Determining two diodes' currents

In summary: The question is poorly designed and does not make sense. The question should be revised or removed from the exam. In summary, the conversation revolves around a confusing and poorly designed question on analyzing diode circuits. The question includes options for different states of the diodes, but there is no clear explanation for these options. The question is deemed an "abomination" and reflects badly on the examiner. The conversation also includes a suggestion to remove or revise the question.
  • #1
JasonHathaway
115
0

Homework Statement



Assuming that D1 and D2 are ideals, determine ID1 and ID2 according to the table below.

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Homework Equations



Circuit Analyzing methods (KVL, etc...)

The Attempt at a Solution



I've confirmed my solutions for the first three cases with final answers of the book I use and also with Multisim.

But for the fourth, while replacing the diodes with "on-switches", I used superposition to calculate the currents. I've ended up with ID1=ID1'+ID1''=12+9=21 mA, and ID2=-9 mA.

My answer is correct for ID2, but that not the case for ID1 (The answer should be 12 mA). Looks like the effect of the 9V source on ID1 was ignored. Why is that?
 
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  • #2
Because there is no reason for it to have an effect - the diodes are basically replaced with short circuits.
The D1 short basically isolates the two halves from each other.
 
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  • #3
My circuit analyzing again :S

Thanks :)
 
  • #4
This is indeed a weird question. For the circuit shown, there are not 4 possible states, there is only one! For the options to make sense, either the "diodes" need to be SCRs or something similar (with gating arrangements not shown), or each diode needs an associated series switch---but in the schematic this is clearly missing.

I had no idea what to make of the exercise, not knowing what could be meant by a diode being off even though it may be forward-biased. :confused: :confused: :confused:

Now I can see what was intended, but this abomination reflects badly on the examiner. I'd grade him Epic Fail! :devil: :devil:
 
  • #5
The exercise is on the "assumed states" method for analyzing diode circuits.
 
  • #7
NascentOxygen said:
This is indeed a weird question. For the circuit shown, there are not 4 possible states, there is only one! For the options to make sense, either the "diodes" need to be SCRs or something similar (with gating arrangements not shown), or each diode needs an associated series switch---but in the schematic this is clearly missing.

I had no idea what to make of the exercise, not knowing what could be meant by a diode being off even though it may be forward-biased. :confused: :confused: :confused:

Now I can see what was intended, but this abomination reflects badly on the examiner. I'd grade him Epic Fail! :devil: :devil:

My thoughts exactly
 

FAQ: Determining two diodes' currents

How do I determine the current through a diode?

To determine the current through a diode, you can use Ohm's Law, which states that current is equal to voltage divided by resistance. In this case, the voltage is the voltage drop across the diode and the resistance is the dynamic resistance of the diode.

Can I use a multimeter to measure the current through a diode?

Yes, you can use a multimeter to measure the current through a diode. Set the multimeter to the appropriate current range and connect the diode in series with the multimeter. The multimeter will then display the current through the diode.

What is the difference between forward and reverse diode currents?

Forward diode current is the current that flows through the diode when it is forward biased, meaning the anode is at a higher potential than the cathode. Reverse diode current is the current that flows through the diode when it is reverse biased, meaning the anode is at a lower potential than the cathode.

How do I calculate the dynamic resistance of a diode?

The dynamic resistance of a diode can be calculated by taking the change in voltage across the diode and dividing it by the change in current through the diode. This can be represented as Rd = ΔV/ΔI.

How does temperature affect the current through a diode?

Temperature can affect the current through a diode in two ways. First, as the temperature increases, the forward voltage drop across the diode decreases, resulting in an increase in current. Second, as the temperature increases, the reverse current through the diode also increases. This is due to the increase in thermal energy causing more charge carriers to be present, resulting in a higher reverse current.

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