Solve Diode Circuit Problem: Homework Equations & Attempt at Solution

[dashkin111]

Homework Statement

See attachment

Homework Equations

We are to assume the voltage drop across diodes is .7v (don't use the diode equation!).

The Attempt at a Solution

I first was assuming that both diodes were "on". Then my work is as follows:

V1 is the voltage directly above diode D1 (the left most diode)...
$$I+ \frac{V_{1}-.7-(-5)}{5k\Omega}=\frac{5-V_{1}}{10k\Omega}$$

$$I+ \frac{.7-.7+5}{5k\Omega}=\frac{5-.7}{10k\Omega}$$

$$I=-.57mA$$

Now since I is negative, one of my assumptions is wrong? So now I assume the rightmost one is "off" (D2).So.. then
Solving for I
$$I = \frac{5-.7}{10k\Omega}$$

$$I = .43 mA$$

Solving for V
Well.. since there's no current, v=-5?
Am I approaching this correctly?

 

[Gokul43201]

So now I assume the rightmost one is "off" (D2).


So.. then
Solving for I
$$I = \frac{5-.7}{10k\Omega}$$

$$I = .43 mA$$

Solving for V
Well.. since there's no current, v=-5?



Am I approaching this correctly?

You're on your way. In this second case, what would be the value of V1? Does this agree with your assumption?

 

[piercas]

Your approach is correct. However, there are a few things that can be improved upon.

Firstly, when you assume that both diodes are "on", you should also assume that the voltage drop across each diode is 0.7V. This will make your calculations easier and more accurate.

Secondly, when you assume that the rightmost diode is "off", you should also assume that the voltage drop across it is 0V. This will also make your calculations easier and more accurate.

Finally, when solving for the voltage and current, it is always good practice to check your answers. In this case, you can check by calculating the total current going into the circuit and making sure it equals the total current coming out of the circuit. This will help catch any mistakes in your calculations.

Overall, your approach is good and you have solved the problem correctly. Just remember to make those assumptions and double check your answers in the future.