Solving Diode Resistor Circuit Homework

[yoyo13]

Homework Statement

Find Voltage/Current across each diode:

----R---
|...|
V...D
|... |
----R---

Repeat 50x until:

----R----
...|
...D
...|
----R----

V = power source
D = diode
R = wire resistance
. = empty space

Homework Equations

for diode:
V = 0.04654 * ln(I/(0.62E-19)) + I*6.97

for wire:
R = pl/A = 0.02 ohms

Final diode voltage = 2V
Final diode current = 20mA

The Attempt at a Solution

Attempted to use v = ir with wire resistance to find voltage over last-1 diode, but did not work out as current got higher as worked back to source.

 

[Redbelly98]

Welcome to PF

It took me a while to figure out how the circuit looks from your description.

It sounds like you are on track to solving this. The diode currents (and voltages) should get higher as you get closer to the source.

 

[Mene]

I would suggest using Kirchhoff's circuit laws to solve this diode resistor circuit. The first law, also known as Kirchhoff's current law, states that the sum of currents entering a node (or junction) must equal the sum of currents leaving that node. This means that the current entering the node at the top must be equal to the current leaving the node at the bottom.

Using this law, we can set up a system of equations to solve for the current and voltage across each diode. We can start by labeling each node and assigning a variable for the current and voltage at each node. Let's call the node at the top A, the node between the first resistor and diode B, the node between the second resistor and diode C, and the node at the bottom D.

Using Kirchhoff's current law, we can write the following equations:

At node A: Ia = Ib + Ic
At node B: Ib = Ic + Id
At node C: Ic = Id + Ie
At node D: Id = Ie + If

Since we know that the final diode voltage is 2V and the final diode current is 20mA, we can set up another equation using Ohm's law for the resistor and the diode:

2V = 0.02 ohms * 20mA + 0.04654 * ln(20mA/(0.62E-19)) + 20mA * 6.97

We can then solve this system of equations using any algebraic method (substitution, elimination, etc.) to find the voltage and current at each node and determine the voltage and current across each diode.

In summary, solving this diode resistor circuit requires the use of Kirchhoff's circuit laws and Ohm's law. By setting up a system of equations and solving for the unknown variables, we can determine the voltage and current across each diode and successfully complete the homework assignment.