Sinking & sourcing current, pnp & npn

J

Jani Miettinen

Guest
I'm studying electronics on my own (as a hobby), reading right now
Art of Electronics, browsing the web to fill some of the gaps (yes,
there are quite some) and toying with CircuitMaker (which helps a
lot to understand the stuff).

Sinking and sourcing current have been referenced to several times,
but they have never been explained in any usable detail. So, here
are the questions -- for now, more might follow ;) :

What is the difference between sinking and sourcing current?

Pnp and npn transistors differ somehow in this respect -- but why,
and what does that mean in practice?

Thanks in advance!
 
Jani Miettinen wrote:
I'm studying electronics on my own (as a hobby), reading right now
Art of Electronics, browsing the web to fill some of the gaps (yes,
there are quite some) and toying with CircuitMaker (which helps a
lot to understand the stuff).

Sinking and sourcing current have been referenced to several times,
but they have never been explained in any usable detail. So, here
are the questions -- for now, more might follow ;) :

What is the difference between sinking and sourcing current?

Pnp and npn transistors differ somehow in this respect -- but why,
and what does that mean in practice?

Thanks in advance!
-------------------------
Click to expand...
It is like a switch upstream or downstream of a load.

An NPN is best downstream of the load, emitter to ground, which sinks
current to ground to turn on the load, and this is because it needs a
base current provided by a voltage that shouldn't vary any more than it
needs to in order to stabilize the turn-on point.

The base current makes the collector path voltage drop suddenly grow
and stand the base up higher so the base voltage has to grow as well,
and it can chatter on or fail to turn-on evenly.

If it was on top the load, as seen from a +V high, Ground low diagram,
then the voltage needed to turn on the base would vary right when it
was ramping up to turn-on, due to the voltage drop through the C-E path.

The PNP is best upstream of load, upside down, emitter up to Vcc,
because then we must ground the base to turn it on, and it mirrors the
NPN case, except upside down, and prevents that base instability at
turn-on.

-Steve
--
-Steve Walz rstevew@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public
 
R. Steve Walz wrote:
Jani Miettinen wrote:

I'm studying electronics on my own (as a hobby), reading right now
Art of Electronics, browsing the web to fill some of the gaps (yes,
there are quite some) and toying with CircuitMaker (which helps a
lot to understand the stuff).

Sinking and sourcing current have been referenced to several times,
but they have never been explained in any usable detail. So, here
are the questions -- for now, more might follow ;) :

What is the difference between sinking and sourcing current?

Pnp and npn transistors differ somehow in this respect -- but why,
and what does that mean in practice?

Thanks in advance!
-------------------------
It is like a switch upstream or downstream of a load.
Click to expand...
It can be a switch. It can also be a linear amp. I don't see any
assumption that the question refers to switching use only.

An NPN is best downstream of the load, emitter to ground, which sinks
current to ground to turn on the load, and this is because it needs a
base current provided by a voltage that shouldn't vary any more than
it needs to in order to stabilize the turn-on point.

The base current makes the collector path voltage drop suddenly grow
and stand the base up higher so the base voltage has to grow as well,
and it can chatter on or fail to turn-on evenly.

If it was on top the load, as seen from a +V high, Ground low diagram,
then the voltage needed to turn on the base would vary right when it
was ramping up to turn-on, due to the voltage drop through the C-E
path.

The PNP is best upstream of load, upside down, emitter up to Vcc,
because then we must ground the base to turn it on, and it mirrors the
NPN case, except upside down, and prevents that base instability at
turn-on.
Click to expand...
Well, I will query the use of the word "best" here. One can have a
push-pull or source sink with either a collector output or emitter
output. Both methods have disadvantages and advantages. Since this is
your reply, I will it it to you to expand on this.

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
Jani Miettinen wrote:
I'm studying electronics on my own (as a hobby), reading right now
Art of Electronics, browsing the web to fill some of the gaps (yes,
there are quite some) and toying with CircuitMaker (which helps a
lot to understand the stuff).

Sinking and sourcing current have been referenced to several times,
but they have never been explained in any usable detail. So, here
are the questions -- for now, more might follow ;) :

What is the difference between sinking and sourcing current?

Pnp and npn transistors differ somehow in this respect -- but why,
and what does that mean in practice?

Thanks in advance!
Click to expand...
The words sourcing and sinking just refer to the two possible
directions of current. If the switch or control element is on the
positive side of the load that switch or control element is said to
source current. If the switch or control device is on the negative
side of a load, it is said to be a current sink. This is all based on
the convenient fiction (positive current convention) that current
consists of positive charge moving. So a source lets charge reach the
load, and a sink lets charge leave it (and sink down the drain).

Not technical, at all (or even accurate).

--
John Popelish
 
John Popelish wrote...
Jani Miettinen wrote:

I'm studying electronics on my own (as a hobby), reading right now
Art of Electronics, browsing the web to fill some of the gaps (yes,
there are quite some) and toying with CircuitMaker (which helps a
lot to understand the stuff).

Sinking and sourcing current have been referenced to several times,
but they have never been explained in any usable detail. So, here
are the questions -- for now, more might follow ;) :

What is the difference between sinking and sourcing current?

Pnp and npn transistors differ somehow in this respect -- but why,
and what does that mean in practice?

Thanks in advance!

The words sourcing and sinking just refer to the two possible
directions of current. If the switch or control element is on the
positive side of the load that switch or control element is said to
source current. If the switch or control device is on the negative
side of a load, it is said to be a current sink. This is all based
on the convenient fiction (positive current convention) that current
consists of positive charge moving. So a source lets charge reach
the load, and a sink lets charge leave it (and sink down the drain).
Click to expand...
Right. For conventional "current-source" circuits, which use the
transistor's collector for their output, PNP or P-channel types
can only source current and NPN or N-channel types can only sink
current. But note, it's common practise in the industry to refer
to both NPN and PNP types as "current sources," even though in fact
the NPN type is a more accurately called a current sink.

Enjoy your studies, Jani, and best wishes.

p.s. Good book choice!

Thanks,
- Win
 
Kevin Aylward wrote:
R. Steve Walz wrote:
Jani Miettinen wrote:

I'm studying electronics on my own (as a hobby), reading right now
Art of Electronics, browsing the web to fill some of the gaps (yes,
there are quite some) and toying with CircuitMaker (which helps a
lot to understand the stuff).

Sinking and sourcing current have been referenced to several times,
but they have never been explained in any usable detail. So, here
are the questions -- for now, more might follow ;) :

What is the difference between sinking and sourcing current?

Pnp and npn transistors differ somehow in this respect -- but why,
and what does that mean in practice?

Thanks in advance!
-------------------------
It is like a switch upstream or downstream of a load.

It can be a switch. It can also be a linear amp. I don't see any
assumption that the question refers to switching use only.
--------------
Click to expand...
Rule one for teaching: Start simple.


An NPN is best downstream of the load, emitter to ground, which sinks
current to ground to turn on the load, and this is because it needs a
base current provided by a voltage that shouldn't vary any more than
it needs to in order to stabilize the turn-on point.

The base current makes the collector path voltage drop suddenly grow
and stand the base up higher so the base voltage has to grow as well,
and it can chatter on or fail to turn-on evenly.

If it was on top the load, as seen from a +V high, Ground low diagram,
then the voltage needed to turn on the base would vary right when it
was ramping up to turn-on, due to the voltage drop through the C-E
path.

The PNP is best upstream of load, upside down, emitter up to Vcc,
because then we must ground the base to turn it on, and it mirrors the
NPN case, except upside down, and prevents that base instability at
turn-on.

Well, I will query the use of the word "best" here. One can have a
push-pull or source sink with either a collector output or emitter
output. Both methods have disadvantages and advantages. Since this is
your reply,
-----------------------
Click to expand...
Mostly disadvantages if you disregard the load drop that lifts the
base reference at turn-on.


I will it it to you to expand on this.
Kevin Aylward
----------
Click to expand...
Is this english?

-Steve
--
-Steve Walz rstevew@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public
 
"R. Steve Walz" <rstevew@armory.com>:
An NPN is best downstream of the load, emitter to ground,
which sinks current to ground to turn on the load, and this is
because it needs a base current provided by a voltage that
shouldn't vary any more than it needs to in order to stabilize
the turn-on point.
Click to expand...
This does make sense.

Earlier I experimented with op-amp integrator *) and found out that
bipolar transistor could not be used (at least I couldn't figure
out how) to reset the integrator capacitor due to the instability
of turn-on point. I suspect this is somewhat a similar situation,
but of course a bit different.

*) like this: http://www.maxim-ic.com/tarticle/images/A207Fig01.gif
 
Winfield Hill <whill@picovolt.com>:
Enjoy your studies, Jani, and best wishes.
Click to expand...
Thanks!

p.s. Good book choice!
Click to expand...
It is! :)

I have to say that reading The Art of Electronics is inpiring and
enjoyable. It's amazing how you have managed to pack so much
information into it without having it filled to overflowing.

Figuring out why the bad circuits are bad circuits is probably one
of the most educational parts of the book. At first, from the
beginner's point of view, it seemed that absolutely nothing was
wrong with them but soon it was clear why they would not work as
advised.
 
R. Steve Walz wrote:
Kevin Aylward wrote:

R. Steve Walz wrote:
Jani Miettinen wrote:

I'm studying electronics on my own (as a hobby), reading right now
Art of Electronics, browsing the web to fill some of the gaps (yes,
there are quite some) and toying with CircuitMaker (which helps a
lot to understand the stuff).

Sinking and sourcing current have been referenced to several times,
but they have never been explained in any usable detail. So, here
are the questions -- for now, more might follow ;) :

What is the difference between sinking and sourcing current?

Pnp and npn transistors differ somehow in this respect -- but why,
and what does that mean in practice?

Thanks in advance!
-------------------------
It is like a switch upstream or downstream of a load.

It can be a switch. It can also be a linear amp. I don't see any
assumption that the question refers to switching use only.
--------------
Rule one for teaching: Start simple.
Click to expand...
Rule two. Don't simplify so much that it becomes meaningless.

The PNP is best upstream of load, upside down, emitter up to Vcc,
because then we must ground the base to turn it on, and it mirrors
the NPN case, except upside down, and prevents that base
instability at turn-on.

Well, I will query the use of the word "best" here. One can have a
push-pull or source sink with either a collector output or emitter
output. Both methods have disadvantages and advantages. Since this is
your reply,
-----------------------
Mostly disadvantages if you disregard the load drop that lifts the
base reference at turn-on.
Click to expand...
Oh. You think so. If this were true, just why do you proposes that,
essentially, all audio power amps use emitter follower outputs. This
amounts to 10000's of designs, and billions of actual product sold. How
do you explain that non emitter follower output op-amps are few and far
between.



Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
--
Want someone to fix your computer remotely?
Check out Network info at this site:

http://www.onecomputerguy.com/tips.htm
"Jani Miettinen" <jomietti+news@mappi.helsinki.fi> wrote in message
news:Xns93F6BE60C2173janimmydejacom@130.133.1.4...
I'm studying electronics on my own (as a hobby), reading right now
Art of Electronics, browsing the web to fill some of the gaps (yes,
there are quite some) and toying with CircuitMaker (which helps a
lot to understand the stuff).

Sinking and sourcing current have been referenced to several times,
but they have never been explained in any usable detail. So, here
are the questions -- for now, more might follow ;) :

What is the difference between sinking and sourcing current?
Click to expand...
Sinking is bringing the ckt to 0v or low. Sourcing is bringing the ckt to
the source voltage or high.

Pnp and npn transistors differ somehow in this respect -- but why,
and what does that mean in practice?
Click to expand...
NPN is negative emitter, positive base, negative collector material.
Biasing the base more negative caused conduction. More positive cuts it off.
PNP is positive emitter, negative base, positive collector. Sourcing the
base causes conduction. sinking the base cuts it off.

Thanks in advance!
Click to expand...

---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.518 / Virus Database: 316 - Release Date: 9/11/2003
 
Kevin Aylward wrote:
R. Steve Walz wrote:
Kevin Aylward wrote:

R. Steve Walz wrote:
Jani Miettinen wrote:

I'm studying electronics on my own (as a hobby), reading right now
Art of Electronics, browsing the web to fill some of the gaps (yes,
there are quite some) and toying with CircuitMaker (which helps a
lot to understand the stuff).

Sinking and sourcing current have been referenced to several times,
but they have never been explained in any usable detail. So, here
are the questions -- for now, more might follow ;) :

What is the difference between sinking and sourcing current?

Pnp and npn transistors differ somehow in this respect -- but why,
and what does that mean in practice?

Thanks in advance!
-------------------------
It is like a switch upstream or downstream of a load.

It can be a switch. It can also be a linear amp. I don't see any
assumption that the question refers to switching use only.
--------------
Rule one for teaching: Start simple.

Rule two. Don't simplify so much that it becomes meaningless.
------------------------
Click to expand...
The best initial use of the transistor to teach is switching.
It involves the limits of performance, and discusses biasing.


The PNP is best upstream of load, upside down, emitter up to Vcc,
because then we must ground the base to turn it on, and it mirrors
the NPN case, except upside down, and prevents that base
instability at turn-on.

Well, I will query the use of the word "best" here. One can have a
push-pull or source sink with either a collector output or emitter
output. Both methods have disadvantages and advantages. Since this is
your reply,
-----------------------
Mostly disadvantages if you disregard the load drop that lifts the
base reference at turn-on.

Oh. You think so. If this were true, just why do you proposes that,
essentially, all audio power amps use emitter follower outputs. This
amounts to 10000's of designs, and billions of actual product sold. How
do you explain that non emitter follower output op-amps are few and far
between.
Kevin Aylward
-----------
Click to expand...
Why don't you do the math on one right here and find out, eh?

-Steve
--
-Steve Walz rstevew@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public
 
R. Steve Walz wrote:
Kevin Aylward wrote:

R. Steve Walz wrote:
Kevin Aylward wrote:

R. Steve Walz wrote:
Jani Miettinen wrote:

I'm studying electronics on my own (as a hobby), reading right
now Art of Electronics, browsing the web to fill some of the
gaps (yes, there are quite some) and toying with CircuitMaker
(which helps a lot to understand the stuff).

Sinking and sourcing current have been referenced to several
times, but they have never been explained in any usable detail.
So, here are the questions -- for now, more might follow ;) :

What is the difference between sinking and sourcing current?

Pnp and npn transistors differ somehow in this respect -- but
why, and what does that mean in practice?

Thanks in advance!
-------------------------
It is like a switch upstream or downstream of a load.

It can be a switch. It can also be a linear amp. I don't see any
assumption that the question refers to switching use only.
--------------
Rule one for teaching: Start simple.

Rule two. Don't simplify so much that it becomes meaningless.
------------------------
The best initial use of the transistor to teach is switching.
It involves the limits of performance, and discusses biasing.


The PNP is best upstream of load, upside down, emitter up to Vcc,
because then we must ground the base to turn it on, and it mirrors
the NPN case, except upside down, and prevents that base
instability at turn-on.

Well, I will query the use of the word "best" here. One can have a
push-pull or source sink with either a collector output or emitter
output. Both methods have disadvantages and advantages. Since this
is your reply,
-----------------------
Mostly disadvantages if you disregard the load drop that lifts the
base reference at turn-on.

Oh. You think so. If this were true, just why do you proposes that,
essentially, all audio power amps use emitter follower outputs. This
amounts to 10000's of designs, and billions of actual product sold.
How do you explain that non emitter follower output op-amps are few
and far between.
Kevin Aylward
-----------
Why don't you do the math on one right here and find out, eh?
Click to expand...
Its your reply, I don't want to intrude to much. I'll give you a hint
though. Output impedance.

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
Kevin Aylward wrote:
R. Steve Walz wrote:
Kevin Aylward wrote:

R. Steve Walz wrote:
Kevin Aylward wrote:

R. Steve Walz wrote:
Jani Miettinen wrote:

I'm studying electronics on my own (as a hobby), reading right
now Art of Electronics, browsing the web to fill some of the
gaps (yes, there are quite some) and toying with CircuitMaker
(which helps a lot to understand the stuff).

Sinking and sourcing current have been referenced to several
times, but they have never been explained in any usable detail.
So, here are the questions -- for now, more might follow ;) :

What is the difference between sinking and sourcing current?

Pnp and npn transistors differ somehow in this respect -- but
why, and what does that mean in practice?

Thanks in advance!
-------------------------
It is like a switch upstream or downstream of a load.

It can be a switch. It can also be a linear amp. I don't see any
assumption that the question refers to switching use only.
--------------
Rule one for teaching: Start simple.

Rule two. Don't simplify so much that it becomes meaningless.
------------------------
The best initial use of the transistor to teach is switching.
It involves the limits of performance, and discusses biasing.


The PNP is best upstream of load, upside down, emitter up to Vcc,
because then we must ground the base to turn it on, and it mirrors
the NPN case, except upside down, and prevents that base
instability at turn-on.

Well, I will query the use of the word "best" here. One can have a
push-pull or source sink with either a collector output or emitter
output. Both methods have disadvantages and advantages. Since this
is your reply,
-----------------------
Mostly disadvantages if you disregard the load drop that lifts the
base reference at turn-on.

Oh. You think so. If this were true, just why do you proposes that,
essentially, all audio power amps use emitter follower outputs. This
amounts to 10000's of designs, and billions of actual product sold.
How do you explain that non emitter follower output op-amps are few
and far between.
Kevin Aylward
-----------
Why don't you do the math on one right here and find out, eh?


Its your reply, I don't want to intrude to much. I'll give you a hint
though. Output impedance.

Kevin Aylward
------------
Click to expand...
Which my switching examples didn't need to concern themselves with,
of course. My point exactly in asking you to do the gain and stability
analysis.

-Steve
--
-Steve Walz rstevew@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public
 
R. Steve Walz wrote:
Kevin Aylward wrote:

R. Steve Walz wrote:
Kevin Aylward wrote:

R. Steve Walz wrote:
Kevin Aylward wrote:

R. Steve Walz wrote:
Jani Miettinen wrote:

I'm studying electronics on my own (as a hobby), reading right
now Art of Electronics, browsing the web to fill some of the
gaps (yes, there are quite some) and toying with CircuitMaker
(which helps a lot to understand the stuff).

Sinking and sourcing current have been referenced to several
times, but they have never been explained in any usable detail.
So, here are the questions -- for now, more might follow ;) :

What is the difference between sinking and sourcing current?

Pnp and npn transistors differ somehow in this respect -- but
why, and what does that mean in practice?

Thanks in advance!
-------------------------
It is like a switch upstream or downstream of a load.

It can be a switch. It can also be a linear amp. I don't see any
assumption that the question refers to switching use only.
--------------
Rule one for teaching: Start simple.

Rule two. Don't simplify so much that it becomes meaningless.
------------------------
The best initial use of the transistor to teach is switching.
It involves the limits of performance, and discusses biasing.


The PNP is best upstream of load, upside down, emitter up to
Vcc, because then we must ground the base to turn it on, and it
mirrors the NPN case, except upside down, and prevents that base
instability at turn-on.

Well, I will query the use of the word "best" here. One can have
a push-pull or source sink with either a collector output or
emitter output. Both methods have disadvantages and advantages.
Since this is your reply,
-----------------------
Mostly disadvantages if you disregard the load drop that lifts the
base reference at turn-on.

Oh. You think so. If this were true, just why do you proposes that,
essentially, all audio power amps use emitter follower outputs.
This amounts to 10000's of designs, and billions of actual product
sold. How do you explain that non emitter follower output op-amps
are few and far between.
Kevin Aylward
-----------
Why don't you do the math on one right here and find out, eh?


Its your reply, I don't want to intrude to much. I'll give you a hint
though. Output impedance.

Kevin Aylward
------------
Which my switching examples didn't need to concern themselves with,
of course. My point exactly in asking you to do the gain and stability
analysis.
Click to expand...
But I pointed out that switching was not assumed in the question.

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
Kevin Aylward wrote:
R. Steve Walz wrote:
Kevin Aylward wrote:

R. Steve Walz wrote:
Kevin Aylward wrote:

R. Steve Walz wrote:
Kevin Aylward wrote:

R. Steve Walz wrote:
Jani Miettinen wrote:

I'm studying electronics on my own (as a hobby), reading right
now Art of Electronics, browsing the web to fill some of the
gaps (yes, there are quite some) and toying with CircuitMaker
(which helps a lot to understand the stuff).

Sinking and sourcing current have been referenced to several
times, but they have never been explained in any usable detail.
So, here are the questions -- for now, more might follow ;) :

What is the difference between sinking and sourcing current?

Pnp and npn transistors differ somehow in this respect -- but
why, and what does that mean in practice?

Thanks in advance!
-------------------------
It is like a switch upstream or downstream of a load.

It can be a switch. It can also be a linear amp. I don't see any
assumption that the question refers to switching use only.
--------------
Rule one for teaching: Start simple.

Rule two. Don't simplify so much that it becomes meaningless.
------------------------
The best initial use of the transistor to teach is switching.
It involves the limits of performance, and discusses biasing.


The PNP is best upstream of load, upside down, emitter up to
Vcc, because then we must ground the base to turn it on, and it
mirrors the NPN case, except upside down, and prevents that base
instability at turn-on.

Well, I will query the use of the word "best" here. One can have
a push-pull or source sink with either a collector output or
emitter output. Both methods have disadvantages and advantages.
Since this is your reply,
-----------------------
Mostly disadvantages if you disregard the load drop that lifts the
base reference at turn-on.

Oh. You think so. If this were true, just why do you proposes that,
essentially, all audio power amps use emitter follower outputs.
This amounts to 10000's of designs, and billions of actual product
sold. How do you explain that non emitter follower output op-amps
are few and far between.
Kevin Aylward
-----------
Why don't you do the math on one right here and find out, eh?


Its your reply, I don't want to intrude to much. I'll give you a hint
though. Output impedance.

Kevin Aylward
------------
Which my switching examples didn't need to concern themselves with,
of course. My point exactly in asking you to do the gain and stability
analysis.

But I pointed out that switching was not assumed in the question.

Kevin Aylward
--------------------
Click to expand...
No, it was correctly assumed for the answer to such a newbie question.

-Steve
--
-Steve Walz rstevew@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public
 
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