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Class D Switching Power Amplifiers and Power D/A conversion

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Old 13th March 2005, 01:18 PM   #21
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Hi analogspiceman,
this is Micro-cap 7 -isn't best, but very useful for me.
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Old 13th March 2005, 01:39 PM   #22
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Quote:
Originally posted by IVX
Hi analogspiceman,
this is Micro-cap 7 -isn't best, but very useful for me.
I recommend that you try LTspice. It's free and in my opinion is faster, more powerful than Pspice (don't know about MicroCap) and easier to use. The link to the download is at the start of this thread (it is only a few megabytes).

By the way, it seems that THD as reported by the .four command is not reliable with these class D simulations. The numbers vary too much with the integration method, tolerance setting, maximum step size, total interval, etc. I can get either of the LeapFrog or the UcD design to come out with better THD by playing around with the simulator settings. Worse, there is no simulator control set up that consistently yields the lowest THD. The numerical noise is just too high to measure low THD reliably. That must wait for the actual hardware, it seems.

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Old 13th March 2005, 02:20 PM   #23
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Quote:
Originally posted by analogspiceman


By the way, it seems that THD as reported by the .four command is not reliable with these class D simulations.
Thanks for mentioning it. I was recently wondering about trying the Fourier analysis. I am not good with math anyway.

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Old 13th March 2005, 03:09 PM   #24
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Do you plan to build LF amp?
My modest DIY experience, in the real implementation of the class D amps, doesn't show even 50% THD matching vs simulations (MC7, P-spice), and i've feeling that it isn't only from the bad quality of the implementation/equipments etc. :-)
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Old 14th March 2005, 02:51 AM   #25
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Pardon me, D5 and D7 are drawn like Zeners, but in the datasheet BAT54 are schottky. What is this dioda, what is the purpose in this CCT?
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Old 14th March 2005, 02:54 AM   #26
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Quote:
Originally posted by IVX
Do you plan to build LF amp?
My modest DIY experience, in the real implementation of the class D amps, doesn't show even 50% THD matching vs simulations (MC7, P-spice), and i've feeling that it isn't only from the bad quality of the implementation/equipments etc. :-)
I have no immediate plans to build an either of these designs although it might be fun to do a layout - and then, who knows?

Class D THD can be sensitive to layout imperfections via self EMI - bad layout may increase THD. Simulated Class D THD can be sensitive to computational imperfections - bad time step quantization may increase THD. So, in your experiences, which way did it go?

By the way, I am attaching the LTspice files for the two schematics shown earlier. (Remember, the first post in this thread has a link to where one may obtain a free copy of LTspice.)

Regards -- analogspiceman
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File Type: zip classd_leapfrog_ucd.zip (5.3 KB, 298 views)
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Old 14th March 2005, 04:07 AM   #27
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Quote:
Originally posted by analogspiceman

By the way, I am attaching the LTspice files for the two schematics shown earlier. (Remember, the first post in this thread has a link to where one may obtain a free copy of LTspice.)

Regards -- analogspiceman
You've given some great ideas.
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Old 14th March 2005, 05:16 AM   #28
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Quote:
Originally posted by analogspiceman

So, in your experiences, which way did it go?

Regards -- analogspiceman
I don't know..i'm just a DIYer.
!!!Seems your amp will be well work without input+feedbacks_summing opamp. I just now check this out. Sure that opampless circuit much more preferable.
Maybe replacing ifb inverting opamp is possible also, with symmetrical mirrors instead? And all this come to the fully differential view (i'm saw it somewhere without ifb though..;-)?
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Old 14th March 2005, 07:29 AM   #29
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Hi analogspiceman, I played with the UcD circuit to see how I could adjust its performance. I was wondering if you'd like to see what I came up with. I don't think it is as optimized as I could get it, but I thought I'd post the LTspice circuit how I got it after a while. I was wondering how it compares to the leapfrog method, in your opinion. I added rc passive damping to the output and adjusted the feedback.
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File Type: zip classd_ucd180-2.zip (2.4 KB, 256 views)
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Old 14th March 2005, 07:40 AM   #30
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Quote:
Originally posted by lumanauw
Pardon me, D5 and D7 are drawn like Zeners, but in the datasheet BAT54 are schottky. What is this dioda, what is the purpose in this CCT?
Hi lumanauw, those diodes are schottky, and their purpose is to prevent the driver input transistors from saturating. They speed the circuit response and makes its operation smoother and more linear. They are called baker clamps in this application.
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