triple darlington?

[Kevin Aylward]

is there any reason you can't make a triple darlington transistor,
No.

with Hfe=Hfe^3 by adding a third transistor to a darlington pair in
the same configuration?

Its called, now get this, "a Triple"

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

 

[andy]

is there any reason you can't make a triple darlington transistor, with
Hfe=Hfe^3 by adding a third transistor to a darlington pair in the same
configuration?

 

[andy]

Its called, now get this, "a Triple"

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

ok, thanks.

 

[CFoley1064]

Subject: triple darlington?

From: andy [email protected]-online.co.uk
Date: 7/22/2004 2:32 PM Central Daylight Time
Message-id: <[email protected]>

is there any reason you can't make a triple darlington transistor, with
Hfe=Hfe^3 by adding a third transistor to a darlington pair in the same
configuration?

Hi, Andy. I would guess you mean something like this (view in fixed font or M$
Notepad):

"Triple"
C
o
|
.---o---o
| | |
|/ | |
Bo-| Q1 | |
|> | |
| |/ |
o-| Q2 |
|> |
| |/
o-| Q3
|>
|
o
E

created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

First you need to understand that all transistors have some leakage current
when they're "off". With the combined beta of the "triple", the low microamp
or high nanoamp leakage of Q1 will be amplified by Q2, and then be enough to
turn on Q3. So, even if you have no current whatsoever going into the base,
significant current will be flowing from the collector to the emitter. Not
only that, but the leakage current is temperature dependent, so your triple
transistor characteristics would change dramatically once it was powered up.

Darlington transistors are great for switching things on and off, and they do
have their uses, but there's reasons you don't see them everywhere. Keep
learning about transistors, you'll see why.

Hfe of a regular darlington is usually well over 1,000, anyway. That should be
enough. But it is a good question. I remember asking this myself back when I
was learning this stuff (midway through the Pleistocene Era, as I remember)

Good luck, and keep learning
Chris

 

[andy]

Hi, Andy. I would guess you mean something like this (view in fixed font or M$
Notepad):

"Triple"
C
o
|
.---o---o
| | |
|/ | |
Bo-| Q1 | |
|> | |
| |/ |
o-| Q2 |
|> |
| |/
o-| Q3
|>
|
o
E

created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

just tried this out under linux using 'wine' - neat program.

First you need to understand that all transistors have some leakage current
when they're "off". With the combined beta of the "triple", the low microamp
or high nanoamp leakage of Q1 will be amplified by Q2, and then be enough to
turn on Q3. So, even if you have no current whatsoever going into the base,
significant current will be flowing from the collector to the emitter. Not
only that, but the leakage current is temperature dependent, so your triple
transistor characteristics would change dramatically once it was powered up.

Darlington transistors are great for switching things on and off, and they do
have their uses, but there's reasons you don't see them everywhere. Keep
learning about transistors, you'll see why.

Hfe of a regular darlington is usually well over 1,000, anyway. That should be
enough. But it is a good question. I remember asking this myself back when I
was learning this stuff (midway through the Pleistocene Era, as I remember)

thanks - that was the sort of thing i wanted to know - i.e. how long can
you keep adding transistors b4 it gets ridiculous.

 

[Kevin Aylward]

Hi, Andy. I would guess you mean something like this (view in fixed
font or M$ Notepad):

"Triple"
C
o
|
.---o---o
| | |
|/ | |
Bo-| Q1 | |
|> | |
| |/ |
o-| Q2 |
|> |
| |/
o-| Q3
|>
|
o
E

created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

First you need to understand that all transistors have some leakage
current when they're "off". With the combined beta of the "triple",
the low microamp or high nanoamp leakage of Q1 will be amplified by
Q2, and then be enough to turn on Q3. So, even if you have no
current whatsoever going into the base, significant current will be
flowing from the collector to the emitter.

Note that practical Darlington's and triples usually have base emmiter
resisters to reduce leakage and speed up turn off.

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.