"Sam Goldwasser" wrote in message
...
"Bradley1234" writes:

Okay, way back somebody said a diod is a diod, not a resistor, so the
theme
became what is a diode, not what is a photodiode.

So thats why I mentioned the electrical properties of a diode being used
for
a variable resistance. Of course its not a bidirectional resistance,
but by

In no way, shape, or form, is a diode generally used like a resistor or
behaves like a resistor.

AHA, here is a problem, a diode changes its resistance, if you say it
doesnt, then please explain the effect on the current flow while its in the
circuit. If you ignore how the process takes place internal to the PN
junction and observe the diode operates, why would it not simply be a
component that appears to change resistance?

Ive never said a diode can used as a replacement for a resistor, the
resistor is typically linear, a diode is non linear, for a voltage applied
it is not a constant resistance unlike a common resistor, but I say the
diodes reaction is resistive.



any other name becoming a variable resistance to current flow. (yes non
linear) I described the simple effect of recombination in the depletion
region at the PN junction that changes based on bias, to which you said
this
was incorrect.

I said: "Not really" as an explanation of how a photodiode worked. And
while
it some reasonable information about what happens when voltage is applied
to a PN junction with respect the electrons and holes and width of the
depletion region, etc., I doubt anyone who didn't already know how a diode
worked would have after reading it. There was no attempt made to relate
the textbook description to circuit behavior.


Its my observation that many people do not understand WHY a diode works, but
most everyone knows the diode tends to block current in one direction and
permit it in the other. Ask them why? I offered a simple model of the
depletion region which changes based on bias, So maybe your saying not
really was saying a photodiode doesnt work that way, when I was describing a
standard diode?

Ask people why does an LED emit light? its a very interesting and hard to
explain phenomenon, I would estimate that most people do not know exactly
where the light comes from or why. and hard to explain meaning some
foundation of chemistry, minority/majority carriers, etc

What does a transistor do? its simply a controlled resistor also. Ive
known "experts" say a transistor generates power, it creates power where
none existed before, power comes out, nobody knows why, probably the crystal
creates the energy.




In photodiodes? If the photodiode is biased and light is applied the
amount
of current flow should change. Net effect its resistance has changed.

The current is proportional to optical power and is more or less
independent
of applied voltage. That's not what is normally considered to be a
resistor.

The current? so we agree that current changes. Im saying its because the
resistance changes, not because power is created inside a diode that is
adding to the circuit. Are you saying optical power is transferred right
out of the diode? It comes in as light and is converted to current?

Im saying light affects the depletion region that causes a change in
resistance, its proportional to incident optical power but assuredly not
linearly proportional



The website mentioned shows a non standard photodiode, and yes I did the
search, interesting product line

Yes, but the first sentence was a good summary of how a silicon photodiode
works.

But Im still wondering how Im wrong, perhaps we were talking apples and
oranges, I said a pn junctions resistance changes by the variable depletion
region, you said not really. So then am I still wrong? or do we agree on
theory?


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