Discover something????

fredos · 19th October 2006, 05:23 AM

Here a pic of an idea I just have and try...5 watts RMS, but at 3Mhz switching frequency, open loop, with booth fet ground referenced...Drain signal is a bit poor, but sound quality seem incredible!

fredos

www.d-amp.com

classd4sure · 19th October 2006, 05:48 AM

Hi Fred,

Where's the discovery in this? 3Mhz open loop good?

Did you get the subject field cleared by the powers that be ... font's not too big or anything? It's kind of in a grey area after all.

If I had a pro audio site/business, I wouldn't be posting a schematic like that, and with that title, and certainly not to make a point

sawreyrw · 19th October 2006, 06:26 AM

Fred,

I agree with ClassD. What the h*** is it? How does it work?

Rick

fredos · 19th October 2006, 06:37 AM

Just the idea to put 2 flyback convert out of phase to be able to drive mosfet on common source. It's exactly the same principle of dual forward DC converter, when one push, the other pull on freewheling...Nobody have seen that??? Drain voltage go over twice the supply with some garbage, but dont seem to affect sine wave..And dead time between 2 switch dont seem to have effect too... I can push it to 3 mhz before to feel the output get warm. Sorry if I dissapoint you guy, but that was an idea and I have try it. Dont know if I can got ''bigger result'', but idea work on breadboard with cheap components...And work on first try without any calcul...I use a LM361 to drive the CMOS and first drivers with a 5-12V level shifter...Really simple!

Take a better look at schematics, I have do it just for you!

Fredos

Eva · 19th October 2006, 07:35 AM

A 3 Mhz switching frequency imposes a 333ns period, which means that every half cycle lasts for 166ns when the amplifier is idle. In order to achieve class D operation, each MOSFET must be fully turned on and then fully turned off within that 166ns period, and each switching event should last for a very small time in comparison with the main switching period.

Now, how much do you think that a IRF640 takes to turn on and turn off with a 10 ohm gate resistor and considering the high and non-linear typical MOSFET output capacitance in the Vds<25V range?

What a nice linear amplifier you have built, indeed (the filtering is done at MOSFET gates). Next time take the dust out of one of your oscilloscopes (assuming you own one capable of showing a 3Mhz square wave without too much "edge rounding"

) and use it to check if your stuff really works as expected (including your commercial amps

)

A circuit producing some sound, even at high powers, does not neccessarily have to be working properly or as expected.

BTW: And yes, you have discovered linear amplification

fredos · 19th October 2006, 08:01 AM

Read post EVA...Mosfet begin to warm at 3Mhz....I saw that drain wave form was sine at that freq...I'm not stupid! :-) Yes it play sine wave and music, but in PWM, not linear...Just wish to find the camera in box to show you pick...Thank's to think that I'm beginer!

Fredos

Elvee · 19th October 2006, 08:40 AM

Hi Fredos,

I'm afraid you only get an output signal thanks to the imperfections of the real components:
The average voltage at the drains of both FETs must be 0; the waveform might be widely assymetrical, but it doesn't matter: the volt-second product across a perfect inductor has to be 0 over a period of time, otherwise the current will climb indefinetely.
Your inductors have some series resistance, which allow some AF signal to leak through; with better inductors you'd get nothing.
LV

classd4sure · 19th October 2006, 12:06 PM

Quote:

Originally posted by Eva
...

Fred, why I wouldn't have posted that to make a point if I were in business.

Eva, you didn't account for the variation in delay imposed by the different gate drivers ?? I expected some third harmonic generation out of that

mitch90 · 19th October 2006, 03:18 PM

Hello.
I had similar idea few months ago, but frequency was not that high and without feedback loop it is useless.

Mitch.

Jaka Racman · 19th October 2006, 03:46 PM

Quote:

What a nice linear amplifier you have built, indeed (the filtering is done at MOSFET gates).

Wrong, it is actually a resonant converter, so it "works" in a way.

19th October 2006, 07:35 AM	#5
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	A 3 Mhz switching frequency imposes a 333ns period, which means that every half cycle lasts for 166ns when the amplifier is idle. In order to achieve class D operation, each MOSFET must be fully turned on and then fully turned off within that 166ns period, and each switching event should last for a very small time in comparison with the main switching period. Now, how much do you think that a IRF640 takes to turn on and turn off with a 10 ohm gate resistor and considering the high and non-linear typical MOSFET output capacitance in the Vds<25V range? What a nice linear amplifier you have built, indeed (the filtering is done at MOSFET gates). Next time take the dust out of one of your oscilloscopes (assuming you own one capable of showing a 3Mhz square wave without too much "edge rounding" ) and use it to check if your stuff really works as expected (including your commercial amps ) A circuit producing some sound, even at high powers, does not neccessarily have to be working properly or as expected. BTW: And yes, you have discovered linear amplification __________________ I use to feel like the small child in The Emperor's New Clothes tale

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19th October 2006, 05:48 AM	#2
classd4sure Account Disabled Join Date: Feb 2004	Hi Fred, Where's the discovery in this? 3Mhz open loop good? Did you get the subject field cleared by the powers that be ... font's not too big or anything? It's kind of in a grey area after all. If I had a pro audio site/business, I wouldn't be posting a schematic like that, and with that title, and certainly not to make a point

19th October 2006, 06:26 AM	#3
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	Fred, I agree with ClassD. What the h*** is it? How does it work? Rick

19th October 2006, 06:37 AM	#4
fredos diyAudio Member Join Date: Mar 2005 Location: Quebec	Just the idea to put 2 flyback convert out of phase to be able to drive mosfet on common source. It's exactly the same principle of dual forward DC converter, when one push, the other pull on freewheling...Nobody have seen that??? Drain voltage go over twice the supply with some garbage, but dont seem to affect sine wave..And dead time between 2 switch dont seem to have effect too... I can push it to 3 mhz before to feel the output get warm. Sorry if I dissapoint you guy, but that was an idea and I have try it. Dont know if I can got ''bigger result'', but idea work on breadboard with cheap components...And work on first try without any calcul...I use a LM361 to drive the CMOS and first drivers with a 5-12V level shifter...Really simple! Take a better look at schematics, I have do it just for you! Fredos

19th October 2006, 08:01 AM	#6
fredos diyAudio Member Join Date: Mar 2005 Location: Quebec	Read post EVA...Mosfet begin to warm at 3Mhz....I saw that drain wave form was sine at that freq...I'm not stupid! :-) Yes it play sine wave and music, but in PWM, not linear...Just wish to find the camera in box to show you pick...Thank's to think that I'm beginer! Fredos

19th October 2006, 08:40 AM	#7
Elvee diyAudio Member Join Date: Sep 2006	Hi Fredos, I'm afraid you only get an output signal thanks to the imperfections of the real components: The average voltage at the drains of both FETs must be 0; the waveform might be widely assymetrical, but it doesn't matter: the volt-second product across a perfect inductor has to be 0 over a period of time, otherwise the current will climb indefinetely. Your inductors have some series resistance, which allow some AF signal to leak through; with better inductors you'd get nothing. LV

19th October 2006, 03:18 PM	#9
mitch90 diyAudio Member Join Date: Sep 2005	Hello. I had similar idea few months ago, but frequency was not that high and without feedback loop it is useless. Mitch.