LET?

[[email protected]]

I saw a shematic of a transistor represented by two diodes. It gave me
an idea, What if i took two LED's and connected them like the picture
and made a light emmeting transistor? i didn't se the point in it
either than for a little project, but i tried it anyways and connected
the anodes together to make an NPN transistor. It didn't work but i
want toknow why. Is there something more to transistors i don't know?
Thanks in advance!

 

[Andrew Holme]

I saw a shematic of a transistor represented by two diodes. It gave me
an idea, What if i took two LED's and connected them like the picture
and made a light emmeting transistor? i didn't se the point in it
either than for a little project, but i tried it anyways and connected
the anodes together to make an NPN transistor. It didn't work but i
want toknow why. Is there something more to transistors i don't know?
Thanks in advance!

http://www.mtmi.vu.lt/pfk/funkc_dariniai/transistor/bipolar_transistor.htm

 

[Bob Monsen]

I saw a shematic of a transistor represented by two diodes. It gave me
an idea, What if i took two LED's and connected them like the picture
and made a light emmeting transistor? i didn't se the point in it
either than for a little project, but i tried it anyways and connected
the anodes together to make an NPN transistor. It didn't work but i
want toknow why. Is there something more to transistors i don't know?

Yes. Bipolar transistors are three layers of silicon, forming two diodes
(like the picture.) The base is in the middle. If you create a voltage
between the base and emitter, it'll help charges cross over the reversed
diode. Just connecting the anodes of a couple of diodes won't work,
because the charge across the 'reverse biased' one won't be helped into
jumping across the barrier.

--
Regards,
Bob Monsen

If a little knowledge is dangerous, where is the man who has
so much as to be out of danger?
Thomas Henry Huxley, 1877

 

[Pooh Bear]

I saw a shematic of a transistor represented by two diodes. It gave me
an idea, What if i took two LED's and connected them like the picture
and made a light emmeting transistor? i didn't se the point in it
either than for a little project, but i tried it anyways and connected
the anodes together to make an NPN transistor. It didn't work but i
want toknow why. Is there something more to transistors i don't know?

Rather a lot it seems ! Firstly it's important to understand that a
bipolar transistor is a single device. The fact that it can behave like 2
diode junctions doesn't mean that's what its actually made of.

Graham

 

[John Popelish]

I saw a shematic of a transistor represented by two diodes. It gave me
an idea, What if i took two LED's and connected them like the picture
and made a light emmeting transistor? i didn't se the point in it
either than for a little project, but i tried it anyways and connected
the anodes together to make an NPN transistor. It didn't work but i
want toknow why. Is there something more to transistors i don't know?
Thanks in advance!

The difference between two diodes in series and a transistor with two
junctions in series is that the middle node is physically very thin,
so that when you forward bias the base emitter junction, the charge
carriers injected from emitter into thin base layer move more by
diffusion (random movements closely related to thermal Brownian
movement) than by the very small electrical field across to the base
material. So most of those charge carriers wander over to the
collector side of the collector to base junction, where they suddenly
experience the effect of the stronger electric field across this
reverse biased junction. This field quickly sweeps those charge
carriers out as collector current.

 

[John Larkin]

Yes. Bipolar transistors are three layers of silicon, forming two diodes
(like the picture.) The base is in the middle. If you create a voltage
between the base and emitter, it'll help charges cross over the reversed
diode. Just connecting the anodes of a couple of diodes won't work,
because the charge across the 'reverse biased' one won't be helped into
jumping across the barrier.

As I discovered when I was, I think, 11 years old!

John

 

[mc]

Two diodes do not make a transistor. The base of the transistor has to be
one piece of material (not two separate diode-cathodes joined by a wire) and
has to be very thin, so that charge carriers can cross it, and so that their
ability to do so is influenced by comparatively small numbers of electrons
injected into it or withdrawn from it.

Having said that... There's no reason you couldn't use LED materials (not
complete LEDs) to make a transistor. I suppose it would light up. It would
also waste a lot of power doing so... As I understand it, the light would
come from the base-emitter junction, which is not particularly useful.

 

[Fred Bartoli]

As I discovered when I was, I think, 11 years old!

Oh, you too...

But then did you try SiGe (one Si diode and one Ge diode) as I did?

 

[John Larkin]

Oh, you too...

But then did you try SiGe (one Si diode and one Ge diode) as I did?

No, that was far too advanced for me. But the OP has us both beat,
with a GaAlAs heterojunction light-emitting nonfunctional transistor.

John

 

[Ben Bradley]

http://www.mtmi.vu.lt/pfk/funkc_dariniai/transistor/bipolar_transistor.htm

The left part of this diagram, showing diodes:

http://www.mtmi.vu.lt/pfk/funkc_dariniai/images/dtob.gif

.... really ought to be tossed into tue bit bucket. It does nothing to
contribute to the understanding of bipolar transistors, and
furthermore is misleading.