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Class D Switching Power Amplifiers and Power D/A conversion

LTspice Ncore simulation
LTspice Ncore simulation
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Old 3rd October 2018, 02:23 AM   #1
analogspiceman is offline analogspiceman  United States
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Default LTspice Ncore simulation

Hello,

I haven't posted here in a while, but I do a lot of simulation with LTspice and have written a number of pages on the LTwiki including most of the Undocumented LTspice page.

Perhaps some may remember the threads on my class d Leap-Frog feedback design methods (including full LTspice models, of course). I have modeled the original UCD amplifier and run some interesting analyses of the distortion (coloration) it produces as it approaches clipping. I can't remember if I posted those models here or on the LTspice Yahoo group.

I thought it would be a fun challenge to try to model the Hypex Ncore design. My resources are the latest white paper and the USA patent. Can anyone point me to other potentially useful material? Is an Ncore schematic available? Do any simulation files already exist?

I have created a 5-pole, 4-zero (I think - haven't derived the transfer function yet) network that reproduces the magnitude loop-gain curve in the white paper. The phase response curve is not published (at least I haven't seen it), but from the simulations (both ac and transient) it is critical to always keep the zeros from drifting into the right-half plane. This is not easy to do without extreme care - kudos to Bruno.

The Ncore design is conditionally (un)stable* and can oscillate both at the intended frequency of several hundred kilohertz or at about ten times lower frequency. By shorting out the second pole pair in the feedback network one may unconditionally kick it back up to its intended operating frequency. This works well in simulation (not surprising as it is key to the operation of the real life Ncore).

The point of going all this trouble is to achieve a significant increase in (flat) loopgain across the entire audio band. When this is combined with an open-loop transfer that has been optimally linearized, the result is extremely low audio distortion without TIM or other coloration (clipping artifacts are still a weakness, at least in the simulation).

Before I upload a simulation file that is off the mark, I was hoping to collect any further detailed information available.

By the way, I hadn't really looked into the Ncore before now - Bruno is a genius.
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* Not sure of the correct terminology for the fascinating feedback topology of the Ncore.
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Old 3rd October 2018, 04:24 AM   #2
kASD is offline kASD
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Welcome back Analogspiceman,

I do remember your leapfrog method and its inherent overcurrent protection feature. Your contribution here has helped in learning so much about the different set of approaches possible in a switching amplifier and ofcourse extracting the different set of waveforms in Ltspice.

I reckon you still main your hefty library of ltspice models, mind sharing it with us.

Here is your typical
NCORE

There is one more exact reference but I can't post it here.

Thanks for this informative thread.


Cheers
KAS

Last edited by kASD; 3rd October 2018 at 04:50 AM. Reason: Clarity
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Old 3rd October 2018, 04:32 AM   #3
analogspiceman is offline analogspiceman  United States
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Here is a related thread I just found on the EEVblog forum:

An experimental 4-th order linear audio power amplifier - Page 1

The subject is not a switching amplifier, but a linear amp that uses a conditionally stable fourth order feedback network with an oscillation detection circuit to quench instabilities by reducing the order to one.

The last post was in 2016. Simulation schematics are presented at the beginning of the thread.
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Old 3rd October 2018, 04:57 AM   #4
kASD is offline kASD
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Just for your reference
Attached Images
File Type: png ncore.png (54.7 KB, 443 views)
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Old 3rd October 2018, 05:48 AM   #5
analogspiceman is offline analogspiceman  United States
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KAS,

Thanks for the link and schematic. On page 86 of the linked thesis both magnitude and phase for loop-gain of the Ncore equivalent are shown. What is the source of the schematic in your second message (post #4)?
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Old 3rd October 2018, 06:02 AM   #6
kASD is offline kASD
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Hi Analogspiceman,

If its ok for you to PM me your email, I can send the file.
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Old 3rd October 2018, 07:07 AM   #7
irs20957 is offline irs20957  Russian Federation
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See this)))
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File Type: jpg ncore.jpg (254.3 KB, 421 views)
Attached Files
File Type: zip nCore.zip (4.7 KB, 58 views)
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Old 3rd October 2018, 01:34 PM   #8
Kuba_eM is offline Kuba_eM  Poland
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Quote:
Originally Posted by analogspiceman View Post
KAS,
What is the source of the schematic...?
The question is addressed to kASD, but maybe he will not offend as I give the source for everyone interested in: it is NAD M22, service manual availiable at elektrotanya.com, for example
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Old 3rd October 2018, 07:18 PM   #9
Reactance is offline Reactance  South Africa
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Quote:
Originally Posted by irs20957 View Post
See this)))
Where did this come from ? seems like the UcD design with a few mods, Ncore? I don't think so
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Old 3rd October 2018, 07:20 PM   #10
irs20957 is offline irs20957  Russian Federation
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NAD M22, NC400OEM
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