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Old 17th May 2019, 10:40 PM   #3911
traderbam is offline traderbam  Europe
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Quiz:
1) You can easily buy a Darlington transistor. Why don't you see pseudo-Darlington/CFP/Sziklai transitors for sale?
Answers submitted include difficulties/performance issues with opposite polarity BJTs on the same die, stability, less good for switching. Better for audio amps to have the dies physically separated for better temp compensation.

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2) What modern device can you buy that has some similarity to a pseudo-Darlington?
Any guesses?
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Old 18th May 2019, 12:16 AM   #3912
Bigun is offline Bigun  Canada
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NAP-140 Clone Amp Kit on Ebay
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Thanks, it’s a selfie.
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Old 18th May 2019, 06:41 AM   #3913
Ian Finch is offline Ian Finch  Australia
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..... Any guesses?
Chipamps with quasi-complementary output stages? Perhaps a voltage regulator of some type? The LM3886 is credited with being a quasi-complementary design with a PNP driver, albeit a pre-driver in the negative rail side of a triple.
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Old 19th May 2019, 10:51 AM   #3914
traderbam is offline traderbam  Europe
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Yes that's true. There are probably many ICs containing them. What I had in mind was a type of 3-pin, power switching device that contains a pseudo-darlington-like configuration of transistors.
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Old 19th May 2019, 03:40 PM   #3915
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IGBT
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Old 19th May 2019, 03:55 PM   #3916
Ian Finch is offline Ian Finch  Australia
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OK, an SCR or thyristor. There's a nice tutorial on them at the link for anyone who doesn't have much experience or knowledge of them, since they are usually seen in early solid state power or motor speed control circuits. I don't recall seeing any serious use for them in linear amplifiers other than as crowbar safety devices. https://www.electronics-tutorials.ws...thyristor.html
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Old 19th May 2019, 07:04 PM   #3917
traderbam is offline traderbam  Europe
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The (very simplified) structure of an IGBT is quite like the Sziklai pair.
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Old 20th May 2019, 03:50 AM   #3918
Ian Finch is offline Ian Finch  Australia
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Ah yes, shades of the eponymous "Alexander Amplifier". https://www.analog.com/media/en/tech...17334AN211.pdf
Have fun with that one
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Old 20th May 2019, 12:26 PM   #3919
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I am not normal. I do not accept the worthiness of something solely based on the authority of the publisher.

For example, I look at that Analog Devices note and wonder how it ever got approved by someone at AD to carry the esteemed AD brand name. I also have to feel sorry for the University of Toronto. Then I remember they are just trying to sell AD op-amps.

Anyhow, I would not tar and feather the IGBT device based on this application note. The IGBT has some very interesting characteristics that can be exploited in linear audio. I am also tickled when I read some IGBT datasheets that include welding in the list of typical applications! A true super-transistor.
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Old 20th May 2019, 06:01 PM   #3920
Ian Finch is offline Ian Finch  Australia
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The point of the design, as I remember from many years back, seemed to be the novelty. Think of the brownie points in the EE small hall of fame when you succeeded in using new types of industrial switching devices as the output devices for a hi-fi amplifier. It caused a stir of interest, at least in the output devices and spawned a number of simplified DIY designs, even here in Oz.

Regarding the facts and figures, Eva's posts in this old thread make interesting reading:
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