Circuit w/ Diodes: Voltages & Conducting?

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Discussion Overview

The discussion revolves around analyzing a circuit with two diodes to determine the voltages across them and whether both diodes can be conducting simultaneously. Participants explore the conditions under which each diode operates, considering ideal and non-ideal behaviors.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether both diodes are conducting or if only the first diode is conducting due to a higher power level.
  • Another participant suggests checking all possible cases (both off, both on, D1 on only, D2 on only) to find a consistent solution, noting uncertainty about whether the diodes are ideal or have a forward voltage drop of 0.6V.
  • A participant proposes that both diodes require 0.7V, implying that D1 will deactivate D2.
  • One participant expresses a need for assistance, indicating confusion about the situation.
  • Another participant challenges the assumption that both diodes cannot be on, asking why D1 couldn't be off while D2 is on.
  • A participant provides a reasoning approach, explaining that if both diodes were on, it would lead to inconsistent voltage levels at a shared node, which is not permissible in circuit theory.
  • Another participant suggests analyzing the scenario where D1 is off and D2 is on to explore the implications further.

Areas of Agreement / Disagreement

Participants express differing views on whether both diodes can conduct simultaneously, with some arguing against it based on voltage constraints while others question this assumption. The discussion remains unresolved regarding the operational states of the diodes.

Contextual Notes

Participants mention potential variations in diode behavior (ideal vs. non-ideal) and the importance of voltage levels across the diodes, which may affect the analysis. There are also unresolved assumptions regarding the specific voltage values and conditions for conduction.

snowJT
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Quiz3-diodes.gif


I'm suppose to calculate the voltages across the diodes.. but I was wondering in this situation, are both diodes conducting, or is only the first one conducting because there is more power in that, and it shuts off the other one.
 
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in diode problems like this usually, you should check all cases to see which is the only consistent one. In this case, there are four cases both off, both on, D1 on only and D2 on only. Now I am not sure whether those diodes are ideal or you put 0.6V across them when they are ON. But the technique is the same. Remember what determines ON/OFF is the potential difference across each of them.
 
they both need 0.7 V, so I'm guessing the D1 will shut off D2
 
some one please help? :(
 
If your guess works, you did good.

Let me ask you:

why couldn't they both be turned ON?
why couldn't D1 be OFF and D2 be ON?
 
lol, its kind of a long explanation.. but even if the 5V turned on much before the 8 V did... but as soon as the 8V kicks in, there is 7.2 volts against the 5 volts.. and so it doesn't go through the diode.. I know its more complicated than that. but...
 
It's really not complicated though.

here's how i'd do the first case (why can't they both be on?)
call the node inbetween the diodes Vx

~the drop across D1 is 0.7, making Vx = 7.3V
~the drop across D2 is 0.7, making Vx = 4.3V

two different voltages for one node isn't allowed, so this is why they can't both be turned on.

Now try acting as if D1 is OFF and D2 is ON, and see what happens
 

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