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Class D Switching Power Amplifiers and Power D/A conversion

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Old 15th April 2012, 04:22 PM   #1
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Default Class D amp simulations?

Hello,

Are there any other simulations of a class D amplifier other than this on the www?

Why high voltage supply rail for class D amplifier?
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Old 15th April 2012, 08:18 PM   #2
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Quote:
Originally Posted by eem2am View Post
Hello,

Are there any other simulations of a class D amplifier other than this on the www?

Why high voltage supply rail for class D amplifier?
Besides looking for simulations in the www, it is really worth to play with simulation on your own computer.
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Old 15th April 2012, 08:53 PM   #3
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...just saw that you posted the same topic in three threads...
Well the reason to chose a certain rail voltage is to allow a certain max unclipped output voltage.
Usually it is not optimal to adjust the output voltage by the filter, because this implies that you will get massive changes in the output voltage depending on the signal frequency. Reasonable filters allow less than 2db change between 20Hz and 20kHz.

Adjustment of the output level usually is derived by adjusting the modulation level.
Do you want to share a certain clue behind your approach?
Or are you just asking?
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Old 16th April 2012, 06:20 AM   #4
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i hear you say output voltage but its the current in the speaker that counts....whether your rail voltage is low or high, you can still get equally high current in the speaker.....just see the simulations......

so why go for a high rail voltage?
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Old 16th April 2012, 06:50 PM   #5
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It seems like you are not targeting a HiFi application.
If you just want to produce a beep at a certain frequency, then you can of course generate high currents (and voltages as well) by a tuned resonance cricuit - by the expense of comparably high current stress in the entire load circuit.

But note, if you just want a beep (alarm signal application ?), then it would be by far more efficient to run the full bridge with the desired beep frequency and just feed that rectangle into the filter.
By using proper snubber caps on the switches, correct dead time and an optimized resonant circuit you can achieve ZVS and avoid switching losses.
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Old 16th April 2012, 06:58 PM   #6
Pafi is offline Pafi  Hungary
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eem2am!

It's quite unpolite to refer to a file which is not accessible without registering to a different forum.

And even if you attached here, don't expect others to use the same simulator as you!

You should show a format which is accessible for everybody. A picture for example.

And the real question seems to be: what you've been misunderstood? (Or not understood at all.)

No need for simulation for this kind of very basic and simple question. If you need simulator for this, then you need to learn basic electrotechnics first. And then you won't need to ask something like this.

Sorry!
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Old 16th April 2012, 07:11 PM   #7
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Thanks Pafi, I will get a picture uploaded....that i can manage.

I dont think edaboard.com forum is a competitor to diyaudio forum though, since this is a specialist audio site, so i doubt diyaudio staff will be concerned.

I am pretty sure that LTspice is the most advanced SMPS simulator of the free simulators available......it certainly can include the most nodes.

When designing an smps, or class D amp, its just standard procedure to get a representative simulation going so that i can check my calculated values using the simulator.....this is just being sensible.

No doubt if you have got money you may be using a much better simulator, maybe not....maybe if you have money you will want to use a simulator for smps which is made by one of the best simulation engineers on the planet (Mike Engelhardt of linear.com)
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Old 16th April 2012, 07:25 PM   #8
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Hi Pafi,
eem2am had posted the files also here, but in another thread.
Why high voltage rails for Class D amp?
Kind of annoying attitude to start three threads for the same topic....

@eem2am:
LT Spice is definitely a very good simulator for switching applications - not just among the free simulators.
Still wondering if you are going for hifi or beep.
If not beep, but hifi:
Most loudspeakers are designed for voltage drive from a low impedance voltage source (Key words: Damping, transfer function). Most woofers will generate a massive booming at their resonance, when driven from a current source.
Further have a look for basic design considerations of the output filter. There were some nice threads around recently.
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Old 16th April 2012, 09:17 PM   #9
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OK thanks Chocoholic, ill do that.

...that thread i post many places because that way many other beginners will benefit from the simulation of the class d amp.......it is the only basic simulation of a class d amp anywhere on the www.

Though in extra reply to Pafi, i tell that most designers are mentally compromised as myself.....and need simulations to get our thick heads into the job at hand.

Maybe you dont believe that most designers are mentally challenged like me?......well in that case, to you i will give proof!!.............i was recently working at a billion dollar global company who has a power supply dept............................400 $10 million dollar prototype units went unstable because the smps designer implemented a control loop which was pitiful.

i soon will post you his output of his 300w full bridge smps.....you will laugh.,,,and you will realise that most designers are thickeys like me.

oh and BTW i do not do just beep...i do for electric guitar


......................................
ok, so here is the output stage of the 220w full bridge with vin = 48v, vout = 29v, fsw = 300khz.

http://i40.tinypic.com/2h7f4p1.jpg

.....notice how ridiculous it is?

......look at where the bulk capacitance is.......AFTER the emc inductor, and with a 220mR resistor in series with the 68uF electrolytic.

Yes, this power supply oscillated like crazy when we changed from a fairchild CNY17-3 opto to a CNY17-3 opto by vishay..(ie same part just diofferent manufacturer)

When the load was added to this output, (the load had a 400uf cap in front of it, this made the resonent freq of the output emc filter go less than three times the crossover freq of the smps and it oscillated like crazy)

yes several million pounds wasted there.

Now do you beleive that there is a shortage of smps engineers and that most are mentally challenged individuals like me?

....i did not design this output stage by the way.........i told the designer i thought it was wrong, and he replied to me "proove it"..........so i wrote to a pal at a semiconductor company......that "pal" then against my wishes, saw how bad it was and went to the overall head of engineering of this big company......i tell you my name was mud for inadvertently going over my bosses heads even though it was not me...it was my "pal" from the semiconductor company.

Ok now we have straightened that most engineers are mentally challenged individuals like myself who need simple simulations to get there heads round a circuit before designing it...................may i re-ask my initial question....

Please does any person know if there is a simple class d simulation anywhere on the www (preferably in ltspice)

Last edited by eem2am; 16th April 2012 at 09:31 PM.
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Old 16th April 2012, 10:04 PM   #10
Pafi is offline Pafi  Hungary
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Everybody make mistakes. I do it many times also. But ignorance different from accident! Simulator prevents the expert form accidents, but cannot replace knowledge. If you can't interprete the results correctly, then the simulator is harmful, not helpful, because prevents using your brain.

I attached a picture to show what happens at different frequencies, if you choose the wrong inductor. It boosts the output at a frequency, but is this what you wanted to achieve? I quess not.

Or do you really ask why to use high supply voltage? You must have heard about Ohm's low!

Quote:
..notice how ridiculous it is?
Actually not. It can be stable. It depends on the details of the feedback, what is not on the picture.

Please OFF your own topic, if you wish!


+ I think pushing PrintScreen is easier than suffering from limited attachment size, and expect others to use the same simulator as you. And much more polite!
Attached Images
File Type: gif Unmatched filter.GIF (18.4 KB, 140 views)

Last edited by Pafi; 16th April 2012 at 10:08 PM.
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