Transistor signal direction question

[TeGGeR®]

My first post here!

I'm trying to understand signal flow through a point-contact transistor.

Just so you know, I have no electrical background, and am not even that
good at math. The apparent squidginess of semiconductors is something that
is baffling me.

Some Googling turned up this sequence (this one page in particular), which
was partially informative:
<http://nobelprize.org/physics/educational/transistor/function/amplificatio
n.html>
(all on one line)

But it does not help answer the question of how current actually flows. I'm
not talking about the actual *electrons*, which do go from negative to
positive, but "current" as normally referred to when considering the
convention that things go from the positive terminal of the battery to the
negative one.

My problem is that there are TWO terminals on the battery, but THREE on the
transistor. Also, the diagrams and animations on the Nobelprize site do not
explain why there are TWO batteries shown. Apparently you are just supposed
to know. And most cars do not have two batteries.

A poster in another group offered this attempt at clarification:
"Think of a Y water pipe. One arm of the Y is smaller than the other.But
the total water flow thru the bottom of the Y divides and part passes
thru the left arm and part thru the right arm.You can control how much
water passes thru the right arm by adjusting the flow thru the left
arm.(but the water pipe does not have any current gain)"

I thought the flow was from emitter to collector, with the base being the
control for E and C, but the above (and the Nobelprize page) contradicts
that, so I'm obviously missing something.

These are pages from my site:
http://www.tegger.com/hondafaq/igniter-operation/index.html
http://www.tegger.com/hondafaq/igniter-operation/badigniter.html

I am sure I have mistakes in there, but no one in the Honda groups have
offered any clues as to what the errors are, if any. All I want is for the
diagrams to be correct.

Any help is quite welcome.

 

[Andy]

RE:
I thought the flow was from emitter to collector, with the base being
the
control for E and C, but the above (and the Nobelprize page)
contradicts
that, so I'm obviously missing something.


Andy writes:

I can't disagree with the statement above. Looks like a really good
simplified explanation to me. However, that only applies for a PNP
transistor.

A similar statement for an NPN transistor would read:

The flow is from collector to emitter, with the strength of that
flow being controlled by the flow from the base to the emitter...

There are many ways of getting a gut feeling for how a transistor
works, and whichever visualization works well for you might
completely confuse someone else. Personally, my mental
model is much like yours, and I designed transistors and ICs
for a half dozen years at Texas Instuments, a while back.

Purists may disagree with this and expound on some damn thing
like hole flow and electron flow. But I think of "stuff" coming out of
the + terminal and trying to get to the - terminal the best way it
can. It works well once your entire thinking uses this.

But be aware that many people are not as flexible in their thinking.
It doesn't mean they are "wrong" or "right", just that their mental
model , that works for them, may not work as easily for you...
.... and when you finally are content and competent with your own
mental model, try to be tolerant of other approaches... :>)))

Andy

 

[Ken Weitzel]

My first post here!

I'm trying to understand signal flow through a point-contact transistor.

Just so you know, I have no electrical background, and am not even that
good at math. The apparent squidginess of semiconductors is something that
is baffling me.

Some Googling turned up this sequence (this one page in particular), which
was partially informative:
<http://nobelprize.org/physics/educational/transistor/function/amplificatio
n.html>
(all on one line)

But it does not help answer the question of how current actually flows. I'm
not talking about the actual *electrons*, which do go from negative to
positive, but "current" as normally referred to when considering the
convention that things go from the positive terminal of the battery to the
negative one.

My problem is that there are TWO terminals on the battery, but THREE on the
transistor. Also, the diagrams and animations on the Nobelprize site do not
explain why there are TWO batteries shown. Apparently you are just supposed
to know. And most cars do not have two batteries.

A poster in another group offered this attempt at clarification:
"Think of a Y water pipe. One arm of the Y is smaller than the other.But
the total water flow thru the bottom of the Y divides and part passes
thru the left arm and part thru the right arm.You can control how much
water passes thru the right arm by adjusting the flow thru the left
arm.(but the water pipe does not have any current gain)"

I thought the flow was from emitter to collector, with the base being the
control for E and C, but the above (and the Nobelprize page) contradicts
that, so I'm obviously missing something.

These are pages from my site:
http://www.tegger.com/hondafaq/igniter-operation/index.html
http://www.tegger.com/hondafaq/igniter-operation/badigniter.html

I am sure I have mistakes in there, but no one in the Honda groups have
offered any clues as to what the errors are, if any. All I want is for the
diagrams to be correct.

Any help is quite welcome.

Hi Tegger...

Wow, flashback! Remember being there 50 years ago. Tubes,
though - not transistors

Now old and stroke damaged, but let's try it anyway...

Back to the water. Fire hose sized hose supplies great
quantities of water at great pressure to the input side
(who cares which; pnp or npn - let's just call it the
input side.

Ignoring everything else, great quantities of water come
out the other end... you load it somehow and use the
result.

Good, but nothing's been accomplished. So - let's put
a small portioning device in between the input and output.
Let's make it water controlled... just a little bit of
water... say from your garden hose. You twiddle the
knob on your garden hose, the valve moves, and you now
control the other (totally separate) great flow of fire
hose quantities of water. Ooops, forgot to name it, so
let's call it the base.

Does this super silly description help?

Take care.

Ken

 

[TimPerry]

These are pages from my site:
http://www.tegger.com/hondafaq/igniter-operation/index.html
http://www.tegger.com/hondafaq/igniter-operation/badigniter.html

I am sure I have mistakes in there, but no one in the Honda groups have
offered any clues as to what the errors are, if any. All I want is for the
diagrams to be correct.

Any help is quite welcome.

Ted, im not an expert on electronic ignition systems, however you diagram
seem A bit wrong to me.

The Darlington transistor is the gizmo that is replacing the "points" of the
Kettering system. It's a kind of electronic switch. The high gain of this
device makes it east to fully saturate it so that it turns on as hard as it
can go when a small signal is applied to its input.

I believe that the emitter should be grounded all the time and the control
signal from the ECU will go to the base (terminal 3 on your diagram)

I'm not sure how the "tach" should be depicted in this case.

in depicting the current flow it would probably be best to only show the
dashed lines through the second transistor as that one will be carrying the
bulk of the current.

here is a site with a basic diagram of an electronic ignition
http://ourworld.compuserve.com/homepages/JET_AV8R/Vision/Ignition/CDI.HTML

 

[Jim Yanik]

My first post here!

I'm trying to understand signal flow through a point-contact
transistor.

Well,nobody uses point-contact transistors anymore.They are all junction
transistors,that's where NPN or PNP comes ffrom,the layers of N-type or P-
type semiconductor.The middle letter is the base element,thus that's how
the base controls the current from emitter to collector.

That site you reference is a bit wrong about "today's transistors".
There are junction or bipolar transistors,AND there are FETS or field-
effect transistors.Both are used in modern electronics.They have different
advantages and disadvantages.

FETS operate more like a vacuum tube;a voltage on the gate controls the
current flow through the P-N junction (Drain and Source terminals).

Bipolar xstrs(short for transistor)operate by use of forward and reverse
bias of the P-N junctions(N-P-N or P-N-P).The amount of forward bias of the
B-E junction is what controls the current thru the C-E junction.
Bias is a small current provided by the "battery" from base to emitter,in
real life provided by a resistor or resistor divider.

Just so you know, I have no electrical background, and am not even
that good at math. The apparent squidginess of semiconductors is
something that is baffling me.

Some Googling turned up this sequence (this one page in particular),
which was partially informative:
<http://nobelprize.org/physics/educational/transistor/function/amplifica
tio
n.html>
(all on one line)

But it does not help answer the question of how current actually
flows. I'm not talking about the actual *electrons*, which do go from
negative to positive, but "current" as normally referred to when
considering the convention that things go from the positive terminal
of the battery to the negative one.

Current IS the flow of electrons.They go from neg to pos.

My problem is that there are TWO terminals on the battery, but THREE
on the transistor. Also, the diagrams and animations on the Nobelprize
site do not explain why there are TWO batteries shown. Apparently you
are just supposed to know. And most cars do not have two batteries.

The battery on the base-emitter circuit is to show the bias supply(B-E
current) needed to operate the base.In real circuits,the base bias(B-E
current) is supplied by a pullup resistor or a divider network of two
resistors.
[B-E=base-emitter,C-E= collector-emitter]

The concept of a transistor (or a vacuum tube) is that a small base-emitter
current controls a much larger collector-emitter current(voltage for a
vac.tube). The ratio of B-E current to C-E current is called current
gain(beta),or amplification.For tubes and FETs,it's voltage
gain(Alpha,IIRC??),the small grid or gate voltage swing controls a much
larger plate or drain voltage swing,resulting in amplification..

 

[NSM]

My first post here!

I'm trying to understand signal flow through a point-contact transistor.

Just so you know, I have no electrical background, and am not even that
good at math. The apparent squidginess of semiconductors is something that
is baffling me.

http://electronics.howstuffworks.com/diode.htm

N