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Old 24th October 2005, 10:24 AM   #11
Pierre is offline Pierre  France
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I am not sure at all about the level-shifter implemented inside the LM311...

Please have a look at another thread that is very active lately : "how to fix this sch". I proposed a simple topology for level-shift, gate drive and bootstrap. It hasn't been tested but should work better or worse. It is in fact the individual stages are very similar to your proposal, but it is simpler, and it uses a level-shifter based on a transistor after the PWM modulator.

Have you implemented that sch in real life?

Best regards,
Pierre
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Old 24th October 2005, 10:54 AM   #12
TroelsM is offline TroelsM  Denmark
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I'm not going for an discrete solution but a cheap and easy one. The inverters are dirt-cheap and do a nice job at "cleaning" the signals.

The schematic hav'nt been implemented yet, but one of these days it will be.

The levelshifter from the LM311 will be fixed soon.

I'll have a look at some of the other threads (again) and return with the updates to the schematic

TroelsM
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Old 24th October 2005, 11:07 AM   #13
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Default Re: Simm of the amp

Quote:
Originally posted by TroelsM
Here's the first set of sim-result's:

The amp dos'nt osc at startup but it starts after a period when the signal goes negative. I don't think this is a problem.

At high pos. voltage at the output the freq drops very much. Hav'nt figured out why. It's very late 4.08 in the morning). Im not gonna work on that now.

TroelsM

You're right, it isn't a problem..... in simulation

I think you'll find it will be in reality. All it takes is a simple circuit to precharge it, and a slightly more complex one to provide a delay at turn on to ensure it has the time to fully charge.

Some level of frequency modulation is natural in most self oscillating amps but it shouldnt' drop too much. That's why it's good to switch at 500kHz instead of 320kHz. Then you dont' really care all that much if it drops down even 150kHz.

There may be ways of limiting it with tweaking feedback as well. I couldn't tell you how though. Maybe Charles can.

Regards,
Chris
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Old 24th October 2005, 11:20 AM   #14
tlf9999 is offline tlf9999  United States
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here it is.

Available on page 5.

http://www.cqpub.co.jp/hanbai//PDF/30391/30391_1syo.pdf
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Old 24th October 2005, 11:27 AM   #15
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Sorry, what's on page 5 exactly?
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Old 24th October 2005, 11:30 AM   #16
TroelsM is offline TroelsM  Denmark
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Pierre: If this is the sch youre referring to (http://www.diyaudio.com/forums/attac...amp=1129882065). Then I don't get it... have you simulated it? The level at the base, at top BD139/BD140's wont ever be higher than approx 5V and it should be min 56v+12v = 68V.

Next point: At the moment of switching the BD's have a very low current gain and the base-curent will be pretty high. In your sch the basedrive wont ever be very high becurse of the 1k resistors.
Thats why I use the 40106-inverters. They give a clean switch and a high "current-gain" ast high Freq.

Please do coment.

TroelsM
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Old 24th October 2005, 11:46 AM   #17
Pierre is offline Pierre  France
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You are right! There is a mistake in that sch. Top of R2 should go to the bootstrap voltage, not to +12V.
No, I haven't simulated it, and I am afraid I don't have much time to do it now, if someone is willing to do it for me...
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Old 24th October 2005, 11:48 AM   #18
TroelsM is offline TroelsM  Denmark
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If I get the time i might simulate it later, but I still think that the current to the bases is way too low to get at fast switch.

TroelsM
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Old 24th October 2005, 11:48 AM   #19
Pierre is offline Pierre  France
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You may be right about base currents also. I only posted the sch as a proposal. Adding a couple of TC427 driver ICs instead of the BD's should work much better, anyway.
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Old 24th October 2005, 12:01 PM   #20
nitrate is offline nitrate  United Kingdom
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Hello all,

Interesting thread, can't wait to see how it developes. What frequency are you planning on running this amp at? I can't see the totem pole driver arrangement going too fast, also why the multiple dead time? One on the fet gate, one in the logic?

You all seem to be using the same schematic/sim software. Which is it?

Keep up the good work!

Mad.P
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