Analyzing Diodes in Series and Parallel: Current and Voltage Calculations

In summary, the question asked for the current and voltage in each diode when connected in parallel and in series, using the ideal diode equation. The given values include the reverse saturation currents, thermal voltage, and a constant current of 0.5 mA. It is mentioned that the diodes are not covered in the circuits class but are being asked in the device physics class. It is suggested to use the same equation for both pn-junction and Schottky diodes for a good approximation. The voltage drop across both diodes will be the same when connected in parallel, and the applied current will be divided between the two.
  • #1
andrew.tkelly
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Homework Statement



The reverse saturation currents of a Schottky diode and pn-junction diode at T = 300K are 5*10^-8 and 10^-12 A, respectively. The diodes are connected in parallel and are driven by a constant current of 0.5 mA.

(i) Determine the current in each diode.
(ii) Determine the voltage in each diode.
(iii) Repeat the previous two parts if the diodes are connected in series.

Homework Equations



Not sure. Maybe...

Ideal diode equation

Id = Is * [exp(Vd/Vt) - 1]

I.d is the current through the diode
V.d is the voltage across the diode
I.s is the reverse saturation current
V.t is the thermal voltage (0.0259)
(not sure if I can use the equation for a Schottky diode)

The Attempt at a Solution



Things that are given:

Reverse saturation current
Thermal voltage
constant current of 0.5mA, however, I'm not sure if I would plug
this value in for the "current through the diode", due to the diodes
being in parallel.

I don't know what to do because we have not covered analysis of diodes in my circuits class, but they are asking this in my device physics class. Is the voltage drop across both diodes going to be the same? Am I suppose to divide the constant current up? Would this ideal diode equation work for both pn-junction diodes and Schottky diodes? Not sure where to start...
 
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  • #2
Using the same equation for both diodes should yield a pretty good approximation. The saturation current determines the "turn-on" voltage knee, and yields values in the right ballpark for both diode types.

Yes, being connected in parallel the applied current will be divided between the two, and they will both share the same potential drop.
 

1. How do diodes behave when connected in series?

When diodes are connected in series, the current flowing through each diode will be the same. However, the voltage across each diode will add up, so the total voltage drop will be the sum of the voltage drop across each diode.

2. What is the purpose of connecting diodes in parallel?

Connecting diodes in parallel allows for increased current carrying capacity and redundancy. If one diode fails, the others can continue to function and provide a path for current.

3. How does the forward voltage drop of diodes affect their connection in series?

The forward voltage drop of diodes should be similar when connected in series. If there is a significant difference in the forward voltage drops, the diode with the lower voltage drop will take most of the current, potentially leading to overheating and failure.

4. What is the overall resistance of diodes in series and parallel?

The overall resistance of diodes in series will be the sum of the individual diode resistances, while the overall resistance of diodes in parallel will be less than the resistance of the individual diodes. This is due to the fact that the current is divided among the parallel diodes, resulting in a lower total resistance.

5. Can diodes be connected in both series and parallel at the same time?

Yes, it is possible to connect diodes in a combination of series and parallel. This can be useful for complex circuits that require specific voltage and current regulation. However, it is important to carefully calculate and consider the effects of such connections on the overall circuit.

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