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

[xxakenoxx]

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 :)

 

[gneill]

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?

 

[xxakenoxx]

Properties? What do you mean?

 

[gneill]

Properties? What do you mean?

What do you know about diodes?

 

[xxakenoxx]

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.

 

[gneill]

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)?

 

[xxakenoxx]

By testing the two diodes whether they are on or off or both? (that's what I remember doing in class)

 

[gneill]

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?

 

[xxakenoxx]

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?

 

[gneill]

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.

 

[NascentOxygen]

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?