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Old 8th October 2009, 01:39 PM   #1
moro696 is offline moro696  Romania
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Default Building a 1000W @ 8ohms class D amplifier from zero

Hi guys, i`m new here only few weeks ago and i saw many people doing class D projects, saw some intresting projects arround here. Cheers to all class D fans
I`m not new in smps/pwm domain, in the last 3-4 months i have learn things about smps fenomens that a year aqo where quite strange to me.
Let me tell you what this project is all about, i want to build a class D amplifier with a rated power of 1000W even more, probably in the future i want to achive 2-2.5 kw. I know it's a lot of power, but there is no need to be sceptic around here, so i want to start this project, i have over 2 years already in pcb design so i think it won't be a problem.
Let me get to the point of this project.
What i want to build is a 1kw @8 ohms in full bridge, non self oscilating triangle, but this will be somewhere at 250-300khz
I want to use LM361 for the main comparator, some 6N137 optocuplors for the optical isolation betwen the Hard switching drives and mosfets.
The output chokes for the Low pass filter wil be some iron powder cores.
I'm not home right now, but tonight i will post a principle schematic of what i wanna achive.
What i wanna ask you guys if you know some documentation regarding the design of feedback uppon this kind of amplifiers, any sugestions are wellcomed.
I wanna say in the end that i want to use this amplifier for 8ohm load and 4ohm load, reading some aplications note from IRF, i saw that the LPF filter is design specific for a single load (ex 8ohm,4ohms,2ohms) i want to do something universal to say so.
What do you think guys?
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Old 8th October 2009, 08:41 PM   #2
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Hi.
The circuit tested by me on 8 Ohm
Are installed IPFB 4227
Power supply +-70V
Attached Files
File Type: pdf 1200W.pdf (78.7 KB, 7232 views)
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Old 9th October 2009, 04:49 AM   #3
moro696 is offline moro696  Romania
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Here is how the finalstage looks http://www.webpix.ro/imagini/final.gif

I used TC429 for drives, they are strong enough to handle 6A peaks. I use them so in the near future probably i will want to handle more power on output.
Anyway now i have a little time for this, i am stil working on designing the amp.

By the way nikula, your schematic looks nice . How did you design the feedback circuit? That's what intrest me more, i saw many problems regarding feedback control. In my opinion a bad feedback causes nasty smoke...
Regarding the choper transistors, i too was thinking to use IRFB4227, they are probably the best solution for high power class D amps.
I will come back latter, now i gotta run to work

Cheers
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Old 11th October 2009, 06:57 PM   #4
moro696 is offline moro696  Romania
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no one nothing?

Last edited by moro696; 11th October 2009 at 07:01 PM.
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Old 15th October 2009, 01:57 PM   #5
cloudy is offline cloudy  Hong Kong
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Quote:
Originally Posted by nikula View Post
Hi.
The circuit tested by me on 8 Ohm
Are installed IPFB 4227
Power supply +-70V

full bridge?
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Old 15th October 2009, 03:22 PM   #6
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Quote:
Originally Posted by nikula View Post
Hi.
The circuit tested by me on 8 Ohm
Are installed IPFB 4227
Power supply +-70V
could u plz provide a pcb to make it
coz the schematic seems hoorrible
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Old 15th October 2009, 06:19 PM   #7
Pafi is offline Pafi  Hungary
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Moro696!

With post-filter feedback: PI controller, and D in the feedback. The PWM modulator can be replaced by a gain of Vdd/V_triangle in the simulation, this way you can adjust the controller's parameters.

Be careful! If you use post-filter feedback, then you must pay many attention for the filter's parasitic effects!
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Old 16th October 2009, 08:35 AM   #8
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Quote:
Originally Posted by nikula View Post
Hi.
The circuit tested by me on 8 Ohm
Are installed IPFB 4227
Power supply +-70V
Upper side driver's VCC is 5V?
No dead time in front of gate driver and high value of gate turn-on resistor?
Very low input impedance?
Care to comment?
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Old 16th October 2009, 08:45 AM   #9
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Quote:
Originally Posted by moro696 View Post
Here is how the finalstage looks http://www.webpix.ro/imagini/final.gif

I used TC429 for drives, they are strong enough to handle 6A peaks. I use them so in the near future probably i will want to handle more power on output.
Anyway now i have a little time for this, i am stil working on designing the amp.

By the way nikula, your schematic looks nice . How did you design the feedback circuit? That's what intrest me more, i saw many problems regarding feedback control. In my opinion a bad feedback causes nasty smoke...
Regarding the choper transistors, i too was thinking to use IRFB4227, they are probably the best solution for high power class D amps.
I will come back latter, now i gotta run to work

Cheers
This looks nice, I like the idea of buffering the gate driver, several comments:
- you must oversize the bootstrap capacitors to handle extra supply current from the buffer
- you should experiment with schottky turn-off, this may be tricky to control dV/dt with such a high gate charge current and parralleled mosfets
- output filter should also have capacitors to ground to kill common mode ripple (you filter only differential mode here). Don't let speaker cable to become an antenna
- why do you want an optocoupler?
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Old 16th October 2009, 09:11 AM   #10
luka is offline luka  Slovenia
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Quote:
Originally Posted by darkfenriz View Post
Upper side driver's VCC is 5V?
I think there is error here, since lower one has 12v, I assume other will have it too
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