MINI LESSON 2 – LIGHT-EMITTING DIODES (LEDs) LEDs
BASIC FACTS
FRAGILE
ORIENTATION ·
The longer
leg is positive or anode (A). ·
The shorter
leg is negative or cathode (K). ·
You can
also tell the negative side of the LED by finding the flat side of the
plastic cover of the LED. LED TECHNICAL DATA The following shows the technical data for
typical LEDs based on their colour. The most important columns have been
circled in red. Notice how different coloured
LEDs tend to have different specs.
That is because they have different semi-conductor material
concentrations in them. We usually go with 20mA for current for
any LED. CALCULATING NEEDED RESISTOR We can simply apply Ohm’s Law over the
resistor to find the needed resistor. We know the current through the resistor
is the same as the current through the LED.
So about 20mA. We know that VR = VS
- VL. So, we use VR = IR x
RR and sub in VR = VS - VL and,
after rearranging, we get R = (VS – VL) / IR. |