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Class D Switching Power Amplifiers and Power D/A conversion

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Old 17th March 2013, 01:56 PM   #331
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Old 17th March 2013, 02:10 PM   #332
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Hi Panya,
Bruno loves you.
Hypex Electronics BV - UcD2kOEM
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Old 17th March 2013, 02:32 PM   #333
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Choco, now its your turn to refrain yourself from loving panya, otherwise..................
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Old 17th March 2013, 03:35 PM   #334
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???

You seem to see even more fun in my comment, than I had planned.

I originally 'thought':
...it appears like Bruno has copied Panya's design and now Bruno is making lots of money with that, so Bruno must love Panya...



P.S.
My design is not intended for making money.
To expensive. To complex. To large.
It is intended to bring fun to DIYers and audiophile listeners.
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Old 17th March 2013, 10:34 PM   #335
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...enough joking.

Panyahui,
I am not sure what your intension is:
Do you want to present your private build of the UcD2k? If so - nice.
Or do you want to promote business by spreading pictures of different copies in multiple threads? If so - clever, but I dislike the business model.
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Old 19th March 2013, 07:42 PM   #336
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Default Alternative Components

The design without shaping network in the feedback of the OP amp is very forgiving regarding the OP amp requirements. Even slower types allow an acceptable operation of the amp.
Attached an overview of tested OP amps and comparators.
Since last week end I am listening to the variations - I will comment in a few days.
Also it turned out that my concerns regarding the very fast comparators were unnecessary - the disturbances on this layout and with the EMI shields are so low that even the 10ns types do not show any misbehavior.
Amazingly the SNR is even slightly better with them.

Regarding alternative parts for the power semiconductors I will go for a further build. Meanwhile the first proto is simply sounding to good - I just cannot go for mayor changes on that one anymore.
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Old 19th March 2013, 08:14 PM   #337
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How come this "SystemD" changed from beeing clocked to become a self oscillating topology ?

Myself i've learned to dislike self oscillating due to the switching frequency dropping as the power output increases, to me this is not acceptable, the switching frequency should remain constant from 0% modulation to 80% modulation as beyond that, propagation delay prevent further modulation, meaning skyrocketing distortion.
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Old 19th March 2013, 09:05 PM   #338
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Quote:
Originally Posted by Tekko View Post
How come this "SystemD" changed from beeing clocked to become a self oscillating topology ?

Myself i've learned to dislike self oscillating due to the switching frequency dropping as the power output increases, to me this is not acceptable, the switching frequency should remain constant from 0% modulation to 80% modulation as beyond that, propagation delay prevent further modulation, meaning skyrocketing distortion.
Tekko i really thought after years being on this forum you would learn from professionally experienced people. im going to re-post this cause i don't want innocent newbies (like myself taking the advice you just posted)

Originally Posted by Eva
Here are some hints left in 2010 by eva regarding self oscillating amplifiers

Self oscillating loops have several interesting properties. For example, open loop gain is automatically compensated against changes in supply voltage, while in clocked modulators it's a direct function of supply voltage. This makes self-oscillating amplifier performance quite independent of supply rail voltage and sagging and improves PSRR dramatically.

Another advantage of self oscillating loops is that switching frequency is automatically reduced as the output approaches the rails, while keeping constant carrier residual amplitude at the output. This results in the minimum amount of switching events for a given carrier residual amplitude. In other words, switching losses are always as low as possible in self oscillating amplifiers. Switching frequency usually drops 2:1 or more before clipping.

Clocked modulators force the output stage to switch always at the same frequency, resulting in many switching events that are not really required, as the output gets closer to the rails and carrier residual amplitude becomes smaller and smaller.

Additionally, post-filter self-oscillating recycles the extra gain due to filter resonance as open loop gain, thus reducing output impedance (and THD too). In other words, the filter can resonate close to 20khz or even at a lower frequency without compromising frequency response.

Once you have put together a prototype which takes advantage of all this (and more), you don't feel like going back to clocked modulators.

Quote:
Originally Posted by Eva
Your main misconception about PWM amplification is assuming that a non-constant switching frequency results in non linearity.

The absolute minimum switching frequency is 2 times the maximum frequency you want to amplify, 44Khz for 22Khz audio.

The main reason for using 10 times higher frequencies (400Khz) is being able to deal with carrier residual with a 12db/oct output filter.

In clocked modulators carrier residual amplitude is maximum near 0V output and drops to 0 when the output approaches the rails (ugly looking waveform btw). Carrier residual amplitude is modulated by audio signal.

In self-oscillating modulators carrier residual amplitude is almost constant and frequency is smoothly reduced to keep it constant. There is no penalty, it just takes advantage of a "feature" of the output filter that you can't use with a fixed clock.

This reduction in switching frequency does not involve any reduction in the amount of negative feedback, so linearity is unchanged.

Another advantage of variable switching frequency is spread spectrum EMI. Variable switching frequency is now being used in many SMPS control ICs. I nearly always use it in clocked modulators too, for example in PFC.
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Old 19th March 2013, 09:55 PM   #339
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Well i do not like the reduction in switching frequency as power increases as it reduces resolution at higher frequencies. The only reason i can think of that ppl prefer self oscillating despite the switching freq drop is that during the power sucking transients, the highers frequencies are already sidechained(lowering the volume of other instruments during the duration of the kick drum) meaning the effect of the drop in switching frequency is hard to notice as its virtually impossible to cause much if any change in switching frequency at the treble range without going deaf as it takes pretty much earphone power levels to bring a tweeter to ear bleeding levels.

Some ppl on this forum have made up their mind though that 400kHz is nowhere even near enough switching frequency to allow an amp to be called hifi, but rather having to be 1MHz and beyond, which increases switching losses and EMI.

BD modulation solves this as a fullbridge approach virtually quadruples the switching freq, meaning a 250kHz switching freq at the fets still gives the same performance/resolution as a 1MHz single ended class d, unfortunately BD modulation cannot be achieved with a self oscillating topology as the output carrier residual is zero at idle, bringing back the so called disadvantages of clocked class d.

The BCA topology is another way of getting away with a lower less EMI generating switching frequency offering less losses in the fets without loosing resolution due to a low switching freq, and even in single ended mode it act like a frequency doubler wheres the standard BD modulation only works in fullbridge as in halfbridge it turns into a regular 1:1 switching frequency output. Also this topology cannot achieve self oscillation as the carrier resudial is also here zero at idle.

The tradeoff with BCA is always having current flowing in the output filter inductors much like the bias current in a class AB amplifier, even though it generates much less if any heat, its still more or less the same power drawn at idle which defuncts the whole point of class D, and is prolly why harman kardon stopped using it and went with a traditional class AB instead in the consumer stuff and left BCA for the professional stuff where power draw on idle is not a concern, yes Crown is infact a division of Harman Kardon IE the same manufacturer.
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Old 19th March 2013, 10:28 PM   #340
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Quote:
Originally Posted by Tekko View Post
Well i do not like the reduction in switching frequency as power increases as it reduces resolution at higher frequencies. The only reason i can think of that ppl prefer self oscillating despite the switching freq drop is that during the power sucking transients, the highers frequencies are already sidechained(lowering the volume of other instruments during the duration of the kick drum) meaning the effect of the drop in switching frequency is hard to notice as its virtually impossible to cause much if any change in switching frequency at the treble range without going deaf as it takes pretty much earphone power levels to bring a tweeter to ear bleeding levels.

Some ppl on this forum have made up their mind though that 400kHz is nowhere even near enough switching frequency to allow an amp to be called hifi, but rather having to be 1MHz and beyond, which increases switching losses and EMI.

BD modulation solves this as a fullbridge approach virtually quadruples the switching freq, meaning a 250kHz switching freq at the fets still gives the same performance/resolution as a 1MHz single ended class d, unfortunately BD modulation cannot be achieved with a self oscillating topology as the output carrier residual is zero at idle, bringing back the so called disadvantages of clocked class d.

The BCA topology is another way of getting away with a lower less EMI generating switching frequency offering less losses in the fets without loosing resolution due to a low switching freq, and even in single ended mode it act like a frequency doubler wheres the standard BD modulation only works in fullbridge as in halfbridge it turns into a regular 1:1 switching frequency output. Also this topology cannot achieve self oscillation as the carrier resudial is also here zero at idle.

The tradeoff with BCA is always having current flowing in the output filter inductors much like the bias current in a class AB amplifier, even though it generates much less if any heat, its still more or less the same power drawn at idle which defuncts the whole point of class D, and is prolly why harman kardon stopped using it and went with a traditional class AB instead in the consumer stuff and left BCA for the professional stuff where power draw on idle is not a concern, yes Crown is infact a division of Harman Kardon IE the same manufacturer.
so you start a poll feeling unsure about yourself "Your favourite self oscillating topology"
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