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Old 16th January 2008, 07:12 PM   #1
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Default Balanced compound-IGBT power amp idea

Have read a few threads about both Circlotrons and IGBT. Have also had an idea for long about a transformer-coupled hybrid, with as much tube-like configuration as possible.

As IGBTs seems to be unsuitable for audio I got the idea of making them from a PNP-power BJT and a depletion MOSFET. This way one can bias the FET higher and thereby maybe make the two transistors work better. The DN2540 has only 200p Ciss, that according to the data sheet is independent of Vds.

I have also added a bias cicuit to get some temperature compensation. The IT is a Lundahl 1635, 1+1:1+1.

The amp is still not built so the question is how it will work IRL?
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Old 16th January 2008, 08:09 PM   #2
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Sorry, noticed the schematic was not the balanced version:
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Old 16th January 2008, 09:11 PM   #3
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It`s well known Circlotron configuration. What`s the peak output voltage for your circit with 24V supply?
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Old 17th January 2008, 06:39 AM   #4
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Hi Bogdan,
Off course the circuit is Circlotron. The twist of it is the output pair configuration. The way I look at it this is the closest to a tube output stage you can get, with transistors and no OPT.

Simmed peak-peak voltage is 40V/8ohm and 35V/4ohm. This would be in the ballbark of 25W/8ohm and 40W/4ohm.

Output impedance is ca 0,8ohm.

About temperature compensation I am not sure how to choose it? With the previous schematic you go from 25-125 degrees C with a change of 1A to 0,8A. If you add a diode-connected BD140 in series with the 33ohm(and adjust the Itrim) you go from 1A to 0,3A.
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Old 18th January 2008, 05:54 PM   #5
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Did some more simming and also added a bipolar version, hope the link of the screendump is readable:

www.eflatjump.se/freqjfr.JPG

Also simmed distortion at 10k/20Vptp for comparision:

1 Bipolar pair: 1,26%
2 Mosfet: 1,16%
3 Depletionmosfet/bipolar pair: 0,26%

I am fully aware of that simmed distortion figures are not reliable as the transistormodels aren´t fully reliable. But to me the distortion figures , the frequency-response together with the temperature-stability points to that version 3 is interesting.

Still I also hope that the DN2540/2SA1302(NJL4302) pair sounds best.
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Old 21st January 2008, 12:45 AM   #6
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Couldn't make out any of the real details in your screendump, but enough to see the general topology of what you're doing. It looks like your method has about 12dB less distortion. I wonder about the temperature stability too. Please keep us posted on your progress. I pointed out the depletion mode DN2540 a few years back, but no one expressed any interest in it.
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Old 21st January 2008, 09:07 AM   #7
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http://ixdev.ixys.com/DataSheet/99192.pdf

http://ixdev.ixys.com/DataSheet/98861.pdf
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Old 21st January 2008, 11:10 AM   #8
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The IXYS TP02N50D could maybe be a suitable replacement for the DN2540. IXYS had no spice model of it though .
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Old 21st January 2008, 01:03 PM   #9
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Quote:
Originally posted by revintage
Did some more simming and also added a bipolar version, hope the link of the screendump is readable:

www.eflatjump.se/freqjfr.JPG

Also simmed distortion at 10k/20Vptp for comparision:

1 Bipolar pair: 1,26%
2 Mosfet: 1,16%
3 Depletionmosfet/bipolar pair: 0,26%

Now, wouldn't be interesting to see a bipolar/MOSFET sim? That is; a small signal driver and a power MOSFET!
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Old 21st January 2008, 01:55 PM   #10
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Hej Bo!

My initial idea was all bipolar.

But I wanted to get rid of the current through the xfmr secondaries and also to get a better temperature stabilisation through the combination of fet/bip.

Will anyway try the version you propose.
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