54 lines
1.5 KiB
Markdown
54 lines
1.5 KiB
Markdown
# Led
|
|
|
|
Leds have polarity, that means they only allow current to flow in one direction. That means LED's are diodes.
|
|
|
|
While in resistors the relations of voltage to current is linear:
|
|
|
|
|
|
|
|
that is not the case for leds:
|
|
|
|
|
|
|
|
|
|
Each led has a specific Vd or voltage drop, it needs that amount of voltage to turn on, after that amount is reached the current will increase exponentially.
|
|
|
|
Because of this we will always need a resistor infront of the LED, because when the current is too high the LED will burn out.
|
|
|
|
Values that are important for the led:
|
|
$$
|
|
\begin{flalign}
|
|
&Vd = \text{Voltage Drop} \\
|
|
&Vf = \text{Forward Voltage}\\
|
|
&If = \text{Forward Current}
|
|
\end{flalign}
|
|
$$
|
|
|
|
Our power source must have more voltage than the voltage drop, otherwise we cant turn on the led.
|
|
|
|
## Example (TLUR6400)
|
|
|
|
First we need to find the datasheet of the specific component, it can be easily found by googling it
|
|
|
|
|
|
|
|
Now lets put that LED into a test circuit and calculate the resistance for it:
|
|
|
|
|
|
|
|
Because we now the Voltage Drop of the entire circuit must be 9v and the LED already drops 2V, we now know that the resistor must drop the remaining 7v.
|
|
|
|
$$
|
|
\begin{align}
|
|
R &= \frac{V}{I} &\text{Ohms Law} \\
|
|
R &= \frac{7}{0.02} &\text{Replace the values} \\
|
|
R &= 350 \text{Ω}
|
|
\end{align}
|
|
$$
|
|
|
|
If we would pack everything into one formulare it would look like this
|
|
|
|
$$
|
|
R = \frac{Vs - Vf}{i}
|
|
$$
|