Author Topic: Compound Pair vs Darlington Pair  (Read 1825 times)

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Offline Lucky-LukaTopic starter

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Compound Pair vs Darlington Pair
« on: December 26, 2019, 05:04:51 pm »
Hi all
I've read that Sziklai pair are more thermically stable than Darlington ones.
Is it because since Q5 has half Q10 voltage bias it dissipates half the heat and the configuration is in such a way more thermically stable?
Is that so? Anything else?

Happy holidays
Memento audere semper.
 

Online edavid

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Re: Compound Pair vs Darlington Pair
« Reply #1 on: December 26, 2019, 05:11:24 pm »
Douglas Self ("Audio Power Amplifier Design Handbook, 5th Ed") says:

Quote
The CFP topology is generally considered to show better thermal stability than the EF, because the
Vbe of the output devices is inside the local NFB loop, and only the driver Vbe has a major effect on
the quiescent conditions. The true situation is rather more complex, and is explored in Chapter 15.

So, I suggest you get a copy and read Chapter 15!
 

Offline exe

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Re: Compound Pair vs Darlington Pair
« Reply #2 on: December 26, 2019, 05:12:52 pm »
Check this one: https://sound-au.com/articles/cmpd-vs-darl.htm . Explains topic quite in in-depth.
 
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Offline Lucky-LukaTopic starter

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Re: Compound Pair vs Darlington Pair
« Reply #3 on: December 26, 2019, 10:03:36 pm »
I've also read that Szikai configuration should behave better against distortion... Is it true?
I've tried a comparison but it looks like that Darlington behaves better. Am i wrong?
 
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Online Kleinstein

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Re: Compound Pair vs Darlington Pair
« Reply #4 on: December 26, 2019, 11:47:01 pm »
The Szikai configuration likes an addition base to emitter resistor with the larger transistor.
Another point to look for it that the  Szikai configuration is more prone to oscillation, especially if the driving side is higher impedance.

The distortion in the class AB power stage depends on the standing current - both types tend to prefer a slightly different current.  Better thermal stability leads to a more stable standing current and could this way cause less distortion. The simulation tends to no include that thermal effect.
 
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Offline David Hess

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Re: Compound Pair vs Darlington Pair
« Reply #5 on: December 27, 2019, 01:54:47 am »
The link Exe provided covers it better than I could.  I have used both structures in class-ab power amplifiers and regulators without problems.  The compound pair takes more care to prevent local oscillation but either can oscillate under the wrong conditions.
 
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Offline MiDi

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Re: Compound Pair vs Darlington Pair
« Reply #6 on: December 27, 2019, 01:43:24 pm »
I've also read that Szikai configuration should behave better against distortion... Is it true?
I've tried a comparison but it looks like that Darlington behaves better. Am i wrong?

When both EF and CFP are biased for lowest crossover distortion, the CFP is better.
There are more distortion sources, recommend reading Self: Distortion in Power Amplifiers.
 

Offline graybeard

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Re: Compound Pair vs Darlington Pair
« Reply #7 on: December 28, 2019, 02:55:13 am »
Check this one: https://sound-au.com/articles/cmpd-vs-darl.htm . Explains topic quite in in-depth.

nice article!
 
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