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I am trying to solve this circuit-

enter image description here

Here is what I have done till now-

  1. Assumed every diode is forward biased.
  2. Used mesh analysis to find that in left mesh the current is -1.63 mA, that means my initial assumption was wrong about D3 diode. And it's reversed biased.
  3. In the right mesh I found 1.74 mA. That means both D1 and D2 are on.
  4. I again solved this circuit by starting with D3 off and D2 D1 on and found out current in the right circuit is 0.678 mA.

Is my process and results correct? Does the values and diode states correct?

And in PartSim my simulation produced this output which is not matching, but why?

enter image description here

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  • \$\begingroup\$ What diode model are you using to hand solve the problem. Exponential model, constant voltage drop model or ideal model? \$\endgroup\$
    – vini_i
    Commented Oct 10, 2015 at 11:20
  • \$\begingroup\$ Your answer for the current is 678uA, the simulator says 757uA, surely you are not using complex maths to do with exponential curves and reverse leakage models, so those numbers match well enough. If the simulator has the right models for the diodes, it's probably closer, but for a back of envelope estimate your number is pretty decent too. In fact my own top-of-head estimate comes to 699uA. Plus about 1.5uA reverse through D3. \$\endgroup\$
    – Asmyldof
    Commented Oct 10, 2015 at 11:23
  • \$\begingroup\$ I am using constant voltage drop model 0.7 V @vini_i \$\endgroup\$
    – simple
    Commented Oct 10, 2015 at 11:27
  • \$\begingroup\$ That means my diode states are correct? D1, D2 on and D3 off? @Asmyldof \$\endgroup\$
    – simple
    Commented Oct 10, 2015 at 11:28

1 Answer 1

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Your diode states are correct. That being said diodes are complex non linear components. The exponential model is the best tool to get the perfect result but mathematically it is difficult to apply for circuit analysis. The constant voltage drop model is meant so simplify this calculation but it won't give you the perfect results. The simulation model is capable of doing the complex calculations of the exponential model and provides a more accurate answer.

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  • \$\begingroup\$ Thank you for verifying my answer and give a reason for the difference. \$\endgroup\$
    – simple
    Commented Oct 10, 2015 at 12:21

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