Get Current and Voltage with a Circuit with Diodes

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Discussion Overview

The discussion revolves around analyzing a circuit containing diodes, specifically determining the current (I) and voltage (V) across the components. Participants are exploring the conditions under which the diodes (D1 and D2) are considered to be in the 'on' or 'off' states, and how these states affect the overall circuit behavior.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants express confusion about the states of D1 and D2, with initial assumptions that both diodes are 'on' due to being in forward bias.
  • Others point out that online resources indicate D1 is 'on' while D2 is 'off', questioning how D2 can be off given the current direction.
  • A participant corrects the understanding of diode states, stating that 'on' means a short circuit and 'off' means an open circuit.
  • Questions are raised about the typical forward voltage for silicon diodes and the implications of D2 being 'off' on its anode voltage.
  • Some participants inquire about the possibility of both diodes being 'on' simultaneously and suggest looking for contradictions in circuit behavior under that assumption.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the states of the diodes. There are competing views on whether both diodes can be 'on' at the same time, and the discussion remains unresolved regarding the implications of diode states on circuit analysis.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about ideal diodes, the definitions of 'on' and 'off', and the potential voltage drops across components. These factors are not fully resolved within the conversation.

roinujo1
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Homework Statement


Find the V and I in the circuit shown below:

upload_2016-10-20_12-21-44.png

Homework Equations


  • D1 or 2 is off=short circuit
  • D1 or 2 is on=open circuit

The Attempt at a Solution


So, my confusion lies with deciding the on and offs of D1 and D2 . My assumption is that both of them are on and that is due to them in forward bias. However, when I looked online, D2 was off and D1 was on. Based on how the current is going into D2, how is D2 off?

Any help is much appreciated!
 
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roinujo1 said:

Homework Statement


Find the V and I in the circuit shown below:

View attachment 107760

Homework Equations


  • D1 or 2 is off=short circuit
  • D1 or 2 is on=open circuit

The Attempt at a Solution


So, my confusion lies with deciding the on and offs of D1 and D2 . My assumption is that both of them are on and that is due to them in forward bias. However, when I looked online, D2 was off and D1 was on. Based on how the current is going into D2, how is D2 off?

Any help is much appreciated!
Your Relevant Equations are backwards, BTW. On=short and Off=open for diodes.

What is the typical forward voltage for a silicon diode? What is the anode voltage for D2 if it is off? And if D2 were on, what would that do to the Anode voltage?
 
berkeman said:
Your Relevant Equations are backwards, BTW. On=short and Off=open for diodes.

What is the typical forward voltage for a silicon diode? What is the anode voltage for D2 if it is off? And if D2 were on, what would that do to the Anode voltage?
Thank you for the response!

Aww, I'm sorry. Yeah it does look like they are bakwards (was in a rush). Thank you for that.

Im sorry, but what do you mean by anode voltage? My assumption was that d2 was forward positive because:
upload_2016-10-20_18-46-39.png
 
Basically, I think I want to know why D1 and D2 both can't be on.
 
roinujo1 said:
Basically, I think I want to know why D1 and D2 both can't be on.
Look for circuit behavior contradiction(s) if you assume that both are on. For a quick evaluation, assume that the diodes are ideal (no forward voltage or resistance). What would be the potential V on your diagram? Determine all the currents through the components (should be simple if you know the potential drops on the resistors and KCL for the junctions). What do you get?
 

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