Solving a Circuit with Diodes: Find V Across Resistor

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Discussion Overview

The discussion revolves around solving a circuit involving diodes and determining the voltage across a resistor. Participants explore the effects of diodes in the circuit configuration and the methodology for analyzing the circuit, including assumptions about diode states.

Discussion Character

  • Homework-related
  • Debate/contested
  • Exploratory

Main Points Raised

  • One participant expresses uncertainty about how to begin solving for the voltage across the resistor and the effect of the diodes in the circuit.
  • Another participant suggests that if the diodes are ideal and forward biased, they can be replaced with short circuits, or with voltage sources of 0.6 V if they are not ideal.
  • A different participant proposes starting by ignoring the diodes to solve for the resistor divider voltages separately, then introducing one diode at a time to analyze the circuit's behavior.
  • There is a question raised about the validity of assuming both diodes are forward biased, indicating uncertainty regarding this assumption.
  • One participant questions the common practice of making assumptions about diode states before checking their validity, suggesting a more direct approach of comparing voltages on either side of the diodes.
  • Another participant responds that while comparing voltages can work for a single diode, the state of one diode can depend on the states of other diodes in the circuit, complicating the analysis.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the assumptions regarding the diode states. There are differing opinions on the approach to take when analyzing the circuit, particularly regarding whether to assume diodes are conducting or to evaluate their states based on voltage comparisons.

Contextual Notes

Participants highlight the complexity of analyzing circuits with multiple diodes, noting that the conducting state of one diode may depend on the states of others, which introduces uncertainty in the analysis.

Ry122
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Homework Statement




http://img832.imageshack.us/img832/6302/20285200.jpg

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Homework Equations





The Attempt at a Solution


I'm unsure where to begin with this.
I need to find the value V across the resistor and I'm unsure how.
What effect do the diodes have in a circuit that's set up in this way?
 
Last edited by a moderator:
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Both diodes are forward biased.
If they are ideal, you can replace them with short circuits. If not, you can replace them by voltage sources of 0.6 V.
 
Ry122 said:

Homework Statement




http://img832.imageshack.us/img832/6302/20285200.jpg

Uploaded with ImageShack.us

Homework Equations





The Attempt at a Solution


I'm unsure where to begin with this.
I need to find the value V across the resistor and I'm unsure how.
What effect do the diodes have in a circuit that's set up in this way?

Start by ignoring the diodes, and solve for the two separate resistor divider voltages. What do you get? Now if you put in one diode at a time, what happens? And then with both of them in at once?

CEL said:
Both diodes are forward biased.

I'm not sure that is true...
 
Last edited by a moderator:
How come when solving these circuits you're supposed to make assumptions about which ones might be on and which ones are off, and then check to see if you're right?

Why can't you just look at the voltages on either side of the diodes and see whether the cathode or anode side is greater?
 
Ry122 said:
Why can't you just look at the voltages on either side of the diodes and see whether the cathode or anode side is greater?

You can if there's just one diode, but in general the A-K polarity of a particular diode will depend on the state (conducting / non conducting) of all the other diodes in the circuit. Your original question above is a good example of this.
 

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