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Class D Switching Power Amplifiers and Power D/A conversion

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Old 17th May 2005, 06:29 PM   #111
LBHajdu is offline LBHajdu  United States
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This seems to be the only thread where someone has actually built a working module, not just simulated.

How does it sound, for the brief amount of time you can run it?
Do you think it will become a functional DIY project?

Leve
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Old 17th May 2005, 06:35 PM   #112
MikeB is offline MikeB  Germany
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Hi !

It does sound quite good, the problem is, the hotter the better...
I think, if solve these "small" problems it will be a functional
DIY-project. I will continue this project later !

Mike
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Old 18th May 2005, 04:46 AM   #113
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Default Driver Stages

Sorry if I missed anything. You were talking about driver stages. have you considered using a MOSFET driver for the output stage or are we designing completly with BJT's here? I was working on a Class-D amplifier as my honors project for my BE degree last year where I used a IR2113 and I successfully got 60-80Wrms out and I could actually listen to decent audio.
The problem I got was the ringing on the edges (because they were so fast!) was getting back into my small signal stages. This was the sole factor stopping me getting more power outputs.
I would like to spend more time developing it, but now I'm tied up with my masters project designing a Hi-Fi CD pickup. Check out my site for the basics of the design (CB800D).



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Old 18th May 2005, 05:48 PM   #114
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Default Re: Driver Stages

Quote:
Originally posted by CarlBenton
Sorry if I missed anything. You were talking about driver stages. have you considered using a MOSFET driver for the output stage or are we designing completly with BJT's here?
Umm the thread is called "my fully discrete Class D" Presumably it's at least partly a matter of sports.

My own reasons for designing fully discrete circuits are cost, flexibility towards optimisation and (believe it or not)... simplicity. In a half-bridge circuit on a split supply, the extra circuitry needed to interface a comparator living around GND and a FET driver living on the negative rail is about as complicated as and more finicky than both functions executed in 3-legged, 2-junction parts.
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Old 20th May 2005, 10:59 AM   #115
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Oops, Sorry bruno. My bad! and yes you are right, is is difficult when dealing with the driver chip referenced to the minus rail! One of the problems I was having.
Well, lets keep it discret from now on then. lol
I am interested in seeing this design. Like "bcarso" said, I too would like a schematic.
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Old 20th May 2005, 11:24 AM   #116
MikeB is offline MikeB  Germany
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Hi !

I did not post latest schematic because it's not fully functional and i
can't recommend for building... I'll have to redesign the driverstage
completely. I will keep it fully discrete, just for simplicity and to keep
it easy to build.

Mike
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Old 24th May 2005, 03:24 AM   #117
Kenshin is offline Kenshin  China
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The fully discreet input stage is too complicated. Perhaps a LM311 will be better.
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Old 26th May 2005, 01:28 AM   #118
sovadk is offline sovadk  Denmark
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It looks to me like you're suffering from a awful lot of shoot throught in your design.

The schematic:
Click the image to open in full size.

The simulation
The uppler simulation shows the gate drive voltages. The lower simulation shows the output voltage and the current through the output transistors.
The problem is that the n-mos turns on before the p-mos has turned off. This gives a lot of shoot through when the output svings from high to low. You'll probably get a lot of distortion because of this.
The deadtime when the output swings from low to high, is very long. You should try to minimize this.
Click the image to open in full size.

I've attached the orcad files.
Attached Files
File Type: zip discrete_amp.zip (78.8 KB, 105 views)
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Old 30th May 2005, 01:39 AM   #119
sovadk is offline sovadk  Denmark
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I've worked on the power stage. This (see the schematic) seams to work well. Theres nearly no shoot through, however the switching time might be too long. You can try to minimize R34, R35 together with R21 to target this.

The basic idea behind this gate driver configration, is to connect the two mosfet gates through capasitors, so that they are always in sync. This also decreeses deadtime.
Shoot through is avioded by taking advantage of the gate threshold voltages. You can't turn one mosfet on before the other one is off.

Click the image to open in full size.

Notice that the mosfet currents have been multiplyed with a factor of 10 to make them visible.
Click the image to open in full size.

I've attached the project if any of you would like to work further.

Regards
Kaspar Sinding Meyer
Attached Files
File Type: zip discrete_amp_rev2.zip (89.3 KB, 119 views)
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Old 30th May 2005, 03:03 PM   #120
Kenshin is offline Kenshin  China
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There's another capacitor coupled toplogy on this forum, use zener to limit gate voltage, use diode to delay.
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