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Problem simulating floating power supply amplifier
Problem simulating floating power supply amplifier
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Old 7th May 2018, 08:00 AM   #1
UltimateX86 is offline UltimateX86  France
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Default Problem simulating floating power supply amplifier

Quote:
Originally Posted by djk View Post
First off, study this follower circuit:

http://www.audiodesignguide.com/my/Cool_Follower1.GIF

The outputs in the original design were three pair of the small plastic TIP41/42 type, replace these with one pair of Semelab BUZ900/905. The one pair will be more than enough for 60W/8R or 100W/4R. The input pair may be any small signal type suitable for 10mA or so, the MPSA06/56 would be fine. Use ±15V for the supply for the input pair and 1200 ohms for the bias resistors (instead of the 390 ohm), use a pair of 100 ohm trim pots (instead of the 0.18 ohm). The BUZ need no emitter/source resistors. The capacitor need only be a 1µF (or larger) film type across the gates of the outputs.

Hook the output of this follower straight to ground, since the sources of the BUZ are the case this is easy, just use no insulator and ground the heatsinks!

To convert to a TransNova output stage all we need is a 5K input resistor to the bases of the input pair and a 100K feedback resistor from the same point to the center tap of the power transformer. We will need a regulated ±15V supply for the input pairs, one supply to drive as many channels as needed. We will need a ±40V supply (30-0-30V 150VA or larger), one per channel is needed.

Set the 100 ohm pots to about 25 ohms, then turn on and adjust for the idling current desired in the output stage. After the temperature and bias stabilize (just turn up the bias until the heatsink is as warm as you want it to be, the actual value is unimportant) then trim these again for DC off-set.

This circuit will only work for lateral MOS like the BUZ or the J50/K135 type. IRF type will blow up.

The amount of power in class A is only limited by the size of the heatsinks, and moves into class AB for loud peaks only.

If BUZ 900D/905D are used with minimum bias (100mA) and suitable heatsinking and supply voltages are used, 250W in class AB is possible out of only one pair of outputs.
HI DJK,

You mentioned Transnova on several topic of this forum, have you tried in practice?

I would like to do something similar.

Click the image to open in full size.

OpAmp used as Input Stage (IS)?
simple Amplifier?
Minimalist A/B fet amplifier

thanks
Best Regards
Seb
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Old 7th May 2018, 03:16 PM   #2
UltimateX86 is offline UltimateX86  France
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Default Problem simulating floating power supply amplifier

HI,

I would like sim a floating power supply amplifier (transnova) but it seems that ltspice does not like it..

amplifier in normal mode : bufferOPA.asc
amplifier in transnova mode : transnovaOPA.asc

https://sites.google.com/site/opampb.../TRANSNOVA.zip

I forgot something ?

Thanks

Last edited by UltimateX86; 7th May 2018 at 03:22 PM.
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Old 7th May 2018, 04:29 PM   #3
sajti is offline sajti  Hungary
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It works with some default opamps...

Sajti
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Old 8th May 2018, 10:56 AM   #4
UltimateX86 is offline UltimateX86  France
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Hi sajti, thanks To your answer

Do you use LT1007 ? I cant read on the screen shot
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Old 8th May 2018, 11:12 AM   #5
sajti is offline sajti  Hungary
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Quote:
Originally Posted by UltimateX86 View Post
Hi sajti, thanks To your answer

Do you use LT1007 ? I cant read on the screen shot
Hi,

yes. First time I tried LT1001, but it was not fast enough.

Sajti
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Old 9th May 2018, 07:45 AM   #6
UltimateX86 is offline UltimateX86  France
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Even with the lt1007 I have -13v DC on opamp output and 30v DC on Vout.

I also tried with diodes like you to bias mosfet, nothing changes
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Old 9th May 2018, 07:51 AM   #7
Mooly is offline Mooly  United Kingdom
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Problem simulating floating power supply amplifier
Have you got the feedback node connected ('out' on satji's image).
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Old 9th May 2018, 08:07 AM   #8
UltimateX86 is offline UltimateX86  France
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I found the problem, the TL model is inverted and as the schema itself is inverted, I confused

Last edited by UltimateX86; 9th May 2018 at 08:28 AM.
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Old 9th May 2018, 08:12 AM   #9
Mooly is offline Mooly  United Kingdom
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Problem simulating floating power supply amplifier
That's good
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Old 9th May 2018, 08:18 AM   #10
sajti is offline sajti  Hungary
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It is good solution to build simple but high power amplifier. QSC did it succesfully.

Sajti
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