Diode Circuit Problem: Find Current in a Given Circuit | Homework Help

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Discussion Overview

The discussion revolves around solving a homework problem related to determining the current through a diode in a given circuit. Participants explore the application of circuit laws and the properties of diodes, focusing on the necessary conditions for current flow.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant expresses uncertainty about how to apply Ohm's Law and Kirchhoff's Laws to the circuit problem involving diodes.
  • Another participant suggests that understanding the properties of diodes is essential for solving the problem.
  • There is a mention of the forward bias voltage of a silicon diode being approximately 0.7V, which is necessary for it to conduct.
  • Participants discuss the need to test whether the diode is forward biased by checking the voltage across it.
  • One participant proposes that they need to determine if the voltage across the diode is less than or greater than 0.7V to understand its state.
  • A later reply suggests assuming the diode voltage is 0.7V to analyze the remaining battery voltage available for the resistors in the circuit.

Areas of Agreement / Disagreement

Participants generally agree on the importance of understanding diode properties and the need to test the diode's state, but there is no consensus on the specific approach to solving the circuit problem.

Contextual Notes

Participants have not fully resolved how to apply the circuit laws in conjunction with the diode properties, and there are assumptions about the diode's behavior that remain untested.

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Homework Statement


In the circuit below, determine the current through the diode
http://img12.imageshack.us/img12/152/jar0.jpg

Homework Equations


V:IR
3V: Va+Vb


The Attempt at a Solution


This is my first time trying to solve a circuit problem involving diodes. I first tried to use previous equations I knew, (Ohm's Law & Kirchoff's Laws) but I don't see how I'm suppose to use these equations. I asked my professor if the problem was accidentally not given enough information but he corrected me wrong.

How should I approach this problem?
sorry I'm too noob :)
 
Last edited by a moderator:
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xxakenoxx said:

Homework Statement


In the circuit below, determine the current through the diode
http://img12.imageshack.us/img12/152/jar0.jpg

Homework Equations


V:IR
3V: Va+Vb


The Attempt at a Solution


This is my first time trying to solve a circuit problem involving diodes. I first tried to use previous equations I knew, (Ohm's Law & Kirchoff's Laws) but I don't see how I'm suppose to use these equations. I asked my professor if the problem was accidentally not given enough information but he corrected me wrong.

How should I approach this problem?
sorry I'm too noob :)

KVL, KCL, Ohm's law, etc., will all work fine. You just need to know the properties of a diode. What are they?
 
Last edited by a moderator:
Properties? What do you mean?
 
xxakenoxx said:
Properties? What do you mean?

What do you know about diodes?
 
I know that there are three types of diodes. For the LED diode, the voltage needs to have at least 0.7 for it to be on.
 
xxakenoxx said:
I know that there are three types of diodes. For the LED diode, the voltage needs to have at least 0.7 for it to be on.

Okay. Here you're interested in just a run of the mill diode. The 0.7V forward bias voltage is typical of a silicon-based diode (diodes made from other materials will have slightly different characteristic turn-on voltages).

So, how might you determine if the diode in your circuit is actually forward biased (and thus allowing current to flow)?
 
By testing the two diodes whether they are on or off or both? (that's what I remember doing in class)
 
xxakenoxx said:
By testing the two diodes whether they are on or off or both? (that's what I remember doing in class)

Well, the circuit you've shown for this problem has only the one diode. But sure, test to see if it is "on". How will you do that?
 
Sorry, I meant should I test that out?
Well, I think I need to find the voltage of the diode if it's less/more than 0.7, right?
 
  • #10
xxakenoxx said:
Sorry, I meant should I test that out?
Well, I think I need to find the voltage of the diode if it's less/more than 0.7, right?

Yup, and make sure it's "pointing" in the right direction; diodes only conduct in one direction.
 
  • #11
xxakenoxx said:
Sorry, I meant should I test that out?
Well, I think I need to find the voltage of the diode if it's less/more than 0.7, right?
Let's assume the diode voltage is precisely 0.7V here. Then how much battery voltage does that leave for the resistors in your circuit?
 

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