readings
Can the loop gain have correspondent bump at 1kHz?
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