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Old 11th January 2019, 04:14 AM   #181
steveu is offline steveu  United States
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OK, so my problem is that the original post is 6+ years ago and Mr. Bayes has abandoned it, hopefully have learned something.
And y'all have hijacked the thread talking about alternate solutions.
OK, besides the QSC floating supply, you can bootstrap the op-amp for up to 2x the chip voltage (~+/-30VDC). However this taxes the input CMR.
And there are rail driven op-amp circuits, but these use more added bits than just making a nice clean "blameless" amp.
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Old 11th January 2019, 07:39 AM   #182
kokoriantz is offline kokoriantz  Lebanon
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Default The rule of the thread.

SSBayes who posted 3 months ago last time had the idea to drive the outputs directly by an op amp . I fully respected his rule .
There are 32 solutions to drive a high power amp by an op amp , the most elegant is to short the output of the op amp and use the current of it's power supplies. I post an example 500w/4ohm CFA topology for you bellow but I don't want to discuss anything about it, as it is against the rule of SSBayes.
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Old 11th January 2019, 08:14 AM   #183
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by kokoriantz View Post
Single supply for all . Dtot 0.000036%@1w/1khz fr>20Mhz , biased 150ma.
Long live the CFA.
Koko, how is the thermal stability of this setup? Does the bias current need some time to stabilize after switch-on? Does it rise when driven hard?

Jan
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Old 11th January 2019, 11:10 AM   #184
kokoriantz is offline kokoriantz  Lebanon
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The thermal stability can't be simulated. It should only be conceived on the real object. As I mentioned ,either you use a emitter resistances and R9 is NTC or voltage multiplier mounted on the heat sink , or the voltage multiplier(BD140) by 2 determined by 3Mohm, is installed upon the PNP transistor (screwed). I have a 50w class A without emitter resistors regulated by this method works perfectly since a decade . You can even by adjusting the two resistors of the multipler and the pull up resistor, program to have a variable bias current suitable for each temperature .

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Old 11th January 2019, 11:43 AM   #185
jan.didden is offline jan.didden  Europe
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OK, thanks. Although with LTspice (and I think also TINA) you can include temp in your simulation.

Jan
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Old 11th January 2019, 12:29 PM   #186
kokoriantz is offline kokoriantz  Lebanon
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Default more temps

I also used several times LM334 temperature dependent current source. It can very precisely adjust the temperature drift . You need to make a piece of metal holder to apply upon the transistor .Calculation of the resistors is relatively simple arithmetic once you know how the bias voltage should decrease vs temperature.
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Old 11th January 2019, 12:41 PM   #187
kokoriantz is offline kokoriantz  Lebanon
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Default correction

Lm reversed
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