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Old 10th December 2007, 02:29 AM   #1
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Hi, Fumac,

For achieving Mhz selfoscilation, is it more about the mosfet choice or special feedback topology or comparator gain, or driver speed, or what? Is there something you can share?
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Old 10th December 2007, 10:51 AM   #2
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Quote:
Originally posted by lumanauw
Hi, Fumac,

For achieving Mhz selfoscilation, is it more about the mosfet choice or special feedback topology or comparator gain, or driver speed, or what? Is there something you can share?
hello lumanauw
i think the most important is the block diagram

fast and low input cap mosfet,
u can take a look at this link (from eva)
Nice MOSFETs for class D from IR (or how they try to impose us the DirectFet thrash)

also need a hard driver for mosfet.

rg
fumac
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Old 10th December 2007, 10:56 AM   #3
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also
u can take a look at this link
1kW Gen2

he is designing a driver for his 1kw d-amp

rg
fumac
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Old 10th December 2007, 04:30 PM   #4
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Hi, Fumac,

How can we set 0V in your diagram block? The +input is used for "high frequeny feedback"?

Currently I've found a way to make it 1Mhz with residual below 30mV, with UCD type selfoscilation, with IRF530-IRF9530, with +/-45V rail. But it is not perfect yet.
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Old 11th December 2007, 05:41 AM   #5
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Hi, Fumac,

I like that you help other members technically. In DIYaudio, we all learn something, especially technical aspect. Kind of "give and take" between members. Maybe you will also learn something from other member that will be usefull for yourself
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Old 11th December 2007, 06:19 AM   #6
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Quote:
Originally posted by lumanauw
Hi, Fumac,

I like that you help other members technically. In DIYaudio, we all learn something, especially technical aspect. Kind of "give and take" between members. Maybe you will also learn something from other member that will be usefull for yourself

hi lumanauw
yes u r right
i remember that i have told u about the design of ur PCB,
how a about the pcb now, perhaps u can send a email to me
thanks
fumac
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Old 11th December 2007, 08:53 AM   #7
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Hi, Fumac,

PCB? No, I haven't draw the PCB yet. The last one really a mess Thanks for your tips. I still experimented on bread-board.

I wanted to ask you about my Mhz modulation. My basic thinking is simple. The selfoscilation frequency seems always appropriate to residual voltage. The less residual voltage, it means higher selfoscilating frequency.
This is what I tought. If input differential needs 1V2 (p-p) to activate the state change (from "on" to "off"), what if we use 2 inverting stages (the comparator and the output stage is inverting), and then since the comparator is inverting, we feed back some of the signal back to the input. So it will, say provide 0V9 (p-p) and the output only have to provide 0V3. 0V3 residual means very high selfoscilation frequency.
I haven't draw anything yet, but this schematic (got it from here) seems to be able to represent my idea.
If you look the output stage (common sources), it is inverting output stage. "on" from the input of totem pole (bcw66/68) means "off" at the output node.
My experiment is like this, I put 47k resistor from pin1 to pin 3 of LM393. I got 1Mhz selfoscilation with IRF530/9530 with this method, but still very dirty oscilation.
What do you think about my method for achieving 1Mhz selfoscilation?
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Old 11th December 2007, 11:55 AM   #8
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Quote:
Originally posted by lumanauw
My experiment is like this, I put 47k resistor from pin1 to pin 3 of LM393. I got 1Mhz selfoscilation with IRF530/9530 with this method, but still very dirty oscilation.
Hi David,
Your driver arrangement is very crude and weak and also suffer when subjected to extreme of dutycycles 0-100%
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Old 11th December 2007, 12:12 PM   #9
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Quote:
Originally posted by lumanauw
Hi, Fumac,
I still experimented on bread-board.

u post the pic is not use our mcd block diagram
just like ucd
we use two paths after and before the output filter
one for osc, one for af feelback

i have heard about a saying from westen:
amp like an amp, osc like an osc.

our two paths r one for amp , one for osc.

dont use bread-board to make a damp
is not a rightway
pcb is the 70%important of a D-AMP
best rg
fumac
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Old 11th December 2007, 12:50 PM   #10
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Hi, Kanwar,

It is the same output stage used in Fredo's Behringer mixer, the same as output stage used in Zetex classD (look at datasheet of ZXCD1000), similiar to JohnW built. I also have no experience with this kind of output stage. It's just very simple to construct.

Do you have idea how to make it (a little) better? Will using 2 totem poles (1 for high 100nF and 1 for low 100nF) can help? Or making it cascaded totem pole (inverting driver, like in Labgruppen TD driver)?
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