Discrete Darlingtons vs. Packaged Darlingtons

rtarbell · 17th January 2006, 07:16 AM

This is probably a newbie quetion, but I never understood why:

How come many class AB or Class B solid state amps that use BJTs for their output stages use discrete-built Darlingtons (sometimes upwards to three - two driver pairs and then the output pair) as opposed to fabricated Darlington transistors (the ones that have two transistors in one package)?

I know that fabricated Darlingtons have lower transition frequencies, but I would *think* that making a discrete pair would also have a low ft...

AndrewT · 17th January 2006, 07:33 AM

Search for the recent thread that discussed this same Q.

You did search??

Damon Hill · 17th January 2006, 07:45 AM

Discrete components allow Class A drivers and more robust (SOA) parts in general; packaged Darlingtons are usually hard-wired so one is locked into the classic configuration and that limits design choices and
flexibility.

Some designs such as the Leach amplifier use a triple Darlington configuration. I don't know of any packaged devices like that. I've never seen a Sziklai/compound-complementary device either.

Ft varies, but there are plenty of audio power devices that go up to
30 Mhz or so, and drivers that go even higher.

I think there have been some hybrid packages that contain a full
output stage, but that locks one into the choice of devices and usually a considerable limit on output power.

Onsemi may have a good idea in packaging a thermal diode with an output device, even though the device is pricey and requires a 5 pin
package with a non-standard pinout array.

peranders · 17th January 2006, 09:09 AM

Besides what Damon says you can also take into account: What does the "market" need? This is usually the industry. If the industry demanded faster Darlingtons the manufactures would also provide it.

myhrrhleine · 18th January 2006, 02:23 PM

What if the pre-packaged darlington doesn't have the specifications wanted?
Using discretes allows for a greater selection of parts parameters.
There are simply more discretes to choose from.

ilimzn · 18th January 2006, 02:53 PM

Exactly. In the years past I have tried several darlington packages and just about the only one I had good success with were the MJ11015 and 11016, and even then just for relatively low supply rail voltage (SOA is not too good).

17th January 2006, 07:16 AM	#1
rtarbell diyAudio Member Join Date: Sep 2005	Discrete Darlingtons vs. Packaged Darlingtons This is probably a newbie quetion, but I never understood why: How come many class AB or Class B solid state amps that use BJTs for their output stages use discrete-built Darlingtons (sometimes upwards to three - two driver pairs and then the output pair) as opposed to fabricated Darlington transistors (the ones that have two transistors in one package)? I know that fabricated Darlingtons have lower transition frequencies, but I would think that making a discrete pair would also have a low ft...

17th January 2006, 09:09 AM	#4
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	Besides what Damon says you can also take into account: What does the "market" need? This is usually the industry. If the industry demanded faster Darlingtons the manufactures would also provide it. __________________ /Per-Anders (my first name) or P-A as my friends call me Tube Buffered Gainclone in work \|Thread

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17th January 2006, 07:33 AM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Search for the recent thread that discussed this same Q. You did search??

17th January 2006, 07:45 AM	#3
Damon Hill diyAudio Member Join Date: Mar 2001 Location: Auburn, WA (somewhere between Seattle and Tacoma) Blog Entries: 1	Discrete components allow Class A drivers and more robust (SOA) parts in general; packaged Darlingtons are usually hard-wired so one is locked into the classic configuration and that limits design choices and flexibility. Some designs such as the Leach amplifier use a triple Darlington configuration. I don't know of any packaged devices like that. I've never seen a Sziklai/compound-complementary device either. Ft varies, but there are plenty of audio power devices that go up to 30 Mhz or so, and drivers that go even higher. I think there have been some hybrid packages that contain a full output stage, but that locks one into the choice of devices and usually a considerable limit on output power. Onsemi may have a good idea in packaging a thermal diode with an output device, even though the device is pricey and requires a 5 pin package with a non-standard pinout array.

18th January 2006, 02:23 PM	#5
myhrrhleine diyAudio Member Join Date: Jan 2006 Location: Avalon Island	What if the pre-packaged darlington doesn't have the specifications wanted? Using discretes allows for a greater selection of parts parameters. There are simply more discretes to choose from.

18th January 2006, 02:53 PM	#6
ilimzn diyAudio Member Join Date: Feb 2005 Location: Zagreb	Exactly. In the years past I have tried several darlington packages and just about the only one I had good success with were the MJ11015 and 11016, and even then just for relatively low supply rail voltage (SOA is not too good).