How is the current through the diode calculated?

Hello, unfortunately I have absolutely no idea how to solve the problem.
Can someone explain to me what I have to do here?

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Traveller5712
4 months ago

Not at all… there is no voltage indication without which the current through the diode cannot be calculated.

isohypse
4 months ago
Reply to  Traveller5712

That’s wrong. It’s all there is.

Traveller5712
4 months ago
Reply to  isohypse

Then tell me the total voltage, which one is on.

isohypse
4 months ago

now?

what do you want to tell me? The task is solved below. Already seen?

Or are you just rolling? Slowly I think it can only be that…

Traveller5712
4 months ago

I = U/R ….

isohypse
4 months ago

Then tell me the total voltage, which one is on.

She didn’t ask? Why do you need these? The question is already answered…

There is

  • The current flowing from the left
  • All R
  • the characteristic curve of the diode

All this is clearly defined (even the total voltage, which is not in demand here)

isohypse
4 months ago

This can be solved exactly graphically: The diode sees as a source

and

Now you cut the corresponding work line

with the characteristic curve. The intersection is about 0.62V.

Lutz28213
4 months ago
Reply to  isohypse

Do I see that you have accepted that on your account the voltage at R2 is determined by the total current (and not by a partial current) at the upper branch? There’s something wrong with that!

Lutz28213
4 months ago
Reply to  Lutz28213

Sorry, I made a stupid mistake. You’re right.

AMG38
4 months ago

If you neglect the differential resistance of the diode, you can determine the substream of a branch and thus the diode current via the current divider.

Lutz28213
4 months ago
Reply to  tobi2247

Don’t be irritated – the differential resistance (start of the characteristic) doesn’t matter!

AMG38
4 months ago
Reply to  tobi2247

You can see at the voltage-current curve of the diode that the current is dependent on the voltage. This dependency is not proportional but exponential.

For example, if you look at 0.5V, a current of 20 mA flows. The resistance of the diode at this point would then be at 0.5V/20mA=25Ohm. This, however, cannot be taken as a generally or permanently valid value for all voltages, for you can see, for example at 0.6V, there flows a current of 40mA. The associated resistance is then at 0.6V/40mA 15Ohm.

As you can see, the resistance has decreased. It thus changes as a function of the applied voltage. Thus, the resistance is not constant but differential.

isohypse
4 months ago
Reply to  AMG38

It is also possible to solve exactly.