I am making a circuit simulation program, and I am not sure how to simulate the behavior of Diodes.
Take this circuit:
------100 Resistor -----LED------
Positive 5V-----470 Resistor-----| |---------Negative 5V
-----------200 Resistor----------
How would you calculate the voltage and current through all of these components?
Also, is it true that with a simple circuit like this:
Positive 5V------470 Resistor------LED--------Negative 5V
That you would subtract the forward voltage of the LED from the Battery's voltage, then use Ohm's law to calculate the current and resistance through the circuit?
voltage = 5;
newVoltage = voltage - forwardVoltage;
current = newVoltage / 470;
resistance = voltage / current;
I don't have a background in electrical engineering - so I am really clueless. Thanks for the help.
Answer
Yes, you are correct in your last example, assuming a red LED with 2.0V over it, the current will be $\frac{(10-2)V}{470Ω} \approx 17mA$. For your first example, I assume you already know that the total resistance of something in parallel is $\frac{1}{R} = \frac{1}{R_1} + \frac{1}{R_2} + \dots + \frac{1}{R_n}$ and you are struggling of how to calculate the total resistance of 100Ω, 200Ω and the LED, right? I am not sure if it is possible to do it that way. Instead look at each of the current paths. Some current will flow through $R_1$ (470Ω) and further through $R_2$ (200Ω). Let's call this current $I_A$. Then some current will flow through $R_1$, through $R_3$ and the LED, $I_B$.
Let's call the voltages over $R_1$, $R_2$ and $R_3$ for $U_1$, $U_2$ and $U_3$. Then $U_1 = (I_A + I_B) \times R_1$, $U_2 = I_A \times R_2$ and $U_3 = I_B \times R_3$. The voltage over $R_2$ will be the same as over $R_3$ and the LED combined, i.e. $U_2 = U_3 + U_{LED}$. You already know that the total voltage over all components is 10V. So
$U_1 + U_2 = 10V$
$U_1 + U_3 + U_{LED} = 10V$
and this gives you two equations with two unknowns, $I_A$ and $I_B$, which is standard math to solve.
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