Sziklai pair for psu?

[throbscottle]

I was just reading about Sziklai pairs, and thought it would be a better choice than a Darlington pair as a PSU pass element. Nobody seems to be doing this though. Any thoughts as to why?

 

[crutschow]

Why do you think it would be better?

 

[atferrari]

I used them in constant current sources / sinks. Of course, they worked OK.

 

[Nigel Goodwin]

Why do you think it would be better?

Presumably it has a lower voltage drop?.

 

[crutschow]

Presumably it has a lower voltage drop?.

It does have a lower base-emitter drop, but I was curious as to why the OP thought it was better.

 

[throbscottle]

Mainly because of the lower b-e drop being same as a single transistor, but also I have read that it is more linear and has better thermal stability, so it just seems an all-round better configuration. But everything I am seeing about them is in context of audio power amps so this may be irrelevant...

 

[crutschow]

Another possible advantage, if you need a Darlington pair PNP power transistor in a series regulator, the Sziklai PNP equivalent would use a small PNP along with a power NPN, and power NPNs use a smaller die and are cheaper than an equivalent PNP.

 

[throbscottle]

Good for dual rail then Well, somewhat negated by the need for a power pnp on the positive rail. Maybe a darlington up there on +, and sziklai pair on -.

 

[audioguru]

I used Sziklai pairs in my audio amplifier designs a few years before Sziklai invented it. They should have my name on them.
Semiconductor manufacturers make many darlingtons but I do not think anybody makes Sziklai pairs. Maybe the patent says a high cost royalty must be paid to make them.

 

[throbscottle]

Audioguru pair. Hmmm, has a certain ring to it!

 

[crutschow]

......................
Semiconductor manufacturers make many darlingtons but I do not think anybody makes Sziklai pairs. Maybe the patent says a high cost royalty must be paid to make them.

It good be the difficulty of making both good NPNs and PNPs on the same substrate.

 

[audioguru]

Audioguru pair. Hmmm, has a certain ring to it!

Yes, like this:

 

[throbscottle]

I got curious and found this thread on the subject, they talk about patents and single die devices...
https://www.avrfreaks.net/forum/sziklai-pair
I've only skimmed through it but this looks an interesting read on the subject from ESP
**broken link removed**

 

[throbscottle]

I had an "Aha" moment. I've been looking at this: **broken link removed** but need a bit more current than the LM5001 can switch. The natural way to connect an external transistor in this negative buck configuration is so it makes an Audioguru Pair with the internal one - or it would do if the internal transistor was bipolar and didn't have the current sense resistor, anyway...