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I am not familiar with circuit analysis, although I can manage to solve basic circuit. However, I am currently stuck with a problem and I am not sure about the solutions.

If anyone could have a look at my solutions I would highly appreciate it.

By using circuit logic I assumed D1 to be OFF and D2 ON. From there, we KVL and current division rules to find the total current I:

10.7 - I*R1 - 0.7 - 0.25I*R2 - I*R3 = 0 and derive I = 1.08 mA

From here we have the following: 

V1 = 10.7 - R1*I = 4.22V
V2 = V1 - 0.7 = 3.52V
V3 = V2 - 0.25I*3 = 2.71V
V4 = V2 -0.75I*1 = 2.71V

We note that V1 > V4 therefore D1 is indeed reverse biased.

For some reason I am not sure about these results, this is my first problem of the sort.

Here is the problem: enter image description here

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  • \$\begingroup\$ Without showing the effort you put in to solve this question, it will be closed due to low effort. So please consider showing your line of thought and ask specific questions were you got stuck. \$\endgroup\$
    – Maxim
    Commented Apr 22, 2019 at 7:43
  • \$\begingroup\$ I will edit my question then with the answes I got. \$\endgroup\$
    – Fenrir
    Commented Apr 22, 2019 at 7:50
  • \$\begingroup\$ Some current will flow through R4, so V3 cannot equal V4. You have a mistake somewhere. \$\endgroup\$
    – Mattman944
    Commented Apr 22, 2019 at 8:25
  • \$\begingroup\$ I agree, but I can't find the mistake. V3 is equal to V4 because of the current division rule I used but then again V3 seems to make sense because it does go to 0 after R3. \$\endgroup\$
    – Fenrir
    Commented Apr 22, 2019 at 8:45

1 Answer 1

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Guess which diodes are conducting. Remove the non-conducting diodes, and replace the conducting diodes with a 0.7V voltage source, + side at the anode. Solve using standard analysis.

Then, verify that your guess was correct. Current should flow into the + side of the simulated conducting diode, if not, it wasn't conducting. Where the non-conducting diode was should have a voltage less than 0.7V (anode V - cathode V), if not it should not have been removed.

For this exercise, it is fairly obvious that current is flowing from top to bottom, so D2 is probably conducting. Replace D2 with a voltage source, then solve. Verify that current is flowing into the anode of D2. Then verify that V4 - V1 is not greater than 0.7V.

If your guesses were wrong (verification didn't work), then make another guess and solve again.

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