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Class D Switching Power Amplifiers and Power D/A conversion

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Old 28th May 2003, 03:48 AM   #41
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ssanmor, I have used two N-channel fets because
(1) I have lots of them and almost no matching P-channels
(2) You can get N-channel mosfets and IGBT's as big as you like. buahahaha..

The fets are driven by one each of International Rectifier IR2121 and IR2125 drivers. The provide isolation, good gate drive, level shifting so you can drive the upper fet, and current limiting.
RC filter? Yeah, I just wanted to see if I could get the thing working properly, not to make it super hi-fi or anything, so at the moment it sounds like reasonable quality AM radio.

charles, It has crossed my mind, and I haven't totally ruled it out but one thing that I am concerned about is the noise it would generate might find it's way into low level cct's and spoil the sound of the rest of the system. Ah well, nothing a magic power cord couldn't fix.

jonathan, buahahaha..
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Old 28th May 2003, 06:30 AM   #42
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Now this IS an interesting thread! My friend and I almost split a tri-path amp module to try it out. but conflicting specs all over their site and a lot of marginal posts about them caused us to get cold feet.

But we are both interested in them and the hype around the bel-canto and the PS audio amps.

Good work Circlotron, and please keep us informed as it progresses.

Sheldon

PS I love your signature line.
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Old 28th May 2003, 06:40 AM   #43
ssanmor is offline ssanmor  Spain
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>>ssanmor, I have used two N-channel fets because
>>(1) I have lots of them and almost no matching P-channels
>>(2) You can get N-channel mosfets and IGBT's as big as you l>>ike. buahahaha..


Ohhhh! That sounds good! It is exactly what I want to do, but I don't figure out how exactly are the driver connected to provide the shift level. This is, for me, the most difficult part of the design. Could you provide more details or a schematic of the driver stage, please?

Thanks!


(And yes, you can get N-channel mosfets quite easily as samples

Best regards
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Old 28th May 2003, 08:57 AM   #44
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Just a quick question... is calculating the power output for class D the same as normal bipolar amps?
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Old 28th May 2003, 09:24 AM   #45
ssanmor is offline ssanmor  Spain
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Assuming that you can go from 0% to 100% duty-cycle, the ideal output power is ((Vcc*0.707)^2) /RL.
For example, for a 8 ohm speaker and +/-40V rails, you can theorethically get 100W.
In practice, it is a little bit less, taking into account the RDS(on) of the mosfets and the duty-cycle limit of your modulator (for safety, it should be somewhat limited from 5% to 95%, for example.

Hope this helps.
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Old 28th May 2003, 11:06 AM   #46
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I think I get it now....
Circlotron's only using a half bridge not a h-bridge. I keep thinking of the lm4651, I'm guessing the h-bridge acts as a bridged amp so it can get over 150w at +-22v into 4 ohms.
Thanks for the help
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Old 28th May 2003, 03:31 PM   #47
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Default Bel Canto

Well I happened to hear the Bel Canto integrated digital amp.

Around 3K I think.

It really sounded good. Nothing bad about it. In fact its signature sound was a mix of tube / SS sound.

I would actually buy it if I had the $$
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Old 29th May 2003, 06:41 AM   #48
ssanmor is offline ssanmor  Spain
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Circlotron,
I have been investigating a bit about IR2121/25 drivers and it seems that the high side driver can work OK simply by connecting the outputs to the gate and source of the mosfet and the digital voltage and reference to, for example, +5V and 0V, so it's done.
The problem is with the low-side one. It seems that it cannot withstand negative voltages referred to COM terminal, so you have to connect this pin to the negative rail. This requires that the logic input is shifted and referrenced to ground.
Could you explain how did you accomplish that? Does your circuit uses any optocoupler? If so, could you draw the driver schematic?

Thanks in advance!!!
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Old 30th May 2003, 08:33 AM   #49
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Default All is revealed (almost)

The modulator cct in the Crown article would work fine, but I used a UC3637 pwm motor control ic because it was already there, and besides, it made things rather simple.
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Old 30th May 2003, 08:58 AM   #50
ssanmor is offline ssanmor  Spain
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Thanks, Circlotron!
I hope that my request for the schematic hasn't bothered you. It is very kind by you to share it with us, because some people doesn't feel like showing their work. You can be sure that it won't be used for commercial purposes, I'am "only" a hobbist.
I will investigate on modifying the circuit for use with the IR2110 driver, that is readily available here, in Spain.

Best regards.

Sergio
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